Studer 928 Story...

[sweetbeats]

Well, as per usual, I really couldn’t let my curiosity rest as to whether or not the original power supply umbilicals, factory supplied spare parts and the original manual were sitting in a closet or in a drawer or shelf somewhere at the university that owned the 928 for most of its existence.

I contacted the university and, with some persistence, was able to reach the current director of the university’s broadcast program and facilities. He was in the position when the 928 was decommissioned and replaced by a digital console and subsequently put up for auction in June of 2015. He unfortunately verified for me that anything that wasn’t included with the 928 at auction “long since went into the dumpster.” It just kills me. I’ve exhausted anything Harman is going to be able to provide as far as spares or documentation, and I’m not getting any response from what is considered the only viable resource for vintage Studer parts and service, Willkommen - Welcome. Apparently audiohouse is operated by a former Studer service manager. Anyway, that’s where that is at. But my conversation led to the suggestion to try and connect with the former broadcast program director who was responsible for procuring the 928 for the university. All I had was a name and maybe the town he currently lives in. But...I’m a persistent bastard.

I found him and talked with him. Nice guy. Loves Studer gear and really loved mixing on the 928 when it was in service at the university. He indicated he had always hoped the 928 would find a home with somebody that appreciated it and would keep it going. I assured him it has. Ironically he lives not too far from me and I’ve driven past his house literally countless times in the last 20 years.

He said this of the 928:

“Great to see [the 928 console] again. One of the best looking consoles ever [I sent him a picture]. Best sounding too, even with the complex signal path. I wanted to put it in a remote truck, it’s strong enough to survive that application.”

He asked me how much I paid for it and when I told him he exclaimed “Whoa that’s a steal...you did good.”

My favorite part of our correspondence though was getting the back-story on the 928 and how it came to the university. Apparently the university was NOT the first owner...and the story goes like this:

“Your 928 originally was sold for $89K to KMEX-TV in Los Angeles, installed for a very short time then replaced by a half million dollar D950 [KMEX-TV’s sister station got a new D950 at the same time KMEX-TV got the 928 and they pushed for equal treatment, so...] Then [the 928 was] re-boxed and warehoused. Was sitting on Studer Canada’s books (Canada handled all broadcast sales) for a while and Switzerland told them to make it go away. I heard about it from our Studer rep and asked her if [our station] could demo it. She had it shipped up from LA and I patched it into the TV station’s production control room. Actually got me in a bit of trouble since I didn’t tell my bosses it was coming for a demo. Liability and all that. But I had the last laugh as the students loved it so much they forced the issue and it was purchased [July, 2002] for $32K.”

Great story.

Here’s another development: I’ve read online that Studer snobs don’t really consider the 928 a real Studer because it was introduced after Harman bought Studer, and there are arguments it is just a Soundcraft console inside. I hadn’t been able to find a correlating Soundcraft product until now...the Soundcraft B400/B800 broadcast consoles.

Brochure and operations manuals here:

B800 | Soundcraft - Professional Audio Mixers

Schematics here:

http://bee.mif.pg.gda.pl/ciasteczkowypotwor/SM_scena/Soundcraft/soundcraft_b400_b800_sch.pdf

At first blush it looks like the Studer is still a bit more sophisticated than the Soundcraft with some elements of the feature set, and I know for fact everything in the meter bridge of a 928 is 100% Studer...modules that came from other 900 series analog consoles. And it looks like the Soundcraft lacks some fancy magic shiz circuitry in the mic amp and group and main output amps...also no onboard patchfield. And the 928 holds claim to the very cool stereo width circuit on the stereo input modules. Physically the 928 says “I’m a Studer.” Both very nice consoles...Since the 928 keeps some of its own best stuff for itself and doesn’t share with the Soundcraft consoles, and since the physical design appears to be Studer, and because there are so many common physical and electronic elements derived from other Studer consoles like the 980 and even the 990, I think it’s more Studer than Soundcraft. But that’s arguable. But I don’t care.

At least the Soundcraft docs have helped me narrow down what the power supply umbilical connectors are at the power supply end. And it looks like parts are relatively available and relatively cheap. So THAT’S something.

 

[ecc83]

That is a good find Sweetbeats. Great to see some schematics and there is definitely some "Soundcraft" in there. I note the summing module p.20 is a hybrid,balanced mixer with busses going to emitters, almost textbook D Self "Small Signal Audio Desgn". The mic pre is very close to his "Padless Preamp" in the same book. I see there is a transformer option?

But what clinched "Self" for me was the PSU that speccs' 17.5V rails NOT 18V. Self actually suggests 17V on the money as it gives virtually zero op amp failures whch HAVE been known for 18 volt supplies. His liberal sprinkling of NE5532s is also a clue (although I doubt there was much else nearly as good or cost efective then? Oh, and the use of "zero output impedance" techniques has DS's stamp although that might be well known to other designers?

Self might be a source of further information but since he is only four years behind my 73 years, maybe don't hang about?

Dave.

 

[sweetbeats]

For those with interest in the direct output functions on the input modules in greater detail, including the “Mix Minus” features:

YouTube

 

[Zacharia]

Hey Sweetbeats...I just wanted to let you know I fully intend you post a picture of my 269 and TSR-8. You had mentioned doing that a few pages back. I just need to clean up my space and get a shot of it.

 

[miroslav]

For those with interest in the direct output functions on the input modules in greater detail, including the “Mix Minus” features:

I wonder if that can be useful for easily/quickly creating alternate cue mixes during tracking...?
You would just take "that" channel's DI output and feed it to a headphone amp/distro...os if someone wants to hear "everything but"...you can do it using the DI feature rather than tying up an Aux bus, which you might be using for a more global cue mix....etc.

There may be other uses...but that's the first thing that comes to mind based on how you described its functionality.

 

[sweetbeats]

[MENTION=89697]ecc83[/MENTION]

That is a good find Sweetbeats. Great to see some schematics and there is definitely some "Soundcraft" in there. I note the summing module p.20 is a hybrid,balanced mixer with busses going to emitters, almost textbook D Self "Small Signal Audio Desgn". The mic pre is very close to his "Padless Preamp" in the same book. I see there is a transformer option?

I have to be honest I haven’t read that book. The mic/line amps between the Studer and the Soundcraft are probably one of the most significant differences between the two...the output amps are one of the other ones. The Soundcraft is much more “garden variety” compared to the Studer, and I’m not really a fan of the line amp signal path on the Soundcraft basically being a pad function switching in a series resistor and then sending the padded line level signal through the mic amp. Functional, yes, but eloquent, no. And yes there is a transformer option on the mic and line inputs on the Soundcraft, which is interesting because the mic/line amp is already electronically balanced. The transformer option in essence exists to accommodate higher level signals. The Studer is very different. The mic amp is standard with a transformer, but with an additional winding that is incorporated into the feedback loop of the 5534 head amp. In theory this would incorporate whatever sonics the transformer offers into the gain loop...and maybe some uniqueness as you overdrive the head amp. This could be good, or maybe it sounds like a$$...I don’t know yet. But it is far less common and I expect done with the intention of achieving Studer’s commitment to “good sound”. The line amp is a completely separate electronically balanced amp designed to handle line level signal on the Studer...not a pad it down and boost it back up arrangement like in the Soundcraft. A transformer was an option on the line input as well on the Studer, but again not for the purpose of balanced interface, but to accommodate higher level signal. I haven’t looked to see if the Soundcraft summing module is the same as the Studer...but the Studer group out and main outs are totally different...again featuring transformers as standard with a third winding incorporated into the feedback loop...easily cleanly drives +6dBu nominal signals into relatively low impedance loads. Specifications cite +23.5dBu at 200ohms I think.

But what clinched "Self" for me was the PSU that speccs' 17.5V rails NOT 18V. Self actually suggests 17V on the money as it gives virtually zero op amp failures whch HAVE been known for 18 volt supplies. His liberal sprinkling of NE5532s is also a clue (although I doubt there was much else nearly as good or cost efective then? Oh, and the use of "zero output impedance" techniques has DS's stamp although that might be well known to other designers?

So, interestingly enough, the Studer audio power rails run at +/-15V. And even more odd the power supply PCB is screened with +17V and -17V...the power supply is actually designed by another company “For Studer”...I assume the supply was designed originally for +/-17V operation and Studer specified to dial it back to +/-15V. Why? I have no idea. It would mean greater reliability though to dial it back, and that was a successfully achieved goal with the 928. I haven’t done a deep enough dive into a comparison of the circuits to identify if there is some reason the Studer *couldn’t* operate at +/-17V...I suspect not, but what would be the point? Yes there would be an increase in headroom, but the most critical input and output amp stages are pretty schnazzy designs replete with genuine Studer transformers...and the non-transformer coupled Input and output stages are all electronically balanced (not differential) and utilize opamps with healthy drive...Studer accomplished a signal path that is +6dBu nominal throughout on +/-15V rails. So I’m leaving it alone. That’s a rabbit trail I don’t need to chase.

And yes there are 5532 and 5534 parts throughout the design which are two of my favorite opamps...they are still respected and, though not new at the time the 928 was on the market, were still a high performing higher tier choice I believe. Also found are the 33078 (I believe a next generation 072), and the 2142 which I don’t see very often, but it has really good specs and lots of drive.

[MENTION=200747]Zacharia[/MENTION]

Hey Sweetbeats...I just wanted to let you know I fully intend you post a picture of my 269 and TSR-8. You had mentioned doing that a few pages back. I just need to clean up my space and get a shot of it.

Cool! Whenever you get to it. Looking forward to it.

[MENTION=94267]miroslav[/MENTION]

I wonder if that can be useful for easily/quickly creating alternate cue mixes during tracking...?
You would just take "that" channel's DI output and feed it to a headphone amp/distro...os if someone wants to hear "everything but"...you can do it using the DI feature rather than tying up an Aux bus, which you might be using for a more global cue mix....etc.

There may be other uses...but that's the first thing that comes to mind based on how you described its functionality.

Yeah...yeah...cool. Wouldn’t likely be an every day thing but could certainly come up as a need to do something like that. And the way it’s designed that “everything but” cue mix could either be the sum of everything assigned to the Master A buss minus that channel’s input source, or a custom mix of any channels with the mix-minus function latched minus that channel’s input source. It would all be a mono mix, but it could be a pre or post fade mix depending on the jumper settings on each strip, and really, like you said, could be a quick and dirty way to get a cue mix out to someone or something that’s either the Master A sum minus an input, or a custom sum of any channels you want summed together. Like, rather than thinking of it as a mix-minus sum, if somebody said “hey can I get a rough mix of the drums and bass in my monitor?” I could take ANY non drum and bass strip with an unused direct out, latch the N-1 button on the drum and bass strips, latch it on the strip with the open direct out jack and *boom* I’ve got a cue mix sum of the drums and bass without using an AUX buss. Thinking through this, though, that would be tricky because I only have direct out jacks setup on input channels 1-12...the mono mic/line strips. I’ll be using those direct outs more frequently as multitrack feeds since there are only four subgroups. I also have the fully independent Master B buss though, which I think will be great as a high headroom multitrack feed for a stereo pair of tracks. The Master A and B outputs and the four group outs have the higher headroom transformer equipped outs...I’m thinking I’ll commonly be sending drum overheads to the Master B buss and other drum mics to the group outs for tracking...but I need to see what sounds best first. Anyway...options. And I think eventually it might not be too hard to equip the console for direct outs on the stereo channels if I need more flexibility, but those are mainly going to be tape and DAW returns. Lots to ponder....

 

[ecc83]

Ooo! Do get Self's book if you can Sweetbeats. Yes, I am sure the Studer circuits are more sophisticated but I just realized I don't have them! The download was for a Soundcraft desk. Do you have the Studer schematics?

Transformer inputs are of course used to give really excellent RFI rejection and a vastly bigger CMRR than is usually possible with electronic balance (though the very clever THAT corp chip manages it!).

Padded mic amps for a line input? I agree not elegant but very common. Self does address this matter in his "Padless Preamp" design. He also goes in to point out that the standard "10+10+10+10k" line input is inherently noiser than the same chip configured unbalanced. For a unity gain balanced input, around -104dBu is the best it can be (NE5532) He does go on to develop a circuit that does give -117dBu out but it needs 6 IC's per channel!

The 33078 is in fact a bipolar i/p chip. The TLE2142 seems to be a "superior" 5532? Much higher slew rate* at 40V/muS and has lower DC drift. The Texas internal map shows a FET in the bias circuit which makes me think it is of the 5532 "family"? It is said to be particularly suited to driving long, "cappy" lines.

15+15V rails only give a loss of 1.1dB against 17V (Self again) so I doubt that will bother you?

*Not that it matters diddly for audio work.

Dave.

---------- Update ----------

Ooo! Do get Self's book if you can Sweetbeats. Yes, I am sure the Studer circuits are more sophisticated but I just realized I don't have them! The download was for a Soundcraft desk. Do you have the Studer schematics?

Transformer inputs are of course used to give really excellent RFI rejection and a vastly bigger CMRR than is usually possible with electronic balance (though the very clever THAT corp chip manages it!).

Padded mic amps for a line input? I agree not elegant but very common. Self does address this matter in his "Padless Preamp" design. He also goes in to point out that the standard "10+10+10+10k" line input is inherently noiser than the same chip configured unbalanced. For a unity gain balanced input, around -104dBu is the best it can be (NE5532) He does go on to develop a circuit that does give -117dBu out but it needs 6 IC's per channel!

The 33078 is in fact a bipolar i/p chip. The TLE2142 seems to be a "superior" 5532? Much higher slew rate* at 40V/muS and has lower DC drift. The Texas internal map shows a FET in the bias circuit which makes me think it is of the 5532 "family"? It is said to be particularly suited to driving long, "cappy" lines.

15+15V rails only give a loss of 1.1dB against 17V (Self again) so I doubt that will bother you?

*Not that it matters diddly for audio work.

Dave.

---------- Update ----------

Ooo! Do get Self's book if you can Sweetbeats. Yes, I am sure the Studer circuits are more sophisticated but I just realized I don't have them! The download was for a Soundcraft desk. Do you have the Studer schematics?

Transformer inputs are of course used to give really excellent RFI rejection and a vastly bigger CMRR than is usually possible with electronic balance (though the very clever THAT corp chip manages it!).

Padded mic amps for a line input? I agree not elegant but very common. Self does address this matter in his "Padless Preamp" design. He also goes in to point out that the standard "10+10+10+10k" line input is inherently noiser than the same chip configured unbalanced. For a unity gain balanced input, around -104dBu is the best it can be (NE5532) He does go on to develop a circuit that does give -117dBu out but it needs 6 IC's per channel!

The 33078 is in fact a bipolar i/p chip. The TLE2142 seems to be a "superior" 5532? Much higher slew rate* at 40V/muS and has lower DC drift. The Texas internal map shows a FET in the bias circuit which makes me think it is of the 5532 "family"? It is said to be particularly suited to driving long, "cappy" lines.

15+15V rails only give a loss of 1.1dB against 17V (Self again) so I doubt that will bother you?

*Not that it matters diddly for audio work.

Dave.

SORRY!!! Gone back to Firef**ks after trying IE again and got the "leave page" hang up. My subsequent hackings resulted in the extra posts.

 

[sweetbeats]

Core operation and service instruction manual for the Studer 928 is available on Studer’s webpage for the console:

928 | Studer Professional Mixing Consoles

 

[ecc83]

Core operation and service instruction manual for the Studer 928 is available on Studer’s webpage for the console:

928 | Studer Professional Mixing Consoles

Thanks for that* took a while to dig down to get the mic pre! Yes, a dedicated transformer circuit. Two edged sword of course, you need a transformer to give "free" gain if you are using just an op amp whereas a hybrid electronic can be about as quiet.

Then the feedback winding is probably mandatory to reduce distortion and its presence means the circuit might not overdrive gracefully? But as you say, never know till you try.

*How long did that download take you? I have just signed up for a new contract and my download speed is now around 24M (9M up) but that manual took well over 3 minutes to come through. Must be lodged on an old server?

Lovely bit O kit!

Dave.

---------- Update ----------

Core operation and service instruction manual for the Studer 928 is available on Studer’s webpage for the console:

928 | Studer Professional Mixing Consoles

Thanks for that* took a while to dig down to get the mic pre! Yes, a dedicated transformer circuit. Two edged sword of course, you need a transformer to give "free" gain if you are using just an op amp whereas a hybrid electronic can be about as quiet.

Then the feedback winding is probably mandatory to reduce distortion and its presence means the circuit might not overdrive gracefully? But as you say, never know till you try.

*How long did that download take you? I have just signed up for a new contract and my download speed is now around 24M (9M up) but that manual took well over 3 minutes to come through. Must be lodged on an old server?

Lovely bit O kit!

Dave.

---------- Update ----------

Core operation and service instruction manual for the Studer 928 is available on Studer’s webpage for the console:

928 | Studer Professional Mixing Consoles

Thanks for that* took a while to dig down to get the mic pre! Yes, a dedicated transformer circuit. Two edged sword of course, you need a transformer to give "free" gain if you are using just an op amp whereas a hybrid electronic can be about as quiet.

Then the feedback winding is probably mandatory to reduce distortion and its presence means the circuit might not overdrive gracefully? But as you say, never know till you try.

*How long did that download take you? I have just signed up for a new contract and my download speed is now around 24M (9M up) but that manual took well over 3 minutes to come through. Must be lodged on an old server?

Lovely bit O kit!

Dave.

---------- Update ----------

Core operation and service instruction manual for the Studer 928 is available on Studer’s webpage for the console:

928 | Studer Professional Mixing Consoles

Thanks for that* took a while to dig down to get the mic pre! Yes, a dedicated transformer circuit. Two edged sword of course, you need a transformer to give "free" gain if you are using just an op amp whereas a hybrid electronic can be about as quiet.

Then the feedback winding is probably mandatory to reduce distortion and its presence means the circuit might not overdrive gracefully? But as you say, never know till you try.

*How long did that download take you? I have just signed up for a new contract and my download speed is now around 24M (9M up) but that manual took well over 3 minutes to come through. Must be lodged on an old server?

Lovely bit O kit!

Dave. GRR! THIS time I "stayed on page" but then nothing moved so I hit "post" again. You can see the result.

 

[sasquatch]

Sweetbeats,if you notice all cards have in-rush current limiting resistors(thermistors?) on the rails eating up some of that rail voltage.Reliability.

Elevated rail voltages increases current and heat putting strain on components or having to up the spec.Cost and reliability.

Studer would have done their homework with regards to quality,cost,reliability etc.....needs to run 24/7 in some situations.

I recall a Neve and Sony console which installed you would have to add 1 ton to the air conditioning system.

Gary

 

[sweetbeats]

So this is a SUPER long post, and I completely respect most of you are not going to take the time or do not *have* the time to read it. But here it is anyway to memorialize the current state of affairs with the Studer.

I have a number of updates…working on several things as I go through the modules and continue to comprehensively test things out, and as I test the modules I’m bringing them in the house and hanging them in a closet so they are in a dry heated space. You see, at the moment the console is out in an unheated detached garage that will eventually become heated/insulated music/recording/recreation space…there’s no room in the house for the frame, but I’m at least getting the modules out of the frame and bringing them inside and then at least keeping the frame covered and dry. I’m making progress on the garage conversion…all of the attic venting is now done, and next up is electrical work…new lighting cans, hang a box for the future pool table lighting, install heating and run the wiring for that, and run dedicated power for audio stuff. Once that’s all done its time to insulate and sheetrock. BUT…in the meantime…


Power Supply Stuff…

The stickiest issue I have regarding the power supplies at the moment is the lack of any technical documentation on them. I’ll remind you there are two versions of the power supplies that were utilized with the 928, the early version like mine, and the later version. The only power supply related documents I have been able to find are related to the later version, not my version which is Studer part number 1.918.210.00. The manual that’s available all over the internet has all the schematics, parts lists and PCB layouts for just the later version. It has installation notes and pinouts for both versions, but nothing else for the early version. I’ve reached out to Harman International (current owner of the Studer name and line of current Studer products), but all they have is the same as what I’ve been able to find already. The power supplies were actually manufactured for Studer by Delaire, Ltd…says so right on the supply chassis. The main PCB in the power supplies is marked DPC 0020 Rev 5 9/96. Delaire Ltd. Is now Advanced Energy. I reached out to them but they didn’t have anything. I was also referred to audiohouse.ch. They are the only official service and parts resource for discontinued Studer products according to Harman International. They were as helpful as they could be but they also don’t have anything more than what’s already available on the internet. The DID help me out with some other stuff though…more on that later. So I’ve resorted to contacting anybody I can find that owns a 928 or is selling a 928 and 1. Asking them if their console has the early or late power supply version, 2. if they have a manual if they can check if they have documentation on the 1.918.210.00 supply assembly and if they do, 3. asking them if they are willing to scan and email or copy and mail the documents to me…and I’m offering to pay. Unfortunately I haven’t gotten past step #1 with anybody yet. I don’t have any current problems with any of my supplies per se, but someday I inevitably will, and these are not straight-forward linear supplies, but switching supplies. I need the tech docs. So I’ll keep trying. I remain surprised it is so hard to find anything on the early version supplies. I’m also working on gathering parts to re-fabricate the power supply umbilical cables. I mentioned in an earlier post the ones I have work, but there are several issues, namely the circular connectors at the power supply end are all missing the threaded locking rings so they aren’t fastened to the power supply chassis when plugged in, plus one of them is missing the strain relief. Well, I was able to figure out exactly what connector brand/model/type Studer specified…it is a Hirose part, specifically a JR21PK-10P(71). And Mouser has them. So I ordered them. They were actually reasonably priced too. I feel fortunate. They were $16 and change each. That might seem like a lot to some for a connector, but for those who have worked with mil-spec style circular connectors like that, they can run over $50 each…sometimes much more. So getting all of them for less than $50, and the fact they were available at all feels like a real win to me. At the other end the DIN 41622 “Tuchel” connectors are missing their hoods, so these connectors don’t latch to the console frame, and all pins/conductors are exposed with no cable clamp or strain relief. There is also a related issue in the there are six 39-pin DIN 41622 connectors on the backplane of the console frame that handle a bunch of I/O, and I have no connectors or hoods for those…until now. I found a fella in Germany selling a bunch of them, all used, but complete and in good condition. He actually had everything I needed for the power supply interconnects, all the I/O interconnects, and a few spares to boot…sold it all to me for $90 shipped from GERMANY. Now, any of you that know about these style connectors know that was a complete steal. Right now you can go to Redco and all those parts would cost about $800. So, I’m relieved. Here’s what I got…and actually a few of the connector blocks are brand new:




Outside of the issues with the connectors, the cable is not the right type. What’s called for is cable comprised of eight to ten 16AWG stranded conductors. What was used for the cables the previous owner fabricated is twelve conductor 14AWG cable. Bigger is better, right? Well, in this case it makes for overly stiff cable, and the OD of the cable makes it so it doesn’t even fit through the strain relief at the power supply end…not sure yet if it will fit through the Tuchel hoods. And its more difficult to get the stranded wire to bond with the solder lugs on the connectors because the wire gauge is too big for the holes in the lugs. I already have at least one conductor that’s popped off and needs to be resoldered. So…again, they work, but…no…that just won’t do. The other thing I’d like to address with the cable is to implement best practices for bonding the console frame with the power supply chassis. Right now that is handled via one of the cable conductors, but the best practice is to bond the chassis over a braided shield in the cable. The current cable is unshielded. I haven’t found the cable yet…its not urgent so I’m just keeping my feelers out. But it feels good to have all the connectors I need for the power supply umbilicals as well as all my audio I/O. Last but not least the power supplies need new cooling fans. At least one of them sounds like the bearing is starting to go, and in general they are too noisy. These are 24VDC 80x80x25mm brushless ball-bearing fans, and the original spec fans move 34.4CFM at a noise level of 30dBA. I found some fans for $9 each that move 37CFM and are a bit quieter at 26dBA. So those are on the way. Oh and at some point I’m going to need to take a trip up to the big city to this unreal hardware store there that has absolutely every kind of regular fastener and every conceivable obscure fastener as well. My power supplies are missing all the chassis lid screws…short counter-sunk metric parts…probably black chrome or anodized is what was there originally, so I need to get those at some point. I also have in the back of my head I need to find a separate rack for the power supplies. Anyway…


Spare Parts…

So I mentioned earlier corresponding with audiohouse.ch over in Sweden in my search for power supply documents. I also reached out to them regarding some spare parts, which I ordered and have received. They were super helpful and patient with all my questions. The first thing I asked them about was a tool to pull the modules from the frame. I read in the manual the console shipped with a set of “module extractors”. See, that would be pretty handy because I hate having to use a screwdriver or spudger to pop a module out. The manual has the part number for the extractor. I thought ”Geez there’s no way they have those things.” Wrong. Plenty in stock, and I think they were, like, $3 each. They look like this:




So cool. So now I have my own set of genuine Studer extractors for the console which is great. I also bought a set for the fella I talked about in an earlier post who originally procured the console for the state university where the console served for most of its life so far. He has a cool little Studer 961. He uses dental picks to extract his modules. Not any more. I also ordered a few spares of some of the fasteners used to screw the modules to the frame. They are a button-head socket cap screw with a captive nylon washer, and then an ‘E’ clip snaps on once the screw is in place on the module chassis to keep the screw in place, but also so you can use the module extractor to hook under the screw and the clip holds it in place so you can pull the module. I’m not missing any, but I thought what if something happens someday and I need a couple…they would be hard to find, and I wanted the Studer spec parts so I ordered a few of those. They were cheap. I also saw in the manual the console ships with a couple fader bridges to lock two mono module faders together for stereo functionality…a convenience accessory, but I wanted some. Here again I thought there was no way they would have them, but they did, and they were around $4 so I got a few. Obviously I don’t need these for the stereo channels, but they could come in handy on the mono input modules or the mono group modules. Last but not least, fader knobs. So, from the factory, the 928 has all grey knobs on mono and stereo input modules, orange knobs on group modules, red knobs on master modules, and green knobs on the VCA master faders. The consoles also ship with an assortment of spare knobs in a variety of colors (red, yellow, blue, green, orange, white and grey…two each) so you can use different color knobs to quickly visually identify what is on certain channels…just however you want…identify stereo pairs or if you are using some stereo modules as effect returns put blue knobs on those…just whatever. Well, during its service life at the state university almost all the grey knobs were pulled off the stereo modules and replaced with the different colors from the spares kit, and the grey knobs are all long gone. Fine. At least what’s in place on the stereo modules are all Studer knobs and the shape matches. But over in the master section the group and master modules have generic P&G fader knobs in white and blue, and they each have numbers on them like “10” or “21”…so somebody made off with those original parts and put numbered channel fader knobs from some other console on the Studer. Wow. No. That just won’t do. So I was starting a search for used spares of fader knobs figuring over time I might find enough to at least replace the non-Studer knobs in the master section. This was in spite of being told “you’ll never find any of those…good luck.” Hey audiohouse.ch do you happen to have any fader knobs available? Yes they did…everything but grey. The irony. Oh well. They had black, red, yellow, blue, green, white and orange. Then the next assumption is they would be horribly expensive. I was prepared for a price of maybe $10-15 each. Nope…$3 each. So what I did is bought enough to have at least four of each of those colors (black, red, blue, green, yellow, white, orange) on top of what is supposed to be in place in the master section and on top of the grey knobs on the mono modules…plus there are two more grey knobs already. That gives me enough to populate all the mono input module and master section faders on the console as it came from the factory, and then I have enough to use colors on the stereo modules plus have 14 spares in different colors. So I’ll probably typically keep grey for live sources…I have a total of 14 of those grey ones so that will cover the 12 mono mic/line modules, and then I’ll have two more if I’m using a couple of stereo channels for live sources when recording. Then I have all those different colors for the rest of the 16 stereo modules…one color if I’m using a module or two as a stereo effects return…there are four assignable effects returns in the master section, but sometimes the EQ and insert functions will be nice to use on an effect, and for sure the stereo width control on the stereo modules will be great on stereo delays or reverbs…flanger…any stereo effect, really. And then other colors for keyboard tracks, or drum tracks…guitar tracks…vocal tracks…you get the idea. I don’t know why I get so excited about these little details…




Troubleshooting Module #27…

The other thing I’ve been working on is troubleshooting a bad stereo input module. So far that is ALL I’ve found wrong with the 928, aside from the left meter for the master A buss isn’t working, but I already know that’s not the meter, so likely a simple connection needing re-seated or a solder joint needing reflowed, although I kind of doubt it’s a solder joint…the quality of the materials, manufacturing and design on this is so nice. But, stuff happens…the frame is designed to easily get to everything while its in service, so once the frame is off the floor I’ll dig into that. But I digress…so module #27 has a bad output on the right channel. I used the block diagram and the channel’s own feature set to narrow down the problem area, which was something at or just post channel fader. In other words when I monitor the stereo signal post EQ and pre-fade its good, but when I monitor it in any of the outputs (i.e. all four groups, both master busses, all six mono AUX busses and both stereo AUX busses) the right channel is bad. I assumed because of how the signal failure sounded it was a bad opamp. So I took my oscilloscope and probed at the output of fader booster amp at the output of the fader…it was bad there…sine wave looks like an amalgam of a sine wave and a square wave. So then I probed the output of the VCA booster amp…bad there. So then I probed at the input coupling cap upstream of the VCA and it was good there…signal goes through that cap, and then through a series input resistor with an RC network loop around the resistor and then hits the input of the VCA…bad there…good before the passive components, bad after. I’m not sure how or why but I knew it couldn’t be the passive components, but I’m not familiar with VCA circuits, so I reached out to a friend of mine. He explained the VCA input is designed as a virtual earth input, which the series input resistor provides. So I should see no signal at the input of the VCA. I was glad for the explanation because that’s how the left channel looked, and before the explanation I was very confused…I *hear* signal, but the scope says there’s none?? Anyway, so the assumption is the VCA is bad. It’s a THAT 2181C part, which I guess is somewhat hard to come by, and they’re not the cheapest component…Mouser happened to have them in stock at $4-ish each. I ordered four of them…so as soon as those arrive I’ll put one in and see if that fixes the issue there.


Extender Cables…

I am also working on fabricating a set of extender cables so I can connect modules to the console frame and work on them while they’re out of the frame. The input and group modules interface with the motherboard via two 64-pin DIN 41612 “eurocard” connectors, and the master and monitor modules use three each. So I want to make up three sets of extender cables. I found the connectors at Mouser, and have those on the way, and I found multicolor 40-conductor ribbon cable on Amazon with the correct pitch (2.54mm) and ends terminated with sockets that should mate well with the solder pins on the connectors…so I’ll put a socket on a pin, solder it together and then slide a small piece of heat shrink over the joint…and then do that 191 more times. Should be effective and reliable, and the total cost for all the parts was maybe $50. I wonder what I Studer assembly would cost…if I could ever find one. And I’m certain that’s not going to happen. I think these will work well. I also bought a set of breadboard 2.54mm pitch 40-conductor ribbon cables terminated with dupont connectors…one set male to female, and one set male to male. I can separate these into chunks or singles and use those to interface with individual conductors in the sockets on the motherboard OR take a module completely away from the frame and power it and troubleshoot it on the workbench…the dupont connectors should interface with the pins on the module connectors and the sockets in the connectors on the motherboard. Could come in handy for motherboard or module troubleshooting/testing, and all of that was, like, $10. I have to say, my experience so far working on module #27 has been a joy compared to working on my Tascam prototype console, mainly because I have schematics, parts lists and PCB layouts for the Studer , but also the way the Studer modules are put together…each module has two PCBs, a main PCB and a “side board.” The component sides of these boards face each other; the solder sides of the pair face out. When I first saw that it looked weird to me and I actually thought it would make it harder to work on it. I can’t understand what I was thinking now. My Tascam has two layers of PCBs too but they are oriented the same way…they face the same way rather than having the component sides face each other. The problem there is then for one layer you can’t get to the solder side. That’s the important side when troubleshooting because you can access all the pins of all the components, but on my Tascam half of each module’s solder side of the PCBs are buried. The Studer modules you can absolutely get to everything with the module assembled. I know this is not unique to Studer at all, but it is new to me and I love it…so much easier to work on. And the PCBs being thick glass fiber type as opposed to the phenolic boards in the Tascam…much more robust and serviceable. I’ll say it again I’m not knocking the Tascam…LOTS of gear uses the phenolic type boards…it is a lower cost material and that’s one of many ways Teac got good gear into the hands of many who otherwise would not be able to afford it. But I’m enjoying the Studer. Oh, and if you need to get to the component side of the side boards, they are so easy to remove, and they connect with short ribbon cable and connectors so it is entirely possible to remove the fasteners that hold the PCB, and tip it fully away from the main PCB with everything still connected…On that note, I’ll close this extra long post with a short YouTube video that covers a little closer look at the anatomy of one of the mono input modules…excuse the fact I captured the video in the kitchen with the module sitting on the stove top…I have to use a variety of spaces since I lack a dedicated workbench right now until the garage conversion is done. Anyway, enjoy!

YouTube

 

[ecc83]

Well "I" read it Sweetbeats, twice! You are bloody exhausting in your persistence to get this console back to spec! Good on ya.

A couple of suggestions if I may? Cold garage? Here you can buy "Damp Chasers". These are ally tubes of about 10W rating and are about 2 feet long by 3/4" OD. They are designed to go in pianos and organ lofts in unheated churches and similar places. They never get hot enough to burn a pinkie but create just enough heat in a confined space to keep damp at bay.

The SMPS units: I do not for ONE moment wish to denigrate your electronics skills Mr S but these are BASTARDS to fix! Often suffer "domino" semiconductor failures and you can spend a day replacing parts only to have it blow up in your face again. I know you are keen to keep the whole system as original as possible but, 'twere me I would be building a linear supply as backup using a nice chunky toroid.

All power to your solder iron sir!

Dave.

 

[sweetbeats]

Well "I" read it Sweetbeats, twice! You are bloody exhausting in your persistence to get this console back to spec! Good on ya.

A couple of suggestions if I may? Cold garage? Here you can buy "Damp Chasers". These are ally tubes of about 10W rating and are about 2 feet long by 3/4" OD. They are designed to go in pianos and organ lofts in unheated churches and similar places. They never get hot enough to burn a pinkie but create just enough heat in a confined space to keep damp at bay.

The SMPS units: I do not for ONE moment wish to denigrate your electronics skills Mr S but these are BASTARDS to fix! Often suffer "domino" semiconductor failures and you can spend a day replacing parts only to have it blow up in your face again. I know you are keen to keep the whole system as original as possible but, 'twere me I would be building a linear supply as backup using a nice chunky toroid.

All power to your solder iron sir!

Dave.

Dave, thanks for the suggestion on the damp chaser! I’ll have to look into that. I remember my mom used to have something like that in her Steinway baby grand...!

And, yes, you are spot on regarding the switching mode supplies. I know they are much more difficult to repair/troubleshoot than a linear supply. My preference would be linear supplies. I’ve got switching supplies. So for the time being I want to have the best chance at getting help to rectify issues if they come up and not having the tech docs is not going to help. If/when the supplies start having issues, I will likely look into linear supplies at that point.

 

[miroslav]

So this is a SUPER long post...

I love it...you're now going through the same scavenger hunt for parts and schematics I went through with my Trident.
It sucks that it's hard to find things, but you know this process when you're dealing with older analog gear.

After I overhauled mine with the recap and rechip...I took inventory of the spare parts that came with the console, and then I set out to see what else I could turn up. I managed to find enough of what I could need, and luckily, the company (Omeg) that made the pots for the console, was still in business. I got some great help from them, pot-by-pot (you wouldn't think there are at least a dozen different types on the console) they found all the right replacements...so I ended up buying a whole bunch. I will probably at most need maybe a handful over the next few years...but I figured I should get enough now while they were available even if I didn't use them.

I also didn't have your problem with the PSU...since mine had already been replaced with better options, plus all the PSU cabling going the console was redone...but I can appreciate your desire to get a handle on that...because the PSU and cabling are key to the whole console operation.

And don't even tell me about schematics...I had to work off of "close-enough" schematics...and finally found the right ones just this past year, after I completed all my work on the console...but now I have it for the future.

It doesn't look like you're going to need to do any recap/rechip with your Studer...so that's a lot of time, effort and money saved...and yeah, those channel PCBs look immaculate and so perfectly laid out. The ones on the Trident were very clean, and the layout wasn't as thought out as perfectly as the Studer, it has more vintage analog look to it, but it's less complicated than your Studer circuitry, so not hard to follow and work on.

Just keep plugging at it...and IMO, the faster you dive in and get all the necessary stuff sorted out, the better. You know how it goes when you kinda leave something go, and you plan to get to it later on...and then 2 years go by and you never get a chance to do it. So just keep going with it and stay motivated with your future goals in mind.

 

[miroslav]

Dave, thanks for the suggestion on the damp chaser! I’ll have to look into that. I remember my mom used to have something like that in her Steinway baby grand...!

Not really sure where/what you need...but if it's to keep the moisture from building up and keep it kinda "warm"...there's also the gutter/water pipe heat coils you can find in Home Depot. You wrap them around whatever...and plug them in, and they give off just enough heat.
I wouldn't keep it covered in sealed plastic, as that might trap moisture in...maybe something porous that will breathe a bit.
There's also the moisture trapping containers that you can buy for putting in clothes closets and whatnot. It's some type of moisture sucking silica gel in a large plastic cup...and you just remove the seal and it sucks up the moisture, and after awhile you find that the cup is full of water...but once you use them, you toss them, so that can get more expensive than a coil or like Dave said, some kind of Damp Chaser.
Check the music stores online that handle expensive pianos and acoustic guitars...there are a few devices for maintaining the right humidity...but you're kinda fighting an uphill battle if it's a unheated garage scenario, and out there where you are, probably at least a few more months of cold/wet weather.

Another option...if you have the storage space inside...pull all the channel cards and master cards, etc...bubble wrap and store them inside...and leave the fram in the garage.

 

[ecc83]

Hi Mir', my idea would be to put the chasers inside the desk, at the bottom and throw a couple of blankets over the thing.

Dave.

 

[Muckelroy]

Sweetbeats,

Are you sure the "~" button sends tone generator to the channel? Does that button not swap the phase of the signal? I seem to remember on an Otari console, that exact same symbol was on a button used to swap the signal phase.

 

[sweetbeats]

Sweetbeats,

Are you sure the "~" button sends tone generator to the channel? Does that button not swap the phase of the signal? I seem to remember on an Otari console, that exact same symbol was on a button used to swap the signal phase.

Hey, Muck! How are ya?

The “~” sources the tone generator tonthe respectice channel...the symbol looks like a little sine wave. The button that looks like an “O” with a slash through it is the phase reverse.

[MENTION=89697]ecc83[/MENTION] I can get the Dampp Chaser through Wal Mart...I think I’m going to get a couple 24” ones, one for the MM-1000 and one for the Studer.

Quick update, my son and I fixed the bad R channel on module #27...it was the VCA. I desoldered the part and he soldered in the new part. He’s picked up soldering really quickly...he’s got nice technique!

I also got all the parts to make the extender cables and it’s going to work really well...also got the replacement fans for the power supplies.

 

[ecc83]

Audio manufacturers cannot seem to decide on the symbol for phase (which of course is really "polarity") Some use Theta, horizontal line and others Phi, vertical line through an ellipse.

NOT! That I know any Greek or advanced math! Google and Wiki are my very good friends!

Dave.

 

[sweetbeats]

So last night I finally finished conducting comprehensive function testing on all 28 input modules. I did not test the remote start/external mute control facilities of the modules since I don’t expect I’ll ever use those features, but I don’t have any reason to think they don’t work, and I’d need to make a DB9 pigtail to do the testing...bigger fish to fry...knowing me curiosity will get the best of me at some point and I’ll check those things out anyway, but for the time being...

I’m happy to report all 28 modules, with a couple small exceptions (more below), are 100% and sound GREAT.

The only issues I’ve run into are:

* all the mic trim pots on the mono input modules 1~12 need servicing...they are scratchy
* mono input module #12 has an isssue with the automatic CUE defeat; when an input module fader is at infinity (all the way down), and you engage the CUE buss (aka solo buss), as soon as you raise the fader the CUE assignment is supposed to be automatically cancelled. That doesn’t work on module #12, but I already know where to look. The P&G faders on the 928 have a little microswitch to accomplish the CUE cancel feature. I can’t hear that little switch making its tiny little *clik* sound when I pull the fader all the way down or raise it from infinity. So I’ll open that fader up. Likely the switch is stuck or needs replaced. Easy-peasy.
* stereo input module #28 has a dodgey right channel. It works if you press on the dress panel to the left of the stereo width filter control block...sometimes the signal stays for a bit and other times it cuts out again as soon as you release pressure. Should be pretty easy to fix. It’s definitely an issue with the module because it happens regardless of what slot I install the module in the frame. I’m guessing it’s a bad solder joint, but it should be easy to find and fix.

That’s IT!! That is amazing to me considering the console has been moved at least 4 times since its original install at the TV station in California, and it’s nearly 20 years old...I think that speaks to the quality of the design and build. There was a problem with the right channel being dead on stereo input module #27 as I mentioned in earlier posts, but, again, that was traced to a failed VCA, which has been replaced fixing the problem.

Next I’ll test out what I can of the master section, though, again, there will be functions I don’t test because there are remote signal out/external mute control functions, etc...stuff like that. And I also don’t yet have cabling made up for all the 39-pin connectors which handle a lot of the I/O to/from the master section, and trying to clip on to the relatively small pins in the connectors on the backplane sounds like a pain. Hm...I DO have all those DIN 41622 connectors I got though...and several of those still have a chunk of the multi-conductor cable attached...maybe I could, with relative ease, make a 39-pin test pigtail with one of those...I think I’m going to do that. Anyway, I’m more and more pleased with the acquisition as time goes on.