Soundtracs MX Story...

Thanks, Johnny!

It'll look awesomer :drunk: when it gets cleaned up, but all in good time.

It was good getting the chance to work with it a bit last night. I'm a "nester" (I get to know something by tinkering on it and spending time with it...takes the mystery out and builds confidence) and I don't like mysteries in my midst so it was just a bit of a fresh breath being able to tinker a bit, and then to be able to easily get all the channels to come up and route to all the group and main busses, and then to have it be as quiet as it was was just affirming. It really has a plain appearance and the control set isn't really that exciting, but I'm excited about the straight forward flow of the mixer. I think it'll be really good to work with. I always want all sorts of contingencies accomodated...all sorts of "what ifs" but I'm learning that its more important to have what's needed to accomodate a particular focus and go deep on that rather than being able to do all things. Its counter-intuitive to me but after testing out the Ampex MM-1000 audio functions it just became so clear that that machine is the focus, and that I just need something that can feed that recorder and handle playback...something that has the I/O for what I have and am going to use and forget bells and whistles for a rainy day...the rain may never come and then no fun is had in the meantime because all time is spent getting ready for what never comes. Again, counter-intuitive to me, but I guess I'm learning otherwise.

The feel of the switches and the construction overall of the MX is really nice and solid. Its a heavy frame when loaded but when I tipped it back up to store it after the tests were done I had to lift from one corner rather than in the middle of the armrest and there is just no torsional flex in the frame at all. Very solid, and the protrusions at the back are just so handy at this time for tipping it up and not having to worry about the jacks and connections on the back.

Everything still tells me I made a very good decision when opting to pursue this mixer.

Oh, also, I have gotten advisement several times to look for burnt traces or discoloration on the PCB in the PSU especially around the rectifiers for the +/-17V rails. Nothing...it all looks new-ish in there. Tells me that, though its over 20 years old, I don't think it was ever driven hard at least not on a frequent basis.
 
PSU Progress

Been working on mods to the PSU both in components and thermal management...I'm adding a fairly sizeable finned heatsink to the back where there was none...here is the back of the stock PSU:

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The 5 staggered screws along the upper right of the back are where the internal heatsink bar attaches...this is just a plain 'L' shaped piece of aluminum that mounts the PCB and upon which are mounted the regulators...no additional heatsink outside the case. Maybe that's okay but I'm mounting the bridge rectifiers underneath the PCB, so additional surface area would be good...plus I don't feel the stock arrangement is up to par. Even after having the mixer on for about 20 minutes the other night the back of that PSU was HOT...and that was just due to the regulators. See what I'm talking about:

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BTW I drilled all the holes you see in the center-rear portion of the PCB to enhance cooling for the bridge rectifiers.

So, here are the heatsinks I'm using from spare parts:

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These were originally regulator sinks off of the reel motors of a Tascam 48. Notice the one on the left is shorter...it used to be identical to the one on the right. To make them fit nicely on the back I had a machinist friend of mine mill off two fins so when you put them together they look like this:

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The stock arrangement is for that heatsink bar to be attached using self-tapping metal screws into the aluminum bar...I'm going with stainless 10-32 machine screw hardware for tighter fastening especially for the bridge rectifiers which will be direct-mounted to the case right behind the lower part of the heatsinks. So of course I had to drill out all 10 mounting holes in the back of the case:

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Here is a mock-up of how it will look...still have to drill the holes in the left heatsink but then it will be ready to mount up:

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What's nice about how these parts fit is that they'll cover up none of the factory silk screening. :)

The PCB is totaly recapped already but there are still some components to mount and solder in as well as mounting the rectifiers and doing some wiring there related to their new locations.

Coming along...
 
I'm so excited...its coming back together nicely (the PSU rebuild). I'm finished with fabbing all the parts, everything is soldered onto the PCB, the rectifiers are mounted, and I've spread heatsink compound all over the place (not literally...there was just a lot of surface area to cover with the new heatsink pieces, the original 'L' PCB bracket, the rectifiers and the regulators)...the compound was different than what I'm used to using when working with computers...that stuff is really thin. This stuff was a couple bucks more but made by GB and on paper at least it has at least 3X the heat transfer performance of typicaly compound...its thicker and actually a little gritty. Hope it works okay, but regardless I've got that smeared all over everything and I just need to plug the wires up to the rectifiers, remount the PCB, plug the connections back up to it and then cross-connect the rectifier outputs to the PCB...then clean up a bit. Nobody will ever see it once its mounted but the back of the case looks, um...bada** with the new heatsink and the stainless socket-head cap screws...like when companies started making aftermarket "billet" acoutrements for cars, though this will actually be functional. I'll put pictures up later but I should have it all put back together and burned in in the next day or two and then hopefully soon I can do some comparative before and after testing.
 
Done...

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New screws and washers on the face...still a little battle scarred and it'll stay that way. I see it as a worthy soldier with faded fatigues but with honor, a good heart, sharp mind and a strong body ready for another tour of duty. ;):cool:

And this is kind of funny...literally just after finishing up I actually read what is screened on the back:

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Whoops! Dang! I had no idea...probably just voided the warranty! :spank:

Okay, so I'm sending an email to Steven Magalnick to get his blessing on my work and then I'll power it up, scope the rails and then do some noise tests.
 
Its always such a leap of faith for me...hitting power switch after upgrades repairs or mods...I've screwed up enough times to dread what may happen immediately or shortly after the *click* of the power switch...taking precautions, double and triple-checking things, getting into a quiet work area so I can hear sizzling, putting the cover on in case something goes *BANG*...listening, looking, smelling...I dread it yet can't wait to get it over with like an exam.

The PSU is humming peacufully, no bad smells or sounds...everything is nice and cool...several minutes now. I'm working down on the floor with the MM-1000 towering over me; its waiting patiently for its mixer.

Time to get some data...
 
Okay...everything looks like its doing what its supposed to do and the rails look clean...time to see if I can do some comparative testing...
 
Detail of the outcome of post mod objective testing here...

Definitely improvements, though I don't know if you'd call them drastic...thinking not...but I'm still happy I did them, and it now stays much cooler...and my testing is limited to noise levels. Who knows what these mods may do for the sound of the mixer?

At any rate, the PSU refurb/upgrade is done.

OH! And a news flash...the side panels are NOT high impact plastic...painted MDF.
 
The lumberyard is essentially in my shop. I have a very large stack of the walnut, BUT I'm still just going to repain the stock panels. It would be lovely to have walnut replacements, but I'd want them to be the same shape and they are actually a pretty complicated piece (for me) to fab.
 
Received a couple spare channel strips that I purchased....haven't unwrapped them yet and not sure when I'll get to it. $100. Tough to swallow since I only paid $300 for the board but these strips will provide all the replacement pots and knobs needed to refurbish all the strips so its worth it since the best price I found for the pots and knobs would cost WAY over $100 and this way I have lots of additional spares.
 
Okay, so its been awhile since I've done anything with the Soundtracs because of the construction activity on my house...the mixer is still in storage, but curiosity got to me the other day and there may be a couple select caps that I want to upgrade on the channel strips. I'm getting ready to put in a Mouser order so I thought to add to the order what I'd need just to try the upgrades out on a couple channel strips.

Here's a bit of a bummer...The two spare channel strips I bought were out of an "early" MX mixer. I was under the impression that the differences between the early and late mixers was little more than cosmetic and differences in the I/O jacks. Well, no. The strips are quite different. I'd say they are different enough to almost be called cousins. The bummer about this is that the two strips I bought won't provide the replacement pots I thought they would. Same brand of pots (Omeg) but the calues and taper types don't match up. There are a total of 6 pots on my mixer with broken shafts. The spare strips, even though they have 14 pots each comprised of 5 different types (10k, 22k and 100k pots, some of them dual element and a mix of linear and log c taper), will only provide 2 of the 6 pots needed. What I'll have to do is transplant healthy shafts into the pots with the broken shafts. I pulled one of the pots last night off of one of the spare strips and they are easy enough to disassemble, so at least I have a solution to employ when I get to doing that.

BUT...something I've not seen before in grounding...all the pots except one have nylon washers inbetween them and the dress panel for the strip. The one pot is allowed to touch a bared metal surface on the panel. This means Soundtracs went to the extent of ensuring that the ground path between the electronics of each strip and the dress panel went through one path eliminating the potential for loops. Neat.

Can't wait to be able to get the mixer out of storage and freshen it up. There are some high-grade components on the channel strips.
 
@ sweetbeats

EXCELLENT thread sweetbeats!!!:D

Wicked way JEALOUS!!!

That is one hell of a console!
I tend to droooool over M-3700's & M-3500's,
but that Soundtracs board looks to be a better score!

Can't wait to hear the end results.
Hope everything goes smooth for you when you power that
badboy up with it's new innards!
 
Thanks!

You mean power it up with the upgraded caps?

I already tested the power supply mods detailed earlier, and the results were pleasing...IIRC an approximate 4dB drop in the noise floor and no more problems with the mixer getting starved when working hard...and MUCH more effective cooling for the PSU.

I'm anxious too.
 
Oh phew...

A friend helped me move the mixer from the shop into the utility room outside my new sound room. It'll park there for a bit until the room gets finished, but at least its out of the damp cold shop where the animals somehow get in and like to urinate, mainly on MY STUFF!!

Wow...I'd forgotten how big it is...its...big. Its one thing when its in a large shop, but then I get it into the little utility room which is about 72" x 90" and it takes up over 2/3 of the long wall...looks big...
 
And phew again, its in my new sound room now thanks to my wife. She's helped me move more equipment than anybody. She's better at coming up with safer methods that are more simple too. I used to think I knew the best way to move stuff but her ways always seem to work better so now I do this crazy thing and ask her how she thinks we should do it...:D:rolleyes:

Ampex, meet Soundtracs. This is the first time the two devices have been in the same room! I've got the mixer on the floor for the time being because I've got some cleanup to do and its a whole lot easier and safer to tip it up on the floor rather than on a table:

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So my plan was to tip it up, pull the bottom panels off, vacuum/dust it out really well, wipe down the exterior of the frame really well and then get it up on the table and then just take my time getting the strips cleaned up and (as necessary) repaired starting with the master section. I wanted to do it this way to avoid 32 strips and a master section laying on the floor. *^&@#$(!@ Soundtracs really put this thing together to take a beating, but that means that in order to get the bottom panels off you have to drill rivets out on the sides. Seems like a cheap way to fasten stuff together but in reality the rivets hold more tightly and more reliably and honestly there wouldn't really be a reason to take the panels off with modular strips, SO...I'll be taking all the strips out and the master section, get the frame cleaned up nice and THEN put it on the table. It'll be easier to get up on the table unloaded anyway.

I think I mentioned this earlier but it REALLY is a sturdy frame...absolutely NO discernable torsional deflection. You can lift it up at one corner and the opposite corner rises as if it is being lifted/support just the same. Pretty impressive for a 5.5' long frame...no creaking/rattles/squeaking when moving it...solid chunk.
 
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Ah, so that's where the soundtracs is! :D All looks amazing Cory! Plan for the cleanup of the mixer sound real good! We're 90% done!! Yey!!
 
Ah, so that's where the soundtracs is! :D All looks amazing Cory! Plan for the cleanup of the mixer sound real good! We're 90% done!! Yey!!

Welllll...not so fast.

A number of things have transpired here...nothing earth shattering but it will involve a little time if I want to have this done right and never have to pull it apart like this again:

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And actually the meter bridge has been removed since that picture was taken.

There are two main issues going on...the lesser issue is that the bottom panels have been distorted due to improper placement either during storage, transport or use...I knew this all along as it is easy to see where they are dented and pushed in when you tip the mixer up, but being able to have a good look things with all the modules out I can see that the cabling is getting pinched at certain points...there's no longer any clearance in between the bottom panels in sections and the input channel and group channel cards. This has damaged a couple of the cable sections, one for the meter bridge and one that goes from the jack panel to the master section. One cable is definitely bad and may be the cause of noise in the system from the meters when the oscillator is engaged...see here right in the middle of this picture you can see the tear in the ribbon cable:

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Here is the other one...a spot where the ribbon cable was smashed. This cable may still be good as the insulation is still intact...I'm going to test continuity on this one and if it is still good I'm going to use it for the meter bridge cable just in case any strands have been compromised...I don't want to use it for carrying audio signal. The area in question is also right in the middle of the following picture...the darkened distorted area in the middle of the ribbon cable:

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I need help...does anybody have any of that ribbon cabling laying around? I can't find that in short lengths anywhere. It is the same stuff used for IDE drive connections in personal computers (1.0mm pitch 40-conductor 28AWG stranded cable)...seems I can get 100' if I want no problem but I only need 2'.

Anyway, that's one issue that needs to be resolved and once I'm done cleaning the meter bridge and can bolt that back up then I can get some wood blocking under the bottom panels in strategic locations and then push things back closer to their original positions to restore the clearance by standing in spots and hopping a bit. It'll never be "straight" because of some creasing and stretching of the metal from the damage...you just can't really ever get rid of that but I can at least restore the clearance and that's good enough for me. You can see some of that creasing and denting in this picture...you can't really see the overall bowing up of the panels in the center but just trust me its there:

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So that's the easy issue. The more challenging issue is with grounding. I knew this was going to be something with which to contend as soon as I read "star-grounding" in the manual. I've had the good fortune of reading a 1995 AES publication regarding grounding in audio systems written by AES member Neil Muncy. Neil has made significant contributions to the audio industry and the AES. So a lot of the publication is over my head but it is written in a way such that a lay-person can get the important nuggets and at least be armed with enough info to start looking at his/her systems and potentially addressing noise issues that are grounding related. The bottom line is that the audio industry has been at odds/disagreement over what consititutes proper grounding, and this leads to inconsistent treatment of grounding and when systems aren't compatible in the methodology used the door is open for problems...problems that even the "silver bullet" of balanced audio cannot fix. I see three main facets to this issue: 1. ensuring that each signal "ground" only has one path to a common system ground reference, 2. that those paths are as short as possible with respect to the point where the signal enters or leaves the system, and 3. that care is taken to how signal conductors are routed and to keep them as far as reasonably possible from higher voltage pathways and particularly unregulated paths.

Here's a practical application: a mic input jack on your mixer; if the common ground reference for audio systems in the mixer is the chassis to which the jack is mounted, then pin 1 of that mic jack should ideally be bonded to the chassis right there where that jack is mounted, where that signal enters the system. My mixer, and plenty others are not...in the case of my mic jacks, jacks are mounted to jack PCB's in groups of 8, and pin 1 from each jack is common on the PCB and then one wire from each ground trace on the PCB goes to a single ground lug down behind the master section...see here in the middle of the pic:

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That means that, for channels 1~8, the ground wire for those mic jacks stretches several feet. So that is a breach of the best practice of having the pin 1 to chassis ground reference connection being as short as possible. That length of wire, in spite of the shielding properties of the metal chassis, can STILL pick up EMI and even RFI, not to mention it is open to picking up internal interference. Remember the other issue with facet #1? That each pin 1 conductor only have ONE path to the chassis so that no ground loop exists? Well, the Neutrik XLR jacks on my mixer have variable conductivity between pin 1 and the shell of the jack, and the jacks are riveted to the chassis, and there is variable conductivity there as well. I measured resistances in the mega-ohm range (not so concerning but it IS indicative of the existence of some secondary path) down to 17.5ohms...so does that make sense? Pin 1 of each mic jack goes to its jack PCB which has a common path via the PCB trace to a wire to the star-ground lug, and each jack ALSO as a path to the chassis through the shell of the jack and its mounting to the chassis. So we've got long ground runs AND secondary paths. Here is a pic of an XLR jack PCB...you can see the lighter brown areas on the PCB are the traces on the other side, the largest of which are the ground traces...the black/red/green wires coming off the PCB are the signal wires from each jack that go to the respective channel card, and then at the top right of the pic you can see a terminal with TWO green wires coming off of it...that second wire is the one fro that jack PCB that heads on down to the star-ground lug:

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The other jack PCB's for each set of 8 channels are a whole 'nuther story (line in, insert and direct out)...the jack bodies themselves are plastic, so no secondary path to the chassis there, but there is still the same problem of the lengthy common wire to the star-ground lug...and there is a whole additional layer of issues unique to each PCB. The three boards themselves are the same part, but each one is a slightly different assembly as there are components mounted to some as well as a multipin connector because on some M-series models (namely the MRX) there is an integrated patchbay "sidecar" in the frame which interfaces the I/O jacks at the jack PCB...so it isn't a simple matter of isoating the grounds and tying them back to the chassis at the jack...here is a shot of the trace side of one of the jack PCB's:

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Let me just recess for a moment to mention that I'm tickled to be getting consultation on this from Neil Muncy himself. There are some seriously nice folks in the audio world. Neil and I have been able to become somewhat acquainted over on the recordist.com Ampex List and we began dialoging about audio system grounding back when I was having grounding issues with my Ampex MM-1000. He's taken time to help educate me and I contacted him with an "Ah-HAH!" when I opened up the Soundtracs mixer and found what I found.

We've now identified that there is potentially a tertiary system issue with how grounding of the modules takes place because there are two grounds carried on that big snakey ribbon cable that interconnects all the cards. So I'm going to take some time with the schematics and the hardware tonight and isolate what travels where as far as grounding, make sure the chassis ground reference is formidable at the point that the power umbilical connects to the backplane and then listen, listen, listen to Neil as we chip away at these issues one by one.

WHY go to all this trouble? HOW could it be done so improperly in the first place? The M-series mixer design dates back to 1982...the audio world is STILL at some odds about audio system grounding even today...it was VERY much an issue in 1982, and EMI/RFI was also not as large an evil and even lesser so in Europe where the Soundtracs mixers were designed and built. Today? With cell phones and other digital transmissions? Data conduits? Its a noisy world we live in. Plus I can see the radio station that's down the street from the studio windows. Lastly and probably the greatest contributing factor to why I'm doing this is that its me...I can't help myself. I have it opened up. I want to do it right, do it once. I don't want to have it opened up again to deal with noise issues and since the mixer is THE HUB for audio in the studio I want to know I have done everything reasonably necessary to limit noise infiltration into the system and to be able to work backwards from the mixer with any issues as they occur...to have a reference standard to which everything connects.

So I'll post updates to this issue as we chip away at it.

Here is a video I captured a couple days ago after I had everything opened up and the lights started flickering on in my head of just how extensive the issue is...the "What were they thinking" at the end is genuine...that was a genuine "waaiiiit a minute...THAT'S not good..." moment:

YouTube

Aside from all this grounding stuff I'm enjoying getting familiar with the guts of this thing, and though I have encountered the previously discussed areas of improvement with the power supply, and now these grounding issues, my strong sense is that this is a great mixer...high quality components were used throughout...the PCB layouts are elegant and demonstrate clear attention to good design, and I still really like the feature set. I am really pleased with the build quality. And I'm also just enjoying this type of design; the single channel modular design...the ribbon cable connections are quick-release latching type and the I/O connectors are low-friction type as well so the modules are super fast and easy to remove. I think it took me maybe 25 minutes to unload the entire frame? I don't want anybody thinking that it is a dud or that I regret getting into it. Like I said before you'll find grounding issues in lots of stuff...I'm simply going to be applying what has come along since it was designed.

Some more pictures in no particular order...

Pile -o- channel strips:

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Pretty master section...love those glass fiber PCB's that let the light glow through:

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Mommy, lookit all the jacks!

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The aluminum extrusions for the meter bridge as well as the armrest are REALLY substantial and quite intricate, and another thing I wanted to show you all from a design aspect is that the threaded holes to which the modules attach as well as the bottom panels and backplane are actually heavy-guage yellow zinc-plated steel inserts. For one thing it would be relatively tough to strip one of these out but if you DID it would be simple to replace that section...I've seen lots of mixers where the strips fasten right to the extrusion or a formed steel panel which is fine but in the field you can only fasten and unfasten those joints so many times before the threads become compromised...eventually they will fail. Now in most cases I wouldn't think it would ever be a problem unless the mixer WAS a dud and you were having to constantly take stuff in and out, but it is simply a better design; better engineering, and it DOES make a difference in the overall rigidity of the frame because you CAN apply more torque to the fasteners between the extrusions and the backplane and bottom panels than would be comfortable without the insert design:

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Trying not to rabbit-trail. Very anxious to have this thing up on the table and connected up, but I've come this far and done so much work with the room and the Ampex tape deck that I can't compromise what I know with what I do. Hopefully I can get to the bottom of this grounding thing in reasonably short order and finish getting the frame cleaned up.

BTW, overall the condition of the mixer is good...dusty but otherwise clean inside...NO corrosion at all anywhere.
 
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For those of you that are gluttons for punishment, below are links to a seven part YouTube video series covering my initial exploration into the grounding scheme of the MX mixer. This series doesn't yet cover any solutions, but rather sets the stage for what presently exists and poses some questions about what may need to be addressed.

YouTube

YouTube

YouTube

YouTube

YouTube

YouTube

YouTube
 
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