Refurb M3500 into an M3700, or M3700 into an M3500....?

sr71rules

Member
An interesting opportunity has come my way and I can't think of any better group of people to discuss it with...

A couple months ago I bought a Tascam M3500 in fairly good condition. It has some minor cosmetic issues and a few technical issues but nothing catastrophic. The only major issue I've found is that the right balanced out on the master bus doesn't work. The unbalanced RCA jack does, just not the XLR.

The other day I came across a guy not (too) far from me selling an M3700 with some issues for $200. Considering I just spent more than that amount on ebay for 8 channel modules for spares, I've committed to buying the M3700 and am picking it up next week. The guy who owns it says the second fuse in the power supply keeps popping and as such the inputs don't work. Sounds.. interesting. In my conversation with him it's also come up that 1/2 of the channels have been modded with 'burr brown' chips. I suspect a bad channel is causing the issue with the power supply but I'm not in any way an expert.

The question now is, which board should I harvest from and which should I rebuild?

From what I've gathered the 3700 and 3500 differ only in respect to automation. The 3700 has it, the 3500 does not. The 3700 has VCA automation controlled by an onboard computer sync'd via MIDI? I've also heard that the automation is noisy but I don't know what that means. The faders on the 3700 are noisier than those on the 3500? Is that true only when automation is enabled or are they just more noisy all the time?

I think it would be a lot fun to get the automation system working on the M3700 and I would enjoy the project even if I never use it on a paying session. It appeals to my inner geek and I've always been fascinated with older technologies and how they relate today. That being said, if using the M3700 with it's automatable faders will degrade the quality of sound going to mix bus even when I'm not using the automation, then I would prefer to not do it. Does anyone know? Has anyone used both?

The M3700 has the full 32 channel meter bridge that I desperately want for my M3500 and that alone is worth the $200, to me at least. If beyond that this board is just a pile of spares I'm fine with that but, as I said, I'm a geek and I love a fun project.

Step one will be to pull each channel module out and look it over for burn marks, ect. to see if I can find the problem channel strip. If I'm successful it'll just be a matter of cleaning up the board and testing every function and plug. Any further ideas? Right now the plan is to drive out and pickup the board a week from today so it's not a great rush nor do I need this board to go into use for a session ASAP. I'm in the process of moving my studio to a new location and things at the old location are still running fine... though sadly without the help of these M3000 series boards :D

Robert
 

briank

analog for the people!
From what I've gathered the 3700 and 3500 differ only in respect to automation. The 3700 has it, the 3500 does not. The 3700 has VCA automation controlled by an onboard computer sync'd via MIDI?

It's VCA automation that can control both the channel and monitor fader positions as well as channel, monitor and aux mutes and EQ in/out. You can sync MTC or SMPTE time codes at various frame rates; there's a panel with a flip-up door just above the automation module with some DIP switches that lets you set your sync options. For connectivity you have MIDI i/o/thru as well as balanced and unbalanced AES SMPTE. I have used the dynamic auto via MTC with both my Alesis HD24's on board MTC gen as well as ProTools HD via a cheap Turtle Beach 1x1 USB interface (though ProTool's MTC gen settings can be fussy, that certainly isn't the Tascam's fault!). I also use the snapshot mode for simple fader and switch recalls when I leave a mix overnight, very handy to quickly figure out if my studiomates have bumped the faders or switches while I was out!

I've also heard that the automation is noisy but I don't know what that means. The faders on the 3700 are noisier than those on the 3500? Is that true only when automation is enabled or are they just more noisy all the time?

It's the VCAs that people are saying are noisy, and yes you'll notice a slightly higher noise floor with all the VCAs switched in (that's what all those "Bypass" switches at the top of the faders do, when in you're bypassing the VCA auto) and all channels un-muted, but in my opinion (and experience), it's misleading to suggest that automated mixes will be noiser. Frankly I use the auto in my M3700 for quieter mixes, because automating the channel and aux mutes results in a much quieter noise floor than if you were mixing with all the channels open but bypassed. The VCAs do make a modest tonal change to your signal, that's true, but again you have the bypass switches so you only need to switch in the VCAs for the channels you're actually automating, it's a nice touch of compromise on a board like this. In the end, frankly with these boards I'd worry more about what the grounding scheme and PSU are doing to the noise floor than the VCAs; you may have already found this with your M3500.

I think it would be a lot fun to get the automation system working on the M3700 and I would enjoy the project even if I never use it on a paying session. It appeals to my inner geek and I've always been fascinated with older technologies and how they relate today.

The M3700's auto is actually pretty good especially for this level of board, with its sync options and its ability to either do snapshots or full dynamic fader and switch moves, and it's also quite easy to learn and use in my experience. This was the first console auto I've used and I had the hang of it at the end of the first session. Whether it's worth it in your situation I couldn't say, but unless you're doing really delicate classical music or something like that with this board (in which case...yer nuts :D ) I think it's dubious to suspect that the auto will make your mixes "worse" especially if you're selective with what you do and don't use more auto than you really need.
 

sweetbeats

Reel deep thoughts...
I'm living vicariously through you...and happy to have you be the one pondering frankensteining the two together. :)

But it IS an exciting idea. I feel comfortable encouraging you because you sound like you've already made your mind up, are committed and seem at peace with it.

If it was me I'd be focusing on the M-3700 for the same reasons that you are curious about it, but also because the meter bridge is already on it.

I don't know anout the automation "noise" and such, but others do so hopefully they'll chime in.

Just to be sure, you do know that the faders themselves are not automated/motorized right?

And as far as troubleshooting the fuse issue step 1 is always to isolated the power supply rails and make sure they are putting out the right voltage and then if you have a good meter to set it to AC and test the DC rails for AC components. A DC power rail should produce...DC voltage, ideally NO AC voltage. I can't tell you how much I appreciate having an analog oscilloscope here for doing this because it lets you SEE the waveform, to really see what's going on. A lot can get by even good DMM's.

If the PSU looks good I'd be looking at the schematics to see what is powered by that fuse and see if that narrows the issue down to something obvious. Short of that, if it is on one of the audio power rails (+/- 15V) then I'd pull the power from each board powered by those rails and then one by one add them in to the system until the fuse blows.

Another comment, depending on how far the "Burr-Brown" mods went on the boards, 16 channels fully modded with BB chips (I'm assuming they are probably OPA2134's...if it is something better then you really can be excited) would be worth at least a good chunk of the $200 for the chips alone.

Sheesh...M-3700-32 with full meter bridge...with the exception of the rare balancing kit that is the pinnacle of the M-3000 boards.
 

briank

analog for the people!
Just to be sure, you do know that the faders themselves are not automated/motorized right?

Just to clarify, the faders ARE automated but are not motorized. Instead, the automated fader moves are shown by a pair of up/down LEDs on each channel. They are both lit when the fader is at null position, and one or the other lights up when the VCA fader position is above or below the actual physical fader position respectively. But yes, you will be waiting a very long time for those faders to move on their own ;)

Another comment, depending on how far the "Burr-Brown" mods went on the boards, 16 channels fully modded with BB chips (I'm assuming they are probably OPA2134's...if it is something better then you really can be excited) would be worth at least a good chunk of the $200 for the chips alone.

Yeah, if you have 2134s, those are real assets. I priced priced doing 16 channels of my 32ch M3700 with 'em and at today's prices, your $200 was probably more than worth the upgraded chips alone.

Sheesh...M-3700-32 with full meter bridge...with the exception of the rare balancing kit that is the pinnacle of the M-3000 boards.

It is. Although these days I'm keen to upgrade my M3700 to a big monster large format console like an MCI, I will definitely miss my M3700 automation when it's gone.
 

sweetbeats

Reel deep thoughts...
...frankly with these boards I'd worry more about what the grounding scheme and PSU are doing to the noise floor than the VCAs; you may have already found this with your M3500.

Ahhh +20 to that. Worth looking into with anything in your studio AFAIC.

My Soundtracs MX desk has some grounding re-work to be done when I get to it as pin 1 of all the XLR inputs are star grounded to the chassis in 8-channel lumps. Each of those wire lengths introduces a small ground loop and potential inductance issues. I'll be grounding each one as close as possible to its jack.

Brian, thanks for the excellent summary of the VCA automation features of the M-3700 and some of the benefits. That was a good read.

Yes, I should have omitted the word "automation" altogether from my statement about flying faders. You cleared that up.
 

sr71rules

Member
You all are dangerous friends to have! At least I'll have a project for the long winter months...

I did know it doesn't have flying faders. I've come to terms with the lack of motion... Blinking lights will have to suffice! I'll be too mesmerized by the meter bridge :)

Thank you for the excellent information Briank. Really awesome! So many questions answered. I didn't know the automation system was so powerful. I thought it was just volume and mute on the main faders. I was modertaly excited to get such a good deal on some spares.. now I fear I won't be able to sleep until it's safely in my house.

I'm certainly going to try and refurb the M3700 and based on Briank's info I suspect it will find itself in quite a few of my mixes.

I've not had any noise issues on the M3500 board yet but I keep hearing people talk about the grounding being a problem. Am I missing something? Is it something that will only present itself when it's hooked up to a dozen XLRs strew across the studio? Should I do grounding work proactively? I've always been obsessed with the mains wiring of my studios to be sure everything is grounded properly but with the M3000 series lacking a ground pin on the power supply I suppose some other solution is in order...

I had been considering the mod'd channels a liability and perhaps the root of the power supply issue... now I'm looking forward to A/B'ing the channels to see what the sonic difference is. Perhaps I'll post a few sound clips down the road so people can hear what modding a board can do to the sound...


Thanks for all the input thus far. I knew I came to the right place. Ever more proof that digital is newer but newer doesn't always mean better.

Robert
 

timkroeger

Custom Title User
Don't be too enthusiastic about the chip tuning, I did 4 channels and the master section on my M-3500 with BB OPA-2132 and I didn't really notice a difference to the stock chips. It may be my ears are missing some training or the monitors are not up to par (Yamaha HS80M active) but I simply couldn't make out a difference.

I did some tests with OPA-2604 chips and it was really difficult to keep them from oscillating. They got pretty hot, unpleasant to touch and in order to generate so much heat you need some current. Tha bad thing about it is: you don't hear them oscillating. You don't notice it unless you touch the chips or put a probe to them. The 2604s need more current than the stock chips or the 2134/32s anyway so if someone does half a board with them, a power supply upgrade might be due. If your board is modded with 2604s instead of 2134s, and your 16 x 5 = 80 chips are madly oscillating at about 3MHz maybe that's the reason for the PS blowing a fuse? On second thought it does sound more like a short somewhere. You should have a look at by what chips the stock ones were replaced.

Nice info on the LED indicators for snapshots. I didn't know that. I wouldn't be concerned about the VCA being noisier or not. I read that somewhere too, but I don't think Tascam would have sold the M-3700 if it was that much worse.

Cheers
Tim
 

miroslav

Cosmic Cowboy
Don't be too enthusiastic about the chip tuning, I did 4 channels and the master section on my M-3500 with BB OPA-2132 and I didn't really notice a difference to the stock chips.

There was a guy (I use to have the links) who spent a HUGE amount of time, effort and money doing all kinds of upgrades to his 3500. He documented the entire process and the large variety of chips he tried. There was always some kind of tradeoff it seemed no matter which chips he picked...or not much difference from the stock.

I considered doing some upgrades to my own 3500...but based on comments similar to yours, I decided to not bother as long as my board stayed functional...and here it is, 20 years since I bought it and it's still kicking without any real issues in the entire 20 years (knock on wood).

A couple months ago I bought a TASCAM M3500 in fairly good condition. It has some minor cosmetic issues and a few technical issues but nothing catastrophic. The only major issue I've found is that the right balanced out on the master bus doesn't work. The unbalanced RCA jack does, just not the XLR.

The other day I came across a guy not (too) far from me selling an M3700 with some issues for $200. Considering I just spent more than that amount on eBay for 8 channel modules for spares, I've committed to buying the M3700 and am picking it up next week. t

Good luck with your project. I personally don’t get too hung up about not having the 3700 automation with my 3500...I don’t think it’s all that critical. I had 32 channels of outboard MIDI automation, which did the same thing as what you get with the 3700…and I only used it for a short time, then it sat around unused for a number of years, and I finally sold it to a guy in Canada last year.
With my hybrid analog/digital setup…I have even less need for automation, especially when it’s only basic mute/level automation, like the 3700 has. I can automate much easier in the DAW…and I just let it all play out through the 3500 as I mixdown OTB. :cool:

Anyway…the only thing I regret is that I didn’t buy the 32 channel version of my 3500…of course, I bought mine new so it was a matter of a couple of thousand to go for the 32 instead of the 24. I think I paid about $8k for my 24-channel w/full meter bridge...but I'll tell you, even during mixdown, I rarely exceed my 24 channels…and on the rare occasion I needed more..the 3500/3700 have the additional Tape Monitor channels…so I would just use those if I needed more than 24.

My advice is that you focus on refurbishing whichever console has less issues and better chance of running with full functionality…rather than getting in too deep with the 3700 just for the sake of the automation. Heck…if you want to utilize the 32–channel meter bridge even if the 3700 has un-repairable power issues…you could always swap all the 3500 modules (plus those spares you bought) into the frame of the 3700…and then still use it’s 32-channel meter bridge. :)
 

sr71rules

Member
Always the voice of reason Miroslav! I shall of course endeavor to end up with the most reliable setup. The automation will be a project of fun if the 3700 is workable. If not, I won't cry over it. I had initially been considering swapping my 3500 channels in the 3700 frame to use the meter bridge but with some encouraging here I will attempt to get the 3700 going. Perhaps I can use the M3500 strips to 'unmod' the M3700 strips if it looks like the mod is issue. Tim's information seems to suggest that they could in fact be the whole issue. Lots to think about... Nothing can be decided however until I can open up the M3700 and see what's what.

Any thoughts on ground microslav? Have you done any electrical work on your board?

It's going to be a busy winter!

Robert
 

miroslav

Cosmic Cowboy
The only thing I've done mod-wise to the 3500 is to permanently rewire the preamps and balanced I/O connections to Pin 2 +/hot instead of the Pin 3 as TASCAM had it. It wasn't a big deal, but it took an afternoon to do it.

AFA grounding issues...I dunno...it's never been a problem where I needed to do any internal grounding scheme mods. I mean, I don't really hear any substantial ground hum or anything like that. All in all...it's a pretty quiet running board for me.
That said...I did focus in getting my external grounding done as best as possible...between the console and outboard gear.
I run everything off of Furman 1225 voltage regulator boxes, and then I ran additional ground wires rom some of the rack gear where I found some minor hum issues...plus I made sure my patchbays were all grounded together and tied back to the other gear in yourtypical "star grounding scheme.

I've heard of people doing internal grounding mods to the 3500...but you have to be careful not to end up with more issues than you had. Grounding can be a tricky thing when you have lots of racked gear...sometimes just one piece can upset the whole thing.....

Short anecdote....
There was a guy who wanted to mod his console for more "pro" performance. He wanted everything balanced and as clean and quiet as possible...etc.
One day I was in a music store and he comes walking in and starts talking to the sales guy...practically with tears in his eyes.
Apparently his entire studio burned down...the console caught fire! Like some studios, he just left all the gear on, 24/7...and when he wasn't there one day...:eek: :( :D
 

timkroeger

Custom Title User
There was a guy (I use to have the links) who spent a HUGE amount of time, effort and money doing all kinds of upgrades to his 3500. He documented the entire process and the large variety of chips he tried. There was always some kind of tradeoff it seemed no matter which chips he picked...or not much difference from the stock.

Yep, he went with a combination of 2604s and 2134s (which are lower in price than the 2132s) if I remember correctly and he was certain that it made a great difference. As I said already, I found I couldn't make out a difference but that may be my ears.

I linked all three archived threads from the rec.audio.pro newsgroups in my M-3500 refurbishment thread. You seem to be needing some kind of google account now to access those pages. I have one already, otherwise I would have been reluctant to create one. But I say it is a worthwhile read, so go ahead and register. If google asks for your mobile number, jsut don't provide it ;) Theses threads are the only reason I actually started to mod the console, I even wrote Jim Williams from Audio Upgrades if he still had some info on the M-3500 mods he had done but he did the mods more than 10 years ago and didn't know any specifics anymore.

My advice is that you focus on refurbishing whichever console has less issues and better chance of running with full functionality…rather than getting in too deep with the 3700 just for the sake of the automation. Heck…if you want to utilize the 32–channel meter bridge even if the 3700 has un-repairable power issues…you could always swap all the 3500 modules (plus those spares you bought) into the frame of the 3700…and then still use it’s 32-channel meter bridge. :)

If I'm not mistaken you can swap the meter bridges. I don't remeber how they're connected to the board but I think it wasn't soldered but just some connectors. I may be mistaken though. The manual should provide some hints on that.

Cheers
Tim
 

sweetbeats

Reel deep thoughts...
There was a guy (I use to have the links) who spent a HUGE amount of time, effort and money doing all kinds of upgrades to his 3500. He documented the entire process and the large variety of chips he tried. There was always some kind of tradeoff it seemed no matter which chips he picked...or not much difference from the stock.

I considered doing some upgrades to my own 3500...but based on comments similar to yours, I decided to not bother as long as my board stayed functional...and here it is, 20 years since I bought it and it's still kicking without any real issues in the entire 20 years (knock on wood).

Hear-hear...and I'd be okay if somebody just flat-out told me my hearing sucks but I modded two channels of my prototype Tascam M-500 mixer...tried a host of different chips and in the end I liked the stock strips better. Andevery now and then I ponder potential future mods of my Soundtracs MX desk but the end user speaks loudly...Steven Magalnick, the "Soundtracs Guy" has been involved in exploring a number of mods at the request of customers over the years but ended up reversing them, again, at the customer's request because they didn't like the sound modded as much as stock.
 

miroslav

Cosmic Cowboy
I'm sure there are small mods that can make a difference...but my thinking is that it's always about a total design concept...so swapping out a chip or cap or two doesn't really change the total design concept.
If you want a Neve...you have to buy the total Neve design...etc...etc...etc.

The TASCAM engineers were going for a less expensive design that still sounded pretty good, and I think they achieved that with the 3500. I'm sure if they were trying to clone a Neve (or whatever)...they could have taken their design to a much higher level...BUT...it would also have cost a LOT more than the 3500.

Tim
Yes...the bridge and everything else will just pop out of the frame. I think (?) the OP has a 24/3500 and a 32/3700...so he may not be able to move the 3700 bridge to the 3500...but he sure CAN move the 3500 "guts" into the frame of the 3700...and he has extra 3500 modules to fill out the additional space of the 32-channel frame...
...assuming he doesn't get anywhere fixing the 3700 power issues.
 

sr71rules

Member
From looking at the channel strips in the M3500, the metering is attached via a connector and not hard to move around. I had been considering moving the meters on the group busses to the last 8 channels of the board. The M3500 I have has 8 LED meters and two VU meters. The VU can show CR, Studio, or the Stereo Bus. The 8 LEDs can show tape ins 1-8, 9-16, 17-24, or groups 1-8 but cannot show tape in 25-32. Not an issue on the 24 channel board but not ideal for a 32 channel board...

Perhaps I can work out a way to use both sets of meters... This project may make me into an evil genius!
 

miroslav

Cosmic Cowboy
Not an issue on the 24 channel board but not ideal for a 32 channel board...

Mmmmmmmm...if I'm not mistaken....THAT'S how it normally is on a 32-channel 3500/3700.
IOW...if you had purchsed a brand new 32 channel board...your metering would be the same as you describe it....only the first 24 channels of Tape Input would be availble at that "main" meter section.
Think about it...most tape decks stop at 24 tracks...so that's why they didn't wire the Tape Ins beyond the 24th channel on the main section bridge. :)
 

timkroeger

Custom Title User
Might be the case with the 8 bar meter bridge but the 32 bar meter bridge can either show 32 inputs, 32 tape ins or aux 1-6 on bars 17-22 and group 1-8 on bars 25-32.
 

sr71rules

Member
Oh, I understand the logic... but I still want meters on everything! :)

A Google image search for the M3700 shows the bridge has four buttons for the meters. Tape In, Aux/Groups, Input.. and an unlabeled one? Off? My short bridge also has 4 buttons.. perhaps they just didn't use that last button on the full bridge but left it there to keep things simpler in manufacturing? What's left to meter?

This image says M3500 on the bridge, but I can see the automation computer and extra buttons on the faders...Tascam M3700 Image

Assuming it's the same as my M3500, those buttons change the LED meters and not the VUs which are controlled by separate buttons in the master section of the board.

I love talking about this stuff.. almost as much as I love using!

Robert
 

miroslav

Cosmic Cowboy
Right...the extended bridge shows for each track...24 or 32.

When they designed the main meter section...they didn't provide switching for more than 24 Tape Inputs...which makes sense.
When you add the extended bridge...you actually lose/change some of the switching options of the main meter bridge section. I have the written instructions, as I received my extended bridge separately from the console...so I had to connect it while at the same time disconnecting some of the original options of just the main bridge section.

And really...when you have the full meter bridge....why would you need to view various Tape Inputs on just the last eight meters of the bridge??? :D
So it all makes sense. Once the extended bridge is hooked up...some of the functions of the original meter section change, and it all becomes ONE meter bridge with each channel strip having it's own meter and no need to "share metering".

Think about it.....you will have "meters on everything" when the extended bridge is there...no need to have "everything" on just the main (8-bar) bridge.
 

sr71rules

Member
Isn't that interesting... Starting to make sense.

In the picture I linked to you can see the break in the bridge just before the last 8 LED meters.
 
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