Tascam M-___ Story...

I don't know, man...you know a LOT more about this stuff than I do. All I know in this is what I'm told by folks who design this stuff and know the Ampex machines that are helping me.

Anyway, your schematic you are only looking at is the schematic for the plug-in record amp card only for the AG-440/MM-1000 electronics. You aren't seeing the rest of the electronics module. Here's the rest of it:

http://torridheatstudios.com/documents/Ampex/Ampex%20440%20Electronics%20Schematic.pdf

Ok, well that helps because I now see there is an octal socket for an optional input transformer but I am still confused!
The REC level pot is 100k (which makes sense re the emitter follower) and therefore, as I suggested, this indicates a 10k transformer. Even if it was a 600 Ohm type it is only being loaded by 50k at the lowest?

Then I see a coupling cap! 4 microfarads at 25V 4C23 on the wiper of the pot.

But, if you have ex Ampex Men on the case I can only continue to wonder.

Once AGAIN! Many thanks for your patience.

Dave.
 
So, 4C23 is really only there if the optional octal mic transformer is used. There are three types of plugin transformers, mic, line and impedance matching. The line transformer is the one usually used. Best practice is to bypass 4C23 if not using the mic transformer. Don’t know if that makes any difference to your inquiry.
 
So, 4C23 is really only there if the optional octal mic transformer is used. There are three types of plugin transformers, mic, line and impedance matching. The line transformer is the one usually used. Best practice is to bypass 4C23 if not using the mic transformer. Don’t know if that makes any difference to your inquiry.

Heh! Just adds to this old fool's confusion Sweets'! "best practice" but not original design? A transformer is just as much "AC coupling" as a capacitor and in general produce more distortion. (and even a TINY bit of DC from say a not perfectly zero offset will make that much worse)

I shall have to leave this and let you get on unmolested mate! I am of the Old School, "just give me the numbers" brigade.

Best of, Dave.
 
Throwback First Impressions Videos from 2008!

Greetings, everybody...the Tascam M-__ project is not dead, just taking a back-seat at the moment due other priorities. In the meantime I was doing some data archiving and consolidating and found 5 videos I captured shortly after bringing the M-__ home. These videos were a second run of videos using a higher quality capture device that somewhat duplicate videos I captured the same day I unloaded the console when I got it home. Those first run videos are posted early in the thread. The videos cover first impressions, initial known details, features and issues of the M-__ as well as evidence the console is a prototype. For some reason I never posted these higher quality second run videos. I'm not sure why. At any rate, I've done that now, and here they are as a fun throwback to the very early days of the M-__ in my midst...Enjoy!

YouTube

YouTube

YouTube

YouTube

YouTube
 
Last edited:
So I feel good having accomplished *something* on the M-__ project...the console in its entirety remains in a closet sitting on the wrist rest after it was stored away in preparation for our baby last Spring. Things have been busy since then. What I did finally do was completed the next step of testing on the modified line amplifier project, the line amplifiers that drive the PGM, AUX and STEREO output busses. A quick refresher: I accepted some expert help in taking Teac’s high headroom discrete output stage amp design that was designed for the M-__ (and is found on the M-50 BALANCE AMP output, and a simplified lower headroom variation is found on the LA-40mkI) and significantly modifying it to, primarily, maintain good stable specs down to very low inpedances in order to be better suited to drive the relatively low impedance inputs on my Ampex MM-1000 and 3M M-64 tape machines. Where we left off was verifying the test amp is producing the proper gain. I’ve already verified the thing doesn’t self-destruct when powered, runs cool at idle, and takes clean tone at the input and produces clean tone at the outputs with some gain. So I did all the tests regarding the gain at different stages in the circuit and sent off for feedback...waiting for a reply. But I think it’s doing what it’s supposed to do. IIRC the next step is to load test it with a dummy load, and if it survives that then the next step is to conduct distortion analysis. Along the way there may be tweaking of some component values, but in the end the hope is to have a circuit I can replicate across all I/O modules and the master module that will kick sonic ass. Here is the crazy setup...it’s a bit of a mess since I have to temporarily setup wherever I can find some space:

0A6AE547-A795-46CE-99C6-9BB80F0A1F66.jpeg


And here’s some other news that’s exciting for me on this project...so...another quick refresher, the I/O modules don’t currently have balanced outs or ins on them. The above line amp will take advantage of unstuffed sections of the PGM BUSS amp boards on the I/O modules and provide for a balanced output amp. The structural backplane of each module are already punched for the XLR jacks for balanced line in and line out jacks, but I want to maintain accessible unbalanced line in and out capability, so I want to reconfigure the backplane of each I/O module so there is, for instance, an RCA line out jack, but then also a balance amp line input RCA jack to the modified line amp, and then the XLR balanced out. Think of the BALANCE AMP section on an M-512 or M520. So, yes...I would use one of those jumpers like on the ACCESS SEND/RCV jack set on the M50/M-500 series, or on the M-30 or MX-80...And then I’d have the same thing for the input...balanced in on XLR to an unbalanced out on an RCA jack, and then an unbalanced in on an RCA jack to the rest of the module, with the RCA jacks jumpered for normal balanced in configuration. Why do this? Why not just have the balanced in jacks? Having access to both the RCA jack and the XLR makes it very versatile...I can easily bypass the balance amp circuitry when unnecessary (when interfacing unbalanced gear), but still have access to the balancing amp if I want to balance/unbalanced some other input or output *anywhere* on the console, or with external gear, like a bunch of mini LA-40s...like having 12 “LA-10” units in a sense. This seems consistent with the M-50/M-500 series derivative of the M-__, and maybe even what was considered or proposed at some point with this prototype console. So...long story short as far as this post goes, if I’m going to do the above, that means I need 24 of those jumpers. I found a source that actually had that many on hand, all with the correct “TASCAM” script and all in excellent condition. They weren’t a bargain, but the price wasn’t outlandish either, and doing it this way saved me heaps of time I don’t have sourcing them onesy-twosey or having to buy multiple MX-80/M-30/M-50/M-500 series units, scavenging the parts and reselling to try and make some of my money back. I present to you, a pile of TASCAM jumpers:

CC0E85B0-A3E3-4DDA-8A37-40D9EA9BD8ED.jpeg


That’s all for now.
 
Hello to the group! I just picked up a Tascam M-520 in perfect condition for $525 and I just had a quick question for the group! I'm wondering if I use an RCA-TS snake running from the direct outs of each channel (with RCA) into a Neutrik TRS Patch Bay (with TS) if I'll run into any issues. The chain would be..

Interface outs via Neutrik TRS Patch Bay > Tascam M-520 IN on PB , connected to M520 by TRS to XLR snakes (using the XLR Inputs on the board and turning on the pad of the console) - then out of the M-520 and back into the Patchbay using RCA-TS Snake via direct outs on the board > and finally patching the outputs of the board on the PB into the inputs of the Motu 16A inputs on the PB for storage.

My question is.. will I have a problem using TS into the Neutrik NYS-SPP-L bay? I'd just simply try it out but I'd need to purchase the cables beforehand and I'd rather avoid that if it's not the right way to go PLUS I need to have it up and running in my studio so it so the studio can function.. so I won't have time to order different cables and wait for them to arrive. SO I figure that's what this forum is for! Any thoughts?
 
Shouldn’t be a problem. If you have more questions about this I’d like to offer a suggestion to start a new thread. That way your question is highlighted, doesn’t get buried in an unrelated thread, and also doesn’t take somebody else’s thread off topic. Thanks. Hope that helps.
 
To all those who may wonder from time to time if the Tascam M-_ project is dead or gone, the answer is no…still have it, no intention of letting it go…am currently working on setting it up as something of a “Studio B” console…one of the input/output modules has been apart for some years because of research and reverse-engineering that was done in that time, but now that I have some space and more of a purpose for it, I’m getting that module put back together, and in the process implementing a punch-list of modifications and tweaks gathered over the past…well bunch by this time…of years.

I bring you, M-_ carnage:


IMG_0769.jpeg

And a short video:

https://youtu.be/HB3aBoUtYKM?si=leockVA-b-llJ0g3
 
Can we all just appreciate for a moment the number of push switches on each input/output module? There are two rows of them…here is the row with 30 switches:

IMG_0772.jpeg

The other row, removed in the picture above, has 12…42 push switches in total on each module…two 3-position toggle switches…and including stacked pots and the slide potentiometer of the channel fader, there are 23 potentiometers on each module…67 controls total on each module.
 
FYI, for anybody that’s interested, some of the tweaks/mods I’m doing include replacing all the power rail decoupling resistors with new parts, replacing select 5% carbon film opamp feedback loop resistors with 1% metal film parts, adding just a couple HF bypass caps in the signal path on the EQ board, and replacing and socketing some of the opamps, and in those instances adding a small value cap across the power rails at each opamp as insurance against oscillation, though likely nothing I’m putting in would be unstable enough to oscillate. What I want to underscore here is, lest anybody go thinking they should just start replacing all 5% carbon film resistors with 1% metal film parts, or that changing opamps is “better”, everything I’m doing is supported by extensive analysis and testing, and with intended purpose…none of it is carte blanche. And none of it is wild stuff. The opamps I’m putting in are considered vintage at this point…I simply believe, after a lot of years of doing this sort of thing and listening and testing, they sound better, but without trying to turn the console into something it’s not. I don’t want to sterilize it, I just want it to sound more like itself if that makes sense. And all the resistor stuff is to 1. hopefully achieve an incremental improvement in the noise floor, even though the console is pretty quiet already…but there are a lot of amp stages…! And 2. maybe achieve some incremental improvement in channel-to-channel tracking, and stereo tracking when using a single input/output module as a stereo input module. Again, the opamps being used are not latest/greatest parts…just TI-branded 5532 and OPA2134 parts, in place of NJM2041 and TL072 parts. And there’s nothing wrong with a 2041 or a TL072…they are everywhere in lots of your favorite gear and even in some coveted gear. I just happen to be able to test and make sure different opamps are actually happy in a given circuit electronically, and then listen to identify if I can even hear a difference, and if I do, decide whether or not it’s a good difference or a bad difference. I generally like the sound of circuits that use the 5532, and where that doesn’t work as an upgrade I find the OPA2134 to be a very stable and good performing alternative to the 072 or the 2041. I’m sure plenty of people would call me a fool to go to the trouble of testing, disoldering, installing just to put in what many consider to be obsolete parts rather than the latest and greatest fastest chip. But often times those folks are going for input=output neutrality, and anything toward that goal is good, and anything otherwise is not good. Again, my goal is to just help the console sound more like itself. Changing opamps is no silver bullet, and there are lots of caveats. So I proceed conservatively and with an objective in mind, a pre-conceived answer to the questions “why am I doing the change, what’s the purpose, the desired outcome, and is it worth it?” Sometimes it’s just curiosity. Anyway, that’s what I’m working on, but just here and there, because the console is now almost back together and fully functional and I want to put it to some use and, while I’m at it produce some new videos that go into better detail as to the functions and operations of the console…something of a video manual in case it’s of interest to others, and, just as importantly, to help me when I forget some needed detail about a particular function. Like all the SOLO functions…there are 5 on each input/output module…where does each one tap the signal path? And which ones are in-place and which ones are not? I can’t remember. This will all become better as I use it more, but it would be nice to document a baseline for reference. Anyway, modules 1 & 2 are partially modified, module 9 will soon be fully modified. Then I can just use it for awhile and get used to it, and be able to identify if even the partial treatment is worth it, and if the full treatment brings any worthwhile benefit. I’m reasonably certain the partial treatment is worthwhile…we’ll see about the full treatment. But it will be nice to be able to just play with it and A/B the different versions.
 
Here’s another thing about the M-_ I want to clarify: it’s size.

I think it’s hard to tell how big it is from any pictures. I don’t know why but in every picture it just looks smaller than it is…something about the design I guess it could just be scaled down and still look normal. And of course with SMT technology, were it made today it could be much smaller…but on the other hand it’s really roomy for accessing controls which is nice. But people over the years mistake it for an M-50 or M-512…like even argue with me. The footprint of the M-_ is significantly larger than an M-50/M-512.

Anyway…

Let’s compare some channel strips…let’s take a large-format FOH console like a Yamaha PM3500…here’s a picture of one of those:

IMG_0774.jpeg

Now, of course, the Yamaha is much wider than the M-_…that console above has 40 mono input and 4 stereo input channels and full master section…but it looks deep right? Like lean way over to see what you’re doing with the controls at the top of the strip. And then here’s another one, my Studer console:

IMG_0612.jpeg

A mixing “desk”…not as imposing as the Yamaha, but still a chunk…still have to stand up and lean over a bit to really see what’s going on at the top of the strips. Then here’s the M-_…

IMG_0695.jpeg

I mean, it doesn’t look puny, but I think this next pic will surprise you…here is, in order from left to right, a Yamaha PM3500 mono input module, a Tascam M-_ input/output module, and a Studer 928 mono input module all right next to each other:

IMG_0773.jpeg

Yes, that’s right…overall the Tascam module is the longest, and it is about as wide as the Yamaha and Studer combined. I think I posted a pic in this thread years ago of the M-_ next to an M-512…if I can find it I’ll add it to this post.

Okay here’s the pic:

IMG_0777.jpeg
 
Last edited:
Module #9 is back together…

IMG_0784.jpeg

I had a little trouble locating all the hardware for it to mount everything back together. That led me to the question how long was the module in pieces. I recollected I originally took it apart in order to do some collaborative reverse-engineering of the EQ module. And then I was, like, sheesh…when was *that*…I looked back in emails…over 6 years ago. The console hasn’t been all together in over 6 years. So, for the first time in over 6 years, here’s a pic of the whole thing together:

IMG_0790.jpeg
 
Back
Top