Tascam M-___ Story...

  • Thread starter Thread starter sweetbeats
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Yeah it takes time using it to get used to what's where, and there are many aspects I'm still fuzzy on...all the SOLO points...the REMOTE functions to name a few. It's just easy to get physically lost in the former sea of beige, but also operationally lost particularly if there are multiple things muted on multiple channels, but certain busses are not effected by certain mutes...the functionality is good, it's just easy to go "wait...why am I/am I not hearing that there?", and then remember one of 60 mute controls found amidst the 12 channels is activated. With time it will become more familiar. I really haven't mixed any projects on it, just played around, and an actual project would force the acclimation.

To your earlier comment about the missing components, yeah...I tried following the traces to see if I could gather whether it's for input or output and at what point in the signal chain it interfaces...I'm pretty sure it is an output. The interesting thing is there is space and sites for another set of regulator transistors...on that same PCB is a regulator circuit for the +/-18V rails that power the +4dBu output circuitry. Usually that regulation happens centrally in the power supply...that's the way it is in the M-500 mixers but for some reason in the M-__ the power is rectified in the PSU and then runs unregulated at +/-35V and then regulated in each module...in the master section too...but there is room on the heatsink for another set of regulators which seems strange unless there was to be even higher power rails for the missing circuitry...there are some +8dBu circuits on the board too so maybe there was intended to be balanced +8dBu outputs for the PGM busses, which was the broadcast standard. Dunno. But fun and interesting to surmise.
 
Here's modules 1, 2, 9 as 10. Remedial work all done to 1 & 2, recap and deep clean all done for 9 & 10. Just waitin for that ceramic cap to arrive for the EQ board on module #12 and I will be officially at the halfway mark fully refurbishing the I/O modules.

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Also was taking a closer look at the PGM BUSS board...it definitely was designed to accommodate balanced I/O...There's all kinds of stuff on it, but judging from the blank holes in the backplane Teac had ideations of balanced returns and balanced group outs on this conceptual platform. I'm using LA-40mkIIs for that, but it looks like if development continued this mixer would internally house the functionality of 3 of those units.
 
Question.

Each channel strip has a buss out jack which makes for a total of 12 buss outs even though its an 8 buss assignment design.

How are those buss out connections configured, wiring wise? Is the first channel hard wired as the PGM 1 buss out and so on down the line?

I'm used to seeing PGM buss outs in a master section area on most mixers and that's not the case on this one!?

What's the deal on how all that works...if you know?

Cheers! :)
 
It's a true inline console popularized by MCI starting with the JH-400 desks. What that means is that each "strip" contains all the circuitry and connections for its inputs and group outputs and all the controls are on that strip.

Each module is identical, and the PGM group routing is dependent on the slot into which the module is plugged in. So the module in slot 8 is the one with the buss master control (red knob at the very top of the strip) and the PGM group 8 output jack.

The 4 AUX busses route to the modules plugged into slots 9~12.

Make sense? So even though it *looks* like a really complicated 12x2 mixer, it is a true 12x8x2. With three independent inputs per channel. And insanely configurable aux and monitor busses. And per channel meter sourcing. And a 12x2 global remote source switching matrix...and a global source switching matrix for the monitor buss on all 12 channels...6 mute points...5 solo points...4 band eq with fully parametric mids, one low-pass filter and two hi-pass filters...there's more, but I digress.

Got the caps all sorted and grouped and prepped the tails for the last 6 modules.

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Thanks for the explanation, Cory! Now it makes sense to me! :)

I'll also add my kudos to you here for all the hard work you're putting into recapping and cleaning up all the internals!

Cheers! :)
 
So at the end of the night I got that bypass cap installed on the module #12 eq board and got that module put back together, deep cleaned and recapped module #3, and disassembled and deep cleaned module #4 which is ready for recapping. Progress. #12 and #3 are leaned up by the M-512, and module #s 5, 6, 7, and 8 await their fate...

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Here you can sort of get an idea of how the orange color caps I added helps with some visual delineation of the controls.

Bad picture.

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Another thing...I pulled the power supply out of the rack...

Reminder this is just a scantly modified PS-520 power supply (from an M-520).

I had originally left the PSU as stock as possible in case it needed to be reverted. Those days are gone. That PSU belongs to the M-__ and it's time to do some work on it.

After all the mod work with the power supply and grounding I did on the Soundtracs MX32 console I used to have, I am going to beef up the M-__'s power supply and make sure the grounding is proper. Later I will want to look at the mixer frame to make sure the proper grounding conventions propagate there but for now I'm just starting with the power supply.

I'm going to:

• Remove extraneous wiring that used to go to the 18V regulators that are gone
• improve jumpers installed in lieu of the 18V regulators
• Replace the 15V regulators with lower noise/higher PSRR parts and install mini heatsinks on these TO-220 board-mounted components (no sinks in place on these parts and they are discolored)
• Replace the 15V supply bridge rectifier with a higher spec bridge.
• upgrade the stock main filter caps for the 15V regulated and 35V unregulated bipolar rails from 4,700uF to 10,000uF.
• Replace the HF bypass caps on all rails with newer higher spec parts.
• Check and modify as-needed the ground scheme.

I think that's all there, but will see if there is anything else when in there. There's nothing wrong with the stock supply, but these mods may reduce the noise floor, and there are a lot more active devices in the M-__ than an M-520 so the filter cap upgrade is a just-in-case measure.
 
Got the power supply opened up...holy smokes the ground is all wrong in here...and I even added to the problem with a mod I did...sheesh! :o

The building ground (which *should* be physically connected to physical earth via a ground stake to local code) should be connected to the power supply chassis as close as possible to the point of entry into the chassis. I've got that covered as the PS-520 uses a two-prong power plug with a ground lug on the chassis.

Then the chassis ground of the power supply should be connected to the mixer chassis through the power supply umbilical. This should ideally be via braided shield or otherwise in the cable. That's not covered and I knew that...won't mess with that unless I encounter RF infiltrate because it would involve replacing the cable itself. BUT...I do have two conductors in the multi-conductor cable dedicated to chassis ground interconnect.

All metal parts of the mixer chassis should be thoroughly bonded together. This is something I know needs to be checked...its on my list.

The 0V leg of the power rails in the power supply should stay isolated all the way up to the mixer and then bond to the mixer chassis as close as possible to the entry point into the mixer chassis. This is another area I know needs to be addressed...the 0V rails go all over the place and then here and there tie to the chassis or don't at all...so I know about that and it needs to be addressed...the *problem* I'm seeing is all the 0V rails tie to the chassis in the power supply...arg. So That will be part of my mods to the power supply is to isolate those rails. Its all coming back to me...the work I did on the ground scheme on the Soundtracs MX32 console...
 
Arg...its a puzzle.

I've got the power supply in one place and the mixer frame and cable are in another. I really need the two together with the modules all out of the frame to work this out.

There's going to have to be some reconfiguring to make this work right.
 
Transported the frame to my place tonight where the power supply is so I can tackle the ground scheme issues. Take a look at the verrrry first picture I posted with this thread...it's the M-__ in the back of my car north of the grapevine headed home. Popped the back of the same car open tonight to unload the frame and had me a reminiscent moment, though the frame is lookin a little better now than it did back then. ;)

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A little better? Ha! It's a remarkable transformation! TASCAM should be paying you for all the hard work you've put into preserving their heritage!

Cheers! :)
 
Yeah, like Jeff said. It's incredible. A true labor of love.
 
Well I'm pleasantly surprised...all portions of the frame are effectively bonded together, so I can check that off the list.

I've decided to re-do the power supply cable...I have a section of stepper-motor cable...braided shield, 12 conductor...perfect number of conductors and good quality cable. It'll be done right for proper grounding, and there's some reconfiguring of the pinout I need to do anyway.
 
...

I figured I should tie ground from the power supply to the larger chassis with a wire, but I didn't realize I should also ground from the power supply to the wall, with a wire and banana plug. Thanks for the info!

Does my custom M520 umbilical cable also carry ground thru it?

:spank::eek:;)
 
A Reel Person said:
I figured I should tie ground from the power supply to the larger chassis with a wire, but I didn't realize I should also ground from the power supply to the wall, with a wire and banana plug. Thanks for the info!

Does my custom M520 umbilical cable also carry ground thru it?

:spank::eek:;)
Click to expand...

Grounding is a funny thing, and *always* before making changes to any grounding scheme or element of the ground scheme its wise to have a firm grasp on what exists. There are best practices for grounding in audio systems, but you can have a train-wreck of a device and change one element to the best practice and end up making things worse, or even unsafe, before they are better.

So that's my opening "YMMV" preamble. And I only know what I know from my experiences working under consult with people I consider experts on my own projects. I'm not an educated professional by any means. But the results of said consult on my Soundtracs MX32 console were amazing, and the studio is 0.1 miles from the highest powered AM band radio station transmitter in my state; a crucible for proper grounding.

So back to your M-520...yes, ideally the chassis of the mixer frame and the power supply (in the case of an external power supply) should be bonded, and ultimately in the ideal world those should tie back to the building ground which *should* tie back to an effective actual earth ground. I think local code in my county requires two 6' or 8' copper rods in the ground. The chassis ground to actual earth is more of a safety matter than an audio matter.

Your M-520 power supply cable I made for you does indeed bond the PSU and mixer chassis together through pins 12 and 13 at the PSU, and go to pins 12 and 13 at the mixer and then to the chassis as well as other points. In the M-520 the cable is not shielded, and ideally the ground bond should propagate through the shield and then bond to the mixer chassis as close as possible to the entry point into the chassis, so there may be opportunities for improvement. And the other matter is making sure all metal parts of the chassis are bonded together, making sure audio grounds have only one path back to the ground reference point (chassis) and that those paths are as short as possible. there are also opportunities for improvement in the power supply chassis with how the chassis ground was derived and how the 0V references for the power rails propagate to the mixer, and how they are handled in the mixer.

BUT...

Are ya having trouble with RF interference? No? Then leave it alone. The worst thing you can do is take a working system and start messing with it because of something some guy on the internet said wasn't "right". :facepalm:

I had to go to some lengths with my Soundtracs console and am doing the same with the M-__ because of the extenuating circumstances at my studio. You can hold ungrounded scope probes up in the air at my place and see that the RF interference is *loud*.

Bottom line: your M-520 cable I made is to OEM factory spec regarding cable type, connectors and pin-to-pin interconnect...
 
This is me about to trim the last tail off the last new capacitor on the M-__. It's taken awhile, but it's good to finally have it 100% recapped. That's 1098 capacitors. I know that pales in comparison to a recap job on a large format mixing desk, but IMO it's a lot for a 12x8 console. There are more updates but I'll get to those later. Time to put this last refurbished I/O module back together.

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