Inspired to modify my Tascam

After seeing Erics Tapco mod, I was inspired to try a similar thing with this old Tascam board that I got real cheap. I origionally got it for the VU meters, and the XLR's, but then I thought what the hell. It is also full of 4558's and also has a 7351 which looks like it's linked to the clip led but I'm not sure what else. This is driven by a +15, 0, -15 supply which immediately made me think about the Green pre. Isn't that based on an old nupert reve board?

So the question:

Does anyone have a schematic, and maybe scan or layout (I know that's asking al lot) of the boards/modules that the Green is based on (a*m*e*k?) . What are they based on? If you can't say here, please PM me.

I like the Green a lot and would like to try and stuff this mixer with those, but I need a good eq circuit to go with it.

I will post the schematic for this later as I don't have a scanner here.

Some pics:




The links to bigger images of the abover are:

http://mhumhirecords.org/DIYpics/mixer.jpg
http://mhumhirecords.org/DIYpics/strip.jpg

Thanks for any and all thoughts!

Joel
:guinness:

I've always thought that these were decent boards as-is. (Except mine: it was in a fire and still smells like smoke 20 years later.)

The 4558s are not big problems because TASCAM isn't stupid. The whole board runs at fairly low levels, where a 4558 can do the job fine. Keep the sliders near the shaded areas, trim input gain to keep the meters from banging, it is fine.

You could replace 4558 with TL072 in most places. One place that may not be cool is the pan/bus driver; I'll look at the schematics.

Yes, it is "Japanese" in the sense that what you put in is pretty much what you get out. I don't like boards that make my sounds "better".

These guys are old enough that you might just replace all electrolytics preemtively. But don't bother with cheap caps. The originals are pretty good.

Aw shucks PRR-I wanna have some fun with this board! Thanks for your thoughts though.

Joel

One mod that should yield some improvement without affecting the basic character of the board is to redo the grounding of the channel PCBs to a star ground. In stock form, the ground is daisy-chained from card to card via the ribbon cable, terminating back at the power supply. The stock crosstalk figure is something on the order of -60dB, which is "ok" but not great; reworking the grounding should improve this.

They also used TL072s in the mic preamps and the EQs, and some odd headphone driver IC (!) as buss summing amps. And no, I wouldn't just stick 5532s in their place, especially not in the EQ.

The M30, which is very similar to the mixer in the pic, used TL072s, NJM072s, and 4560(?). For all I know, Tascam may have made some fairly drastic changes in the internals while keeping the same cosmetics.

PRR gave some very good reasons (in the "4558s everywhere" thread) why you can't always just slap a 5532 in any circuit that used a 4558, but apparently nobody wants anything but the easy answer around here.

The cards only have two 4558's and one 7351 which I don't really know what that does. I'm certainly not only looking for the easy answer-I guess I have a hard time believing this is such a good mixer, considering I paid peanuts for it. There are no TLOwhatums that I can see. I haven't looked in the master section yet though. I haven't even plugged it in yet. There are a couple of inductors in the eq section. There is also a transformer on each card (output?)

Since I have 16 of these cards to play with-I figure it wont hurt to mod two of the channels and see what difference it makes.

Joel

> full of 4558s

Should ALL be NJH4559D, a significantly improved 4558. I would not rus to replace 4559s. (The only other chip is HD7400, which they say is a quad comparator, but is clearly a TTL logic chip, 2-input gate, only used to boff the overload LEDs.)

Because of the way they split functions across dual-chips, I don't see a great alternative. Fer example: in the 201C channel strip, IC4 has a variable tone filter in one side, the bus/pan driver in the other side. The bus driver should have high output current capacity (it sees as little as 1K). 5532 comes to mind, but the tone-filter has up to 150K of unbalanced bias resistance which in a 5532 might give 0.15V of offset and pop (probably less, but not zero). And there is only one pair of 0.01uFd bypass caps for the whole board: super-chips will need more, especially on that long board.

In the 210 Submaster board, IC2a drives the output and also runs at higher nominal level than any other part. This begs for 5532. IC2b is the meter driver, and 5532 is "too good for a meter", but it will work and 5532 isn't expensive enough to care. IC1 might profitably be 5532, but you will need rail bypass caps.

The headphone amps run on just +6.5V. This may be ample for many 32Ω phones, but if you favor hi-Z cans then you should replace it with something eating +/-15V. (Or take an output from the top of R96 R108 to an external can-amp.)

Super-size C18 C19 in channels, C16 C17 in submaster, two 10uFd caps on the power rails in each board. I would be thinking at least 100uFd.

For modern hot mikes, the mike transformers might not stay clean at high levels. The ratio is 1:5.

There isn't an obvious place to get phantom, unless you are sure all your mikes eat +15V fine. Get an external 48V supply and buss it to the XLRs. Or just use the dang 0,-20,-40 Pad: that's what it is for. (That was one great feature of this board: true transformer floating inputs that would eat line-levels. Just watch your Phantom!)

They are 4558's.

Joel

I have a M-2524 Tascam around I'm looking for the schematic also to modify.
Anyone have it?

cheers!
Fabio

There seems to be some confusion since I haven't posted the schematic. Today is a snow day (didn't I just say there's no snow in Albuquerque!) but I WILL post it today somehow. IC 1 is the 7351, IC 2 and 3 are 4558's.

Joel

id rather have a snow day than a hurricane day :green:

why not listen to it to see if you like it first? Just because it can be improved doesnt mean that you'll like the sound of it better. Who cares what specs are, ultimately, really. Nobody listening to the mix you made is ever going to ask you what the signal to noise ratio is, they only care if it sounds cool or not, right? I have 4136's in the echo send on my console, everyone and their brother told me to change those things out when I got the board, which I intended to do, until I listened to it. Its not in the main signal path, and it would pretty much suck if it was, but in the echo send, yeah, the chip sounds pretty terrible and slews like a turtle, but its actually kind of cool in the echo send. You might like the way the thing sounds for your application, you migth want to change it, but Id be listening to it first before I did anything.

dave

LISTEN to it first? Are you crazy?

It doesn't have Burr-Browns in it, so it must sound bad!

[facetious mode OFF]

Thanks guys-As a said in my first post, Dave, I hadn't even intended for this to be used as a board. I got it so cheap that I was planning on stripping it and using the meters, xlr's, etc in other applications. After seeing the Tapco, I got inspired to ask about modifying the board to use it. OF COURSE I'll listen to it first. If I love it, I love it and that'll be that. But being a newbe, it is sometimes hard for me to trust my ears-especially thru my crappy monitors. I figured I'd put it out there and see what people think. That said, even if I DO love what I find, I'm still gonna change a couple of channels to see what the differences are. That's the only way to learn right?

Joel

> I have a hard time believing this is such a good mixer, considering I paid peanuts for it.

And we paid peanuts back in 1975: only $1,500, when all other 8-4 boards were $10,000.

It won't take 24/7 abuse like an API. They are $2 knobs, $7 faders. But if it has not had its knobs/sliders worked thousands of miles, they are fine.

I've always thought these were under-appreciated, at least since "sexier" mixers appeared. No nonsense fine mixing.

Main fault is that they are HUGE by modern standards. I can get 8 channels in 1/8th the bulk now. But they are right-size for fat fingers. Much more comfortable to work long sessions than some teeny-knob mixers.

And impressive looking. Polish the sides, get the wrist-strip recovered in fine leather.

> There are no TLOwhatums that I can see.

Not invented yet. That may have been the next generation of TASCAM boards.

> I haven't even plugged it in yet.

Do it. Maybe it was cheap because there is a major fault. Or maybe a minor fault never attended to. Anyway if it has been in the cellar a while, you need to get the 'lytics re-formed before you do any serious listening.

> redo the grounding of the channel PCBs

I see your point, but I'm not sure it is a real problem. Maybe it should be, with the bus-ground, but I've had high level flowing through to headphones for cueing, and not heard it in the house. I think there is more subtle engineering in there than it seems at first glance. There is some risk that hasty star-grounding would make things worse.

60dB was pretty darn good in the day, and even today.

Noise level at the mike could be a few dB higher. At least in my work and room, maybe not in small home studios with pop music.

> They are 4558's

Yours may be an earlier model than mine (they are both "Model 5"). 4559 may have been a production change. (I have a suspicion that 4559 was made FOR this board and related products.) This is for-sure the obvious upgrade, except it seems to be hard to source NJM 4559 in quantities less than a crate-load.

> I'm still gonna change a couple of channels to see what the differences are.

Sure. Put 5542 in all positions, plus 0.1uFd rail bypass caps within 2 inches of each chip, and see if the offset makes it scratch or pop. If not, it should be a very sweet board.

Note that upgrading a channel may not change the sound if you listen through the un-modded master sections. Listen to the Direct Out, straight to good amp and speakers.

The EQ is functional but not always to my taste. However it has nearly no effect with knob centered, and you can always patch-in something sweeter at the Access jacks.

The meter lamps are part of the charm, but burn out in time. Get some white LEDs and fix it permanently. It would be extra sweet to have a brightness knob.

Great ideas! Thanks PRR!

I lied-I did plug it in and talk thru a mic jut to see the VU meters move...I'll get it hooked up to my system in the next few days...big work going on at the house...hopefully getting our rough-in electrical inspection and gas line inspection in the next day or two. It'll be nice to have clean power.

:guinness:

Joel

> I did plug it in and talk thru a mic jut to see the VU meters move...

Cool. But when you reach a point that the electrician and plumber won't step on it, plug it in and leave it on for a few days. I'm not really in the "break-in" camp, but gear that has been stored for years will sometimes be a bit nasty right out of the cellar, and settle-down after some hours with power applied.

Here's the schematics:

Line Module:

http://rattletree.com/DIYpics/linemodule.gif

Monitor module:

http://rattletree.com/DIYpics/monitor.gif

submaster module:

http://rattletree.com/DIYpics/submaster.gif

Hope this helps...

Joel

Hey, I didn't know it used input transformers. Are they any good? This might be a cool mixer to have after all. That's a cool idea for an overload indicator too.

I?m with butta? on this one ? can?t imagine a 5532/4 not being supreme here. But do mod one channel and compare with the rest first.