Identification of Beyer-TX mic-pre card ?

Anybody recognizes this 5 channel mic-pre card perhaps ?



TXs are 1:3 (200 to 2k) but I'm curious to the rest of the circuit - in other words, whether this card could be interesting for a complete set of mic-pre's (so using it more or less as is) - or just for getting the TXs from it.

Maybe someone here recognizes this kind of card ?

Thanks,

Peter

What kind of chips do you have on that board? Do you have a pinout, etc.? If they are decent or socketed amp chips they are similar to a Dukane module I have which sounds very clinical. Very good for dynamic mics on guitars and tube mics on instruments... Yes I did rack it and set it up myself too.

What kind of chips do you have on that board? Do you have a pinout, etc.? If they are decent or socketed amp chips they are similar to a Dukane module I have which sounds very clinical. Very good for dynamic mics on guitars and tube mics on instruments... Yes I did rack it and set it up myself too.

Click to expand...

Thanks for the response.
Don't know the chips, I've seen this up for sale, it's not mine (yet?)
W.r.t. Dukane-module, hmm, TX-input and clinical - what kind of circuit is it after the TX ?

Regards,

Peter

My input has a LM386 or something like that after the TX. It's been a while since I racked it... It's unbalanced out as is a lot of my gear but I keep the cables under six feet in the studio. I have a big ol' tower o' preamps in the jam room and everything plugs there right below the digital interface.

What do your chips say on them? From the (fuzzy) picture it looks like there are smaller opamps to the left and larger ones to the right. It's hard to tell what's going on there. Put up more pictures and I could make a better guess...

So far I only know the exact typeno's of the TXs, I'm in the process of obtaining more info from the seller. And yes, a few more pics @ higher res. wouldn't hurt ! :wink:
So now it's hard to say - he'll be telling me the opamp-types but apart from that I doubt I'll be able to get more specifics. If the price is reasonable I can go for the TXs and see the complete card as a potential usable thing - otherwise I get the TXs from it.
But it looks like there are quite some discretes going on as well - some in metal cans but also several plastic (~TO-92 etc).


Hmm, LM386, that's the small power amp IC, if I'm correct. Or perhaps '387, that's that dual low-noise pre.

Thanks,

Peter

If they go at a decent price, I think they'll definitely be worth having. Looking at the bad pic, it more or less looks like what's inside some Studer boards.

Transformer+opamp micpres like the Studers are often very good sounding.

Jakob E.

Thanks, that's encouraging !
The seller only could tell me so far that it has a 48-pin connector (dunno in how many rows) and that there's something like this on the PCB:

bn 50 931/ 2 ls

Click to expand...

He'll be telling me more today.

Thanks,

Peter

from Jakob:

Transformer+opamp micpres like the Studers are often very good sounding.

Click to expand...

Being curious, I found some Studer-schematics using a 1:3.16 input-TX and a 5534 (service manual R-DAT D780). +/-12V.
Interestingly/remarkably, they're using a fixed 22dB gain in the 5534,
it's only the following 3307* that has switchable gain in 12dB steps.
For 'hot' mics they suggest a modification that changes the 5534 into
a unity gain buffer, and then the next opamp does the gain.

W.r.t. noise it doesn't sound like the optimal way to do a mic-pre, but who am I ? And hot mics are already giving a healthy signal.
And if it sounds then it sounds. OK.

BTW, those TXs are in that schematic labelled as being Studer-made -
I understand that'll most of the time be a Beyer, right ?

OK, back to the (indeed poorly) pictured card, I'll see what info emerges this evening.

Thanks / regards,

Peter

FWIW, just guessing a bit more from the picture, it looks like per channel there are some (say four) discretes after the TX, then some opamps and maybe there's an opamp-based output-driver assisted by some more discretes.

The smaller IC in the red socket doesn't fit this idea though,
as are the five metal-can transistors. :wink:


Another scenario could be that it's all discrete with some from signal-ruining (I'm not expecting virtual earths here) from a 14p. CMOS switch-IC :evil:

Ouch, just got some more info: the large ICs are indeed CMOS stuff: '4027, a.k.a. dual flipflops ! :roll: :shock:

But thats strange, MC14027BCP (full name) is a 16 pin IC.
OK, then not all those ICs are the same, what I (wrongly) assumed so far.

Some other tidbit: datecode 8118, so this card is early eighties.

FWIW, let's just keep adding info :wink:

The card seems to be made by BeyerDynamic themselves. I've just bought it, hope it shows up soon for further inspecting (& using...)

I'm contacting Beyer, let's see what they can tell me. I'm just trying the info@... address, if someone happens to know a more specific email-address for schematic requests of 1981-stuff please tell :thumb:

Regards,

Peter

:twisted:

Well, warm up the guns... If you are wanting to make mic preamps out of these my vote would be either :

1) Jensen 990c
2) Any high quality amp chip, I hear the ne5534 likes a 1:3.5 or so step-up. I think there's a guy selling 8 packs of the old Signetics brand 5534s on evilBay still.

Mine are unbalanced out and still sound great. I plan on adding balancing transformers eventually, when the budget allows.

I used a +/-15v power supply out of an old video clock, and the input schemo off of www.jensen-transformers.com/as/as016.pdf

In fact, they even have the adaptation for the ne5534 at www.jensen-transformers.com/as/as017.pdf



Good luck, and keep us updated

Hi & thanks,
Despite the dual flipflop IC (...) I expect there's usable stuff there, apart from those TXs (TR/BV310.003.002, ratio 1:3.16, 200 to 2kOhm).

I think to see a fair amount of discretes on thad bad pic though.
Or yes, can do 5534 too, I got me a rail when RS started to run out of stock.

As I understood from the seller they are already mic-pre's, seems to be coming from a German-radio station.

Mine are unbalanced and still sound great.

Click to expand...

What are you using for TX & opamp ? You mean unbalanced out ?

Bye,

Peter

My preamp is pretty simple. After the phase and pad switches it goes:

Input transformer -> opamp -> out

That's it. Switchable bass rolloff that's passive in the output leg. I don't use it.

Yes, unbalanced on the output. It will be easy to throw some isolation transformers in there when I get the urge. It's hard to find the urge because it sounds fine already.

It is a dual opamp, and you can switch between mic/line in.

The circuit is so simple it hurts. Very 'clinical' sounding as I said before. How appropriate, because I believe Dukane designed it for some kind of medical use...

No idea which type/brand of TX you use, but I remember being told here (by Jakob if I'm right) that those small Beyer TXs distort in a nice way.
I'll have a listen when the board arrives.

I agree with you, simple often does the trick. I'm not familiar with any Dukane-stuff - didn't even know it wasn't originally for audio.

Bye,

Peter

FWIW, I bought that card & the thing arrived today. Only one 553X, the other ICs are all logic and even an optocoupler as it seems.
Lots of discretes though. Only had a quick look at it, hope to trace part of the circuit tonight.

Hey! I saw that board on www.marktplaats.nl last week. Nice to know someone from here bought it :grin:

Hey! I saw that board on www.marktplaats.nl last week. Nice to know someone from here bought it

Click to expand...

Right, it's from there ! Funny you saw it. Now it's here and I'm trying to trace the circuit.
Double layer, dense packaging...

Various kinds of discretes and also some 4-pin-metal-can type I've never seen before: BRY39...
www.datasheetarchive.com to the rescue, as always...
But it'll be out of the signal path.

First stage uses BC239C, BC413C, BF245B, BC309B (one of each for each of the five channels).
Further on there's '5534, H11F3 (one of each), ... and a bunch of MPSA14's.
I guess this will be related to the 'conference-nature' of the card,
maybe some sort of limiter. Just guessing so far.

To be continued, I hope it can be used in this form with only a
few modifications - not wanting to rip out those 1:3 TR/BV-TXs right away.
FWIW, will put up better pics as well - who knows someone knows more about it
- it was indeed hard to make much of the original provided pic.

Regards,

Peter

With the actual card here, I could do a better search now.
FWIW, turns out there was a recent recent ebay-action...
so here already some better pics:
http://cgi.ebay.at/ws/eBayISAPI.dll?ViewItem&category=12050&item=7515962075&rd=1

http://i23.ebayimg.com/01/i/04/12/71/1b_1_b.JPG
http://i15.ebayimg.com/03/i/04/12/62/00_1_b.JPG

This kind of looks like a summing card of some sort... I can't say for sure...

I know getting transformers off of a !#$@%#$ PCB is not usually fun.