Picked up a german broadcast rack with 15V PSU and a few modulse, help...

[b0b]

Hello,

couldn't help myself today when I saw a broadcast rack for sale at a market in Berlin. I'm hoping I got a bargain but I might just be a heap of junk...

It's a 3U rack enclosure for 8 modules. Here's a few pictures:

Front view:

http://twin-x.com/groupdiy/displayimage.php?pos=-3424

Back view:

http://twin-x.com/groupdiy/displayimage.php?pos=-3425

It came with two mic preamps which I don't think are super good. They are model "TM4 B", nothing else is specified. There's one NE5534 opamp and 4 transistors, no x-formers.

Mic pre:

http://twin-x.com/groupdiy/displayimage.php?pos=-3422

When I bought this unit I thought I might be able to fit it out with some classic german mic pre modules. The rack has a 15V PSU and the modules have 64 pin connectors. Anyone know i this is a universal standard or if this is a complete custom build?

 

[audiox]

Looks like a custom product made by some small engineering company in the 90s. It is possible that the rack (made by Rittal) is the most valueable part of your purchase...

I think the other cards look more interesting than the mic amp. If you post pictures of them, we can probably tell you more. If possible, take the pictures directly towards the component side (not in angle like the mic pre picture).

There are similarities between DIN 41612 connector pinouts of different manufacturers but as far as I know there is no standard. But those connectors are manually wired so it is easy to rewire them for your other eurocards.

E: typing errors

 

[[silent:arts]]

TM [4b] sounds like Thum & Mahr, and the red SB-4 card reminds me of some cards where I have stolen the transformers for my Pultec clone (never finished).

let me guess the former owner: Deutschlandradio

 

[Michael Tibes]

When I bought this unit I thought I might be able to fit it out with some classic german mic pre modules. The rack has a 15V PSU and the modules have 64 pin connectors.

As far as I know the sought after modules are all running on +24V, not +/- 15V. This doesn't mean it totally has to be crap, but it doesn't look like a huge bargain either.

Michael

 

[helterbelter]

What price did you pay for it ?

 

[diyfanatic]

but it doesn't look like a huge bargain either.

depending on the price but it could be a great donor...

BTW I love the psychedelic carpet!!  ;D

 

[b0b]

Thank you all for your answers. Here's some more pictures

Mic pre, top view:

BIA-SUM module, "TM3 B":

BOA 1T module, "TM5 A":

SB-4 module, "SEBE-4 L":

Power supply, TM1 C":

I got it for €20 so it's not a big loss if the modules aren't great. I though I might be getting two decent pres for €10 each... I need to replace the big caps in the PSU as one leg on each is broken. That's about €7 in additional components. Otherwise it looks ok.
The “psychedelic carpet” is a yoga matt Didn't want to scratch the floor...

 

[diyfanatic]

20€ is not so bad!!!

 

[audiox]

TM4B. Textbook mic pre circuit with unbalanced output.

TM3B sum module. Horrible layout. Especially the "ring" that collects all the magnetic interference. The blue cardhandle is probably the most useful part of this card.

TM5A looks like a small mono power amp built around two transistor buffer inside the op-amp feed back loop. The input transformer could be usefull.

SB-4 must be a limiter (probably mono, I can see only one VCA). Looks like a feedback design (sidechain input taken after the VCA). Try if it sounds good. If not, you can used it as a base for some compressor project.

 

[b0b]

TM4B. Textbook mic pre circuit with unbalanced output.

TM3B sum module. Horrible layout. Especially the "ring" that collects all the magnetic interference. The blue cardhandle is probably the most useful part of this card.

TM5A looks like a small mono power amp built around two transistor buffer inside the op-amp feed back loop. The input transformer could be usefull.

SB-4 must be a limiter (probably mono, I can see only one VCA). Looks like a feedback design (sidechain input taken after the VCA). Try if it sounds good. If not, you can used it as a base for some compressor project.

Thank you very much audiox! I have to fix the PSU and then I can try them out.

Is there any point in putting in bigger/better caps on the PSU as I have to replace them anyway? They are 4700uF 40V at the moment...

And if anyone has any pointers on what kind of modules I could search for to fill up the rack all information is greately appreciated, manufacturers, specific modules, anything at all. Mainly looking for mic pres, possibly EQs and comps as well, if there are any...

 

[audiox]

Is there any point in putting in bigger/better caps on the PSU as I have to replace them anyway?

Probably not if the original designer has done his job. 18Vac/4700uF/15Vdc sounds fine for currents you get from 78/79 series regulators. Someone here published an Excel calculator for that. You can use it if you don't want to do the math. The capacitors are less than 20 years old, so they are most likely ok. If you have oscilloscope you can measure if the ripple goes close to the output voltage (load connected).

Maybe it is possible to save the old caps. If there is any of the welded copper pin left of the capacitor side, you can repair it by soldering. Not an optimal solution for use in OB van but I guess that is not your application.

 

[helterbelter]

Well, even 20 euro for the rittal rack only is a decent price... 

 

[b0b]

Probably not if the original designer has done his job. 18Vac/4700uF/15Vdc sounds fine for currents you get from 78/79 series regulators. Someone here published an Excel calculator for that. You can use it if you don't want to do the math. The capacitors are less than 20 years old, so they are most likely ok. If you have oscilloscope you can measure if the ripple goes close to the output voltage (load connected).

Maybe it is possible to save the old caps. If there is any of the welded copper pin left of the capacitor side, you can repair it by soldering. Not an optimal solution for use in OB van but I guess that is not your application.

Thanks for that. I'm quite new to electronics on the whole. This should be a great learning experience. The caps will be easy to fix as the legs broke at the pcb so i still have 10mm of leg. They broke because there was no cable tie holding them in place. So with fixed legs, a cable tie and no OB van I should be fine then.
I'll start by disecting the PSU design as that is the simples circuite and then move on to the mic pre. The limiter is a bit complex for me for now.

One last question, audiox you said the mic pre is "textbook", is that good or bad? I know it wont be a neve or anything, but is it or might it be made in to a good transformerless pre or maybe with a output transformer for balanced output?

 

[audiox]

One last question, audiox you said the mic pre is "textbook", is that good or bad? I know it wont be a neve or anything, but is it or might it be made in to a good transformerless pre or maybe with a output transformer for balanced output?

You can find that circuit and its variations in many mixers (from cheap Behringers to more sophisticated large consoles). I would describe it neutral. But listen and make your own conclusions.

Using output transformer probably makes it less neutral. Once again it is your decision if you like it or not.

 

[b0b]

You can find that circuit and its variations in many mixers (from cheap Behringers to more sophisticated large consoles). I would describe it neutral. But listen and make your own conclusions.

Using output transformer probably makes it less neutral. Once again it is your decision if you like it or not.

Thank you very much for all the information!