VEB Studio-Akustikk Leipzig 'VV625.11' Preamp Channels

[alhe]

Calling experts on german audio gear, and/or general analog design

I just got my hands on some old East-German preamp strips from VEB Studio-Akustikk Leipzig. I would like to rack them to use as recording preamps into my daw.

These are from a expansion unit who connected to the main mixer by a shared 12 pin plug. I believe there were six channels total. Looking at the schematics I am not quite sure how to connect a single channel for xlr output. There is three pins with outputs A, B and C, and there is a fourth output labeled 'Abhören vor regler', which roughly translates to 'Listen before regulator'.

Referenced to as KL 1 (lower middle of pic 2) there is a connector labeled -12 db.

I feel like I should be able to figure this out myself, but if you could just help me get started it would be much appreciated.

Schematic: https://dl.dropboxusercontent.com/u/37695815/KSG625-VV625.11.pdf

 

[alhe]

Front panel:

 

[tzman]

Maybe Volker can chime in here, but I'm pretty sure "Abhören vor regler" translates to "Pre fader listening".

 

[Majestic12]

"Abhöre vor Regler" means pre fader listening, that's right.

 

[alhe]

Okay, thanks ! My German is not the best.

 

[ln76d]

Good topic
I have the same preamps, exactly mixing desk. I was planned to sold it cheap, but maybe this would be a good occasion to keep it
There is VST plugin based on the EQ from this desk. I'm courious what's special in it
At the gearslutz there is a topic with most of schematics for the whole desk.

 

[alhe]

That's interesting ! Do you know what plugin this is? The EQ is inductor based, and there's a pretty big transformer in there. Probably the same as in the preamp.

 

[alhe]

So I am guessing KL 1 is line out and I can use that to bypass the fader entirely. The preamp runs on a single rail 24v dc supply. Current draw is ca. 50 ma per the schematic, but think I should go a bit higher; 200 ma?

Coupling cap is a 100 uF electrolytic. Should probably be replaced.

I am modifying a ML-12 PSU from Whistlerock Audio to run two 24v rails including phantom.

 

[sluishuis]

Hi

These amlifiers come in two versions. One is the disko 72 version with 2 inputs on each channel and 2 rail outputs (A + B). The broadcast-version (Klein Studio Gerät 625) was also used for outside broadcasts. These amplifiers have 2 rail outputs (A+B) and a variable aux  ("C") and has one input. Originally there are two 5 pin inputs. The first is balanced audio in. The second is the same input but when pins 1 and 3 are connected phantom power (12Volts!) comes on pins 4 (+ fase) and 5 (- fase). Pin 2 is ground. Old Gefell micro's used 12 volts.
The 3rd connector- the big black one- is a "Trennklinke" connector. In fact it's the insert to put a eq in line with the mix-bus output. Both desks had also very special EQ filters.
You can connect line sources and microphones- these amlifiers meet the highest broadcast standards at that time. I have the KSG 625 complete (with the intercom section/ red light signalling part and oscillator) and also the Disko '72. Maybe they look odd/old fashioned, but the sound is still great studio quality. The desk is mono, but with A + B to Left and Right you can also run the unit in stereo-mode. It's also possible to connect fader start or fader on signalling because there is a microswitch attached on the very special faderconstruction.

 

[ungifted]

This pre schema looks like channel stripes from Tesla EPP 102 mixer - EJM543, same transistors (KC509), very similar schematics.

 

[alhe]

Hi Sluishuis! Great info, thank you. Apparently I have the broadcast version, the KSG 625. So I am looking at one input and 12v phantom power. So, If I understand this correctly, rails A and B are the same output, but they can be switched to provide different levels of gain?

I also have a 625.111 unit that looks identical to the other channel strips, except it has different looking, black knobs, and two inputs. Would this be similiar to the Disko 72? - Funny name, btw.

 

[alhe]

Interesting, ungifted 

 

[ln76d]

That's interesting ! Do you know what plugin this is? The EQ is inductor based, and there's a pretty big transformer in there. Probably the same as in the preamp.

Sorry, this is no VST plugin it's preset (?) for Nebula plugin software. It's called KGB625

I  don't even know if my desk is 625 or disko 72. There's a lot to work with it and probably i will sell it sooner or later

 

[alhe]

I'll be sure to check that out. Nebula is great software.

I actually got hold of two extra channels and the original PSU from someone in Germany. What's interesting is that these channels have been modded. I will look into the mods and post them here if anyone's interested. 48 volts phantom is also possible.