TAB U73 vari-mu racking and mods

[imrc]

Hello, this is my first post on this forum even If I have already learned lot of stuff thanks to you.

I have a TAB U73 compressor/limiter that I want to mount in a rack and add the controls for the attack and release time, threshold...

Are there some folks here who have already done these mods ?

Here is the schematic :
http://www.digital-synthologie.de/vari-mu/download/u73.gif

Thanks in advance for your help.

Teo & Axel

 

[NewYorkDave]

Hmmm... Interesting circuit. One of its features bears resemblance to something I did in my own compressor circuit.

Is there a more legible copy of the schematic out there?

Sorry for the hijack... Carry on.

 

[imrc]

a very good copy of the schematic is available at Kubarth's website

http://audio.kubarth.com/rundfunk/index.cgi

Thanks for your interest

 

[Michael Tibes]

I've just rechecked the description at Kubis: the U73 is switchable between compressor or limiter (the compressor function is somewhat like a softknee limiter), the U73b additionally has switchchable release constants and the U83 is only a limiter. The description is relatively detailed, but only in german.
What the varicom does is still a mystery to me...

You have the U73 without 'b'?

Michael

 

[imrc]

I confirm that I have the U73 only (without A nor B). There is no release switch, wich is one of the mods I'd like to add.

 

[Michael Tibes]

[quote author="kubi"]And last but not least a Varicom is a nice way to link two U73x limiters for stereophonic tasks in Oxford, not Aarhus mode.[/quote]
So that means that 2 U73 being linked without varicom are in Aarhus-mode - averaging the peak levels between L & R ?

Michael

 

[jensenmann]

Michael, you forgot to send me your Varicom as christmas present last year. How about this year :wink:



:green:

 

[jensenmann]

Inner SWR Mülltonne ist demnächst ein Yamaha PM3000 drin - und ich weiß wann und wo :wink:

 

[imrc]

Hello,

Are there some menbers of the lab who have already done these mods on a tab U73 that would help me ?

It seems that some functions are already present with onboard trimmers. For
example H&E people use to add the release (0.3-10s) as on the TAB U73B, and the threshold control.

Here is an example of adding a gain control, a ratio control...:

 

[Michael Tibes]

[quote author="jensenmann"]Michael, you forgot to send me your Varicom as christmas present last year. How about this year :wink:



:green:[/quote]

Uuups, wasn't that you where I sent it to??? :roll:

Michael

 

[Michael Tibes]

[quote author="imrc"]Hello,

Are there some menbers of the lab who have already done these mods on a tab U73 that would help me ?

It seems that some functions are already present with onboard trimmers. For
example H&E people use to add the release (0.3-10s) as on the TAB U73B, and the threshold control.[/quote]

I assume you can't read german, can you? The trim pots are well documented in the manual, but all is written in german.
Adding the release time constants should be a matter of comparing the schemo of the U73 and U73b which has those built in. The basis of both units is the same. I don't know how wide the range of the internal trim for the threshold is, if it makes sense to take that one outside as a threshold pot (that would still be easy...).
Perhaps a little more brain needs to be put into the gain and ratio things, but even this shouldn't be too difficult for those who really know how a vari-mu works (which means not exactly for me...).
Anyway, I could help translating for you. In fact I feel like I did exactly that in another thread a while ago, maybe you do another search?

http://www.groupdiy.com/index.php?topic=15416&postdays=0&postorder=asc&highlight=varicom&start=0 was a thread with a little talk about the varicom. Shame I still haven't found the time to play with it...

Michael

 

[API]

[quote author="kubi"][quote author="Michael Tibes"]What the varicom does is still a mystery to me...[/quote]

Actually it's an external side chain for the U73x limiters.

Varicom is an add on for the U73x to add a program dependent release time, which is also selectable from slow to fast. It also adds the possibility to make the compression more or less bass independent (what you might know from the super sidechain thiggy for the GSSL), and it also adds switchable attack/hold time constants.

Especially the program dependent release time is a beautiful thing as it makes it easy to squeeze the juice out of your signal without any "pump" effects or increased distortion at low frequencies unlike other compressors which sound awfully bad when driven hard.

And last but not least a Varicom is a nice way to link two U73x limiters for stereophonic tasks in Oxford, not Aarhus mode.

There was the normal Varicom as an add on for U73x limiters and a U73 Varicom, which is a U73 with a Varicom built in. And yes, there were some more sub versions.[/quote]

I must say that this is the best description of the Varicom ever!
Finally I understand what this realy does!!
I have 2 U73b´s and a Varicom which been on my bench for years but I never got round to recap them and rack them up.
I have tried to understand the German paper on the Varicom for years, but never did.

One final thing, if you know, what exactly what controls do what on the Varicom?
Which setting is for the program dependable realese time?
And which is the Sidechain filter and attack hold time constant settings?
I only see two controls.
I guess the small "screwdriver" hole is for adjusting the Meter.
Speaking of Meter, what does it show?

To many questions, I know, but please try to let me know if you know.

Thanks,
Dennis

 

[mad.ax]

Hello Michael

[quote author="Michael Tibes"][/quote]

"I assume you can't read german, can you? The trim pots are well documented in the manual, but all is written in german."

-You're right, we can't read german, especialy german technical abbreviations...

"Adding the release time constants should be a matter of comparing the schemo of the U73 and U73b which has those built in. The basis of both units is the same."

-Yes, it should be easy to replace the 5 Mohms and 100nF (numbers 55 and 82) by a 6 positions switch and its associated components as drawn in the U73B schematic.

"I don't know how wide the range of the internal trim for the threshold is, if it makes sense to take that one outside as a threshold pot (that would still be easy...)."

-Looks like both the trim and pot have the same value (100K), I'll just have to play with the trim to see if a log pot should be more apropriate.

"Perhaps a little more brain needs to be put into the gain and ratio things, but even this shouldn't be too difficult for those who really know how a vari-mu works (which means not exactly for me...)."

-which means not exactly for me neither!
but thanks to your translation, I allready know that I could play with the (number 62) 100k trim to add a "make up gain"

"Anyway, I could help translating for you. In fact I feel like I did exactly that in another thread a while ago, maybe you do another search? "

-I did just that, and found this thread:
http://www.groupdiy.com/index.php?topic=5495&highlight=u73
Thank you very much for your help!

Axel