Rare tube compressor: Lomo 600U-17 ( Ломо 600У-17 ) - SCHEMATIC FOUND !!

[thomasdf]

Hi folks
So I just got back from a trip to Russia, and I bought a pretty rare tube compressor there.
It's a Lomo 600u-17. I guess it's from the late 60s, it was manufactured in USSR by Lomo, the famous brand. But apparently this compressor is pretty rare, and was taken out of a huge cinema / broadcast / "kinap" setup.

I tested it before buying and it sounded really interested, but was poorly set up I believe, because when too much compression was going on, it acted like a very fast tremolo / mute on the peaks.

The seller gave me hand drawn schematics, but I'd like to get as much info as possible, especially a setup manual or operation manual.

It has a single rotary switch on the front, with the following labels: bypass, 20:10, 16:10, balance "K", balance "Э". From what I have heard and understood, 16:10 most likely acts like a "vocal preset" with a HPF on the sidechain. Or behaves like it.
It also has 3 trim pots inside hand labeled balance K, balance Э and the third one is a threshold setting, according to the seller.
Transformer in & out to a 16 pins amphenol connector. Tubes are 2x 6К4П (6K4P) and 2x 6Н3П (6N3P).

I intend to rack it with a beefy and stable PSU (250V for HT and 6,3V of course) , and to add an input and output attenuator too. (Btw, what's the best way to do that? T Pad? ) It could be great if I could add a gain reduction meter... but maybe it's too complicated?

So any help is welcome regarding this! I know there are some tube gurus around here...

Here are a few pictures!

larger pics : http://imgur.com/a/ECnOn

Thanks a lot

Thomas

EDIT: HERE ARE THE SCHEMATICS, SEE PAGE 2

 

[mjrippe]

There's one on ebay and the seller says they have all the docs.  Maybe they will share?

 

[thomasdf]

Héhé nicely spotted! I contacted him and he sent me a pixelised schematic, then offered me a good discount but still not as low as the price I paid for mine. I agreed not to post his schematic online for now on, even thought it is barely readable. TBH it gives an overall good view of the design but you can't do much more with it.
I contacted him again and offered to PAY for the full schematics, operation manual or any info and told him to name his price ... he refuses to sell schematics or any documentation. Apparently he had a hard time gathering the info, he contacted many former employees and designers from the Lomo factory, had to drive back and forth between Moscow and St Petersburg etc
That's why I offered money for this info and told him that if he loves this piece of gear so much, he should be happy that a young dude like me wants to take good care of it... but the only thing he is able to tell me is that schematics are free if I purchase the compressor. Go figure... Just a simple email with info for easy and fast money... but he is not interested for some reason. I believe he is angry because someone offered a better deal? Still trying to figure out things with him and cut a deal, but it looks like a dead end to me. Maybe somebody else can be more convincing? But I doubt it!

 

[jackies]

I will attempt to contact him and ask if he would accept money for the copy of the schematic.
I am Russian and have good people skills.
8)

 

[emrr]

good luck.

If you have a pixelated version, you have most of what you need.  Measure the values and pencil in.  A 1000 piece jigsaw puzzle is more difficult. 

 

[jackies]

That's also true.
Also the bit about not sharing is a complete bullsh*t, I (may) understand not sharing a copyrighted schematic of a device that's currently in production, but this is an ancient schematic from a country that doesn't even exist anymore! And there's no copyright laws in Soviet Russia!

 

[thomasdf]

Thanks guys for your help! For now on he agreed to sell me the schematics + PSU schematics + operating manual with voltage charts when his unit is sold. Maybe that's tomorrow, maybe that's in ten years
Jackie, I am sending you a PM

 

[thomasdf]

So I will put it in a rack soon, and I am preparing stuff for the PSU, etc.
Now I have 2 (rookie) questions:
What is the best way to add pads on the input and ouput (balanced?) is there a simple way with pots, or should I go with metalfilm resistors and switches?
Is it easy to add a gain reduction meter to a compressor like this one? I have some lovely bakelite meters around and they are just collecting dust right now...
Many thanks
Thomas

 

[Whoops]

Looks interesting,
I never heard about this Lomo brand.
Was Lomo a Russian company of pro audio products?
Or a foreign company that was manufacturing in Russia?

What other products did they produce?

Wish you get the schematics and make it work

 

[thomasdf]

Quoted from Wikipedia:
LOMO (Russian: ЛОМО́) or Leningrad Optical Mechanical Association (Ленинградское Oптико-Mеханическое Oбъединение Leningradskoye Optiko-Mekhanicheskoye Obyedinenie) is a manufacturer of advanced optical instruments, medical equipment, consumer still and movie cameras, projectors, lenses, film editors, splicers, professional sound recorders for motion-picture production based in St. Petersburg, Russia.

I was told they also made weapons and other secret military stuff.
Anyway, as far as audio is concerned some of their mic are in the Neumann U67 league, check the 19a19. They also made sh*tty dynamic mics, so basically covered a lot of things: tube preamps, solid state preamps and limiters, mixing desks, etc etc
In the optical field they made crazy good lenses used in soviet cameras such as Zenit, Zorki, Fed, etc... which are most of the time crazy good cameras (Built with German scientist they "invited" after WW2. American took the rocket scientists and russian took the optical guys from Zeiss, Leica etc...). For instance, the Zorki 1 is a perfect copy of a Leica 3 for a fraction of the price!

 

[Whoops]

Ok, now I see, I knew a Lomo company from photo cameras, now I see that somehow it's the same company.

Cool stuff to know

Thanks

 

[thomasdf]

Hello everyone

For those interested in having a look and helping me, I have drawn a schematic as clear as I could in Eagle...
Please do not use it commercially, and only on GroupDIY. Do not repost it without my written authorisation.

It is a first for me, so please excuse me if it is not very clear (drawn from hand drown notes the seller gave me, plus a friend of mine who cleared up some points for me). Also, I know the components of no names yet...

I am still interested in any information you could give me about the two mysterious "balance" positions on the switch.

Also, I will soon wire two 600 ohms T pads as input and output attenuators.
I would love to add a gain reduction meter with a balance function if it has any use... How can I do that?

Correct me if I am wrong, but maybe I can seek inspiration in the 436C meter circuit?

I am still hesitating between diode or tube rectified PSU...

Edit: schematic removed : contained mistakes

 

[gyraf]

I would love to add a gain reduction meter with a balance function if it has any use... How can I do that?

You could probably shunt the 120R at the "ratio" switch with a DC-reading moving-coil meter. Maybe just a 1mA or so..?

Jakob E.

 

[thomasdf]

Hello Jakob

Thanks a lot, I'll try that!

Thomas

 

[thomasdf]

Hi everyone,
Just to keep you updated. Been pretty busy but I managed to hook up the compressor to the diode rectified PSU of a Federal clone I built. When loaded, that PSU delivers approx 205V. I know that when checking the tubes' datasheet another 45V would be great but I thought to for testing purposes that would be enough. The 6.3VAC is coming straight from the PSU transformer (Edcor).

Anyway, all I am getting is pretty loud 60hz hum and the audio is very weak

My concern is that I noticed the ground cable that connected the comp ground to the PSU ground was quickly getting hot, so I quickly turned everything off...

Do you have any idea what could cause this?

Edit: here is the only "official" version of the schematics I have... sorry it is so small... maybe I should redraw it one day..
Is it me, or both ends of the output transformer are connected to the ground??!  ???

 

[emrr]

I read no indication you checked or replaced any caps.  Could also be a short somewhere.  Wire heat means too much current. 

 

[thomasdf]

You are right emrr! It has never been recaped. The seller told me in english / russian "recap no noo!" I understood back then that it meant all the caps were fine. But maybe it was more like "it has never been recaped" haha
It was on my to-do list... There are not a lot of caps in it, shouldn't be long!

 

[Script]

What are the "Balance K" and "Balance E" settings for on the Lomo? I don't get it.

 

[thomasdf]

I may be taking a wild guess but I suppose they are balance settings for each pair of tubes. I don't know which is which, and I don't know why there is a switch position for that. Probably related to a meter function? I'd love to crack that mystery and Have a nice looking meter

 

[gyraf]

Two balance controls: One balancing the two cathodes and one adjusting a screen grid to match the other.

My guess is that you'll have the find the setting combination that minimizes control-voltage breakthrough to audio. At least, this is how we do it in the G10

This is in line with that switch pos 4+5 feeds input audio directly into sidechain.

Jakob E.