TG1 - advice from any one who has built it...

[fripholm]

I'm getting  roughly -76dBFS self noise vs -35dBFS with 751A.

Wow, -35dBFS is a lot! I thought my units were noisy but they're far from that. At unity gain from input to output I'm getting about -85dBFS, which translates to roughly -72dBu.

I'm using Multicomp 1N751A from Farnell. They are dirt cheap and I had my six matched pairs after testing about 30 pieces.

 

[Ilya]

Wow, -35dBFS is a lot! I thought my units were noisy but they're far from that. At unity gain from input to output I'm getting about -85dBFS, which translates to roughly -72dBu.

I'm using Multicomp 1N751A from Farnell. They are dirt cheap and I had my six matched pairs after testing about 30 pieces.

Yeah, this is absolutely unusable. Besides, central zeners are much more expensive.

Do those Multicomp zeners give unity gain or are you using an 1:2 trafo at the output?
Just put an order for a boatload of those zeners, 2 wks leat time though...

 

[fripholm]

Do those Multicomp zeners give unity gain or are you using an 1:2 trafo at the output?

When calibrated correctly, the compressor stage should have a gain of about +14dB when not compressing - which it has in my case. The output stage provides even more gain, so a 1:1 OPT is more than enough.

 

[Ilya]

When calibrated correctly, the compressor stage should have a gain of about +14dB when not compressing - which it has in my case. The output stage provides even more gain, so a 1:1 OPT is more than enough.

Well, going through the gain staging of this compressor, and following the notes (~V and dB, written in the original schematics), I would argue that this device requires step-up on the output because it looses around 4 dB. If you look at the output of the VT10, it shows -19.2 dB (~0.085V). After VT10 it goes to the unity gain buffer (VT11/VT12) and to the output attenuator S3. Output stage is designed to have 14 dB gain with the S3 set to 0. Doing simple math: -19.2dB+15dB=-4.2dB. This is almost exactly the figure I'm getting on the output if I set all the levels according to the notes in the schematic.

I wonder where your unit is getting those extra 4 dB. What are the signal voltages on your D2 and D4 anodes? It should be -26dB (~0.039V) with input signal at -0.8dB (~0.707V)

 

[fripholm]

Sorry, didn't want to add to any confusion. I was going by my own version of the PCB which is slightly different and was designed to give more gain in the output stage (amongst other changes).  :-X

 

[Ilya]

Got the Multicomp 1N751 zeners from Farnell today. I'm not impressed with the curves at all - they are all over the place and the actual knee is very different from piece to piece. But there's good news as well - they are not as noisy as the ones I've got from Mouser.

With these zeners the signal drops dramatically. I estimate a loss of around 12-16 dB. I suppose (I'm almost sure) this is because they have a rather sharp IV curve. I've managed to find some original zeners as well, but they haven't arrived yet. I have some ideas that may help to bring the gain back to unity with current zeners. Going to play a bit more with this guy until the NOS parts arrive.

 

[Randyman...]

So, I have a full TG1 kit still sitting in the box with nice AML transformers and all.  Time has gotten the better of me, and between that and a lack of cunning schematic decoding skills and the "Test in situ" type values for this build, I'm looking for a brave trustworthy soul that would be willing to assemble it for a generous fee.  Any takers or leads?  Please PM or email from my profile.

I wish I had more time!!!  I'd prefer to spend my time using this gear in the studio with what little free-time I have these days  ;D

Carry on - Thanks!  8)
Randy V.

 

[moltenwok]

Hmmm interesting-could be the missing link. I do have an original RS168 here to compare

 

[moltenwok]

Here she is

 

[jplebre]

I think I'm about ready to give up on this.

My first DYI acceptance of failure. I just don't have time for this. and this is a £1k door stopper that I have lying around.

Anyone wants it, come make me an offer https://groupdiy.com/index.php?topic=68538.msg872305#msg872305

 

[willbart]

Hi
Just bought a TG1 clone, with no Link.  I've got a few 2-in/2-out line transformers here, can I use one of these?

I'm not really sure where I'd take the link from either, I don't suppose anyone could give me some ponters could they?

Many thanks!

 

[Ilya]

Hi
Just bought a TG1 clone, with no Link.  I've got a few 2-in/2-out line transformers here, can I use one of these?

I'm not really sure where I'd take the link from either, I don't suppose anyone could give me some ponters could they?

Many thanks!

You don't need transformers for linking. In the schematic there's a special link connection. You need to connect link points between the compressors and you're good to go.

 

[willbart]

You don't need transformers for linking. In the schematic there's a special link connection. You need to connect link points between the compressors and you're good to go.

Thanks Ilya
I didn't build this myself, dont have a schematic - have attached a pic of one of the channels - there are a few unused points, can't see one marked Link. I've found an old circuit diagram but can't find an obvious place.
Any ideas?

Also, as well as a normal link, I was hoping to fit an 'emphasis' pot on each side to fade between the sidechains so one can be independently controlled by the other.
Would this work as I'm imagining? I'd have to break the circuits at the link point, then insert the pots there. 
The link switch would just bypass the faders.

Thanks

 

[salomonander]

hey,
finally finishing this up. help me out here.... did igor mess up on the opamp holes - or am i stupid? my opamp sockets wont fit the pcb.... i have the standard sockets from capi and the holes are too small....... cheers

 

[desol]

Sometimes I wonder if the parts Igor had access to were different than mainstream components we normally see here. lol

Just based off of when I was putting the parts list together for this project. Weird lead spacings, diameters, etc for parts that didn't seem to be available or make sense. One of the things that kept me from actually building this up...

 

[salomonander]

Sometimes I wonder if the parts Igor had access to were different than mainstream components we normally see here. lol

Just based off of when I was putting the parts list together for this project. Weird lead spacings, diameters, etc for parts that didn't seem to be available or make sense. One of the things that kept me from actually building this up...

so im not stupid! thats great news cheers

 

[Rob Flinn]

If you look at some of Igors pics you can see he uses  quite a lot of Military surplus parts.  I believe that they are plentiful in Israel.

 

[desol]

If you look at some of Igors pics you can see he uses  quite a lot of Military surpus parts.  I believe that they are plentiful in Israel.

I knew something was off, or on, whichever way you want to look at it. I was like, 'how is he getting 20uf radial capacitors?' lol

I couldn't source those from anywhere but china at the time I think. I believe they were approx 8mm diameter.

 

[mrclunk]

I've 4 channels of this half built...
Will get back to them one day.
Did anyone ever work out why the output transistors were burning up?

 

[Rob Flinn]

I've 4 channels of this half built...
Will get back to them one day.
Did anyone ever work out why the output transistors were burning up?

I built a couple of these and never had any issues with the output transistors ..................