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

[thomasdf]

Hello
Thanks for your fast answer. That project is a bit more expensive than what I thought (even if I don't necessarily mirrored VU's)... I'll think about it twice. Since I love that comp I'll probably end up building it, but I have a few other piece of gear that I need to take care of first.

Best,

Thomas

 

[late]

Anyone knows what can cause this
https://dl.dropboxusercontent.com/u/20579799/TG1.mp3

Weird because it stops when set hpf on like 40hz. T_G and T_F are about 5.00v on working channel when hpf off. Bad channel jumping so much that my multimeter shows overload. But when i set hpf 40hz or so then it shows about 5.00v. Anyone have idea what can do this?

 

[bieckmusic]

sounds like a cool techno remix... sorry couldn't resist.  just wondering, did you do Igor's TG fix mod?

 

[late]

sounds like a cool techno remix... sorry couldn't resist.  just wondering, did you do Igor's TG fix mod?

Yes. Have tested both channels with same cables and front panel pcbs.

 

[Biasrocks]

Anyone knows what can cause this
https://dl.dropboxusercontent.com/u/20579799/TG1.mp3

Weird because it stops when set hpf on like 40hz.

DC offset somewhere?

Mark

 

[late]

I disconnected R3 and R11 so the sidechain was out. Then i soldered them back and it worked well. After 5min it started do that old problem again. Maybe the problem is in sidechain section. But i cant understand where.

 

[jplebre]

I disconnected R3 and R11 so the sidechain was out. Then i soldered them back and it worked well. After 5min it started do that old problem again. Maybe the problem is in sidechain section. But i cant understand where.

quick question, sorry to hijack your thread
disconnecting R3 and R11, would it give nominal gain through the audio path?
I'm asking this because I'm having terribly low o/p and can't really figure out why.

 

[bruno2000]

Could someone post a diagram of the "Hold" switch with values for the 5k r/log option?
Thanks!
Best,
Bruno2000

 

[e.oelberg]

as far as I remember this ( I built my unit 2 years ago) you can't just use stepped switches. You have to build one and measure every step on the second running signal to get a working stereo unit.

 

[bruno2000]

as far as I remember this ( I built my unit 2 years ago) you can't just use stepped switches. You have to build one and measure every step on the second running signal to get a working stereo unit.

Sounds like a plan, but I've got to start with the first switch and have the starting values, but don't know which way they go.
There's also that 100k trimmer across the whole thing.
Thanks for your help!
Best,
Bruno2000

 

[etheory]

I've just discovered that in their infinite stupidity Australia Post has returned my meters and hundred of dollars worth of original TG parts for my build to America where I bought them from, without contacting me with any of the 3 required notices of delivery, or managing to find the perfectly filled out address on the package.

Now I will have to wait around 3 months minimum to even know if the package is still available as it is returned via carrier pigeon to sender.

Very very upset since I was sooooo looking forward to getting to this build.

Having said all that, massive thanks to Frank and Bruno2000 for helping me out with finding all the bits. I just hope one day soon I can get them to actually built it 

 

[jplebre]

Hi Bruno

I built it with log values but I'm not happy with the result. Most of the more drastic stuff happens towards the end of the spectrum but the clicks are too far apart to make use of it. By the time it starts to get into the distorting/very coloured range, you have one click at the beginning of that range and then all the way up (smashing).

I have an issue with the gain recovery bit (VT9 section) so it MIGHT be why.

But I am going to swap the hold for a linear, as the original schematic says handwritten and barely visible.

Anyway values are:
330
390
470
620
750
910
1k1
1k8
2k


There's some discussions about this earlier.

Igor also installed a 100k trimmer. This is crucial to get both sides to match!

Cheers
J

 

[e.oelberg]

I don't know if you need stepped control here. If the unit is in stereo mode, compression is anyway linked and you can set it pretty good with a pot. Stepped output is useful though

 

[bruno2000]

Thank you both for your replies!  I have the option of Igor's stock 12 position switch in the r/log mode, or a 24 position switch configured as a 10k pot.  Looks like I'll have to try each.
On Igor's switch board, which resistor goes in position #1, the 330r or the 2k?
Best,
Bruno2000

 

[late]

I disconnected R3 and R11 so the sidechain was out. Then i soldered them back and it worked well. After 5min it started do that old problem again. Maybe the problem is in sidechain section. But i cant understand where.

quick question, sorry to hijack your thread
disconnecting R3 and R11, would it give nominal gain through the audio path?
I'm asking this because I'm having terribly low o/p and can't really figure out why.

Yes.

 

[late]

Got my tg1 working but still sounding difference. This is in comp mode. Ch1 gives more output and not so limited. Vt13,14 gives differences but same bc184 or bc109 pair gives different result in both channels. Very hard to get matched channels?

https://dl.dropboxusercontent.com/u/20579799/Tg1_Ch1.mp3
https://dl.dropboxusercontent.com/u/20579799/Tg1_Ch2_Broken_Before.mp3

---
Ch2 D6 was bad. Now it work and have good transistors in vt13 and 14. What transistors must be selected, just vt13,14?

 

[etheory]

In theory, since this design lacks a lot of feedback to help correct for component tolerance differences, unless you match each of the long tailed pairs, you will get a bit of variation.
The most important LTP to match, are the two NPN BJT's sitting below the zener diodes.

Also, matching the zeners is crucial. Distortions and offsets are governed entirely by the balance of the main voltage controlled attenuator section compromising the NPN LTP and the 4 x zeners.
The better this match, along with trimming the currents through each side to be as equal and opposite as possible, will give the best performance.

At least that's what the simulation tells me.

 

[trampo]

Hi All

I have completed my TG using the original 2501 diodes and original transistors etc and although the unit works great, I cannot calibrate it for unity gain.

Can anyone confirm that by having the hold and the gain makeup in the central position I should get unity gain on the main board?

If I inject  a 1K signal at .707V I am getting around .450V out!

Any help would be much appreciated.

Trampo

 

[bruno2000]

Well guys,

it's the new year and I've decided to try my luck again with the TG1 doorstopper / boat anchor that I have stashed away in hopes of some time getting it together..

Anyway, the +- 20V points are good as are the +- 28V and the signal is entering the board, however it gets beat up in the process..

This is a spectrograph power cycle of the board.. first you have a nice healthy signal coming through the relays and when you switch it on through the opamp input, look at the spectrograph. There's a click, some weird harmonics (weak weak signal). The other click and healthy signal is of course when I switch it off and relays click the signal back. I can only get this weak signal if I turn compression on (THD off) and take HOLD to the rightmost extreme (which puts the VU to above +10 on sintech's VU scale).

These are the oscilloscope scans of the testing points on the PCB:

T_A

T_B

T_C

T_D

T_E

T_F

T_G

T_H

T_J

T_K

I could use some help debugging this, as it's way over my head, all these transistors and how it works together. Just so to repeat, symptoms are extremely low output signal and high distortion.

I know this is an old post, but what was the fix for this?  I have a similar problem.
Thanks in advance!
Best,
Bruno 2000

 

[bruno2000]

I disconnected R3 and R11 so the sidechain was out. Then i soldered them back and it worked well. After 5min it started do that old problem again. Maybe the problem is in sidechain section. But i cant understand where.

quick question, sorry to hijack your thread
disconnecting R3 and R11, would it give nominal gain through the audio path?
I'm asking this because I'm having terribly low o/p and can't really figure out why.

Did the low output get fixed?  I'm having the same kind of problem.  Seems like I'm missing about 15dB of gain in "THD" mode.
Thanks!
Best,
Bruno2000