[BUILD] fripholm's TG1 Zener Limiter boards - support thread

[Bernardo]

Yew it is the same distortion, I have discovered what happens when I turn the output potentiometer completely.
Could it be a transistor?what strange that it is the same in both channels.

 

[fripholm]

Could also be the output stage oscillating. Might happen if you don't use an output transformer as it somewhat relies on its load. What happens if you connect one?

Other than that, try the usual. Triple check all solder joints, connections, components and their values. Clean the board thoroughly etc.

 

[Bernardo]

thanks for all the indications, I have checked everything and it seems to be fine.
the unit works perfectly in bypass mode, also in limiting and thd but up to half or three quarters of the output potentiometer, when I put the output potentiometer to the maximum it distorts everything, in both channels.
when I inject a signal into the central pin of byp2 it saturates the output.
so it must be the output stage of the two channels.
I remember that I installed 139 and 140 in the opposite direction the first time I turned it on, but I replaced the 4, what other transistors are involved in the output stage?
Could it be that my transistors are high or low gain?
Thanks a lot

 

[fripholm]

Did you check with an output transformer as I suggested?

If you have a look at the schematic - everything to the right of the output gain potentiometer is part of the output stage. You'll find two additional transistors there. You could also temporarily try to increase the value of C22 to maybe 10n or even 47n or a small resistor value (up to ~200 ohms) in series with the output.

 

[Bernardo]

I do all the tests with and without an output transformer, both ways saturate equally when I put the output potentiometer to the maximum.
I have changed the c22 for 47nf and it has improved somewhat, but it continues to saturate, I have also put the 2 200R resistors at the output and I do not notice a difference.
my next step is to order new transistors and replace the ones in the output stage.
Thanks a lot

 

[Rob Flinn]

I do all the tests with and without an output transformer, both ways saturate equally when I put the output potentiometer to the maximum.
I have changed the c22 for 47nf and it has improved somewhat, but it continues to saturate, I have also put the 2 200R resistors at the output and I do not notice a difference.
my next step is to order new transistors and replace the ones in the output stage.
Thanks a lot

Had you considered testing the output transistors before spending money on replacing them possibly unecesarily ? Just a thought ....

 

[Bernardo]

Hello Rob, how are you?
I changed the output transistors 139 and 140, the problem persists.
Thank you

 

[fripholm]

Last orders!

On June 30th, "Deutsche Post" will discontinue the product I was using for years to internationally ship my boards. This means that I won't be able to offer affordable worldwide shipping WITH TRACKING anymore.

I won't take that risk and ship without being able to track packages and I have to announce that I will stop selling PCBs outside Germany from July on.

I'll still be here to help if needed and time permits.

There are still a few boards left from the last batch, so feel free if you want to order in the next couple of days. See the first post in this thread for more info on how to contact me.

I won't share gerber files. Please don't ask!

Thanks!

 

[alphasnk]

Hello Rob, how are you?
I changed the output transistors 139 and 140, the problem persists.
Thank you

Juanaca what you describe happened to me as well, it seems like it's the output stage going into self oscillation, i fixed it with that capacitor + a resistor on the output. I hope it can help you!

 

[Bernardo]

Hi alphasnk thanks for the reply!!!!
Could you tell me the value of the resistor?
I see that the capacitor is 150pf
Thanks a lot

 

[tommia]

5 years of Fripholm's limiter comes to an end. Thank you for this nice project!



Ps: Hope to finish mine this year

 

[SmokeyJoe]

Well well, maybe we have our culprit...
All bc559 are B not C, Low low hfe. Will swap them all and hope to get it right :-X

@dunk91
Did you figure out if the BC559Bs were causing the problem? Just realised I ordered a load of Bs instead of Cs...doh.

 

[alphasnk]

Hi alphasnk thanks for the reply!!!!
Could you tell me the value of the resistor?
I see that the capacitor is 150pf
Thanks a lot

i dont remember the value i used unfortunately, try something like from 10R to 100R/150R! you're super close to having your zener finished dont worry

 

[SmokeyJoe]

i dont remember the value i used unfortunately, try something like from 10R to 100R/150R! you're super close to having your zener finished dont worry

The build guide says:

"In some rare cases the output stage can become unstable and start to oscillate which results in distortion and excess noise. Connecting a small series resistor (try 22 ohms) between the output connector and the OPT can help."

Does that help at all?

 

[alphasnk]

The build guide says:

"In some rare cases the output stage can become unstable and start to oscillate which results in distortion and excess noise. Connecting a small series resistor (try 22 ohms) between the output connector and the OPT can help."

Does that help at all?

Yes it does, add the 150pf capacitor as well as i showed on the photo and it wont oscillate. Raise the input step by step and replace the resistor for a bigger one until it doesnt oscillate anymore!

 

[JMan]

Am I seeing correctly in the picture that the cap is in parallel with the transformer, across the primaries?

 

[tommia]

Is there a transistor voltage chart for it ? The build doesn't metter.
I'm esp interested in Q7 no gain reduction and with gain reduction

 

[fripholm]

Without signal the collector of Q7 idles at about +0.6 volts. When audio goes through the sidechain, Q7's collector outputs the rectified signal with the peaks facing towards the negative rail.

 

[tommia]

@fripholm : Thanks for that.

 

[SmokeyJoe]

Evening folks. I ordered a big old 30V 160VA transformer for this project as it was the cheapest one I could find.

I've since found some earlier posts stating that a 25V would do the job just fine, which I can get much easier in a smaller size/power.

Is there any disadvantage to using the 160VA one? I can only mount it flat due to the size.