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

[Potato Cakes]

So the noise sounds like the oscillating noise that you posted, but then goes away when I touch the resistors on the output switch (or the wiper if it's a potentiometer) and becomes a radio station.

My next plan is to pull C11 and C12 and try to isolate the source of the problem to one half of the schematic. I don't feel that it's the Zeners as it's unlikely with modern manufacturing that a whole run would be bad, plus then they would have to be matched. But the problem is on two boards, so it's not impossible.

Thanks!

Paul

 

[Potato Cakes]

Also, can I bypass the Zeners and still get audio and not cause a meltdown? Trying to make a list of all the things to try when I get back to it tomorrow.

Thanks!

Paul

 

[fripholm]

My next plan is to pull C11 and C12 and try to isolate the source of the problem to one half of the schematic.

If you want to bypass the sidechain completely, you also want to short out the bases of T7 and T8, or SCIn1+2. This way, the sidechain circuit won't get any input signal.

Also, can I bypass the Zeners and still get audio and not cause a meltdown?

The quick and dirty way: you could replace the Zeners D1, D2 and D3, D4 by a 120k resistor for each pair. This makes T1 and T2 act as an ordinary long tail pair without compression capabilities. Works in theory - without guarantee... 

 

[Mike Havok]

Would this be a suitable power transformer?

http://www.mouser.com/ds/2/410/media-1067235.pdf

https://www.mouser.co.uk/ProductDetail/Triad-Magnetics/VPT30-1670/?qs=wkKrz7WmEgMzASoQ2znXHg==

And does someone have a link to a suitable bridge rectifier on Mouser?

Thanks

 

[Potato Cakes]

It is not.

It needs to be 2x30V. The one listed is 2x15V

Here's a whole list of rectifiers:

https://www.mouser.com/Search/Refine.aspx?Keyword=2KBP

I used the Vishay 200V 2A version.

Thanks!

Paul

 

[Mike Havok]

Thanks Paul, gone for that Vishay 200V 2A.

This is the right trafo then isn't it?

https://uk.rs-online.com/web/p/toroidal-transformers/1233098/

 

[Potato Cakes]

Correct.

 

[Potato Cakes]

Did all the things to by bypass the compressor settings and the diodes and still the same noise. Still completely clean when bypassed. Giving it a second listen, I would say it does like the MP3 you posted, without the sweeping frequency noise in the background. When I pull my output pot connection is does make the same sound. So I'm guessing it is something in the output stage, but what is escaping me. I'll start looking over the BOM and see if I misplaced anything, which is what it must be at this point.


Still getting loud pops when switching in/out. I am using the same square push button switches from Don Audio as you have in your stereo build.

Thanks!

Paul

 

[Potato Cakes]

I replaced the Zeners with the 120k resistors and it is now clean, though it does sound broken in Comp and Limit modes, which I think is to be expected without D1-D4. The channel used is the one that needs major adjustments to the THD section as running audio through in this mode is much more distorted that what I think this is intended to be. Nonetheless, with no audio program playing it is very quiet. So now I need to find some more suitable Zeners than what I have. Any recommendations on which brands/part numbers would be best?

One thing I am noticing with the dynamics section is it bottoms out the compressor on the first big transient it sees from a drum kit, pinning the meter. Then the gain reduction stabilizes from there until the next quiet passage then repeats as above. I do not know if this will go away with properly working Zeners.

On a side note, the radio station thing happens regardless if it is working properly. If you touch the top of the capacitor behind the output header you turn the unit into a fixed AM radio preamp.

Thanks!

Paul

 

[Potato Cakes]

The Zeners I am using are Central Semiconductor 1N751A TR.

Thanks!

Paul

 

[fripholm]

I replaced the Zeners with the 120k resistors and it is now clean, though it does sound broken in Comp and Limit modes, which I think is to be expected without D1-D4.

Exactly, as this was supposed to be a test with the sidechain bypassed. But good to know it's clean. Are you still getting the loud pops on switching, when the diodes are out of the circuit?

So now I need to find some more suitable Zeners than what I have. Any recommendations on which brands/part numbers would be best?

These are the ones I'm using (they are dirt cheap, so take a lot of them): http://uk.farnell.com/multicomp/1n751a/zener-diode-0-5w-5-1v-do-35/dp/1861484

Edit: Newark in the US sells them as well.

One thing I am noticing with the dynamics section is it bottoms out the compressor on the first big transient it sees from a drum kit, pinning the meter. Then the gain reduction stabilizes from there until the next quiet passage then repeats as above.

This can happen, when the control voltage feeds through to your audio signal. Have you checked, whether your audio looks like described in the guide "Fine Tuning, step 1"?

Also, have you done any mods, like the hold control? If so, I would suggest you remove it for the moment, as this makes troubleshooting even harder.

 

[Potato Cakes]

I haven't been able to do the Fine tuning I on this board as the output was so lo and the distortion so high I couldn't get a good enough image on the scope to do this step. The other board I was able to do this step, but didnt really go much further as I was trying to solve the noise issue. I'm not going to worry about it until the diodes are changed out.

I do not have any mods. Everything is as per build guide.

I'm hoping to get the parts by the end of next week before I head out of town.

Thanks!

Paul

 

[ToBSn]

So now I need to find some more suitable Zeners than what I have. Any recommendations on which brands/part numbers would be best?

Haven't continued my build yet. But stocked 3 different zeners.
My plan was to add some socket and try out which ones sound best.

Got the diodes from MultiComp, FairChild and also from Diotec "ZPD5B1"

 

[core13]

Hello
I will build it soon and I have little question. maybe it's a dumb question but I don't know where to search
concerning bypass pushbutton what do I need concerning lamp voltage please? 12v is fine?
what is the one on this picture?
http://www.ttx-sound.net/foren/IMG_7840.JPG
is it possible to wire it like the original for comp1 comp 2 and limit and have a dedicated switch for thd?

thank you

 

[fripholm]

concerning bypass pushbutton what do I need concerning lamp voltage please? 12v is fine?
what is the one on this picture?

https://www.don-audio.com/Classic-British-Console-Pushbutton-Switch-Illuminated-Yellow

This is the switch. They are illuminated with an LED, so you can use a wide range of voltages as long as you connect an appropriate resistor in series to limit the current.

 

[mrdarwin]

Hi!
Considering to build this machine...
a simple question:
Every DIY versions of this limiter need matched 1N751A, but can we use any 5.1v zener diode here?
Because all bom are available where I buy my components except 1N751A...

 

[Mike Havok]

Hi!
Considering to build this machine...
a simple question:
Every DIY versions of this limiter need matched 1N751A, but can we use any 5.1v zener diode here?
Because all bom are available where I buy my components except 1N751A...

I've ordered 500 Fairchild 1N751A's and I wont need that many so I could sell you some for a reasonable price if you wanted?. I'm in the UK but shipping wont be much I don't think

 

[dogvoid]

Hello everybody!!

Waiting for PCB

I found a very good option as audio transformers Carnhill

Input: VTB9046 2: 1
Output: VTB9070 1: 1.7

Does anyone know anything about it?

On the other hand, I have seen in other models a HI / LOW switch. I must review the scheme, but I think it is a switch that cancels or activates the pass through the input transformer, some information?

Thanks !!!

 

[mro]

Hi,

Carnhills are excellent. F.E. Chandler uses them in their clones.
I was thinking VTB9046 and VTB2281 for the output.
Best contact Collin@AML. He sells them. A very helpful guy.
The I/O transformers bypass was a feature offered in some other TG1 clone project here on groupdiy.

Best,
P

 

[shot]

It's been months this unit was left untouched on my bench (literally)!
I'm rebuilding my studio so I had no time to work on it.

Today I went to check out what is going on and try to pass some signals.
What I noticed is that it has pink noise combined with signal ONLY when gain reduction is happening. I don't know if it's the same issue Potato Cakes has since on my unit there's no radio signal in the noise. This is just pink(ish) noise.

I didn't try to see what's up with channel two. My diy time today was a bit limited.

I noticed that it has nothing to do with R22 and R7/R8 trimmers. The amount of noise is the same regardless of the trimmer position. But it has to do with the amount of low end in the incoming signal. I filtered the incoming signal (HPF in the plugin playing the test loop) and if it had no low end then the noise would disappear. It would still compress but without noise in that case. But that would be some heavy high passing, like everything below 500hz!
Also, I couldn't get R7/R8 to flatten the waveform. No matter what, some dc was always there.

I'll continue some other day, probably this weekend, when I have more free time.

Just felt need to report my current status for now



Luka