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

[fripholm]

Pots are wired hot= 1, cold / wiper = 2, drain = 3.

I'm not sure what you mean by that.

When done correctly, the output gain pot should get to full level when fully CW but *not* fully silenced when turned the other way.

When you look at the output gain pot from the front panel side with the pins facing down, the pot's rightmost pin is soldered to pin 1 (the square pad) of connector OUTPUTGAIN. The pot's middle pin goes to the pad in the middle of that connector and the remaining connection goes to pin 3.

 

[ron_swanson]

I'm not sure what you mean by that.

When done correctly, the output gain pot should get to full level when fully CW but *not* fully silenced when turned the other way.

When you look at the output gain pot from the front panel side with the pins facing down, the pot's rightmost pin is soldered to pin 1 (the square pad) of connector OUTPUTGAIN. The pot's middle pin goes to the pad in the middle of that connector and the remaining connection goes to pin 3.

Thanks for the reply fripholm!

Sorry, the I/P and O/P gain pots I have are numbered, hence my number reference.  Based on your response above, the numbers on my pots are in reverse to your instructions.    Also, 'yes' full CCW is not exactly 'no volume' . 

Does the installation instructions above also apply to the I/P gain control wiring?

So, after a quick re-wire to match your instructions, seems to work correctly now, but immediately ran into an issue where the right channel gain level was significantly less than the left channel .  The pot would sometimes be fully functional (matching the response of the right channel O/P gain volumes) and other times next to nothing.  Of course, the right channel was my channel of focus when trying to assess the reverse pot issue, so this volume cut in / cut out issue was probably muddying the waters.     

Gently tugging on the connecting wires, I noticed that would cut the volume in or out.  Thinking I had a bad solder or broken wire, I pulled the pot, measured just to confirm proper working order, re-wired  with new wire and again, wiggling the connecting wires resulted in the audio cutting in and out.  So, bad pot?  Ran out of time last night, but I'll replace that and go from there. 

Noticed a couple of other issues that again didn't have time to look into, but will work on that myself a bit before requesting assistance.  More troubleshooting fun ahead it seems!

Thanks again for the response!

~ Greg

 

[Ilya]

Bad pot is highly unlikely. They almost never break. Look somewhere else. If you can consistently reproduce a fault (for example, pulling a wire cuts out the signal) check for bad solder joints. These are more likely to cause the trouble than the pot.

 

[ron_swanson]

Bad pot is highly unlikely. They almost never break. Look somewhere else. If you can consistently reproduce a fault (for example, pulling a wire cuts out the signal) check for bad solder joints. These are more likely to cause the trouble than the pot.

Hi Ilya,

Yes, that too is a possibility and something I will check into and keep in mind as well.   

That said, while checking this pot, I was able to stabilize the cable so only the connection to the pot and an inch or so of the wire connected to the pot could move.  A little tug / wiggle cuts in and out. 

I agree though, a damaged pot seems unlikely, but also easy to rule in or out.

Thanks for the response!  Much appreciated!

~ Greg

 

[TwentyTrees]

Bad pot is unlikely, but not impossible. Especially on the cheaper ones, too much heat (from an iron set too high) can wreck the connection between solder tags and carbon track - as I found out recently on a cheapo generic 6-gang one off eBay!

 

[ron_swanson]

Bad pot is unlikely, but not impossible. Especially on the cheaper ones, too much heat (from an iron set too high) can wreck the connection between solder tags and carbon track - as I found out recently on a cheapo generic 6-gang one off eBay!

TwentyTrees, 

Build pots are new Bourns from Mouser.    So, as you and Ilya have suggested, while the pot is a problem possibility, it  is only a suspect at this point. 

Thanks for the chime in!

~Greg

 

[fripholm]

Does the installation instructions above also apply to the I/P gain control wiring?

Yes, exactly.

You could try and temporarily connect the two circular pads of the input and/or output gain connectors. In this case there would be no attenuation at all and you'll be able to rule out a faulty pot and see if the level drops go away.

 

[ron_swanson]

Hello All!

< snip>

Thanks in advance!
Greg

After replacing the suspect pot and tending to a few other issues, it seems my build is mostly working  - at least as far as I can hear and have tested so far...

First, regarding the pot issue... likely I jacked it up with some solder along the way.  After going back over my notes, I was reminded that I had a time with the wiring on that specific pot and ended up having to re-wire it.  I suspect that some solder got loose when trying to clean up the lugs in anticipation of a second wiring try.  A new pot fixed the issue.  Thanks again to those who chimed in with assistance!

I believe I have now have the unit more or less working short of completing the final adjustments.  I've been able to set the meters  and I've got my oscilloscope traces adjusted as described in fripholm's Fine Tuning I documentation section.

I am having a bit of a head scratch trying to perform the Fine Tuning II steps though....  When I throw my unit into THD mode, I can hear distortion on both channels when running program audio through the channels and I can control how much distortion is in play by adjusting the input gain controls, but not hearing or seeing distortion when pumping 1Khz tone even when input gain is fully CW.  (In case this matters, when put into THD mode the meters are no longer moving which I assume is correct as the documentation indicates that THD mode removes the side chain.)  So, not sure what may be going on here?  Either way, the distortion seems to to be pretty even between the channels when playing program audio, but then again that's a perception as of course program audio is not a controlled source.

Any thoughts on what may be going on with my THD tuning?

Cheers, Greg

 

[fripholm]

Correct, THD mode removes the input to the sidechain (not the sidechain itself - parts of it are needed to bias the compression circuit) and meters won't move.

At which level do you run your test tone in dBu or volts peak-to-peak? Maybe the level is too low...? At healthy levels of >0dBu with the input fully CW you should be getting lots of distortion.

 

[ron_swanson]

Correct, THD mode removes the input to the sidechain (not the sidechain itself - parts of it are needed to bias the compression circuit) and meters won't move.

At which level do you run your test tone in dBu or volts peak-to-peak? Maybe the level is too low...? At healthy levels of >0dBu with the input fully CW you should be getting lots of distortion.

Hi fripholm, Thanks for the response....

I believe I was, but ended up going another route (using my DAW in conjunction with software scope) when checking which provided more clarity.  Seems my build is complete now - at least as far as I can tell.

I took the time to design a custom PCB for the pinned Sowter I/O's, lo-signal relays and power for the LED British style link and bypass switches which after a second attempt (minor, non-critical mistake) worked as desired.  Not a super complicated electronics accomplishment and probably a noob mess as the PCB mostly consisted of input / output routing, but my first try at designing a PCB. 

A couple of questions mostly for clarification / education...

1.) When I put my unit into THD mode, there's a noticeable jump in output volume when switched from comp or limit mode - even with minimal comp or limiting.  Is this normal behavior or something that would point to mis-calibration or other issue not understood on my end?

2.)  Since this build requires a bit of micro-adjusting that results in resistor values not manufactured (R7, R8, R22, R56), is there an electronics / design reason why the PCB isn't designed with trimmers in place rather than having to run parallel resistor calculations and / or wiring resistors in series?  Not complaining or asking for any changes, just interested in what the thought process was for something like this?

3.) Would there be a reason why one could not configure parallel resistors for R22 & R56 instead of series wiring?  If so, what would I look for to read up on why one is preferred over the other in a situation as this build requires? 

Lastly, for fripholm, thank you for making this project possible.  The build was challenging and fun.  Lots of wiring!!!   

For anyone who has added to this thread and the forum in general, thanks a million!!!

Cheers, Greg





 

 

[Potato Cakes]

I thought had posted a ways back when I built mine that I was getting about a 7dB jump when switching to THD mode. Just seems to be the way it is.

For the trimmers vs resistors, I image the boards were made to the original schematic and then the tweaking method was developed by fripholm during testing. Since you don't technically have to match them perfectly or if you're making a mono channel, the resistors on the BOM can be used as is.

Thanks!

Paul

 

[ron_swanson]

I thought had posted a ways back when I built mine that I was getting about a 7dB jump when switching to THD mode. Just seems to be the way it is.

For the trimmers vs resistors, I image the boards were made to the original schematic and then the tweaking method was developed by fripholm during testing. Since you don't technically have to match them perfectly or if you're making a mono channel, the resistors on the BOM can be used as is.

Thanks!

Paul

Hi Paul,

Ok.  I've read through this thread a number of times, but obviously not retaining everything as I should.  Thanks for the heads up reminder.    As such, I'll consider the THD volume jump a non-issue.  7(ish) dB is what I'm seeing also.

Cheers!
Greg

 

[fripholm]

1.) When I put my unit into THD mode, there's a noticeable jump in output volume when switched from comp or limit mode - even with minimal comp or limiting.  Is this normal behavior or something that would point to mis-calibration or other issue not understood on my end?

I just checked; when the input signal is low enough to not trigger any compression at all, there's no volume jump at all in any of my units when switching to THD.

2.)  Since this build requires a bit of micro-adjusting that results in resistor values not manufactured (R7, R8, R22, R56), is there an electronics / design reason why the PCB isn't designed with trimmers in place rather than having to run parallel resistor calculations and / or wiring resistors in series?  Not complaining or asking for any changes, just interested in what the thought process was for something like this?

As Paul already said, I was going by the original schematic and initially  just didn't think of using trimmers in these places - as simple as that. When I realized that there's actually some demand for these PCBs, I already had sold a bunch of boards from my very first batch and people were beginning to stuff them. So I kept it at that.

3.) Would there be a reason why one could not configure parallel resistors for R22 & R56 instead of series wiring?  If so, what would I look for to read up on why one is preferred over the other in a situation as this build requires?

Yes, the procedure described for "Fine Tuning I" could theoretically also apply to resistors R22 & R56. But the precision of their values is not as critical as in no. 1, where paralleling resistors with just standard E24 values can result in pretty exact numbers - which is an advantage in this case. Additionally, I find that series resistors are easier to mount when you just have a single solder pad on each side - which brings us back to point 2.) 

 

[ron_swanson]

Thanks for the responses fripholm....

I'll check out the THD levels when I get a moment to see if lowering the input levels acts as you suggest.

Here's a picture of the innards of my build...  I reluctantly used your front panel design after spending a fair amount of time without coming up with anything I liked better.    I know that's not technically DIY approved protocol, but I'm happy with the look.

 

[ron_swanson]

Another....

 

[warpie]

Looking great!

 

[fripholm]

Yes, looks awesome - pretty clean and tidy wiring. Wish I had the patience to get results like this...

I reluctantly used your front panel design after spending a fair amount of time without coming up with anything I liked better.    I know that's not technically DIY approved protocol, but I'm happy with the look.

I feel honored, though. Much appreciated, thanks! 

And apparently you're not the only one as I've discovered the other day. See the upper right corner of this video  ;D

 

[TwentyTrees]

... See the upper right corner of this video  ;D

Hilarious!  ;D

And a great looking build, Greg. Tidy!

 

[MrBlomski]

Thanks for the responses fripholm....

I'll check out the THD levels when I get a moment to see if lowering the input levels acts as you suggest.

Here's a picture of the innards of my build...  I reluctantly used your front panel design after spending a fair amount of time without coming up with anything I liked better.    I know that's not technically DIY approved protocol, but I'm happy with the look.

What are those PCB with trannies on? I do not have those in my build......

 

[ron_swanson]

Yes, looks awesome - pretty clean and tidy wiring. Wish I had the patience to get results like this...

I feel honored, though. Much appreciated, thanks! 

And apparently you're not the only one as I've discovered the other day. See the upper right corner of this video  ;D

Nice find!  TG1 in the wild!!!

What are those PCB with trannies on? I do not have those in my build......

MrBlomski, the PCB in the back with the Sowters is a custom prototype PCB I designed and had made overseas. 

The board hosts a voltage regulator for the meter and switch lighting, the I/O trannies, lo-signal relays (and  flyback diodes), audio in and out connections, and an option to add the resistor as indicated might be required in fripholm document (page 2).  In my build, this is just a wire - no resistor as my unit doesn't show signs of oscillating no mater how I hit it  - at least so far.