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

[Hobbyist]

It looks very nice! A few things could help with the hum and overall layout:

1) I would have used 24v relays and eliminated the extra wiring and boards involving having the 12v psu. They can usually handle 150% of the rating, so 28v is totally fine. That would clear out a good amount of space. I daisy-chained +28v to each relay +, and switch the - to actuate them. No pops whatsoever when I switch bypass, link, or auto release.

2) I would use shielded cable for I/O XLR’s and transformers to boards, as well as I/O gain switches. I left the output XLR shield disconnected at the output trans side so no loop is possible, and it drains at the star ground via Pin 1 of the XLR.

3) My grounds tie to one star chassis point only: Pin 1 of I/O XLR’s, mains earth, and psu output (6 total). Input trans secondary signal cable - (Pin 10) and shield (Pin 6) go to the output - on the pcb, and I made sure to not tie any L or R channel pcb signal grounds together until they meet at the psu out ground via STROM. I probably spent the most time carefully planning all of that out, based on the information @SmokeyJoe linked above.

I hope this helps! If I think of something else I’ll report with more.

I've missed the post with the grounding information. Thank you for bringing light into this @SmokeyJoe. The 12v rail is just because I had the components nearby. good one to put 24v in stead and get rid of a lot of cabling and experimental behaviour .
I'll start with these 3 points you gave. Will report back when i've results. Appreciate your time guys for helping me out.

 

[SmokeyJoe]

Ok I think I'm happy to call this done. Thanks to everyone who helped me troubleshoot. I don't know how some of you manage to get such neat interiors - mine looks like a tangled mess of spaghetti in comparison!

A couple of adjustments are still bugging me a little, if anyone has any suggestions.

- Outputs track perfectly until the threshold is reached, at which point there is a ~0.4dB difference between channels in unlinked mode. Fine when linked so I'm not too bothered, but the perfectionist in me would like to see them match.

- Noise floor is quite high and doesn't match between channels: -79dbFS on ch1 and -75.5dBFS on ch2 on my interface input meter with input/output knobs at 12 o' clock. It increases and decreases when adjusting both knobs, and with both knobs cranked it's about -55dBFS on both channels, which is pretty high but I doubt I'll use it like that. I think the imbalance is caused by the THD adjustment - I had to adjust FT2A and FT2B quite heavily to get a good match.

Interested to know what noise floors others are getting?

 

[studiosus]

Does anyone still have some pcbs for this nice project? I really would like to get a pair!

 

[Shroomystic]

I would also be highly interested in a pair of pcbs !
Or maybe there could be set up a action for aquiring some pcbs together.
Would be super nice to be able to build this project.

 

[fragletrollet]

Just a little reminder that measuring noise in reference to dBFS is arbitrary if not specified towards your soundcards maximum output level. If my soundcard has ten dB higher headroom than yours our readings will differ accordingly, and it does not say anything about the actual noise floor as a specific level. Reference to an analog dB

Beautiful build tho! My pcb's are all assembled but gathering dust in a cardboard box. Running out of room for all these rack units!

 

[warpie]

Looking at the schematic, R83 is 11k. The original schematic calls for 100k. Is this a typo?

 

[SmokeyJoe]

Just a little reminder that measuring noise in reference to dBFS is arbitrary if not specified towards your soundcards maximum output level. If my soundcard has ten dB higher headroom than yours our readings will differ accordingly, and it does not say anything about the actual noise floor as a specific level. Reference to an analog dB

Beautiful build tho! My pcb's are all assembled but gathering dust in a cardboard box. Running out of room for all these rack units!

Yes you’re absolutely right, thanks for that. I’ve since been making measurements of other builds in dBu.

Any progress on your build? I found all the wiring took a fair amount of time!

 

[fragletrollet]

Not in the slitets. It, together with several other fine projects, are all built up but without enclosure, resting in cardboard boxes.

But! I just ordered another 26U's of rackspace, so soon might be a more sensible time to rack it up...

 

[Hobbyist]

I'm back with the completed unit for the second time. After extensive testing, I'm happy with the results.
My initial design had so many problems, so I decided to make a complete overhaul. I've used KiCad to create a new (my first) PCB for the LED power, relays, and trimmers. This new setup works flawlessly, eliminating any unwanted pops, and less pain with the calibration process for me.
One of the significant problems in my first design was the PSU; it interfered with both the in- and output transformers. I left the 12v PSU out and added 24v relays and new 2-pole switches. Finally, I relocated the complete primary PSU to an external enclosure. No hum - same (normal) noise.

Thank you all for the assistance!

 

[warpie]

I'm back with the completed unit for the second time. After extensive testing, I'm happy with the results.
My initial design had so many problems, so I decided to make a complete overhaul. I've used KiCad to create a new (my first) PCB for the LED power, relays, and trimmers. This new setup works flawlessly, eliminating any unwanted pops, and less pain with the calibration process for me.
One of the significant problems in my first design was the PSU; it interfered with both the in- and output transformers. I left the 12v PSU out and added 24v relays and new 2-pole switches. Finally, I relocated the complete primary PSU to an external enclosure. No hum - same (normal) noise.

Thank you all for the assistance!

Well done! Very neat!

Are these Elma and Blore-Ed switches?

 

[Hobbyist]

Well done! Very neat!

Are these Elma and Blore-Ed switches?

Hi, thanks!

They are older Elma Type 3 switches. No Blore-Ed switches used.

 

[altfidelity]

I'm back with the completed unit for the second time. After extensive testing, I'm happy with the results.
My initial design had so many problems, so I decided to make a complete overhaul. I've used KiCad to create a new (my first) PCB for the LED power, relays, and trimmers. This new setup works flawlessly, eliminating any unwanted pops, and less pain with the calibration process for me.
One of the significant problems in my first design was the PSU; it interfered with both the in- and output transformers. I left the 12v PSU out and added 24v relays and new 2-pole switches. Finally, I relocated the complete primary PSU to an external enclosure. No hum - same (normal) noise.

Thank you all for the assistance!


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Hi, completely unrelated question...
What does the "feed" switch do on the GSSL build?
Nice face-plate design BTW, do you have any CAD files of it?

Thanks!

 

[Hobbyist]

Hi, completely unrelated question...
What does the "feed" switch do on the GSSL build?
Nice face-plate design BTW, do you have any CAD files of it?

Thanks!

Sure, I've installed a pair of Lundahl LL5402 output transformers, switching between the original Gssl or the Lundahl version using a board with 4 relays to connect the transformers and set the output resistor values (100R).

- The front panel is made using the Frontpanel Designer app and ordered directly from Schaeffer AG. no CAD, just with the .fpd file.

M.

 

[Shroomystic]

Is anybody flying around here with a stereo pcb set ?

 

[vitopower]

In the manual for v2.5, p.2, I'm having trouble understanding the diagram.

In order to have the non-bypass signal be the correct polarity, should I wire the output transformer secondary in correct or opposite polarity with the primary?

 

[thelivingroom]

In the manual for v2.5, p.2, I'm having trouble understanding the diagram.

In order to have the non-bypass signal be the correct polarity, should I wire the output transformer secondary in correct or opposite polarity with the primary?

Opposite from the primary. Looking back at my photos, I wired the secondary how one normally would, and just swapped pins 2 and 3 at the output XLR. You can do the swap at the secondary or XLR.