G-PULTEC problems, please help!

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strange behaviour indeed. never had that problem. photos of the wiring and build would maybe help us figure out the problem.
I ultimately solved my problems.

Filter pcb was wired in reverse. Output from the trafo was wired to the output of the filter board and the input of the gain stage to the input of the filter board.

Furthermore I had to change inductors because the DC series resistance of the ones I had was too high and the HF boost was completely attenuated by it.

I attach a few plots ;)
 

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  • 03_LOW BOOST.png
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  • 05_HI BOOST BROAD.png
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glad to
I ultimately solved my problems.

Filter pcb was wired in reverse. Output from the trafo was wired to the output of the filter board and the input of the gain stage to the input of the filter board.

Furthermore I had to change inductors because the DC series resistance of the ones I had was too high and the HF boost was completely attenuated by it.

I attach a few plots ;)
glad you made it work!
 
Hey folks, just finished my G-Pultec build and getting a lot of low end roll off in bypass - looks like it’s right across the spectrum but worst from around 300hz. Round trip signal level is also ~3dB down with a 1k tone.

I've measured AC signal voltages with white noise:

XLR in hot: 0.255v
XLR in hot/cold: 0.56v
Filter in: 0.556v
Filter out: 0.062v
XLR out hot: 0.186v
XLR out hot/cold: 0.471v

I've checked that all connections between boards and connectors are correct - in goes to in and out to out, right?

Edit:
I've just tested it into a high impedance mic input and the signal loss with a 1k tone is now only 1dB. Possibly an impedance issue with my interface?

Interestingly with white noise, the return signal is actually ~5dB up after the bypassed Pultec (same with mic or line input). That’s weird, right?
 

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Ok I think it must be an impedance issue. If I go via my TG1 clone, which is 10k input and 600 ohm output, the bass rolloff is only below 40-50Hz. I thought my interface would be up to the task but apparently not (RME Babyface Pro FS).

Ultimately I wonder if some kind of buffer box with a high input impedance and low (or 600 ohm??) output impedance would be the way to go here - is anyone able to point me to a project on here?
 
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@gyraf picking up the discussion from the other thread, testing frequency response directly after the input trafo suggests that the issue is indeed with my interface's ability to drive it (first graph). I previously built a driver circuit in an attempt to overcome this and it flattened out the response nicely (second graph). However, based on some measurements I took at the time, I was concerned that the THD was a bit high, although this time I don't think the results are too bad (third graph). Any thoughts on this?

G-Pultec Trafo Only.pngG-Pultec Trafo plus Driver.png
G-Pultec Trafo Only Driver Distorion.png
 
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