G-PULTEC problems, please help!

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gyraf

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The low cut consists of a 100nF (low freq) all the way to to 10nF (high freq) capacitor, that is partially shorted out by the 100K lowcut pot. At max. cut, the pot is at 100k in parallel with the capacitor chosen, at minimum (or no cut) it's a short across the capacitor.

If it "cuts everything", you probably don't have the capacitor across it - check continuity between pot and capacitor, both ends..:
G-Pultec - Filter Explanation.JPG

/Jakob E.
 

Blissy

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The low cut consists of a 100nF (low freq) all the way to to 10nF (high freq) capacitor, that is partially shorted out by the 100K lowcut pot. At max. cut, the pot is at 100k in parallel with the capacitor chosen, at minimum (or no cut) it's a short across the capacitor.

If it "cuts everything", you probably don't have the capacitor across it - check continuity between pot and capacitor, both ends..:
View attachment 85462

/Jakob E.
Thanks Jakob! Just found Part of the issue. Looks like there is an error on the PCB from Analog Classics. The connection (green in your low cut Schematic) is missing from this PCB The string of caps where going no where. My next problem is the low boost. I put the EQ on a analyser and discovered there is a significant level drop when inserted and with the low boost at MAX the frequency response in the low-end is almost flat at Minimum boost the roll of starts at around 125. No Actual low boost. Currently looking for more PCB errors any other tips on what might cause such an issue ?
 

Blissy

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update for anyone else who stumbles upon this. There seems to be a few Errors on the Analog Classics PCB. As I mentioned above the green link in Jakobs Low Cut Schematic was missing on the PCB leaving the low cut circuit open. Also on the Amplifier PCB, both the 470ohm and 470k resistors are labeled 470K which was causing massive low end loss ( creating a HPF at 1.5k instead of 1.5hz I believe)
All working now! Thanks Jakob for putting this out into the world nearly 20 years ago (if the schematic date is correct)
 

joshk34`

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update for anyone else who stumbles upon this. There seems to be a few Errors on the Analog Classics PCB. As I mentioned above the green link in Jakobs Low Cut Schematic was missing on the PCB leaving the low cut circuit open. Also on the Amplifier PCB, both the 470ohm and 470k resistors are labeled 470K which was causing massive low end loss ( creating a HPF at 1.5k instead of 1.5hz I believe)
All working now! Thanks Jakob for putting this out into the world nearly 20 years ago (if the schematic date is correct)

Thanks for the tips, Blissy. About to start the same project with the same board. How did you manage the work around for the lack of connection with the capacitors? Just ran a wire between the two points?
 

Blissy

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Thanks for the tips, Blissy. About to start the same project with the same board. How did you manage the work around for the lack of connection with the capacitors? Just ran a wire between the two points?
Hey Josh,
here is an image of the error, I just connected it to the closest pad.
Red Circle shows where the connection is on the original gyraf design and green Line is the jumper I put in to resolve it.
its a great projects and sounds killer, happy to help
Cheers J
 

Attachments

  • Analog Classics PCB Error.png
    Analog Classics PCB Error.png
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JerryPbury

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I’m finishing up a pair of these so this was very timely info as I have the same boards. I also took the opportunity to change my 10k linear pots on the low boost to log pots.
 
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