G-PULTEC problems, please help!

[gyraf]

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..:


/Jakob E.

 

[Blissy]

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]

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]

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]

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

 

[joshk34]

Perfect! That's exactly what I figured. Good looking out!

 

[JerryPbury]

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.

 

[front247]

hey hello has someone to sell the pcb pultec kit? I can't find anywhere in Europe ... best regards

 

[gyraf]

hej cześć xt ma kogoś do sprzedania zestawu pcb pultec? Nie mogę znaleźć nigdzie w Europie ... pozdrawiam

In english, please?

/Jakob E.

 

[front247]

In english, please?

/Jakob E.

Already corrected .. sorry

 

[Lakewood]

Hi!

I'm going to build two mono units and have two question regaring ELMA switches for the LOW FREQ. SELECT, HIGH FREQ. SELECT and HIGH ATTEN SELECT switches:

• These have to be 2x6 switches, am I correct? Do I need shorting or non-shorting switches?
  I found some at Don-Audio:
  
  Elma Drehschalter Typ 01 Lötösen 1 Ebene 2 x 6 Nicht-Kurzschließend 01-1264
  Elma Drehschalter Typ 01 Lötösen 1 Ebene 2 x 6 Kurzschließend 01-1263
  
  
• I'm going to use the PCB set from Creative Clowns (LINK): As the FREQ. switches are not labeled on the PCB, how do i know how to connect the ELMA switches with the PCB-board? Where would be PIN 1, 2, 3, ...

Many thanks in advance,
Leo

 

[andow]

Hi!

I'm going to build two mono units and have two question regaring ELMA switches for the LOW FREQ. SELECT, HIGH FREQ. SELECT and HIGH ATTEN SELECT switches:

• These have to be 2x6 switches, am I correct? Do I need shorting or non-shorting switches?
  I found some at Don-Audio:
  
  Elma Drehschalter Typ 01 Lötösen 1 Ebene 2 x 6 Nicht-Kurzschließend 01-1264
  Elma Drehschalter Typ 01 Lötösen 1 Ebene 2 x 6 Kurzschließend 01-1263
  
  
• I'm going to use the PCB set from Creative Clowns (LINK): As the FREQ. switches are not labeled on the PCB, how do i know how to connect the ELMA switches with the PCB-board? Where would be PIN 1, 2, 3, ...

Many thanks in advance,
Leo

Take shorting switches or you might get popping when switching.

These PCBs obviously are designed for Lorlin switches. So just check the datasheet of these and you'll know how to connect the Elmas. (or just look at the traces of the board... )

Grüße von Graz nach Graz!

 

[Lakewood]

Thank you andow, that helped well

I have another question regarding the power transformer of the G-Pultec: The schematic shows two power transformers used for the build
On the Don Audio website, I found a single transformer version which is optimised for the G-Pultec build. LINK

A simple wiring instruction shows how to connect the single trafo to the SRPP board but shouldn't the voltage of the two green secondary wires be 12V instead of 9V?

 

[Whoops]

shouldn't the voltage of the two green secondary wires be 12V instead of 9V?

If the Gpultec schematic I’ve seen it’s correct, that 9VAC winding will be for the heater supply which is 6,3VDC

the 9VAC (or 12VAC) will go through a full bridge rectifier, so 9VAC x 1,414 = 12,7VDC after rectification.
Then the 12,7VDC will go through the LM317 to be regulated to 6,3VDC

LM317 just needs 9,3V at its input to be able to regulate to 6,3v (3v dropout voltage) you would hitting it with 12,7 which is higher and has a margin, so all good.

Following the same trail of thought, if the transformer Tap was 12v instead of 9V it would work also, the LM317 will just have to work a bit more

 

[moamps]

Such calculations should take into account the voltage loss at the rectifier, the voltage ripple at the input of the regulator and the real Vpeak/Veff ratio, which in reality is never 1.41, but 1.30 to 1.35.
I would in any case recommend the use of an LDO regulator (e.g. TLV1117adj) and a schottky diodes in the rectifier if the input AC voltage is 9VAC.

 

[Lakewood]

Hi!

I have another question regarding the schematic and the pcb:

Is it relevant that the middle PIN2 of the 'HI BOOST Q' pot is connected with PIN1? Or can it also be connected to PIN3 instead?

Because (if i read the schematic and the PCB correctly) in the schematic PIN1&2 are connected, and on the PCB PIN 2&3 are connected.

Kind regards, Leo

 

[gyraf]

Leo - it matters, and you're right, the dot is on the wrong side in the schematic for the Q.

For inductor EQ's lower series resistance equals higher Q.

I think original was dubbed "bandwidth", which is Q when it goes the wrong way around - thus the err..

/Jakob E.

 

[1wildthing]

Hi everyone! I finally received the don audio’s toroidal Transformer and I’m trying to measure secondaries. May be I’m doing something wrong but I’m getting strange values.
Measuring from single windings to chassis ground I get:
Green 1 16.29vac
Green 2 9.52vac
Red 1. 130vac
Red 2. 74.6vac
Blue 1. 13,5vac
Blue 2. 10,10vac
Could you please tell me if this is a normal behavior? Am I measuring in the right way?

 

[Harpo]

Hi everyone! I finally received the don audio’s toroidal Transformer and I’m trying to measure secondaries. May be I’m doing something wrong but I’m getting strange values.
Measuring from single windings to chassis ground I get:
Green 1 16.29vac
Green 2 9.52vac
Red 1. 130vac
Red 2. 74.6vac
Blue 1. 13,5vac
Blue 2. 10,10vac
Could you please tell me if this is a normal behavior? Am I measuring in the right way?

No. There is no relation to chassis ground. You measure AC voltage across both (in this case same color) transformer secondary winding ends.

 

[1wildthing]

No. There is no relation to chassis ground. You measure AC voltage across both (in this case same color) transformer secondary winding ends.

Thanks a lot Harpo! Blame on me.