G-PULTEC problems, please help!

[1wildthing]

thanks guys once again for your precious help, I’ve finished the build. Everything seems to work as expected but I’ve noticed a small roll-off in low frequencies (35-40hz) even when eq is bypassed in comparison to the dry signal.
Is this a normal behavior or is depending on something I did wrong?

 

[gyraf]

Being a soft bypass, where amplifier is still in circuit, this is probably normal to some degree. Also, overload characteristics and such are still in play in bypass..

/Jakob E.

 

[1wildthing]

Being a soft bypass, where amplifier is still in circuit, this is probably normal to some degree. Also, overload characteristics and such are still in play in bypass..

/Jakob E.

Thanks! However the overall sound is amazing. Great piece of gear. I'm already thinking of building a second one for a stereo pair.

 

[Bonsaimaster]

Dear All,

I am using a G-Pultec as a gain stage for a Classi PEQ Eq board. I have not gotten the parts for the EQ board. However in the bypass )gain stage only I have high gain output. I have Carnhill 10K:10K on the input and Carnhill 9600k:600 on the output. Any way to decrease the gain to utility gain? Thx!

 

[gyraf]

..the GPultec requires around 20dB of makeup gain - so the gain stage delivers approximately this - and it's not meant for variable gain.

If you need it at unity gain, you can possibly wire it up with some feedback, as it's an inverting amplifier

/Jakob E.

edit: Here's a good article describing the idea behind the SRPP gain/output stage used here: http://www.valvewizard.co.uk/SRPP_Blencowe.pdf

 

[Nyquist]

Hello peoples. I'm staring to gather components to build a pair of these EQ's. Question on transformer if I may.
I have some KT transformers. the spec are as follows

1:1
600:600ohm
DC resistance 15ohms
Max output +18 dBv into 600ohm load
20-20Khz 0.1dB 600ohm

Would they be suitable for SRPP build? Thanks in advance.

 

[gyraf]

for input, yes - for output you'll probably want 2:1

/Jakob E.

 

[Nyquist]

Thank you Jakob

 

[Lakewood]

Hey! I have a question regarding the Power transformer from Don Audio and the pcb from creative Clowns:

https://www.creative-clowns.com/product-page/pultec-style-eq-pcb-set
https://www.don-audio.com/g-pultec-mono-power-trafo-sec-220v-9v-5V
As the pcb is obviously designed for 2 Power transformers, is There a way to wire up this Power trafo from don audio?

Kind regards, Leo

 

[gyraf]

You should probably ask Don audio about that, not us..?

/Jakob E.

 

[dario84]

Ive been using 2x of these: https://eu.mouser.com/ProductDetail/553-VPT12-2080

but this is what I found on don audio page about the one mentioned :

 

[ToneShack]

I am going through the BOM and updating it. I have a couple of questions. Does anyone know if the Alpha SR26 series rotary switches fit the PCB? And for SW1, is it a 2 position/2 pole rotary switch or a 3 position/2 pole?

 

[tedsorvino]

Hi. Has anyone a (preferably European) current working Bom, compatible with the creative clowns pcb set? If not could you please provide a link to something relevant that exists online?

 

[paolomunarini]

Hi. Has anyone a (preferably European) current working Bom, compatible with the creative clowns pcb set? If not could you please provide a link to something relevant that exists online?

I am working on one from creative clowns at the moment. I will send here a complete BOM when I'm sure I got all the needed parts.

At the moment I sourced everything from banzai music except for rack enclosure (tme) and lundahls (sourced here on the black market).

 

[tedsorvino]

I am working on one from creative clowns at the moment. I will send here a complete BOM when I'm sure I got all the needed parts.

At the moment I sourced everything from banzai music except for rack enclosure (tme) and lundahls (sourced here on the black market).

What size of (power rating) resistors and film capacitors (voltage rating) did you order? Could you please send me your list, as a pm, because I would also like to order from banzai (or tme)

 

[paolomunarini]

What size of (power rating) resistors and film capacitors (voltage rating) did you order?

Resistors everything 0.25W except for the dropper for the HV PSU, which is 3W (gyraf specifies for 2W, but I went safe)

Inductors I tried with CTC inductors from banzai

All poly caps are 63V mks2 from Wima (some need stretching of the legs in order to fit on the pads), except for the 4u7 on the output stage, which is a Wima mkp4 250V.

Electrolytics are 350V for the HV, 25V for the heaters.

For the HF part I went with parallel combos of styros

Rectifiers are vishay 2W06G510H and the fuse holder is SKU24178 from banzai.

Edit:

From this BOM a 2k2 resistor is missing. I went with rotary switch bypass and toggle switch power. A jewel light is also missing.

 

[tedsorvino]

Resistors everything 0.25W except for the dropper for the HV PSU, which is 3W (gyraf specifies for 2W, but I went safe)

Inductors I tried with CTC inductors from banzai

All poly caps are 63V mks2 from Wima (some need stretching of the legs in order to fit on the pads), except for the 4u7 on the output stage, which is a Wima mkp4 250V.

Electrolytics are 350V for the HV, 25V for the heaters.

For the HF part I went with parallel combos of styros

Rectifiers are vishay 2W06G510H and the fuse holder is SKU24178 from banzai.

Edit:

From this BOM a 2k2 resistor is missing. I went with rotary switch bypass and toggle switch power. A jewel light is also missing.

Thank you Paolo for that. Figured most things out.

 

[bigidibo]

Regarding voltage at the output cap. I do get something around 98V. Is it important to get around 125V?
At the heater, I have 6,08V and 242V after the step-down resistor. Do I need to change 1k resistor to get in a 125V zone?

Thanks

 

[gyraf]

Naa, I wouldnt worry, 98 is close enough for jazz...

 

[bigidibo]

Wonderful! Thank you! Care to explain a bit, what is changing in the circuit if you have lower voltage there?