G-PULTEC problems, please help!

Hi guys,

just finished up a couple of Gpultecs, front and back by grandmasteraudio. Sowter chokes, Mullard tubes. Needless to say they sound hella dope. Big thanks to jakob and all the usual heads.

Ive made a couple of mistakes with my cap value selection and am having a bit of trouble figuring out which ones on the schemo. Does anyone have a table of cap values and associated freq's to hand?

Hi guys, bit more time to test now it's not so late at night.

It's only the first position on the boost sections that are incorrect; 20hz (it's letting almost all freqs through), and 2khz (the freq boosted is too high).

Any ideas what caps I need to change? I have real trouble reading multi pos switches on schemos.

Thanks a lot
Jake

The first position is the 100mH/18nF combo on the high boost switch. Is that what you would like to know? From the looks of it on Gyraf's schematic, the dot indicates the final position in a clockwise rotaion.

Thanks, that's what I figured for the high, but I got confused with the first position on the low boost as the schemo seems to show 2 switches. If the dot indicates the last position (I thought it might be first position) then I guess my problem is either with the 100n or 2u2.

Cheers

I thought the same thing at first, about dot = position 1, but then I looked at the pcb to make sure instead of giving you a guess. The low boost is a double pole switch. If you look at the naming, it's SW3a and SW3b.

Cheers

PS - be careful with the switch names, it looks like Gyraf's numbering of the switches on his schem is diffrerent than on the pcb drawings.

thanks a lot

My pleasure, hopefully you get it sorted out.

Hey snipsnip ,
                      Congratulations !! 
                                                  Looks Great !! 
                                                                          ... and dont they sound Awesome  ;D

they do sound wicked. Love them.

I do have a bit of an issue with one of the voltage regs shutting down now and then even though ive got a pretty big sink on it. The other channel, using the same brand LM317 is fine.

Anyone think its worth swapping it out for one that may be more reliable. Any brand with more tolerance?

Cheers, and thanks again Jakob, these sound so 3 dimensional.

meet the twins

just tracked some test vocals with them and am pretty floored - great sounding units.

Does anyone know how to wire in the edcor XS1000 transformer instead of the Lundahl 5402? I heard there was a PCB out there to make it simple..

Thanks,
Brice

I've never used it, but I think this is the one people have used it, so I guess it should work.

fat sound and masterclass noisefloor > -100db. I will put some audio samples in here later

VERY good looking!

the panel is just in awe of your great circuit pcbs.

you can use the heel of hand to boost atten the hard positions by a fly and hear the clacks of the frequency knobs...
awesome sound on guitars, vocals,... everything. I love it!!

thank you very much

ncoak said:

meet the twins

just tracked some test vocals with them and am pretty floored - great sounding units.

Click to expand...

Nice looking build there, congrats!

That looks amazing....

Could someone explain to me how this can be built using only 1 toroidal? I see some gpultecs with 1, some with 2 and I'm confused. Sorry if it's a stupid question, I'm new....

I'm going to be building mine soon... I'd prefer to use only 1 if i could.

you use 2 wired back to back for a cheap off the shelf solution.

you use 1 if you can get a custom tranformer that gives you the secondaries you need, which may be a bit harder to find... or perhaps who is selling them in his shop?

If you go with one torroid it looks like some small changes are required to the PS board (at a glance i see only one recifier and an additional voltage reg)

IMO there is nothing wrong with using the 2 torroid solution. I mounted mine on the side of my case and have no noise despite the PS / Amp board being quite close. 

For a single-transformer you'll need two secondaries: A 8-12V 500mA and a 210-230V/50mA (or something around there), but as these are not easy to find off-the-shelf, we did the two-transformer-trick.

Actually, the later years it has become much easier to find ready-made heater/ht-voltage power transformers - some 15 years ago (when we made the GPultec) it was nearly impossible.

There are rectifiers on the pcb for both voltages, you can easily use the dual-secondaries trafo if you find it.

Jakob E.

hey all!

Do you think it is possible with the gpultec to fry an input  on my AD (presonus firestation)??
because I experienced something strange:
I had my fine working pultec as an insert in my soundcard and all of a suddend it was quiet and my input was dead... ??? ???
Could it be that I had to much voltage on my gpultec`s out or something? or just a crazy coincidence?

thank you!
martin