G-PULTEC problems, please help!

[south2577]

Is there a BOM for the G Pultec project?
Or is it a bit loose to have one?

Thanks
Ben

 

[audiophreak]

I just put together a list from the the PCB layout and the Component placement  pdf-file on the Gyraf web page, not very many parts,  I got the WIMAs from TAW, found Bourns and Fastron inductors from Mouser they were inexpensive enough so I got both to try.

Hope this helps

EDIT :  found this thread - http://www.groupdiy.com/index.php?topic=7704.0  - on inductors, Sowter and Cinemag also make inductors that I see have been used, but expensive, and I wanted to build it " stock " first " kind of thing....although I have veered a little  ;D

 

[south2577]

Thanks Audiophreak

More questions to come. 

 

[south2577]

Ok so I'm just getting my head around some things on this build. Newb alert!!
Is this right for pots?
low boost- 10K log not 10K lin?
Low cut - 100K log
High boost - 10K Lin
High Cut - 1K Lin
Q - 2K2 Lin


cheers
Ben

 

[audiophreak]

I believe that is correct, I'm at that point now myself, couldn't find the post that states the correction, but remember that it said the schematic on Gyrafs page was correct and the PCB overlay was not - I also read over the weekend that in Europe the "A" is Lin and "B" is Log - and in US the "A" is for Audio/Log and "B" is Lin _ ( confusing ) so according to the Schematic the Low Boost and Low Cut are Log and the rest are Lin. 

  ... at least that's the way I see it  ;D

someone please correct me if I'm wrong

 

 

[south2577]

I also read over the weekend that in Europe the "A" is Lin and "B" is Log - and in US the "A" is for Audio/Log and "B" is Lin _ ( confusing )
 

Ahh just another example of the world working together. Ha 

 

[gyraf]

Common pot notation:

10KA=10K Linear (european tradition)
A10K=10K Log (japanese/far-eastern tradition)

10KB=10K Log (european tradition)
B10K=10K Linear (japanese/far-eastern tradition)

And yes, use 10KB (log) for low boost

Jakob E.

 

[audiophreak]

  Well put  ... Thanks Jakob 

  Found this thread through search  ;D  on the actual Boost / Cut frequencies, very informative and shows the math,  thought I would post a link here in the help thread.

http://www.groupdiy.com/index.php?topic=32839.0

 

[daveee]

well i got the g-pultec working and i've been using it in the studio for a while now...

one thing i've found - it doesn't sound completely amazing, and i'm wondering why
especially on bass - i seem to lose some of the low bottom end and it seems to be quite 'flabby' if that's even a word.
other instruments like guitars and vocals can sound quite harsh when EQ'd.

i've heard great things about the g-pultec so i'm sure it's something that needs changing in mine - i'm wondering where to start?

i've used llundahl trannys, wima caps and a mullard nos valve. should i maybe try a different valve? any suggestions?
thanks in advance!

 

[Nick Franklin]

well i got the g-pultec working and i've been using it in the studio for a while now...

one thing i've found - it doesn't sound completely amazing, and i'm wondering why
especially on bass - i seem to lose some of the low bottom end and it seems to be quite 'flabby' if that's even a word.
other instruments like guitars and vocals can sound quite harsh when EQ'd.

i've heard great things about the g-pultec so i'm sure it's something that needs changing in mine - i'm wondering where to start?

i've used llundahl trannys, wima caps and a mullard nos valve. should i maybe try a different valve? any suggestions?
thanks in advance!

Would you like to send me an audio file and I'll run it through my G-pultec, then you can compare it with yours and see if you think yours is behaving correctly?

 

[gyraf]

"flabby" could possibly be from too high a output level?

GPultec will do something like +12dBm happily, but not much higher (and NOT the +28dBm that some soundcards has as default for 0dBFS-digital)

Jakob E.

 

[kazper]

Just wanted to post some notes from my recent build.

I had way to low of voltage for the heaters using the 470R and 1.8K near the LM317. I ended up getting usable loaded down voltages by changing the 470R to an 240R and using a 1K in place of the 1.8K. A 2.5K trimmer could be used inplace of the 1.8K to dial in the 6.3. I think you could just change out the 1.8K to a 1.9K and your there too, http://www.electro-tech-online.com/tools-lm317-calculator.html

That LM317 gets HOT.....

I'm also getting 280-290V on the High Voltage supply that I need to knock down a bit.

 

[snipsnip]

That LM317 gets HOT.....

Sure does!

Did you find a good sink for yours? I still need to replace mine.

 

[kazper]

I've been using the first one that was pictured a couple pages back, that was replaced... I have larger ones here but I was going to let it run a bit and take a look at the outside temp before making another move.

Does the higher voltages for the HV+ matter?  I'm trying to understand what it does and why the 30-40V difference would matter.


I need to go listen to them now...

BTW I'm using the 120-120/12V-12V Antek branded transformers, with mixed VA's for the primary (50VA) and secondary (25VA). I can't imagine how that would cause any issues.

 

[kazper]

Sounds fantastic, but I think your going to want MBB switches on everything but the bypass...

 

[gyraf]

Does the higher voltages for the HV+ matter?  I'm trying to understand what it does and why the 30-40V difference would matter.

It matters - because we're already stretching the ECC88's voltage capability to the edge (it's anode voltage is rated some 90-120V depending on what datasheet you consult)

Ca. half of our HT voltage appears across each half of the ECC88 - so the suggested 250V HT shouldn't be exceeded by too much.

On very-high-overvoltage units, there is a tendency of premature burn out of the tube.

Adjust voltage by trying different value resistors between resevoir caps - circuit sounds good between 200 and 250V.

Jakob E.

 

[kazper]

Thanks Jakob... I'll bump it down before putting the lid on it....
I had read up on the tube specs and ended up with more questions so I just posted here.


I posted this stuff over at another thread but since this is the META I thought I would post it here as well.


Front $46 using a Par-Metal plate (just a edited copy of the original one found on Franks site) Thanks to FRANK or someone!
Price is no frills no fills you provide the material ... so the engravings show raw Aluminum which looks great in person!
Holes for the pots are for the low cost Alpha's.
3mm LED ON indicator located in the center of the O in ON, feed off the Regulator 6.3V DC with a 350R resistor in series to the LED +.

Rear $43 using a Par-Metal Back plate (Check Hole Sizes to your parts!!!!!!)
Price is no frills no fills you provide the material ... so the engravings show raw Aluminum which looks great in person!

FPE Files:
http://twin-x.com/groupdiy/albums/userpics/428/GpultecFPE.zip

Delete or customize to your taste. I believe I have a lower cost back unit somewhere but I can't find it at the moment.

 

[kazper]

I ended up pulling the adjustment resistor in the 6.3V section and installing a pot so I could dial it in a little more. An 2.5K-5K pot will work nicely in place of the 1.8K in the SRPP/PSU board for future builders.

I also ended up with 15K total of 3W resistors to get me to 225V in the HV section replacing the 3.3K-2W. I had a 10K and it wasn't low enough to get my 310V after the rectifier down to under 250V. It was close, but no cigar..

Using 120/12V to 12V/220-240 Antek's like I did I would suggest about 12K 2-3W for getting the voltage to 250V, 15K for 225V and 20K for 200V. As Jacob had put it somewhere between 200-250V sounds good in this circuit. I'd order a few values of resistors from 3-20K and experiment. Another word of advise is give it a few min after power up to let the caps fill up and the PSU to line out before taking measurements.

Kaz..

 

[audiophreak]

Hi All,
        Just wanted to post an update, Preliminary results are good with my Dual G-Pultec !    

 waiting to install correct shaft dia. pots - Collin at AML now carries 1/4 inch shaft 20mm pots for the G-Pultec.

so with pots and switches just hanging off control boards, everything works and no humm or buzz !  

have only run a 58 through a G-9 and also a CD player - but so far it sounds great !  

 will post  documentation and pix in a few days.

 Thanks to all !


EDIT -  wanted to also post that I just have the IEC Earth ground to Chassis - circuit is not grounded to chassis and input pin 1 is not grounded to chassis, -  so is this whats called a " Floating Ground " ? 

 

[EHOFFA007]

Getting a Bom together for my 2x single Gpultecs.
Just want to make sure these power traffo's will be ok.

http://www.mouser.com/Search/ProductDetail.aspx?R=VPT24-1040virtualkey55310000virtualkey553-VPT24-1040

24.0V CT @ 1.04A 12V @ 2.08A Parallel
Power Rating: 25 VA
Primary Voltage Rating: 115 V to 230 V
Secondary Voltage Rating: 12 V to 24 V

On the Gyraf PDF it calls for 12v 1.5A.
Thanks