G-PULTEC problems, please help!

[gyraf]

Is there anyway to add a trimmer and tweak the levels? prehaps the 470K before the gainstage?

No, not in any good and simple way, I think. We need all the ECC88 gain we can get, and any trim would cost some gain.

Jakob E.

 

[Kingston]

Is there anyway to add a trimmer and tweak the levels? prehaps the 470K before the gainstage?

If you absolutely must, you have two somewhat easy options but both have drawbacks.

1. you can replace the 10k load resistor just before the SRPP stage with a trimmer (like 22k) and tweak to equalise gain. You can only tweak down the channel that has more gain. Drawback is you lost some gain.

2. measure your 10KA high boost pot end-to-end resistances, and add a trimmer (say, 1-2k) to the one that has lesser value. This is probably the lesser of two evils, as pots will be slightly uneven (then again, they are most of the time anyway).

 

[snipsnip]

Hi Guys,

I have 2 GPultecs fully stuffed, including filter boards and Amp / PSU boards.

I did this before understanding that 1 PSU was sufficient to drive 2 channels.

Im not too bothered about the additional cost of stuffing the boards now its done, but would like to power the pair off 1 pair of toroids. they are rated 15v at 1.7A so I think this should be plenty.

Im guessing I can just take the 15v from the first transformer, then take the 220v from the second transformer and use these 2 feed the 2nd PSU. But would I need to do anything to the section of the 2nd PSU baord that is allocated for the secondary of the 2nd transformer? Or is it OK to just skip that if you already have the stepped up voltage from elsewhere?

Would I need to change the fuse on the 1st PSU at all? On the schemo it seems to suggest its breaking 220, but on the board it looks like its breaking the 15 / 12v line, so Im a bit confused about its role. I assume its there as a failsafe if one of the toroids fails, but I dont really understand much more than that.

As you can probably tell, Im quite far from expert when it comes to PSU stuff, even though I know it should be quite simple!

Thanks a lot
Jake

 

[snipsnip]

Sorry to bump this, but just wondering if anyone out there can help me?

Thanks
Jake

 

[gyraf]

In general it's not a good idea to power two G-Pultec units from one PSU, as the circuit is not made with this in mind. I'm not saying that it is not possible, but it is hard to tell what sort of problems you may run into regarding grounding and such. There has been quite a few builders that had problems with this.

Jakob E.

 

[snipsnip]

Thanks Jakob, I'll just run it like 2 totally seperate channels in one box then. Just trying to save a few ££


Cheers

 

[benlindell]

Just about done with these, just need to do the final mounting, thought I'd share how they're lookin:

 

[JoleFIN]

Looks good

I'm going for both input + output Lundahls and Sowter inductors.. would be great to have all parts top notch but at least now I need to settle for some compromises. Can I use two 2,2uF in parallel to replace the 4,7uF on the main board or is this combination sufficient?

What is the asterisk mark about on the 75 ohm resistor on the filter board? On the 10k resistor it's about the bypass unity gain, it's the same with the 75R ?

 

[gyraf]

the 75R is the correct value - the * was some left-over note for myself...

Jakob E.

 

[JoleFIN]

Ahh ok, thanks Jacob! Found a shop in home town which actually had one piece of the 4,7uF poly cap left on the shelf, so everything's great

 

[audiophreak]

Hi All,
      I see that there is an " Optional "  transformer balanced input which I plan to use, could I also put a 1/4" jack on back panel for unbalanced input and be able to use either ?

  also would anyone have the Sowter inductor part numbers ? ..  and what is the voltage requirement for the small film caps ?
         
  sorry for all the newb questions  :-[
  Thanks,
              Chip
 

 

[snipsnip]

yeah you can use both balance and unbalanced output. Theres a molex header for each if i remember rightly.

The sowter inductor you want is  9930.

Jake

 

[audiophreak]

Thanks  for the quick reply 
    ... just to be sure.. that's the Input, correct ?

 

[snipsnip]

oh, i read output. my bad.

im not sure. i think the transformer does more than just balane on the input.

i'll let someone else answer that one

jake

 

[audiophreak]

  snipsnip , Thanks so much.

      Has anyone used the Sowter input or output transformers in this project instead of the Lundahls ?

  EDIT :  snipsnip  - that Sowter inductor, in the description on the Sowter page it states that this one piece replaces the " Individual " inductors spec'd in the schematic / PCB layout with the leads or taps off of it ... how exactly is that wired ?  - the numerical values of the " taps " listed don't match up except the 22uh , but I see that all the " tapped " values add up to the same 269uh as the 100uh,100uh,47uh,22uh in the circuit layout

.. sorry I'm such a newb  :-[

 

[snipsnip]

The values in the 9930 are equivilent to the ones specified on the PCB, but they are connected in series. its just a drop in replacement for individual inductors.

22mH = 22mH
22 + 47 = 69mH
22 + 47 + 100 = 169mH
22 + 47 + 100 + 100 = 269mH

Using the colour code provide by sowter, you wire it up as per the diagram in the thread below:

http://www.groupdiy.com/index.php?topic=29972.msg363411#msg363411

Dont know anything about alternative transformers Im afraid.

Jake

 

[audiophreak]

  Thanks Jake ! 

                      I think I have everything else figured out... at least for now  ;D

,, very much appreciated,
                                  Chip

 

[audiophreak]

...o.k., another question  :

             a little confused on the power trans set up... in the documents from Gyafs page it shows T1 and T2 as 12v secondaries, but the PCB overlay states 15v for T1.

  so is it T1=15v , T2=12v like the G9 set up ? , or is it T1=12v , T2=12v.  

    alternatively, could I also just use on old tube amp PT that has a 115v pri and a 250v and 6.3 volt secondary?

 Thanks,
            Chip

 

[fallout]

Chip, you can use 2 transformers like Digikey PN: TE62062 (12v). Wire T1's primary for 120v (parallel) and secondary for 12v (parallel). Install the 2nd transformer in reverse for 12v (parallel) and wire the primary side for 240v (series). I hope this makes sense..

-jay

 

[audiophreak]

Thanks Jay, cleared that up for me  ;D