G-PULTEC problems, please help!

[synnys]

no, what harpo said is right. its a 4700uf 25v electrolytic cap

 

[synnys]

If it's only the high boost that doesn't work (but the rest of the controls work perfectly???)  that points to a problem between the wiper of your hiboost pot, the inductor(s), the hiboost caps and the BW pot.  These are all in series, if there is a break somewhere in this series circuit, there is no high boost.  Could be a bad component (but looks like you replaced everything?), miswired pot, broken wire, bad solder joint somewhere, anything.  You could try injecting a (music not tone) signal to the input, turn the high boost halfway up and probe along the above-mentioned parts until you find where the signal stops.

Take a look at the schematic, a simplified way to look at it is as if the "hi boosted" signal travels from the wiper of the high boost pot through the LC circuit, through the Bandwidth pot back to the rest of the circuit. 

good luck

Ok so i just did the following:

i duct taped the tip of the jack coming from my sound card out to a wire and soldered that to the IN on the filter pcb.

(i duct taped the sleeves of two jack cables together with some wire)

and now i'm touching all solder points on the filter pcb with the tip of the jack going into my soundcard. so i can hear the music playing thru the cable.

guess what? the signal NEVER stops. i can hear music on EVERY solder point on the filter pcb.
not every point has the same volume ofcourse, and some points (at the caps) sound EQ'ed. which makes sense.

But it seems the signal path is not broken, how come the high boost doesnt work then?

 

[Harpo]

...and mine is absolutely wired correctly.

Maybe assume it is not.
I'd double check the bypass wire connections (sw2A from schematic = sw1B from pcb silkscreen) that might cause your low ohm reading.

 

[synnys]

bypass switch is good, it works so it must be good,

hi cut and lo boots/cut work fine. just the HFboost that keeps bugging me.

 

[synnys]

Problem solved!

I found out while remeasuring everything, that the 1M resistor above the bypass switch was giving me 1M at both positions of the bypass switch while that should have been bypassed.

So it was a bad connection in the bypass switch after all, but i didn't think of that before because the lo freq circuit was bypassed all right by that same switch!

!

 

[rooster21]

I've got a question for those using the #47 fender lamp.

I have some 60hz hum being introduced when my lamp is connected, a noise reading of -66db@60hz vs -108db@60hz with no lamp. I'm getting power from the 6.3v point on the PCB and dropping it with a 42ohm 2watt resistor.

Is anyone else getting similar values? Any other suggestions on how to power the lamp?

 

[gyraf]

Take AC lamp power directly from one of the the 12V secondaries, with a suitable dropping resistor. That way you don't mess with the regulated DC heater voltages. Just keep the lamp leads twisted, and some distance away from the filter board.

Jakob E.

 

[rainton]

hello everybody,

I also have two GPultecs here. But they are still from the time when I was not DIYing so a friend built them for me some years back.

Now I moved and so did the entire studio and it seems the pultecs didn't like moving too much:

They both work but with one of them when I switch the LoBoost to 100Hz the signal gets pretty loud and some frequency seems to be boosted -
but it's rather in the midrange - definitely way above 100Hz!

The other Pultec does the same thing when boosting at 16khz -> signal level raises and the boost is also somewhere in the midrange - definitely way below 16khz...

I just opened them up and was suspecting the caps at the respective frequency  selection points but a) this merely estimated and b) I don't know which cap is for which frequency...

some help would be highly appreciated

 

[gyraf]

..check integrity and soldering of the capacitor that gets switched into circuit at the failing frequencies..

Jakob E.

 

[rainton]

Thanks Jakob,
I unsoldered all the components in question and checked them with the DMM - they seem to be ok.
After soldering them back to the pcb both units seem to work again

 

[muffy1975]

An output transformer question.

While yo can sub the correct Lundahl for and OEP, can i sub/swap in a Carnhill VTB1148 output transformer. Would this work?

The specs are

Turns Ratio; N1:N2 = 1+1:1.7+1.7 DC Coil Resistances: P12:S1:S2 = 6:6:20:20 (Ohms)


I thought this might be of better quality than an OEP and half the price of the Lundahl.


Thanks for any light/help

Kind regards

Michael de A

 

[gyraf]

Depends entirely on it's inductances - impossible to tell from those specs.

Jakob E.

 

[ibanman555]

Hi Everyone!

This is my first post and I apologize if this has been answered elsewhere (many posts to weed thru!), but some of you may already know the answer...

I am planning on piecing together the G9 Mic Pre, G1176 and the G-Pultec to make a pseudo record channel for my home studio. I'll make them all separately of course, but I'm looking for one thing.  The G-Pultec DIY page doesn't include a list of components like the others, it just helps when ordering all the appropriate parts needed for the build, and also you all may have substituted better parts for the build.

Does anyone have a good current components list for the G-Pultec? I would greatly appreciate it and looking forward to this build, you may see more of me in the future! Thanks in advance!

 

[synnys]

8 2x6 lorlin
4 10k lin
2 1k lin
2 100k log
2 2k2 lin
2 22mH
2 47mH
4 100mH
2 18n
2 12n
2 6n8
2 3n3
6 33n
4 47n
2 68n
4 100n
2 150n
6 220n
2 330n
2 22n
2 15n
2 10n
2 470n
2 680n
2 1u
2 2u2
4 10k
4 1k
2 75r
4 470r
2 1k8
2 2k2
2 470k
2 3k3 2W
2 LM317
4 220u 350v
2 4u7 250v
2 470u 16v
2 4700 25v
2 10u 25v
2 heatsink
8 3pin connector
4 LL5402
2 ecc88 / 6dj8
2 fuse 4at
4 bridge rectifier 350 1.5a


This is a list i made for a stereo pultec.

But all the components are on the silkscrene of the PCB

 

[ibanman555]

Many thanks for the list... helps make sure I don't overlook anything. But I suppose I should just take my time with this as well.

 

[gyraf]

4  10k lin

Circuit works best with one log(lf boost) and one lin(hf-boost).

Jakob E.

 

[mrdarwin]

Hi everybody!
I just finished my first Gpultec with OEP A262A2e output transformers and unbalanced inputs, and it sounds great.
The output level is less 2,7dB than input level... Is it normal? because OEP instead Lundahl?
I'm confused with wiring transformers:
output: OEP 1:2 ,secondary and primary in series and the primary goes to output balanced, so the transformer works for 2:1, is it correct?
Do I have to wire the OEP in the same way like the lundahl(2:1 oep, 1:0.5 lundahl)? inverse?

If I want use balanced input, do I have to wire the OEP in the same way like the lundahl?

thanx!

 

[frazzman]

Quick question - i've built a few of these with unbalanced input (so no input trafo).

Given that Pin1+3 are tied together for unbalanced input, should I still connect pin 1 on input XLR to star ground?

At the moment I have the star ground connected to filter PCB gnd and output pin1 terminal gnd, but I have not connected star gnd to XLR input pin1. Should I???

Everything seems to work fine but I am trying to minimise noise

Thanks

 

[gyraf]

No simple answer. Try to see what works best in your case.

As always, interfacing to an unbalanced input depends on whether the previous stage is electronically or transformer balanced.

But you should connect xlrpin1 to ground in any case.

Jakob E.

 

[frazzman]

No simple answer. Try to see what works best in your case.

As always, interfacing to an unbalanced input depends on whether the previous stage is electronically or transformer balanced.

But you should connect xlrpin1 to ground in any case.

Jakob E.

thanks Jacob, I ended up connecting both xlrs and filter gnd to star gnd and that seems to have given me the best rresult. zero noise in bypass and low boost, interestingly the first freq in the high boost is the most noisy but the rest of the high freq positions get quieter,  particular 6.8k which is just as quiet as bypass. I think others have also noted this finding