G-PULTEC problems, please help!

[gyraf]

Microphonics would probably be a bad tube.

Make sure not to run the tube at more than 250V for longer times, wears out tube quickly.

Jakob E.

 

[MicDaddy]

I've got a 'brrrrring' resonance in mine, thought it was the tube.. removed the tube and it's still there.  It's very glittery and high in frequency and has a short decay.

I first noticed it while using the unit.  I never do any switching while the unit is 'recording' or 'printing' so it hasn't bothered me and I had chalked it up to possibly being an old microphonic tube.  I was installing a new fender lamp and some knobs and noticed the sound still happens even with the unit unplugged (while clacking my new fancy yellow chicken knobs). 

Could it be the Lundahls or the IO inductor??  I've tried tapping the chassis and various components to recreate the sound, but only when clacking switches does it happen.  The Alphas on the front panel don't throw as hard and are not as loud, but with the Lorlin power and Bass Freq switches it's obvious.


EDIT:  It is the chassis.  I'm finishing Gpultec #2 and while assembling the chassis I've been reminded of the all too familiar brrrrrriiiiiiing.  Not sure how I'll dampen it but will try some things.  Doesn't affect the function of the eq but something I will try to remedy.

 

[rooster21]

I have a question about the low frequency band. I've plotted some curves and I'm not sure if I'm getting the correct result. When I change frequencies (at maximum boost) what changes is the slope of the shelf instead of the frequency, the peak always remains at ~35hz, is this normal? I'm building 2 and I have the same result with both.

 

[gyraf]

A shelving filter's cutoff frequency is most often defined at the spot where you have ½ the maximum lift/cut (in dB's) - so at the 9dB point if it's a 18dB boost like the one shown in the plot.

I read something like 300, 200, 150, 100, 80 and 50Hz from the plot - decent enough...

The peak around 35 is because of the built-in (tube/transformer) low-cut somewhere around 25Hz

Jakob E.

 

[rooster21]

Thank you once again Gyraf for clearing that up and putting my G-Pultecs one step further!

Giancarlo

 

[Assistant]

just finished my first pair of g-pultec eqs! 
what can i say? they sound amazing, can´t wait to use em in the next mixdown!

no smoke,no hum and this was my first tube project....more to come for sure
before that i built 2 gssl, 2 studer mastering eqs, 1 ssl9k pre, 1 green mic pre and i´m currently finishing my stereo calrec eq.
have to post some pics sometime....
next up: 1176 rev d, porter net eq, 2 more gssl and i still have the forssell opto boards laying around here.

thanks to everybody in this help thread, i read almost everything here and it helped a lot.
also thanks to gyraf for this project in the first place, gustav for the pcbs, dan from collective for the cases, don audio for the inductors and lundahls.

best
nils

 

[Assistant]

inside pic:

 

[synnys]

Today i finished my second stereo pultec and unlike the first one, which was just perfect (really , this one isn't.

It's got a hum/buzz around -54dB, a very clean one... 50Hz 100hz ect the usual harmonics.

i tried:

- moving the PSU around (i got the one from don audio, so only 1 toroid)
- turning the PSU, even moved it out of the case
- i connected only the grounds of the optional unbalanced input at the PCB to the IEC connector (i use 4 LL5402, so the unbalanced hole was free to connect a ground)
- i connected only the input grounds to the IEC
- i disconnected the output grounds

but it all makes no difference, not even the tiniest bit... hum stays steady at -54dB

So what did i do different from the 1st build.

- I used balanced jack out instead of XLR because it's more practical for my setup (which wouldn't really have to make a difference i suppose?)
- I just saw that i used ECC82 instead of ECC88 in this build by accident, ordered the wrong ones unfortunately (right ones on the way!
- turned the PCB's 180 degrees (which i kind of tested turning, but didn't seem to make a difference)

I know it's not recommended building a stereo in one case cause it's kinda cramped, but hey, the first one was perfect

Any recommendations on what to check next?

 

[okgb]

Look at ANY differences in grounding , is the jack grounded at the chasis , how is the psu
and signal grounded , if you have the first one still , directly compare the two for differences

Seeing the below post  , you don't have the first unit to simply swap the tube  ?

 

[gyraf]

- I just saw that i used ECC82 instead of ECC88 in this build by accident, ordered the wrong ones unfortunately (right ones on the way!

These are not interchangable. Use ECC88 and try again.

Jakob E.

 

[synnys]

unfortunanely i'll have to wait for the postman to bring me some ecc88's, but could that be why i have a hum? cause of a different tube?

 

[synnys]

tubes were right after all! i used the russian 6h1n-eb

and my hum is gone now i changed some wiring on the psu.

noisefloor is now below -90dB  8)

 

[synnys]

my build:

 

[Aleguitarpro]

Hi. I've finished my G-pultec.
I haven't a real problem, but I've found that the unit has a lot of gain.

I haven't the same amount of gain of the original input, when I switch the BYPASS off: to have a right amount of signal,
I've to feed the G-pultec with a very low signal from my DAW.

It's normal?
Because I can't use in my G-pultec a normal signal from my DAW, without lowering consistently it directly from my DAW.

It's possible to put a general gain make up to the circuit?

 

[gyraf]

Gain should be more or less unity (1x) with unit bypassed. If it's not, there is a chance you've done something wrong on the filter board.

The filter board attenuates some 18dB when bypassed or set to neutral - and the amplifier stage just makes a steady 18dB gain (give or take tube parameter tolerances)

Jakob E.

 

[Aleguitarpro]

Gain should be more or less unity (1x) with unit bypassed. If it's not, there is a chance you've done something wrong on the filter board.

The filter board attenuates some 18dB when bypassed or set to neutral - and the amplifier stage just makes a steady 18dB gain (give or take tube parameter tolerances)

Jakob E.

Today I've tested my unit: it boosts 12 db, bypassed and with the filter on (neutral settings).
In the filter board what could boost? You told me that I've made a mistake... maybe in any resistor value?
In the filter PCB I've the correct values in the 4 resistors (75R, 1k, 10k, 1M)...
The condensers values are right, too.
Any idea?

I forget to write that I've used OEP A262A2E transformer instead of LL5402.
I wire it in this way:

LL pin 5 - OEP pin 1 LL pin 10 - OEP pin 5
LL pin 4 - OEP pin 3 LL pin 9 - OEP pin 7
LL pin 3 - OEP pin 9
LL pin 2 - OEP pin 2 LL pin 7 - OEP pin 6
LL pin 1 - OEP pin 4 LL pin 6 - OEP pin 8

As attachment a photo of my build.

Datasheet of the trafo here:

OEP: http://www.canford.co.uk/ProductResources/ig/2739.pdf


Thanks for help!
A.

 

[Aleguitarpro]

SOLVED.

I made a mistake wiring the OEP transformer (exchange primaries and secondaries: the OEP must be wired in a opposite way to the LL... of course... I discovered it in the datasheet in OEP website, that is better than the one I used before: http://www.oep.co.uk/pdf/A262A2E.pdf )
An advice for anyone want to use this transformer: the best thing is to wire directly from their pins, glueing them on the PCB, without any adaptor or pcb.
The pinout to the LL not allow an easy disposition of the trace of the pcb for the OEP: I made an adaptor with a protoboard, but now I rewire them directly from the pins of the trafos.
It's easier and faster.
Sounds great with no noise.

Thanks.

 

[rooster21]

Finished up my pair, here they are!

 

[Aleguitarpro]

I've received a PM about the wirings of the OEP a262a2e in GPULTEC instead using a LL5402.
I prefer to share here the wirings for these transformer to help who want to use them in GPULTEC project.

As I told in my previous posts, in a first moment I made ad adaptor in a proto board.
Then, I've rewired them directly from the transformer's pins into the pcb.
I've fixed them turned over with biadhesive tape in the pcb and soldered directly the wire from the pins of the trafos.
I think that it's the better thing to control the wirings and maybe in a future change the OEP with the LL or other trafos.
A thing to remember is that OEP is reversed respect to LL5402, so the primaries of the LL become the secondaries in OEP and vice versa.

Hope this could help!

Ale

 

[juanjovincenzo]

Hi guys.
A questions.....On an EQ type pultec is possible to use one ECC82 SRPP stage with a combination of a PEQ1 filter passive stage with a MEQ5 filter stage???.  Like Gyraf said about MEQ5 :  "Combine this with the Pultec PEQ1A, and you have just about everything you need EQ-wise."


If is possible  ...... what is the better way to combine both type of filters ......in series o parallel?

Sorry if the question is stupid. :-X

regards
Juanjo..