Build Thread:PQD2

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Hey Gustav, thanks for the fast response. Youre the man!

I'm sure you are right. I just have the regulator free standing right now. I wasn't thinking about how much current the tubes need...like I said first tube project....doooh.  I shoulda noticed since all the pictures I've seen on completed units had it heatsinked. I'll get that heatsinked today and give it another shot.

I have ECC88's. Typo on my part. Thanks for looking out for me.

Last question...I'm wiring up the xlrs now and I'm looking at the schematic.....am I right that pins 1 + 3 go to the transformer and pin 2 goes to ground?

 
I used a small 3cm heatsink with 1cm wings and a silver thermal/conductive paste, does the job nicely


(I wired all the XLR pins to the PCB, and the input XLR's ground pins additionally connected to the mains ground/chassis ground; signal is as clean as it gets)


 
It was totally the heat sink. I got a big one strapped on there now and it's firing up fine. Thanks for all the help everyone.

miszt said:
I used a small 3cm heatsink with 1cm wings and a silver thermal/conductive paste, does the job nicely

(I wired all the XLR pins to the PCB, and the input XLR's ground pins additionally connected to the mains ground/chassis ground; signal is as clean as it gets)

I will wire it up just like this when I'm done testing!

Sounds really, really nice. Thanks for the great project!
 
Dear Gustav,

i've built your Version of the Pultec, thanks for Layout of a Stereo Version. Everything seems to be Okay, it sounds good, distortion about 0,2%, very little Noise ... a hot voltage regulator, but with a bigger heat sink it seems okay.

I'm not satisfied with two things: there is a overall Level drop of 3 dB (Bypass/Hi-Z input), 4dB@600Ohms, and 1,5dB more with the Bypass-Switch off (=Filter in). (And I discovered a 2,5 dB Peak at 24 Hz, measurement above, but it vanishes with a 600 Ohm Load... that might be normal?)

Is there a way to calibrate the Bypass / EQ in Gain leakage, and perhaps the overall Gain?

Thanks ^^


 

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stereo78 said:
Is there a way to calibrate the Bypass / EQ in Gain leakage, and perhaps the overall Gain?

Check the discussion thread for Jakob's PeQ design. Asked and answered tons of times.

Gustav
 
Interested in this project.
Learning and collected already some of the components :)
Always wanted a Tube EQ in my studio. Will take my time on this one..

Good job Gustav !

 
Hey, I got a question regarding the grounding and XLR wiring... I'm a bit confused because of the different layout.
Am I right that I have to connect the XLR pin 1 to PCB pad 2?
So
XLR 1 -> PCB 2
XLR 2 -> PCB 1
XLR 3 -> PCB 3

And should I connect the Input XLR ground pins (1) together and to chassis ground?
And should I wire anything to the ground pad on the PCB or why is it there?
 
Murdock said:
Nevermind, figured it out...
Testing the unit now, will post results later.

Good luck !
Gonna start building mine next week, looking forward to see your version.
which ECC88 did you used?

Best


 
Thanks Hobbyist! I got PCC88 Phillips Miniwatt tubes from Bowie. Can't recommend him enough! Very nice guy and very nice tubes!
Got it up and running! Voltages seem to  be ok.  No smoke  8)
215V after the drop resistor
6.1V at the heater
Lamp is glowing, tubes also.
Should I change the 18k drop resistor to a 15k resistor to get near to the 250V and 6.3V?
But I have another problem... The high frequency boost on my first channel does nothing except at 2.1 Khz. This one works...
I thought it would be a capacitor I accidentally touched with the solder iron and it has a melted spot. But the capacitor is in the attenuetor section and this seems to work fine...
Does anyone have a clue where I should expect the error to be?


 
Murdock said:
215V after the drop resistor
6.1V at the heater

I would make sure the regulator is actually regulating and not just passing DC, since thats a tiny, tad low

Measure the voltage on the input pin of the LM317 to see if its about the same as its spitting out.

No need to change the drop resistor imo.

Murdock said:
]The high frequency boost on my first channel does nothing except at 2.1 Khz. This one works...
I thought it would be a capacitor I accidentally touched with the solder iron and it has a melted spot. But the capacitor is in the attenuetor section and this seems to work fine...
Does anyone have a clue where I should expect the error to be?

Are you sure its 2.1kHz? I think  you have an error in switch programming - the little programming pin, stuck on the wrong side of the switch in position 6. So when you are in 1, you are really in 6, and in 2, you go to 7, which is not a meaningful position.

Even so, and just for the sport of it, it shouldn't  be too hard to trace.

Take a look at the schematic

The HF switch is a 2 pole/6 position switch. (Sort of like 2 switches with 6 positions, moved by one control)

Now, trace what I write in the schematic.

On the first position (2.1kHz), the signal passes through a cap to A1 (two in parallel, but lets call it one to simplify), goes from one pole of the switch to the other (A to C), goes up to C1, and then through all the inductors in series (C2, C3, C4, C5 and C6 are dead) and moves on.

On the second position, the signal passes through the same cap, down to A2, A always goes to C, regardless of the position you're in, and now C goes up through C2, which does not go through the first cap, but still passes through the rest of them in series.

(If you switch is programmed correctly, and the working frequency is in fact 2.1kHz).

Looking for trouble ont he first pole.

Capacitor switched in on A1 and A2 is the same, so its not the capacitor, or the signal  to the capacitor coming to the input (they work on A1!)

It could be the connection from the capacitor to A2.  So basically, see if A2 is connected properly

Looking for trouble on the second pole

The inductors are in series, and on C1, they are all switched in, so you already know the signal makes its way through all of them.

In the second position (C2), you simply bypass one of them, so you could look for trouble on C2 on the switch.

...but

You say all the frequencies over 2k1Hz are dead, and now that you know how to trace the signal though the schematic, you'll see that a missing signal on the A3/C3 would have to be a bum connection around the cap going to A3, or a bad connection from C3. 

Its logically possible that you could have a whole gang of bad connections (fourth, fifth and sixth would be separate to, as you can see), but before testing a hypothesis that involves error stacking, check the simpler one - programming pin error.

And if you thought you didn't know how to read a schematic, I hope I managed to prove you wrong.

Gustav

 
Hey Gustav, thanks alot for your explanation and help, much appreciated!
I measured the voltages on the LM317.
I got 12.83V on the input
          6.1V on the output
          4.86V on the adjust pin

What exactly do you mean by programming pin? Do you mean the little stopping washer? Or is there a pin inside the switch which I also can adjust?
If you mean the stopping washer, than I got that right.

Edit:
resoldered A2 and C2 to no avail, even completely wired a new switch because I thought the old one was maybe faulty.
Still got the same behavior...
Now I will resolder every capacitor in the high section. I hope there is no faulty one...
 
Murdock said:
If you mean the stopping washer, than I got that right.

Just to make 100% sure your switch is not caught on the wrong side of the pin.

Remove the pin, turn the switch fully counter clockwise, then add the pin to position 6 again.

Re:your idea to resolver every capacitor, reread my info/trace the schematic. I tried to make it clear that you could be sure that if the first step (capacitors included) worked, this would not be the reason for fault on step two.

Gustav
 
Yes, I did exactly that. Also, if the switch was programmed the wrong way, and step 1 was in fact 6, than it should have a boost at 18khz right? And that is definatelly not the case. I ran some music through the working channel, boosting at 2.1khz and compared it to the faulty channel, and it sounded the same. So I think it is really boosting at 2.1khz...
So if the capacitors can't be the fault, what can it be? It has to be the switch? No other possibilty?
 
Murdock said:
Yes, I did exactly that. Also, if the switch was programmed the wrong way, and step 1 was in fact 6, than it should have a boost at 18khz right? And that is definatelly not the case. I ran some music through the working channel, boosting at 2.1khz and compared it to the faulty channel, and it sounded the same. So I think it is really boosting at 2.1khz...
So if the capacitors can't be the fault, what can it be?

Broken through plating or similar - i can be anywhere on the identified path. I dont have time to check right now, but I dont see what else it could be off the top of my head.

Try this -  Take a few pieces of wire, and see if you make the connections were investigating directly from the components to the switch pins.

And this - compare the channels with your meter to look for discrepancies on the connections were investigating.

Gustav

 
Yep, seems to be the plating or traces... At A, A1, A2, C and C1 I get the same resistance. At all other I get nothing...
At the working channel I get the same resistance in all steps.
Looks like the signal stops at C2 right?
So I just connected C2  to the 100mH pad with a wire, and still nothing...
(Just to make things clear; the signal goes through, but is not affected by the high frequencies except 2.1khz).

EDIT: Got it!!
It was the inductor...
I have the custom inductors from Don Audio with the adapter PCB and there is no real indicator on how to place the inductor... And guess what, I've put it in the wrong way. Really  weird because I've put it in the same way like the other inductor in the working channel. I should write Aaron, maybe he can make a marking on his inductors...

Anyway, I'm really relieved now... Thanks alot Gustav for your time and help!
I will post pictures and some notes tomorrow.
 
It lives!!  :eek:

IMG_9617.jpg


IMG_9610.jpg


IMG_9603.jpg


I know, I know, it probably is a troubleshooting nightmare and noisier than the default layout, but I'm done and it sounds just amazing! And it is in fact really really quite (except a little buzz on the right channel from the lamp cable, but only noticable when I really crank up the volume to the maximum. I have to shield it somehow).
But I would not build it like that again I think...  :p I think function over looks should be my motto when I start the next project.

So big thanks to you Gustav for this amazing project! Thanks to Aaron from Don Audio for the inductors. Frank from frontpanels. de for making the panel for me. And Bowie for the tubes!
You guys rock!

 
Murdock said:
it is in fact really really quite (except a little buzz on the right channel from the lamp cable, but only noticable when I really crank up the volume to the maximum. I have to shield it somehow).

Are you sure its the lamp cable? Inductor on the right is a bit close to your toroid - could be worth checking if thats the culprit.

Other than that, excellent looking build! And re:trouble shooting - the inductor you are using does make a difference for the trace I posted to help - always highlight info on "mods" in bold to make helping easier :)

Gustav
 
Yeah, the buzz varies when I move the cable around. It also gets alot quiter when I touch the lamp holder... is that an indicator that it isn't making proper contact with the chassis/ground?

And yes, sorry! I should've told you that I'm using different inductors. But your tip on measuring for discrepancies between the two channels got me on the right track. And I also learnt a few different things on the way. So thanks alot Gustav!

EDIT: yep, grounded the lamp holder to the star ground and that minimized buzz by quite a bit. The little buzz that is left is probably because of the inductor being to close to the PT, like you said. But I only can hear it when I turn the level to max... So I'm happy how it is now!
Can't thank you enough!
 
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