Build Thread:PQD2

[wrentema]

PCB grinder is not selling this anymore. I’m gonna build two filter boards from Don-Audio. But if anybody has a PSU/Tube/transformer board laying around please let me know. Happy to take it.

 

[innercityman]

PCB grinder is not selling this anymore. I’m gonna build two filter boards from Don-Audio. But if anybody has a PSU/Tube/transformer board laying around please let me know. Happy to take it.

Or you can build a PQD2 out of two G-Pultec boards. that's what I've planed to do. I don't know if Gustav is still selling them but you can buy them there...

https://analogclassics.com/product/gyraf-pultec-pcb-set/

 

[wrentema]

Or you can build a PQD2 out of two G-Pultec boards. that's what I've planed to do. I don't know if Gustav is still selling them but you can buy them there...

Yeah that's plan B. I think it's better to run it from a single PSU though right? And bring the voltages over to the other tube..

 

[innercityman]

Yeah that's plan B. I think it's better to run it from a single PSU though right? And bring the voltages over to the other tube..

You can build a single psu out of two G-Pultec boards. Gustav explains how he did it on the PQD2 files that are still downloadable from his site. Easy to do.

 

[band_master]

Hey guys,
I'm getting to the end of my build and checking voltages. I'm using the Don Audio trafo and reading 12vac and 275vac on the secondaries. The DC checkpoint for 12.6V is spot on but the DC voltage is 375V before the drop resistor and 363V after. Right now I'm using a 12K drop resistor but am I right that I need at least 125K? Seems pretty far off from the range of values suggested in the bom but I had to source my own parts vs. using kit components.

Here is how I calculated the current draw...



So this is the resistance I need to drop the voltage down to 250V, correct?



BD

 

[Gustav]

Hey guys,
I'm getting to the end of my build and checking voltages. I'm using the Don Audio trafo and reading 12vac and 275vac on the secondaries. The DC checkpoint for 12.6V is spot on but the DC voltage is 375V before the drop resistor and 363V after. Right now I'm using a 12K drop resistor but am I right that I need at least 125K? Seems pretty far off from the range of values suggested in the bom but I had to source my own parts vs. using kit components.

Here is how I calculated the current draw...

View attachment 85549

So this is the resistance I need to drop the voltage down to 250V, correct?

View attachment 85548

BD

Is this with no tubes installed, as your picture would suggest?

If so, consider for your findings, that (I) with no tubes installed is significantly lower than (I) with tubes installed.

Gustav

 

[antisleep]

Got my build done and just about working - but the left channel low boost does nothing. I reflowed the boost + freq rotary switches/resistors/caps, no dice. Started wondering if the boost Lorlin could be faulty, and since my kit came with two extras I removed it (slightly harrowing) and replaced. Same. I guess it's possible that the boost half of the frequency rotary switch is faulty but I don't have a spare so I'd like to try troubleshooting my way to glory. I'm about at the end of my so-so skills, if anyone has ideas.

scott

 

[Gustav]

Got my build done and just about working - but the left channel boost does nothing. I reflowed the boost + freq rotary switches/resistors/caps, no dice. Started wondering if the boost Lorlin could be faulty, and since my kit came with two extras I removed it (slightly harrowing) and replaced. Same. I guess it's possible that the boost half of the frequency rotary switch is faulty but I don't have a spare so I'd like to try troubleshooting my way to glory. I'm about at the end of my so-so skills, if anyone has ideas.

Left channel boost - you mean the high, low - or both? I will venture a guess, that you mean the high end boost, but even if thats the case, it still leaves me unsure of what you mean by "the boost half of the switch"

This may help.

If you have a working channel, set your meter to measure resistance, check the connections around the switch over the resistors. Just compare the "in-circuit" values channel to channel, and see if anything stands out, or if you are losing a connection somewhere. You can get all the steps done fairly quickly.

Gustav

 

[antisleep]

Left channel boost - you mean the high, low - or both? I will venture a guess, that you mean the high end boost, but even if thats the case, it still leaves me unsure of what you mean by "the boost half of the switch"

This may help.

If you have a working channel, set your meter to measure resistance, check the connections around the switch over the resistors. Just compare the "in-circuit" values channel to channel, and see if anything stands out, or if you are losing a connection somewhere. You can get all the steps done fairly quickly.

Gustav

Ah, I typed too fast - low boost. (updated my post since) The attenuate does work - so at least that part of the low frequency switch is working. What I meant by "the boost half of the switch" was the pole on the low freq switch (C35-40) that is tied to the boost switch. Sorry if my half-ass schematic reading skills are showing.

I did in fact try measuring around the resistors last night but I was tired and grumpy and suspicious of measuring in-circuit. Let me try again fresh. Thanks Gustav!

scott

 

[gyraf]

perhaps see the giant pultec thread for filter workings: G-PULTEC problems, please help!

/Jakob E.

 

[antisleep]

If you have a working channel, set your meter to measure resistance, check the connections around the switch over the resistors. Just compare the "in-circuit" values channel to channel, and see if anything stands out, or if you are losing a connection somewhere. You can get all the steps done fairly quickly.

Just did this, including comparing values as the switch is rotated. Statically everything seems okay. While changing boost values the channels behaves slightly differently: on the non-working channel, when the switch reaches (as in starting at 0 then rotating clockwise) the resistor being measured, that resistor's resistance drops much further than the working channel at the same setting. Squinting at the schematic I'm not sure what that implies, but it doesn't seem like it would cause _no_ boost.

EDIT: Measuring Low Boost wiper -> ground, the no-good channel is always shorted. That would explain it. But what explains that? Hmmm.

Jakob, thanks for the link, I'll chew on that info too.

scott

 

[antisleep]

AHA. I found that one side of the bypass toggle switch had continuity on all 3 pins. Faulty switch? Seemed very unlikely, but out of desperation I pulled it off anyway and found a big goop of solder on the switch side of the board, connecting 2 pads. Too much solder + big holes I guess. Cleaned that up, reinstalled the switch, and I'm in business. That's a relief!

Also this photo shows that I definitely did not do a great job cleaning my board, despite trying.

I'll run some sweeps through REW in a bit.

 

[antisleep]

Here are some sweeps, using REW and a cheapo Presonus Audiobox. (Gustav, didn't I see a video where you were visualizing EQ frequency response in real time? If so how were you doing it?)

If I understand correctly, I shouldn't be alarmed by the huge 40hz bump?

Channels look reasonably consistent. Ch2 looks noisy, maybe too close to the power transformers; I mounted them on the side wall so I didn't have to figure a way to recess the bottom cover for the screw, and the ground prong gets in the way of going any further back. If I cut off that prong and run the IEC ground to the other side of the case I can move the transformers back.

Ch 1 HF atten doesn't work. I'm not sure I care, except just knowing it bothers me.

 

[Gustav]

Here are some sweeps, using REW and a cheapo Presonus Audiobox. (Gustav, didn't I see a video where you were visualizing EQ frequency response in real time? If so how were you doing it?)

If I understand correctly, I shouldn't be alarmed by the huge 40hz bump?

Channels look reasonably consistent. Ch2 looks a noisy, maybe too close to the power transformers; I mounted them on the side wall so I didn't have to figure out a way to recess the bottom cover for the screw, and the ground prong gets in the way of going any further back. If I cut them off and run the IEC ground to the other side of the case I can move the transformers back.

Ch 1 HF atten doesn't work. I'm not sure I care, except just knowing it bothers me.

There should not be a 5dB bump at 40Hz - this indicates an error - and if you are getting it on both channels, it could be a value misplaced on both.

For the lack of high attentuation on one channel, you can use the same method as I mentioned/comparing the channels.

Im sure youll get it finished - dont hesitate to post and ask!

Gustav

 

[antisleep]

There should not be a 5dB bump at 40Hz - this indicates an error - and if you are getting it on both channels, it could be a value misplaced on both.

Hm, that bump is present in bypass too. I wonder if it's something goofy with the interface, or using REW for this purpose.

 

[Gustav]

Hm, that bump is present in bypass too. I wonder if it's something goofy with the interface, or using REW for this purpose.

If you unplug the XLRs from the unit, and plug them into each other for a sweep, you will have your answer.

Gustav

 

[antisleep]

If you unplug the XLRs from the unit, and plug them into each other for a sweep, you will have your answer.

Indeed, that's the first step of setting up REW (though I'm guessing my way through it). You measure the soundcard by patching output to input, then apply that calibration to subsequent measurements. I hadn't tried a loopback'd sweep with the calibration applied - looks very flat. So assuming I'm using this stuff right, I wonder what could be causing this odd bump. (or, I suppose, 5dB rolloff)

 

[antisleep]

Sorry for the multi-posts - Gustav, do you have a photo or screenshot of unpopulated PCBs? Since the values are printed under the components, it's hard to check my work.

 

[Gustav]

I dont believe the unit has a 40Hz bump. My guess is, theres an impedance issue, or some other error, when going out-in direct and doing the correction file, ´thats not as bad when mitigated by the PQ2 in/output stages.

Disable the cal file, do a measurement, or just listen - a 40Hz bump of that order would be more than obvious.

For the attentuation not working - try different frequencies. Theres a cap setting the value of each, and if all but one/most/even just one is working, the problem is those caps not making connections.

Maybe the switch is stopped on the wrong side for the frequency select, if its all of them. To check, take out the stop-pole, turn the switch all the way counter clockwise, and insert the stop.

Hope that helps!

Gustav

 

[antisleep]

Removing the calibration drops it down to a ~1.5dB bump at 40hz. Trying it as an insert on headphones with program material, I don't hear that bump so you may be right - which would be great but frustrating. Guess I could use real test equipment.

I sort of suspect this test setup too. The Audiobox is a bit of a toy. I'm having weird problems in Pro Tools just trying to get audio through the bypassed EQ to null. I'll bring the EQ to the studio soon where I have proper interfaces (and monitoring).

Meanwhile I'll ask this again if you don't mind-

Gustav, didn't I see a video where you were visualizing EQ frequency response in real time? If so how were you doing it?

Thanks!
scott