Build Thread:PQD2

[JMan]

Ye, sorry for that stupid question, after i wrote my post with this question i found all the info at don audio........

No worries, I hope that I didn't make it sound like your question was stupid. There is a lot of information to sort through and it is easy to miss things.

Thanx man ! i will order most of the parts at reichelt, so thats really helpfull !

Some people wrote that suoundwise the don audio inductor would be better. is this some magic stardust, rose-water thing , or is it a diffrence ?

Although this wasn't directed at me, I'll say that probably the big benefit of the Don Audio inductors is that you can buy them as a 1% matched pair, which is good if you're trying to build a tight stereo unit. That said, they aren't cheap.

 

[antiehdas]

No worries, I hope that I didn't make it sound like your question was stupid. There is a lot of information to sort through and it is easy to miss things.


Although this wasn't directed at me, I'll say that probably the big benefit of the Don Audio inductors is that you can buy them as a 1% matched pair, which is good if you're trying to build a tight stereo unit. That said, they aren't cheap.

Yes, not cheap at all, especially for the matched pai...but i also read comments on noise problems with the don audio inductors... lot of people say carnhill are the best for the build. they say this one :
CA-18-VTA1444,
i think iust stick to the Fastron single inductors. in the end, even the design from gustav was made for them .

 

[antiehdas]

Have to say it also not makes it easier waiting for all the parts if u allready got the panel at home However, going for the powder-coated blue panel was the right desicion !

 

[JMan]

Gorgeous panel! Did you have it custom made or is that one of the Don Audio ones?

Side note -- this is exactly why I leave panels for the very end of my builds, otherwise I get too excited and can't stand the waiting!

 

[antiehdas]

Gorgeous panel! Did you have it custom made or is that one of the Don Audio ones?

Side note -- this is exactly why I leave panels for the very end of my builds, otherwise I get too excited and can't stand the waiting!

hahaha, yes, it hurts looking at it for weeks now Its from www.frontpanels.de i found photo of the blue version and asked him . cause its not on his homepage.

 

[JMan]

hahaha, yes, it hurts looking at it for weeks now Its from www.frontpanels.de i found photo of the blue version and asked him . cause its not on his homepage.

Awesome. Frank does amazing work, and that panel is no exception!

 

[eltorro84]

Have to say it also not makes it easier waiting for all the parts if u allready got the panel at home However, going for the powder-coated blue panel was the right desicion !

This is a nice panel. I like the slight greenish bue.
Is it this one you ordered? PCB Grinder PQD2 (stereo pultec)

 

[antiehdas]

This is a nice panel. I like the slight greenish bue.
Is it this one you ordered? PCB Grinder PQD2 (stereo pultec)

Yes, exactly !
i can only reccomend, looks beautiful, and its not anodized finished , its powder coated, have to say totally worth the little higher price

 

[Manou161]

Hello everybody,

Last spring I did buy and build a PQ2 kit form PCB Grinder without any mods. Everything worked out well and I’ been using the EQ for the last few months. I really like the sound of the EQ and the stereo balance between the two channels works very good. But still I ran into two things I want to adjust: get smaller gain steps on the low attenuate and lower the noise floor on channel 2.

Adjustment 1: Smaller gain steps on low attenuation
The first thing I want to adjust is the amount of low attenuation per step. As you can see in IMAGE1 the three first boost steps (green) are around 1 dB / step, but the first three attenuate steps (red) are around 3 dB / step. Low boost step 10 is around +10dB while the Low attenuation step 10 is around -22db.

Is it possible to use smaller resistance values on the low attenuation switch? If yes, can someone explain me how to calculate the resistor values to get a constant 1 dB attenuation steps. If this is to complex to explain, does anyone have the resistor values for the mastering version?

Adjustment 2: Noise on Channel 2
The second thing is a higher noise floor on channel 2 (-90 dB fs), compared to channel 1 (-110 dB fs). It’s mostly not audible, but when using the PQ2 on the master bus when mixing, the noise sometimes gets audible in the mastering process.

Everything was done as it was indicated in the assembly guide. In IMAGE2 you can see my PQ2 from the inside. I already moved the cable that connects the two pcbs further away from the power trafo, but It didn’t change a lot. Do you have an idea where this could come from and it could be fixed? Maybe somehow shield the cabling form the power trafo?

Thanks for your help in advance

Best regards,
Manou

 

[Gustav]

Ill do them in reverse order.

2. More noise on channel two.

FS measurements arent much to go by, so not sure what your actual noise floor is. I wouldnt worry about the sides being uneven per se, but...

-90dBU would be better than what I have accomplished in this build, so with the discrepancy (20dB) between your sides, I am guessing you have quite a bit of noise on the right channel - more than usual.


Solutions.

a - turn the transformer

Your transformer "Winding opening" (sorry, not sure what this would be called in english) is pointing towards your front panel. This is a critical spot, since the inductors are susceptible to picking up noise, and this spot is prone to put out a stronger field.

You can achieve a big improvement from this! (also, by mounting the trafos as far away as possible, or even in a separate case)

b - replace the incuctors in the build.

In the kits last years, the included inductors were off-the-shelf types from Reichelt, after I found out, most people replaced them anyway, when I included others (the don audio was very popular, which I never understood). I recommend any shielded type (Bourns or Matsuta, for example)

1. The steps

I measured the steps and resistance relative to the gain in a build at some point, because I was considering doing a 23 step switches build.

Measurements are attached in this post, and youll see the gain, total resistance, added resistance on the given step, and a rounding off to the nearest real-world resistor value.

You can customize your gain based on this, so for example, if you want to do a 1.5dB step, just add the value of 3 steps.

The Low cut and Low boost dont care about total resistance, so you can just add resistance as you please.

The High boost and high cut do care abotu the total resistance, so you need the total to be 1K and 10K respectively (notice, one needs to multiplied by x1000)

To adjust 11 steps, one method would be to do the first 10 exactly how you like, then add the difference in reistance to the 11th.

Or you can do the 11 steps on the switch, cut the trace going from the switch, and make up the difference with a resistor in series there.

_____________

Let me know if my explanation is lacking on any of this, and Ill help the best I can (and sorry, I could only find the sheet in my drawer, not the original file)

Gustav

 

[Gustav]

Just took at look at the sheet and noticed, the added resistance/rounding to nearest was done for an 12 pos switch, but you do have the date in there to build your own gain ladder.

Also, dont worry about a few ohms difference here and there when you juggle a ladder into place

Gustav

 

[erquere]

Hello ! Would someone have a BOM for the PQ2 ? Ok for resistors but not for other parts, i dont want to do **** d’Hénin ordering… Best regards

 

[ja113n12]

Hello everyone,

Foremostly I would like to give a big expression of appreciation to everyone involved in this community and those who have spent a lot of time and creativity to create such interesting projects for us all to build and enjoy our music endeavours with.

Throughout the last two years I have been fighting my way through completing the Gyraf kits, with varied success. I have learnt a lot on the way and the joy from what works so far is more than the hundreds of hours spent troubleshooting.

I thought this kit would be relatively simple, due to having completed two PEQ (mono) kits successfully. The transformer I am using is a 270V / 14V AC transformer. Although it is slightly over the recommended voltage, I suspected I could use a larger bleed resistor to compensate for this.

When I turn the device on, the bleed resistor closest to the fuse starts to burn, which should obviously not happen. The bleed resistors are 470R, 2W. I am using two 400V 330uF large capacitors (should these be 220uF?).

I have tried with both the tubes inserted and without, and the same happens. Could it be that the additional voltage spec from the transformer requires me to use a higher value wattage for the bleed resistor?

Any guidance here would be greatly appreciated. Usually I am confident troubleshooting devices with the power on, but due to the voltages, and fireworks, involved here I am quite concerned.

 

[ja113n12]

Hello everyone,

After thinking about this more and applying some electronics equations, I found that using a 470R resistor as the PSU bleed resistor will create 340W initial dissipation energy with a time constant of 0.16s, which explains them burning out as written above.

Upon checking the documentation closer, I see I have confused R117 & R121 with R114 & R116. The value of R117 & R121 in the photo is actually 5.6M Ohm. Applying the physics, this will dissipate initially 0.3W with a time constant of 180 seconds, which sounds a lot more reasonable.

Going to order some 5.6M Ohm 2W resistors and check this when they arrive

 

[Gustav]

Hello everyone,

After thinking about this more and applying some electronics equations, I found that using a 470R resistor as the PSU bleed resistor will create 340W initial dissipation energy with a time constant of 0.16s, which explains them burning out as written above.

Upon checking the documentation closer, I see I have confused R117 & R121 with R114 & R116. The value of R117 & R121 in the photo is actually 5.6M Ohm. Applying the physics, this will dissipate initially 0.3W with a time constant of 180 seconds, which sounds a lot more reasonable.

Going to order some 5.6M Ohm 2W resistors and check this when they arrive

Sorry, bleeders are 470K in my builds. I just realised its put wrong in the guide, and I never got it corrected (boards were only leaving as part of a kit with the correct values way back when). Which photo are you refering to?

Gustav

 

[ja113n12]

Sorry, bleeders are 470K in my builds. I just realised its put wrong in the guide, and I never got it corrected (boards were only leaving as part of a kit with the correct values way back when). Which photo are you refering to?

Gustav

Hello Gustav,

I am referring to the photo in the build document:



From the photo i was reading the bleed resistor value as gold, green, blue, green (5.6M), from what your reply I see this could also be gold, yellow, violet, yellow (470K). Just realised that my calculation above was wrong; I missed a zero. A 470K bleed resistor will provide safer results. Going to swap with this value and give the unit a test.

Thank you for confirming bleed resistor value, this really helped re-assure me im on the right path!

 

[ja113n12]

Hello Gustav,

I am referring to the photo in the build document:

View attachment 101082

From the photo i was reading the bleed resistor value as gold, green, blue, green (5.6M), from what your reply I see this could also be gold, yellow, violet, yellow (470K). Just realised that my calculation above was wrong; I missed a zero. A 470K bleed resistor will provide safer results. Going to swap with this value and give the unit a test.

Thank you for confirming bleed resistor value, this really helped re-assure me im on the right path!

Everything now works perfectly, the unit sounds amazing. Very happy to have this in the rack!

 

[erquere]

Hi ! Anyone having the BOM of the power board of the PQ2 ?

 

[JMan]

Hi ! Anyone having the BOM of the power board of the PQ2 ?

Would indeed be nice to have, since the schematic is an impossible-to-read mess, at least on my screens.

 

[studiosus]

Hi there,

I have one. But you should double check before you order with your boards..