calrec PQ1549 help thread

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ricardo

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Nescafe said:
I mean only ceramic 11pF and 100pF using silver mica.....
NO.  If the 11p are the ones I'm thinking off next to each OPA, we (Calrec) swapped every single polystyrene 11p in the first M-series 75 channel desk for NPO/CGO ceramics.  This is the CORRECT part to use.  Mica/Polystyrene/Golden Pinnae are all substandard for this.

Guru Scott Wurcer posted some results in another forum that showed silver Mica introduced noise and polystyrenes are microphonic compared to CGO/NPO ceramics.  They are the BEST caps you can buy if their value & voltage fit.  There's an appendix in the John Hardy blurb on their 990 discrete OPA that shows chapter & verse.

Dunno where the 100p but similar considerations hold.
 

musika

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I found this website while trying to learn more about the characteristics of component materials.  This one talks about types of replacement passive components for the purposes of increasing the sound quality.

http://www.bext.com/replace.htm

Here is part of the article specifically about ceramic capacitors:

"Most caps found in audio equipment aren't used for coupling or power supplies, but for signal shaping. These smaller caps vary in quality as much as electrolytics and can benefit just as much from upgrading.

Ceramic disc capacitors were among the first small caps available and they're still used in a lot of equipment, especially guitar amps. They sound terrible, adding a screechy and gritty quality to the high frequencies that's quite unpleasant. They're also microphonic: a ceramic disc can pick up vibrations from the air or through the cabinet and add them (distorted) to the signal. When you find them in audio circuits it's a good idea to replace them with polystyrene (best) or polypropylene capacitors.

As always, there are a few exceptions. Ceramic discs are excellent for bypassing radio frequencies to ground; they're often found connected between the ground side of an input Jack and the chassis to help keep radio frequency junk out of the system. If you find ceramic discs used this way, leave them there. Ceramic discs are also sometimes used on circuit boards between the power supply pins and ground to keep radio garbage out of the active circuits. You can replace the ceramic discs with stacked film or polypropylene caps, but keep the discs around-if the new units aren't as effective, you may need to put the old ones back in.

Mica capacitors are even older than ceramic discs and aren't used much anymore. They behave a lot like ceramic discs and I replace them with polystyrenes when I find them. "
 

gyraf

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This seems like an over-simplified generalization to me. Use ceramics for opamp decoupling, poly for timing, and electrolytics where polys get too big - then you're at a good starting point. You can always experiment from there, just don't expect to hear big differences.

Jakob E.
 

geotone

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I finished the second channel of my PQ1549 yesterday. Both channels working first try, what a joy (and relief...)! Will post pictures once I get the case done, which might take quite another while.

Thank you Gyraf for this project, and thanks to Gustav for producing excellent boards. This forum is such an excellent resource.


/Geotone
 

gyraf

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Thanks for the feedback, Geotone - usually we only hear about problems here.

Good to have some posts that don't look so discouraging for potential builders...  ;D

Jakob E.
 
R

reanimatorstudio

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I'm drawing a frontpanel if you are interested. Nice mod would be to add a gain pot.
 

Nescafe

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ricardo said:
Nescafe said:
I mean only ceramic 11pF and 100pF using silver mica.....
NO.  If the 11p are the ones I'm thinking off next to each OPA, we (Calrec) swapped every single polystyrene 11p in the first M-series 75 channel desk for NPO/CGO ceramics.  This is the CORRECT part to use.  Mica/Polystyrene/Golden Pinnae are all substandard for this.

Guru Scott Wurcer posted some results in another forum that showed silver Mica introduced noise and polystyrenes are microphonic compared to CGO/NPO ceramics.  They are the BEST caps you can buy if their value & voltage fit.  There's an appendix in the John Hardy blurb on their 990 discrete OPA that shows chapter & verse.

Dunno where the 100p but similar considerations hold.

gyraf said:
This seems like an over-simplified generalization to me. Use ceramics for opamp decoupling, poly for timing, and electrolytics where polys get too big - then you're at a good starting point. You can always experiment from there, just don't expect to hear big differences.

Jakob E.

Thank You Ricardo and Jakob, really appreciate the explanation  :)
 

Nescafe

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Hi,

Is that correct that the shelving frequency calculation are:

Low: 1/(2*PI()*SQRT((1500+1/(1/100000+1/27000))*68E-9)  100000 is P4A

High: 1/(2*PI()*SQRT((1500+1/(1/100000+1/27000))*6.8E-9) 100000 is P1A

Thank You.
 

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gyraf

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Seems about right - haven't been there myself.

Try doing the calculation and see if it's estimate fits real-life parameters?

Jakob E.
 

Nescafe

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Hi Jakob,

Yes, and I try to calculate for step switch, the peaking band is done but need to know the shelving, since this eq share the same pot for both peaking and shelving, compromise  ;D

Maybe I should PM Harpo my "Filter Guru"  ;)

Once again Jakob, Thank You for bring this EQ.

Thank U.
 

Harpo

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Nescafe said:
Low: 1/(2*PI()*SQRT((1500+1/(1/100000+1/27000))*68E-9)  100000 is P4A
Seems your SQRT() term is missing the RC factor at the 2nd integrator.
Looks like the low 'shelf' is still a bandpass, just the hpf part kicked down some octaves by paralleling the two series connected 33uFs to the 150nF||680nF.
 

Nescafe

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Hi Harpo  :D

So is that correct the low shelf should be:
1/(2*PI()*SQRT((1500+1/(1/100000+1/27000))*68E-9*(1500+1/(1/100000+1/27000))*(1/((680+150)E-9))+1/33E-6)

And the high shelf formula is correct or using the second intergrator too 6n8 series 33u?

Thank You.

 

Harpo

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Nescafe said:
So is that correct the low shelf should be:
1/(2*PI()*SQRT((1500+1/(1/100000+1/27000))*68E-9*(1500+1/(1/100000+1/27000))*(1/((680+150)E-9))+1/33E-6)
? number of opening and closing parenthesis will be the same and messed up cap value, so result might* be varying between 1/(2*PI()*SQRT( (1500+1/(1/100000+1/27000))*68E-9 * (1500+1/(1/100000+1/27000))*(680+150+33000/2)*10^-9)) and 1/(2*PI()*SQRT(1500*68E-9*1500*17.33E-6)).
*With the hpf part (0.40 - 6.12Hz) this far (8 octaves) apart from the lpf part, I doubt the 1/(2PI()*SQRT(RClpf*RChpf) for center frequency being valid here. Maybe 1/(2PI()RClpf) is giving you a closer result. I'd just build it and measure the response to prove one or the other wrong (or ask a filter guru, I am certainly not).

And the high shelf formula is correct or using the second intergrator too 6n8 series 33u?
The Sqrt() with only a single RC factor within these parenthesis cannot be correct.
The 6n8 isn't in series to 33uF. The 6N8 is in parallel to the series connected 33uFs, IE 6n8||33uF/2=16.5068uF and the 6n8 can be ignored as it will vanish in the 33uF parts tolerances.
 

Nescafe

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Got it, wrong lookin at 33u, there are 2 in series and pararel to the 680n & 150n, same mistake in high section. Thank U Harpo, will make and play with the freq table tonight.

Harpo said:
(or ask a filter guru, I am certainly not).

For me You are a filter guru  ;)

Thank You Harpo, Gyraf and everybody
 

irfrench

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Hi all.

I just wanted to say thanks for making this project available!  I recently decided to re-purpose an old rack mount unit into a channel of this EQ.

tumblr_inline_mvlh01mgN21r2bfgn.jpg


So I cleaned out the old guts, only to find that the PSU was already putting out a helpful +/-15v!:

tumblr_inline_mvlhc8lWpy1r2bfgn.jpg


Quickly populated the boards (thanks Gustav!):

tumblr_inline_mxrkisR3ue1r2bfgn.jpg


Tested, added the ICs, buttoned it up and added a front panel plate to hide the mess:

tumblr_inline_mxrkjtojAU1r2bfgn.jpg


It fired up first time - which is always nice! - so I did some freq. sweeps to make sure all was working OK.  Damn this EQ is flexible!  I only ended up exporting the LOW band as I didn't want to spend ALL night getting plots; so here is a LOW band only set of sweeps!:

tumblr_inline_mxrknhGmhF1r2bfgn.jpg


Thanks again to Gyraf for sharing this and to Gustav for still making the boards!

Ian

:) :) :)

DOH! Just noticed that there isn't a non-Hi Q pair of measurements for Boost.  I'm sure you get the idea!
 

mrkrawn

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Hi guys

I just receive my calrec board rev 5 from gustav.
i just want to know what is the white film on the bottom?
can i solder on it or need to remove it
thanks by advance
 

gyraf

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the white coating on Grinder's pcb's is chemical silver - makes life MUCH easier. Just solder directly on it.
 

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