calrec PQ1549 help thread

[thewotan]

The first problem I had is that at first the EQ didn't work when engaged. That was because I didn't (I don't know why) wired 0v in the PCB output to XLR pin 1. I understand I had no sound because the entire audio path didn't have a 0v reference, could that be correct?

Once I wired that, all was good. I tried to check the boosts and cuts and they all work, minus the High Mid of channel one (it goes up to around 2kHz and no beyond). There's some click and resistance on turning frequency potentiometer, so I'm assuming it is broken. I'll replace it and I expect it to be OK.

And lastly, but this has me puzzled... Bypass LEDs are not working. From what I gather from the layout, pads correspond to Green - 0v - Red, but I can't make this to work. This is the LEDs I got:

https://www.mouser.es/datasheet/2/244/lumex_lumx-s-a0001355871-1-1737718.pdf
If I wire the center leg to the center pad on the PCB, it doesn't work at all. Checking with DMM, center pad has -14.6 V referenced to 0v on the supply, so I understand center pad is NOT ground, right?

Anyway, if I wire the center leg of the LED to the right pad, I have the LED lighting up but only in the leg wired to the center pad and only when the switch is ENGAGED.

With switch DISENGAGED, I have no lights at all. Voltages on the LED pads are as follows (measured in reference to supply's 0V):

ENGAGED

Left Pad 0V
Center Pad -14,6V
Right Pad +14,5V,


DISENGAGED

Left Pad +14,5 V
Center Pad - 14,6 V
Right Pad 0 V


I'm quite certain that this should be easy, but I'm kind of blocked... Is engaging the swtich changing which pad is Ground? It doesn't make any sense (to me, but I know next to nothing...). I tested the LEDs before wiring them, and they worked correctly, and the Bypass switch is working so I'm quite lost about what could it be... Any ideas?

Also, for the Power switch LED... Is it OK if I wire it directly to the PSU or would it affect negatively to the PCBs supply? (I suppose it won't, as it shouldn't be a lot of current)


Thank you all for all the knowledge shared along the years and specially to Jakob for making this awesome circuits!


Cheers all!

 

[thewotan]

Oh, one last question... How can I plot the frequency response of every filter section? Right now I'm checking it with a noise generator inserted in reaper and a frequency analizer, but it would be great if I could save the plots to compare against each channel

 

[HyprDrivr]

300mA should be plenty for both channels.

Check for switch-mode noise on completion just in case (I haven't tried to run these from smps supplies before)

/Jakob E.

Hello again.

I would just like to report back that my SMPS worked like a charm, no noise what so ever and the dual EQ unit is working great.
I will post pics and videos as soon as i have the knobs, they are currently stuck in transit.

 

[thewotan]

Ok, I've been retracing my steps and, as far as I can tell, everything is correctly wired and soldered.

Following the center LED pad on both the PCB and the PCB layout on Gyraf's website, it is connected to the V- rail. Which I don't understand, because that center pad should be 0V, right?

I couldn't find any mention to it through this thread, but I see people are using the same PCBs and (apparently) they are not having any problem with the Bypass LEDs, so I'm totally lost here...

Anybody has got any idea?

 

[Harpo]

Ok, I've been retracing my steps and, as far as I can tell, everything is correctly wired and soldered.

Following the center LED pad on both the PCB and the PCB layout on Gyraf's website, it is connected to the V- rail. Which I don't understand, because that center pad should be 0V, right?

I couldn't find any mention to it through this thread, but I see people are using the same PCBs and (apparently) they are not having any problem with the Bypass LEDs, so I'm totally lost here...

Anybody has got any idea?

You've got a bicolor Led with common anode. You want a bicolor Led with common cathode instead.
No idea why you think the center pin should be 0V. Led's are current operated devices. The two 4k7 in series resistors between +/- supply voltage rails and the Led limit the current needed to ((15VDC - -15VDC) - 2Vf) / (4700R+4700R) = 0.003A = 3mA.

 

[thewotan]

Hey Harpo, thanks for replying!


I thought center pin should be 0V because it seemed like that on the PCB layout. I got so confused with that that I didn't think about getting a LED with a common cathode

Now it all makes sense. I'll get the correct LEDs and finish this ring then

Thank you once again for your help!

 

[HyprDrivr]

Hello Friends
I documented my build of this EQ and have the videos up on youtube.

https://youtube.com/playlist?list=PLqiv8H60yvmQB4V3O_U-bgr68ZYy_8ye4
Might be useful to someone to decide if they can pull this project of.

 

[Bernardo]

Hello, I built this eq some time ago, it seems good and very usable on tracks, but would there be a way to balance the input signal with a transformer? Thank you.

 

[melanstudio]

Hello. Someone accidentally found a drawing on the front panel with the holes.
I would be grateful if you also share a screen printing file on the panel.
Thanks.

 

[ashdot]

How much of a boost is present with controls flat and balanced input and output?

You could try changing the two 10K series resistors at the balanced input to something larger - say 22K should take you down 6dB etc..

I have no proto of this unit around anymore, so I'd appreciate if you could report back with a solution..

Jakob E.

17 years later…
Hello Jakob, which two of the four 10k resistors did you mean?
Thanks!
Izhar

 

[gyraf]

..the two in series with the inputs - just after the input coupling capacitors..



/Jakob E.

 

[ashdot]

..the two in series with the inputs - just after the input coupling capacitors..



/Jakob E.

Thank you Jakob!
Izhar

 

[Zepdave]

Hi all.
I noticed in the PCB layout (rev 4) there are 2 100ks resistors "railing" in parallel to 0 volts, between the HiMid and LowMid gain pots when it should be only one according to the schematic. One of the resistors is marked with "R 70" in the PCB.

Could this be the issue with the output gain mismatch?

I noticed too different bridges between 0 rails that maybe cause ground loops noise? Although I don't hear much noise in this design.

Another one I'm inspecting, the 1 M resistor to 0V in the High Freq section (schematic)... This resistor is bridging the output of IC5A with the + of the IC5B in the PCB layout... 8I

Otherwise, thanks Jakob for the fine job recreating this EQ.

David.

 

[finbase]

Hello folks!

I'm just starting to build this "el classic" eq...

Nevertheless, the 2x 100k rev log pots are indeed very hard to source...
Would these work, what you say? Did I finally find them?

http://www.audiomaintenance.com/acatalog/om-01-059_extended_info.html

 

[JMan]

AML is a good source for these sorts of things, so as long as the 7.5mm pitch is correct (just measure on the pcb if you aren't sure, but I'd bet it is), that's probably your best bet.

 

[jasonallenh]

Hi Frank,

that´s what I did before already. But it´s always good to do it twice.

I sloved the problem meanwhile.

It was a short around the 6n8 by IC5a. Now the other half of my calrec is working too and it sounds very good.

I will do more tests and compare it to other EQs soon.

Thanks for help.

Cheers

Telltale sign of this is having ICs as hot as the surface of the sun. There's a couple points on the PCB that are VERY easy to short

 

[finbase]

Hello folks...
I got the PCBs from Pusherman. Excellent quality and fast customer service!

Nevertheless, there are a couple spots that differ from Jakob's original PCB, and I can't locate them in the schematics either...
Namely the link/insert point and the 22uf cap quite nearby to it... Please see the picture attached!

So, the questions are:
-Should the link/insert points be wired together, or should I just leave them as is?
-22uf cap's orientation is obscure... Which side is positive (+), how should I orientate it?
And the last, and a rather embarrassing n00b question, but I've never done it, so here it goes...
-How do you wire the power on-off LED? What kind of LED is to be used (size, type?) and where the wires go?

 

[blackart777]

Very good EQ great project, thank you all for the help, sharing your mistakes, your advice, it's really very useful.... and of course thanks to Jakob Gyraf audio.

 

[gyraf]

Darn, it looks good, that one

What front panel is that?

Push-button caps from where?

/Jakob E.

 

[wlinart]

Darn, it looks good, that one

What front panel is that?

Push-button caps from where?

/Jakob E.

I think the frontpanel is from pusherman: Gyraf Calreq EQ Stereo – 19″ 2U Anodized Black Aluminium Panel – Pusherman