calrec PQ1549 help thread

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thewotan

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Joined
Nov 26, 2019
Messages
16
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:


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!
 

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thewotan

Member
Joined
Nov 26, 2019
Messages
16
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

Member
Joined
Nov 5, 2020
Messages
14
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

Member
Joined
Nov 26, 2019
Messages
16
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

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Joined
Oct 29, 2005
Messages
2,400
Location
Rahden, Germany
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 4k7 (or 2x 4k7 in series) resistors limit the current needed.
 

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