calrec PQ1549 help thread

Digesting.......

I will work on this and report back here with my findings. Thanks so much for your help so far.

You already have scrapped off the isolation paint at the wire ends of your transformer ?

oh crap! That's not pre-tinned ends? That could be part of the problem my friend....

hi! im wondering if anyone can do some paintjob on the attached picture below. im not sure how to solder the audio ins and outs to the pcb. thank you! /jonas

http://www.pylons.se/kstrand/songs/calrec_eq.jpg

[quote author="Jonas K:strand"]hi! im wondering if anyone can do some paintjob on the attached picture below. im not sure how to solder the audio ins and outs to the pcb. thank you! /jonas

http://www.pylons.se/kstrand/songs/calrec_eq.jpg[/quote]
maybe this way
edit drawing see following post

yes! maby that way. and the black wires circles means i connect it to both those pins aha? and the black cables are from the same ground point on the pcb? mhm? harpo. you are a kind person. /jonas

[quote author="Jonas K:strand"]yes! maby that way. and the black wires circles means i connect it to both those pins aha? and the black cables are from the same ground point on the pcb? mhm? harpo. you are a kind person. /jonas[/quote]
? if you -not neccessarily- use shielded cable like cat-5 or mic cable, connect the shield to the pcb side only. If you don't use shielded cable but 2 single wires for xlr-pin2 to pcb +signal and xlr-pin3 to pcb -signal, drill these tightly together for each in/output, leaving the 0V pin in the middle of your in-/out pcb plug unconnected. Pin 1 of the xlr's connect to your case. Connecting your case/safetyground to supply-0V is a matter of taste. This drawing tidy up hopefully makes it more clear.

wow. thank you! and this is for balanced ins and outs? right?

/jonas

Hi everyone,

my first Calrec is working fine, but I've got a very hard time getting the second one to perform correctly. The PSU supplies voltage close to +/-15, which drops almost one Volt after the diodes. So all the opamps get +/-14V at the proper places, there's no detectable offset at any other pins. The unit passes audio, but the signal looses a little bass and much high end. What's even worse is that the low mid gain pot will change the gain of the whole signal, so much so that there is no output when turned all left. I've checked every connection multiple times, checked the components, changed some opamps etc. for more than half a day now and cannot find the problem. I read someone had a similar problem with a missing jumper, but those are all properly installed. Is there any obvious thing to look at from the schematics that would be in line with this outcome? Could the pots somehow be the wrong type (I checked them soldered in versus the ones in the second Calrec, and they behave the same). Is there an obvious component failure to check?

Thanks!
Gregor

Anyone? I'm running out of options...

If a single band's boost/cut pot affects overall gain instead of just the selected frequency range, then that band's filter isn't filtering.

Look at the schematic, compare to PCB, find and check the filter parts in question.

If you're absolutely sure there's no shorts (check with ohmmeter, not only by eye) - then look for order-of-magnitue errors in component values.

Jakob E.

Thanks Jakob, I've found and adressed these problem(s) now. I had checked and eliminated all accidental connections before, but there were two bad solder joints. Turns out self-etching the boards for this build wasn't the best decision to make...

Anyway, this EQ sounds absolutely faboulus, better than anything else I've ever used, including my Pultec (which will get better inductors now). Thanks for this great project!

There is just one minor flaw left to fix with my Calrec: On one channel the amplitude is at unity gain although it should be at around +6 db at the output (like it is on the other channel) with a balanced connection. Both channels are identical in parts. The output is balanced (I've measured), but the ampitude is too low. The signal to noise ratio of this unit is 10 db worse than the other one, there's hum and a high frequency sine tone at 8 khz (at -82 db peak). It also adds a minimal high end (shelflike) boost vs. the bypass. I've tried to trace the signal to see where the loss might occur, but couldn't to it. My voltmeter won't show any AC on the opamp rails, either measuring between +/- on inputs and outputs or to ground when running a 1k sine wave through the circuit (which I can measure on the in- and ouputs). How can I determine at which part in the circuit the problem lies?

Thanks again!
Gregor

[quote author="living sounds"]On one channel the amplitude is at unity gain although it should be at around +6 db at the output (like it is on the other channel) with a balanced connection.[/quote]
Hi Gregor,
did you measure only balanced (between +/- signal out) or between gnd/+ signal out and gnd/- signal out? For the 2nd option both measured values should be the same, case not, there may be a short between pin 1/2 of Op-amp BAL- or its connected traces, setting this inverter to a voltage gain of 0 (your missing 6dB). Just an idea.

Harpo,

thanks for answering. The output is balanced correctly, with the measurement between ground and + or - reading exactly half of the measurement beween + and -. I'm trying to trace the problem in the signal path, but that's sorta tricky...

Fixed it! There was another broken trace near the input. I'll never use a self-etched board for this kind of project again.

EQ sounds absolutely fabulous and the noise is around - 100db now. I've used 5532 for the (de)balancing and the low end and LM833 for the rest. Elma silmic II as electrolytics. Will post pictures and soundbytes soon.


Gregor

Hi all,
Just had a quick BOM question.

6,8n/63V RM 7,5 or 10mm

is that 6.8nF or is it saying either a 6nf or 8nf may be used?

Also the BOM only specifies Poly. Is that polyester or Polypropylene

6,8nF always means six-point-eight nanoFarad

Mylithra said:

Also the BOM only specifies Poly. Is that polyester or Polypropylene

Click to expand...

Or does it even matter?

..if it really mattered, it'd be specified...

Jakob E.

A small, but a problem nontheless...

one of my calrec - channel is dead when BYPASSED .. when IN it works like dream 

I can't think of anything else than a broken bypass-switch or a broken trace on the pcb....

It's a little hard to pull it out of the rack... so any tip before I do it is most welcome.

Thank's