calrec PQ1549 help thread

[solderboy]

ok, finish with my build. unit ist running und sounds good so far. 2 smal problems:

- unit is to loud. saw other users got the same problem... can someon please show me the right resistors i have to change
- hi mid has a oscilator sounding problem, but only when i fully open the db pot

i was looking for the values of the resistors, seems everything is right. the directions of the caps are like in the rev.4 pdf...

someone?

 

[solderboy]

ok, i changed the 2 resistors in serie next to the balance ic. but seems it´dosnt solved the problem with the gain????

 

[solderboy]

nobody? help!!!!!

 

[Harpo]

nobody? help!!!!!

Why are you surprised when you say exactly nothing to identify the fault ?

unit is to loud. saw other users got the same problem... can someon please show me the right resistors i have to change

'too loud' by what amount ? Factor 2 or +6dB would be easiest to come by with increasing the two 10K input resistor values that connect between input caps 47uF||100nF and opamp IC-input-pin2 and pin3 to 20K each. Different 'too loud' factor will probably be one or more wrong resistor value(s) fitted or a shorted or open connection somewhere on pcb.

ok, i changed the 2 resistors in serie next to the balance ic. but seems it´dosnt solved the problem with the gain?

So by a 50/50% chance you changed probably/maybe prementioned resistors to what value ? Still no number for the 'problem with the gain'.

With unit powered on and all boost/cut pots centered for +/-0dB, measure the AC voltage between input-XLR pins2/3 at a frequency your multimeter can handle, maybe 100Hz. With your maybe doubled up input resistor values to 20K in order to compensate for the last inverting output stage for balanced output, opamp IC-input-pin1 will measure half this measured amount in respect to 0V reference voltage. Same 'half of input AC voltage' for IC6A-pin1, IC8A-pin1, IC10A-pin1, IC12A-pin1, IC-Bal--pin1. If so, you should have overall unity gain, else check for correct feedback and input resistor values at the stage where measured voltage rises to your 'too loud' voltage.

 

[solderboy]

Thank you Harpo!

And sorry for less descripton of the problem. by the way... my english isnt the best and it´s hard for me to finde the right words sometimes. i never got lessions in english... and your totaly right: what´s in my head is in my head and others can´t know it...

ok... i changed the wrong ones! i just saw in the pdf. that one ic is labeled as bal. and next to it i found to 10k resistors in series. nexttime i will take more time to follow the input. now i changed the right ones to 20k and this problem is gone...

Do you can also help me to locate the oslcilator sounding problem in hi mid? would be nice...

 

[Harpo]

Halfway there. With unfortunately missing parts designators of all caps and resistors on schematic and silkscreen, the describtion of a parts location for an identification can get lengthy.
Double check for correct parts values of resistors and caps (some are in nF, some in pF range) connecting to IC7B, IC7A and IC8B as well as the frequency setting stereo rev.log pot P2, the Q setting switch and the 5K1 resistor back to the summing node at IC8A-pin2. Check or maybe reflow solder connections to all previously mentioned parts and/or remove unwanted shorts.
Good luck.

 

[solderboy]

yeah, working fine now! can´t say what was the problem, think it was a unwanted solderbridge. also i canged the 2 resistors at the input to 22k to have really the same level like in bypass. nice sounding unit! by the way... can´t find any information about the db on each filter... how many + or - is it?

thank you very much hapo!

 

[mrkrawn]

Hello boys
congratulation solderboy.
I will buid this eq with quad pot for stereo  in a few days.
I've read this help thread and i i want to now if there are really reverse caps on the board rev5.
I prefer ask to you before do a thing i will regret
thanks by advance

 

[solderboy]

yes, it´s a 100k reverse audio log c-curve pot like in rev.4. for a mono pcb. i got the pots from "das musikding" in germany. they don´t have print contacts, but is working well. another ones i found here: http://www.audiomaintenance.com/acatalog/potentiometers_carbon_16mm_diameter_dual_gang.html but not tested yet.

i guess it will be difficult to find the pot in a quad option. if you find some please let me know. another option is to use 24 position rotary switches...

good luck!

 

[jicama]

Ok Mr. Postman arrived with my next projetc, Im searching for all the compenents from Magnus Johansson BOM, I have 2 questions and I will be very greatful if someone can answer:

1. resistors values, -+ 5% tolerance will work? I went to the electronic store but half of them are 5% tolerance

2. Switches, it says on the list SPUN19035A and SPUN19036A with a Farnell code below 733118 and 733120 but those codes are SPUN191400 and SPUN194700, can I use those with farnell code??

Thanks in advance

 

[G-Sun]

1. resistors values, -+ 5% tolerance will work? I went to the electronic store but half of them are 5% tolerance

I'm not an expert, but I guess +-1% metal film is the standard choice. Not hard to get.

 

[mokkinger]

hi guys,
I have some questions about the calrec EQ. I have two sets of PCBs, finished, one working, and one with a fault, that I would like to find and fix (I didnt populate the PCBs myself, got them from someone on a german forum...)

the PCBs with the fault are self-etched by someone based on gyrafs layout rev2, and the problem is somewhere around IC9b / Low Mid section. I already checked twice for solder blobs, wrong oriented components, and swapped all the ICs...
once I put in IC9, the EQ hums, and only passes audio in bypass mode. once I bridge pins 2 and 3 (the middle ones) of IC 9b it works (I use an oscilloscope to see how the ES slopes change), but then the Lo-Mid Section is disabled...

anybody has a clue what could probably be the fault? where should I continue to nail down the problem?

also a more general question about the stereo EQ: I have one set of Rev. 2 PCBs (the one above with the fault, they look self-etched without silkscreening)), and one of Rev 4 I think, looking newer and more "professional"; they have some parts from different manufacturers (caps mainly)... does it make sense to use these two sets in stereo mode in one unit? from the osc I cant tell the difference until now, but I dont want to put all things together and then realize that L and R sound different...

thanks for help on the falut and for a recommendation how to proceed (desolder different components and use new / same ones on both?)

best,
mark
 

 

[gyraf]

The versions are the same electrically in the pcb versions.

For your error, check continuity and isolation of tracks (and look through this thread for previous problem-fixings)

Jakob E.

 

[jicama]

How come u need  to conect 2 pcbs with the out? Doesn't has to be input connecting out??

 

[gyraf]

Does not compute. Please rephrase.

 

[jicama]

Does not compute. Please rephrase.

In both  pcb's says out... I don't understand conecting 2 outs

 

[gyraf]

look at the schematic, and then at the pcb layout.

 

[jicama]

look at the schematic, and then at the pcb layout.

So is the same  connection, like one pcb divide it in 2 pcb's

 

[jicama]

Hello there almost done with the Eq I only need to get the right pots, does any one knows if this will work?
http://www.ebay.com/itm/6-pcs-C100K-Dual-Stereo-Potentiometer-Reverse-Log-Taper-/400389912481?pt=LH_DefaultDomain_0&hash=item5d391937a1

I have dual 100k log pots, is it possible to wire one part of the pot  backwards?

Thanks for you help

 

[gyraf]

I have dual 100k log pots, is it possible to wire one part of the pot  backwards?

Won't work.

Have you read the page about the project? Some options are mentioned there.

Jakob E.