calrec PQ1549 help thread

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Harpo

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jasonallenh said:
OK, so in looking at the schematic and I'm realizing that according to the schematic, the Shelf Hi switch is supposed to have two decks...
It's a 4PDT (4 pole double throw, not two pole) switch.
... with no connection when ACTIVATED.
with only one of the 4 poles with no connection when ACTIVATED, the 3 remaining poles do connect to other nodes when ACTIVATED. Pg.2 of the schematic/pcb-layout pdf file doesn't show these minor errors from pg.1)
On the PCB, there is only one? Is this correct? My problem is definitely in the vicinity of the shelf switch (ic5b/ic3b gets hot too).
Shelf/peaking Hi-band is built around opamps 3b, 5a, 5b, 6a, 6b. These are dual opamps. How would you know only their b section gets hot?
 

jasonallenh

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Shelf/peaking Hi-band is built around opamps 3b, 5a, 5b, 6a, 6b. These are dual opamps. How would you know only their b section gets hot?
[/quote]

Because 3b and 5b are within the same LM833, according to the layout.  ;)

Flipping the shelf switch still results in no signal passing. The gain knob for the high section has no effect. I'm wondering how one would go about bypassing the band (which is effectively what is happening). This would provide a hint. I'm looking at the 47k resister in series with the wiper of the gain pot...

I'm still doing my own footwork, but I don't have a lot of troubleshooting experience, so hints are sooooper-valuable. I'm going to test the PCBs for continuity- maybe a trace is broken.
 

jasonallenh

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I'm beginning to probe my circuit. When I hit the hi-shelf switch, the signal dissapears from one leg of the hi gain pot... I still have it at the wiper, and 5b, pin 7, so i'm not certain that this is wrong...
 

jasonallenh

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OK! Progress!

Pin 8 of IC 5B was shorted to Pin 7 through the  20k resistor's pad. these are super close together, so they are very easy to bridge.

IF YOU HAVE AN OPAMP GETTING PAINFULLY HOT, CHECK FOR THIS!

I cleared the bridge, and now the signal is passing through to where it is expected. It's really late now, so I can't run a white noise test to verify that the shelving filter is working. However, I imagine since the signal is now present at all three pins of the gain pot, the filter will be working as expected 8)

Now for Channel 2 :p

Right now, the high mid gain control has no effect on the channel, and with all gain knobs set to 0, there's a partial and uneven loss of signal. With the high shelf at max gain, the unit looks like it's at unity :eek:

My first guess is that the high-mid filter has a similar short since the symtoms (no gain, and a hot opamp) are similar. Stay tuned...
 

jasonallenh

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I did a white noise test with all my sweeps, and there is no issue! I've got one fully functional channel now =)

I hypothesized that the 'hot opamp' issue i had in channel one was similar in channel two, and I was right! :eek:

Once again, pin 8 (this time on IC 7a/7b) was shorted to pin 7. GUYS! if you have hot opamps, check for this! You're essentially mixing supply voltage with signal bus, thus the heat.

I corrected this issue, then replaced the 10 input resistors with 22ks for unity gain. NOW my problem is significant signal loss. Taking the unit out of bypass drops the signal waaaaay low. I'll read back through the thread (pretty sure this came up) to see what I can do next. Signal doesn't completely disappear, it just drops about 26dbs.

I'd still like some hints if anyone could help me out  ;)
 

jasonallenh

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Still probing!

I found another short-

Symptom- almost total signal loss between the two connected lugs of the hi and hi-mid gain pots.

Solution- a short. The short was located next to the INPUT IC. If you look at the silkscreen, there are the four pads for pins 1-4 of the input IC. To the right of that are four pads  exactly in line with each other. the first two  are supposed to have continuity, and the second two are as well. My short was between the 2nd and 3rd. If you have a great deal of signal loss in your unit... check for this one. The pads are VERY tight right here, so it's very easy to unintentionally short. I cleared it, and now the whole unit is working...

...except for the low band's hi-q switch.  If I have a boost or cut in this band and I press the hi-q switch, it acts like a bypass and the boost/cut returns to flat.

I'd ask for hints again, but I'm fixing this thing faster than I'm getting hints 8)
 

jasonallenh

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Woke up this morning, had a good 'ol fashioned bacon and eggs breakfast, and went to work. It took me all of a few minutes to find the last short and get the Hi-Q to work in my Low band. Two fully working channels!! 8) 8)

I circled all the traces that shorted throughout this project and kept a log of the symptoms associated with shorts at those locations. I'll be putting together a short guide for US builders... this project is too good to not be seeing more traffic!



 

musika

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Great to hear you will post some debugging notes on the Calrec EQ.  ...And glad to see you got this running.

What did you use for a front panel?  Or did you drill your own?
 

jasonallenh

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musika said:
Great to hear you will post some debugging notes on the Calrec EQ.  ...And glad to see you got this running.

What did you use for a front panel?  Or did you drill your own?

Funny you should ask! My front panel should be arriving today. ;D ;D ;D

I found the FPD file on here somewhere (it all came as a .zip) and modified the design in FPD. I kept the scales (the same ones in Frank's design... I certainly can't take any credit for the panel, I only modified the existing design), got rid of all the infill ($$$), altered the labeling (really trying to cut it cheap here... I used "LMF" instead of "Low-Mid Frequency" less ingraving = less money), and added my logo, which I try to do for anything I build. I also modified drill hole sizes to match my pots/switches.

By the way, as a general troubleshooting rule for this project... TRUST THE DESIGN! all the silkscreen is right. Even those 'backwards caps' from earlier in the thread are fine as they are printed on the PCB. If you put the correct value components in the right places, this design works the moment you turn it on. Everything comes down to solder bridges. There are some pads that are impossibly close to each other, so you really have to be careful. I believe I am very good at soldering, and I still had four bridges total. 
 

tata

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could anyone please help me adding a Q pot instead of the switch?
im planning to build this EQ but one Band per PCB, so it would be kinda 'modular' - here is my redrawn schematics (Hi-Mid Band):

http://beatbybit.com/gears/Calrec/sch_Calrec_Hi-Mid_separated.pdf

if there are any mistakes in it, please let me know

i already built one PQ1549 on Gustav's PCB, and i think i need more.. but a different layout, and some mods.
 

musika

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Very impressive panel.... I like the background color and the knobs that you selected.  Makes it a little easier to see what you are doing.  Thanks for posting this photo.
 

jasonallenh

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musika said:
Very impressive panel.... I like the background color and the knobs that you selected.  Makes it a little easier to see what you are doing.  Thanks for posting this photo.

The knobs were tricky, the freq-select pots are 4mm D-shaft omegs, and the gain knobs were 1/8" bourns center-detented pots from CAPI-GEAR (I chose these because the center detent is much more accurate, so when the knob is centered, there is no boost or cut. others aren't quite that accurate).

That meant I had to source knobs that were visually identical while being mechanically (for different shaft sizes) different. I ordered a bunch of classic collet knobs direct from Elma -available in both shaft sizes- and they fit PERFECTLY. They also have a lot of cap colors available, with and without lines. I chose the colors based on the logo color scheme for my recording services logo-

http://www.ranchomolino.com/
 

musika

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Jason, 

This is great information on sourcing the pots for the EQ.  I had looked at the Omegs for the gain pots, but they didn't have the centers, and that's what I've been waiting on.  Now I just need the time to complete the builds.  I'll PM you about the front panel. 

Are the push caps round (what size did you use?)?  Hard to tell from your photo, they look somewhat cone shaped.
 

jasonallenh

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Yea. the gain pots were tricky... the leads aren't long enough, so I actually soldered jumpers on them to make them longer. The freq. pots were also an adventure... I couldn't source them cheaply, but I found a guy selling a ton of dual gangs with one rev log gang and one log gang. It was cheaper to buy double the necessary quantity and make the dual rev log pots than it was to order from omeg or import from AML.

The switch caps are C&Ks. These are also the pushbuttons I used. Datasheet here: http://www.mouser.com/ds/2/60/Fpush_1nov12-221205.pdf
 

tata

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jasonallenh said:
The freq. pots were also an adventure... I couldn't source them cheaply,..

arent the Alpha dual C100k ones good? 6pcs is about 6 USD on ebay (thats what i use in my builds)
the pins dont fit directly to Gyraf/Gustav's PCB, but its not too hard to bend one row of the pins or add L shaped pins to the solder lug version of the pot.

a new PCB layout for this circuit would not be a bad idea, what you think? at least adding multipins to different pots, switches, etc.

IMG_6952_pq1549_hi-mid.jpg

my demo build of only 1 band, but with small switch and Alpha pots.
 

jasonallenh

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tata said:
jasonallenh said:
The freq. pots were also an adventure... I couldn't source them cheaply,..

arent the Alpha dual C100k ones good? 6pcs is about 6 USD on ebay (thats what i use in my builds)
the pins dont fit directly to Gyraf/Gustav's PCB, but its not too hard to bend one row of the pins or add L shaped pins to the solder lug version of the pot.

a new PCB layout for this circuit would not be a bad idea, what you think? at least adding multipins to different pots, switches, etc.

IMG_6952_pq1549_hi-mid.jpg

my demo build of only 1 band, but with small switch and Alpha pots.

Are those 1/4" shaft? I'd have never been able to match the knobs if I had went that route... I kinda painted myself into a corner with the bourns pots. I saw the alphas, but none with shafts under 1/4"
 

tata

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if anyone knows a good way to replace the Q switch w/ a potentiometer, please dont hold it back..
a dual gang, high value pot? (1M and higher?)
 

gyraf

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If you really want adjustable Q, this will be a different EQ.

Maybe look at similar EQ architecture (state-variable filter) like the TC1140, the AmekM2500 or such.

Jakob E.
 

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