calrec PQ1549 help thread
« Reply #20 on: March 28, 2005, 11:07:01 AM »
Dont forget me   :shock:  :cool:  :oops:  :razz:

Gustav


gyraf

calrec PQ1549 help thread
« Reply #21 on: March 28, 2005, 11:24:58 AM »
I don't think there's any altered orientations between these two versions..

Jakob E.
..note to self: don't let Harman run your company..

calrec PQ1549 help thread
« Reply #22 on: March 28, 2005, 01:14:51 PM »
Quote from: "gyraf"
I don't think there's any altered orientations between these two versions..

Jakob E.


Ok.Ill just try to fire it up with the 33u as they are now then....

Thanks !

Gustav

calrec PQ1549 help thread
« Reply #23 on: March 28, 2005, 06:32:38 PM »
It's sounds great, They are matched well and then I tested with white-noise in stereo at different Q values, the low-end was the only Q that was a little different, and I'm sure it was a pot variance.

I put the 33u's in as show in the PDF, I put the top on and racked it this morning, I can draw but I visually checked the top board. (hard to do upside down).  The PDF was what I used to verify, because that you can use 300%+ zoom in and see a piece of the + in the picture, on the circuit board you got a viarable place on the drill hole and sometimes you could see the + and sometimes not on the board.
I don't think I saw any conflicts, that would have prompted a post.
I'll unrack it again and re-re-verify, don't suppose that could account for the gain variance?

is anyone getting a db gain when the eq is engaged at a flat response curve?

calrec PQ1549 help thread
« Reply #24 on: May 05, 2005, 12:10:58 PM »
Has anyone ever resolved these questions?  I just finished one channel of the EQ, with Gustav's latest board (rev 5?) stuffed according to the silkscreened legend.  Everything works, but I also have the extra gain everyone else does.  So the two unresolved calrec issues seem to be:

1. Extra gain.  Has anyone tried swapping the 5.1K's for 1.5K's?  However, I might actually use this gain to my advantage, as a make-up gain when cutting dB.  I plan on putting an attenuation pot on the output (unless there is a better approach availible for output gain control).

2.  Backwards polarized caps.  Tracing the layout I find two elecrolytic and two tants that don't agree with the schematic.  They are the 22u and 33u located beneath the lo-mid Q switch, and the 22u and 33u located below the Hi freq dB pot (33u not on latest rev).  Gustav, I can't see the pics that you posted earlier.  Is this what you found too?  Finally, are there any issues with these caps being backwards if they aren't seeing a strong DC bias?

An by-the-way, the EQ sounds absolutely wonderful.

calrec PQ1549 help thread
« Reply #25 on: May 06, 2005, 12:48:19 PM »
No, I haven't tried swapping.
and haven't solved the issue.

The only thing that seemed to concern me is gain structure issues,
I'd like to hear the EQ with the right staging and the bypass working.

It becomes kind of a pain with such a gain boost when using it as a insert on a daw.

Gus

calrec PQ1549 help thread
« Reply #26 on: May 08, 2005, 11:13:03 AM »
I just looked at the schematic the gain part is easy.  You have to much gain with the eq in?

  Look at the top right of the schematic make the 100K pull down on the opamp a 10k to 100K audio pot connect the 22 ohm to the wiper your done.

  I would try a 10K pot and a 220uf cap.

EDIT 05-11-2005 The above it not good information.  I did not read the schematic correctly I looked at it fast and thought I saw a unbalenced output

However I was talking on the phone with a member of the lab tonight.   There might be an answer to the gain issue and a possable cool mod soon.

calrec PQ1549 help thread
« Reply #27 on: May 21, 2005, 02:07:24 PM »
I just traced the board layout myself and noted that the 5.1K resistors on the negative input of the op-amps are not replaced by the 1.5K resistors.  The 1.5 K resistors on the board are part of the hi/low shelving circuits and are correct.  

The 5.1K resistors in the schematic are actually 6.8K, 5.1K, 6.8K, 20K on the board.

I have ran my EQ through a spectrum analyzer and everything works correctly.  My overall gain from inserting the EQ is 6.5 dB with a flat response.

calrec PQ1549 help thread
« Reply #28 on: May 21, 2005, 02:45:43 PM »
Ok, like in the original schematic.

But, why is it +6.5db at all, should these not be modded since
this isn't a module in a consnole to have no gian whatsoever when
engaged?

we know the 5 resistors now, right, I'm not a designer, but
should it not be a very simple addition of the bands with higher resistor
values to compensate?

calrec PQ1549 help thread
« Reply #29 on: May 21, 2005, 04:07:22 PM »
I'm pretty much lost on this one too.  It is a terrific box and I am quite happy with it as is.  It's more about understanding how it ticks that's keeping me going.  I also struck out with an attenuation pot.  I tried a variable attenuator similar to what NYDave used in his passive summing mixer (fixed 2K series resistors on + and -, 10KA pot as shunt).  The problem was that the output distorted when I rolled back to just below unity gain.


Nele

fried component
« Reply #30 on: June 24, 2005, 10:32:47 AM »
After a while one of my two calrec channels stopped working. I traced the signal and the problem appeared to be in ic 10A/12A. To the test the ic I dropped it in the output stage of the working channel but I accidently put it in the wrong way.. As I powered up the unit smoke appeared from around the opamp. Figuring I had blown up the opamp I replaced it, but now the unit is distorting! The smoke probably came from another component but I can't see which one.. Any ideas?

The problem on the other unit turned out to be a tiny solder blob shorting the opamp... So now the tables are turned.. the initially working unit is fried and the broken unit is fixed!

adios,
corneel

gyraf

calrec PQ1549 help thread
« Reply #31 on: June 25, 2005, 04:52:03 AM »
check powersupply lines. change opamps one at a time.
..note to self: don't let Harman run your company..

Nele

calrec PQ1549 help thread
« Reply #32 on: June 30, 2005, 03:28:05 AM »
I changed the last two op-amps (11 and 12) and the unit is working again! Strangely enough when I re-inserted the 'fried' opamp(s) there was no distortion anymore, just a decrease in output gain.. In the end one op-amp turned out to be faulty but I replaced the last two to be safe.

Thanks Jakob for your help and designing this unit! :sam:

Adios
Corneel

gyraf

calrec PQ1549 help thread
« Reply #33 on: June 30, 2005, 04:07:06 AM »
Good that you got this fixed.. :razz:

Your problem can very well have come from the unit being fed 48V phantom power by error. The output opamps won't survive this (like many other line-level devices) - so you better keep your phantom under strict control.

Jakob E.
..note to self: don't let Harman run your company..

Nele

calrec PQ1549 help thread
« Reply #34 on: June 30, 2005, 04:28:27 AM »
As I'm not using the XLR's inputs on my desk but balanced jacks (non phantom-powered) that wasn't what happened here. The only thing I did was accidently reverse the output op-amp in it's socket. This caused a lot of smoke and seemed to fry the opamp.. After replacing the opamp there was still a lot of distortion in the channel but after replacing the opamp prior to the output opamp (11a/12b) everything was fine. Time will tell if something else has been damaged but at the moment the unit is behaving very nicely.

Adios,
corneel

gyraf

calrec PQ1549 help thread
« Reply #35 on: June 30, 2005, 06:08:42 AM »
:thumb:
..note to self: don't let Harman run your company..

cannikin

calrec PQ1549 help thread
« Reply #36 on: July 01, 2005, 12:28:06 PM »
Might have found my issue.. :shock:
Tube limiters..yum!

cannikin

calrec PQ1549 help thread
« Reply #37 on: July 01, 2005, 09:51:50 PM »
Ok I didn't find my issue...  :mad:

I am getting absolutely no audio passing through my stereo calrec.  Bypass works.   :roll:

I have checked everything - solder bridges, cold joints, wrong value resistors, cap polarity, replaced IC Sockets.  De-soldered, re- soldered. Made another Mini-PSU.  Nothing.....   :sad:

I have no idea whats happening..  I put a 1kHz signal through the unit and traced it.. around the 1k5 resistors the sound gets really weak. In the Low/Low-mid Pcb I'm not getting any signal to trace.

One thing that I also notice, is that when I hook up my VM to try and read any voltages vdc anywhere with reference to ground.  I get Negative readings.   Example: If I measure Zero out the Mini-PSU with Neg. Probe (black) and the +18 from the Mini-PSU with the Pos. Probe (red)  I get a reading of -18vdc.  then if I take the POs Probe a measure the positive side of a tant or electrolytic I get Negative readings (like -500mV).  I have no idea what the next step is.....  :cry:

One last question, Im not using the bypass LED..  Do I need it to complete the circuit?   Thanks.
Tube limiters..yum!

gyraf

calrec PQ1549 help thread
« Reply #38 on: July 02, 2005, 04:39:51 AM »
- check that your +18 is actually working at the PSU, 7818 pin3. Then check that it reaches the PCB's (measure at all IC's pin8).

- bypass led is not needed for the EQ to work.

Jakob E.
..note to self: don't let Harman run your company..

cannikin

calrec PQ1549 help thread
« Reply #39 on: July 02, 2005, 09:53:21 AM »
Quote from: "gyraf"
- check that your +18 is actually working at the PSU, 7818 pin3. Then check that it reaches the PCB's (measure at all IC's pin8).
Jakob E.


Thanks Jakob.

I checked +18 as you suggested and its definitely NOT +18.  the reading is fluctuating all over the place.   Across 7818 & 7819 I'm unable to get a constant reading.  

For the bridge rectifier is 1.5A OK?  

I'm going to check my Toroid and make sure thats wired correctly too.
Tube limiters..yum!


 

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