gyraf

calrec PQ1549 help thread
« Reply #40 on: July 02, 2005, 10:03:39 AM »
Quote
For the bridge rectifier is 1.5A OK?


Yes.

Measure your voltages with reference to 0V. Check that the 7818 has good input voltage (>+21V). Check that the +voltage reservoir cap is good, connected and working.

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


cannikin

calrec PQ1549 help thread
« Reply #41 on: July 04, 2005, 05:15:14 PM »
thanks Jakob

I had my PSU wired incorrectly.  now I'm getting voltage through my unit.
I switched to 15v PSU.  

Pin 8 of my 5532 is reading 13.78Vdc  (too Low?)

I'm still not getting audio through either unit.   Did a third check of solder bridges .. found nothing suspicious.

Other than that..... Any thoughts as to a next step?
Tube limiters..yum!

gyraf

calrec PQ1549 help thread
« Reply #42 on: July 05, 2005, 02:17:56 AM »
- Check if any of the opamps gets hot. Replace if one is hotter than others.

- double-check all electrolytics that touches the +15V rail, one may be reversed..

- Look for DC at all opamp outputs - if there's more than say 100mV, something is wrong either in that stage or in a previous one.

- Trace signal through the unit. Look at the schematic - and check signal after each eq stage.

- make sure that all ic's gets both + and - supply (measure from top, directly on pin) Also check that none of the opamps has pins bent underneath them when inserted in sockets.
..note to self: don't let Harman run your company..

cannikin

calrec PQ1549 help thread
« Reply #43 on: July 06, 2005, 01:58:20 PM »
HI jakob,

I want to thank you for all your help.  I found my issue by tracing the signal- it was such a silly over-site, I'm embarrassed to post what it was :oops:

Sounds great!

One thing I noticed is that if the High Freq Pot is "all the way up" and db Pot at 80%.  the unit will squeal.. ouch :roll:

I'll re-check everything.. but the unit is still quite usable.. thanks again.
Tube limiters..yum!

calrec PQ1549 help thread
« Reply #44 on: August 11, 2005, 07:01:18 AM »
I finally got my two channels powered up , sent some signal through and have a minor things.

1.The bypass switch on one channel has no "click"  :?  - It doesnt work, even if I hold it in. Anything I could check there, or do I "just" need to replace the switch ?

2.Ive seen this mentioned somewhere, but cant find it in any of the threads linked from the Calrec meta - I have a boost with the eq in set flat. Was there any solution for this ? Its not a big deal, but for A/B I would like it to be even.

Gustav

JayDee

calrec PQ1549 help thread
« Reply #45 on: September 27, 2005, 01:40:36 PM »
I also have a boost while all pots are flat. But I don´t really like it as I think the gain is a bit too high in general.

What do you guys think will be the best way to reduce the gain.

Attenuation at input ?

Changing amplification at output ?

calrec PQ1549 help thread
« Reply #46 on: September 27, 2005, 02:02:31 PM »
I've been dealing with it in the daw.

I'd still like to know a mod way to fix it, because h/w bypass is useless
This way.  If there could be a simple attenutor knob when ingaged, that would rock, that way you could match to bypass..

But I'm not smart emough.

gyraf

calrec PQ1549 help thread
« Reply #47 on: September 28, 2005, 03:20:50 AM »
How much of a boost is present with controls flat and balanced input and output?

You could try changing the two 10K series resistors at the balanced input to something larger - say 22K should take you down 6dB etc..

I have no proto of this unit around anymore, so I'd appreciate if you could report back with a solution..

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

calrec PQ1549 help thread
« Reply #48 on: September 28, 2005, 01:13:03 PM »
Hmm.  Ok, should try that, it's after bypass so that should be cool.
I tried changing the 10k in the bal opamp feedback loop, but I don't understand it well enough..

calrec PQ1549 help thread
« Reply #49 on: September 28, 2005, 01:26:24 PM »
Jakob,

I'd love to have a gain adjust on the output of mine, as makeup gain/attenuation for the unit.  I also lack the design skills to do this.  Do you any suggestions?  Perhaps placing a rheostat where the 10K series resistors are?

Thanks,
Chris


gyraf

calrec PQ1549 help thread
« Reply #50 on: September 29, 2005, 02:38:41 AM »
Not a really good idea, as you need very good tracking of the two resistors to acheive good CMRR on the balanced inputs..
..note to self: don't let Harman run your company..

calrec PQ1549 help thread
« Reply #51 on: September 29, 2005, 09:45:15 AM »
So would a stepped attenuator switch loaded with metal film resistors be OK then?

Thanks,
Chris

gyraf

calrec PQ1549 help thread
« Reply #52 on: September 29, 2005, 10:44:39 AM »
yup, I don't see why not. It will change input impedance though - but this may not be a real problem..

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

cannikin

calrec PQ1549 help thread
« Reply #53 on: October 29, 2005, 10:20:23 AM »
Hey Gyraf,

Can you help me..

I'm trying to figure out how to wire some switches off the board.

I have no idea where to start, I have been looking at the schematic but I can't see it ...

First, what switches should I use SPST, DPST.. etc..
Tube limiters..yum!

Zee1usa

calrec PQ1549 help thread
« Reply #54 on: October 29, 2005, 04:24:04 PM »
Quote from: "Emperor-TK"
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.





This is what I have found also. "the 22u and 33u located beneath the lo-mid Q switch"  the + is labeled wrong on gustav pcb and perhaps the pdf since I believe his pcb was printed from that . According to the schematic it is reverse of the + printed on the pcb.


Jacob & Gustav may want to take note of this if they havent corrected this already. If you could take a minute and confirm this and let me know if i am just blind.

Also there are a few + that did not show up on the pcb, but looking at the schematic will show you the polarity in which they should be oriented.

 :cool:
Quote from: "jrmintz"
Dave,
 The most important thing is to finish something and let it be heard instead of f*cking around making the "perfect" album for twenty years.

calrec PQ1549 help thread
« Reply #55 on: October 29, 2005, 04:40:58 PM »
Hey Guys.
I dont remember what I had circled on the drawing, but I ended up just following the PCB layout PDF, and I have a kewl stereo eq with no problems. It does have the gain thing, but it hasnt caused me any problems, If it gets too hot I just back of the sends on my DAW insert points.  :?

Gustav

gyraf

calrec PQ1549 help thread
« Reply #56 on: October 31, 2005, 03:04:35 AM »
Yes - don't worry too much about the wrongly-polarized caps, as they all are placed at spots with no DC potential. We'll try to fix it at the next update (which could take a while..)

David,

To use "external" switches, you'll need to consult the schematic AND the PCB layout..

Chris,

How did the attenuated-font-end turn out ?

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

gain problem fixed!
« Reply #57 on: November 15, 2005, 03:03:55 AM »
Just to let everyone know who's having gain problems, the fix that jakob gave up top fixes the problem of extra gain. I swapped the two 10k's with 22k's, and I have the same gain with the eq engaged as I do when it is bypassed. Woo hoo! thanks jakob.

Erik Wofford
Stapes Audio

gar381

calrec PQ1549 help thread
« Reply #58 on: November 15, 2005, 01:31:19 PM »
Erik

Which 10k's did you swap??

GARY
RETIRED.....  from 51yrs in Show Biz

gar2520, gar1731,garAM10,gar918 DOAs at  http://capi-gear.com/catalog/index.php?cPath=71_72
NEW Sphere section  http://gar381interests.com/gar381interests.html

gyraf

calrec PQ1549 help thread
« Reply #59 on: November 16, 2005, 03:22:24 AM »
Thanks for the feedback, Erik!

Gary - look earlier in this thread: it's the two resistors in series with the input at the balanced input stage.

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


 

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