tooooo much gain at my new CALREC EQ (prev. pics inside)

Hi,

I just finished my new calrec eq...

signal passes thru ... all filters are working... it sounds great !!

... but I have around 20db more gain at the output, while no freq is boosted...

can you tell me where I should look for solder joints and faulty parts ??I tried to replace the lm833's but without success...
where on the board is the amp section for the whole unit ??

here are some preview pics...

cheers,
mat

http://www.soulset.de/forum/c11.JPG
http://www.soulset.de/forum/c21.JPG
[Edited by Ethan]

Hi Matthias.

Looks great!
Maybe theres a wrong resistor next to the ICs? (20k ohm)
Do you have a scope to trace the signal? Then you'll easily find where the 20dB amplification starts.
You could also use an old ghettoblaster with "line in" for testing... connect a probe to the "line in" connector. (maybe a cap for dc filtering then)
I would buy a scope or signal tracer from ebay for some bucks. :wink:
(could be a good investigation for the future)

Regards,
Frank.

Looks very, very good!
:grin:

Where do get this switches? Pot are Alphasts, right?

@frank: good idea.... but... for the future: i want to make music !!
i have reall enough gear, when my "reichelt-boxes" are empty some day...
(but I know, if you started diy once... you will never stop

@michael: the alps switches are from farnel...
the caps are also from farnell but from another manufacturer... you have to glue them on the switches, because they don't fit directly...

Matthias, I also started just to have a good preamp...

Hey there everyone, I just finished doing all the wiring for my Calrec boards and it seems that i'm having the same volume increase as Matthias. How did you guys solve this problemo?

Have you checked that all functions (on all bands) work? In that case, look for a short or a wrong component in the input or output circuits.

If one of the bands behaves funny, look for a short or a wrong component in that section.

If this brings no light, try PM'ing Matthias..

Jakob E.

Thanks Jacob! the db problem has been solved but a new one has popped up. The low-mid frequency pot creates some really horrible squealing feedback when it's turned almost fully clockwise. For the other 80% or so of the rotation everything sounds fine but at one certain point all this high frequency hash explodes and i'm measuring something like 3v or so off of IC9. Could this occur because i'm using sockets for the IC's or is there some other explaination? Thanks again!

Sockets won't interfere with anything.

What was causing your gain problem?

Oscillation at one of the frequencies could indicate too high a "Q" - check and recheck components and shorts at the band that is behaving wierd.

Jakob E.

Ok, Looks like I'm having the same realitive gain issue.
Mines only about 10 db.. All the bands appear to work.
I did most of a once over, because initially, I could only get it to work in bypass... That nice little insert section.. well, it was so pretty I forgot
to put the jumper accross it... It's really quite a pitty the out gain isn't on a pot, that's such a usable feature when it's not in a board. I've done a bunch of whitenoise band testing and have verified every thing is cool as far as pots and bands go. (The curves all look good and seem to react similar, I don't know what they are supposed to be but they look like a very sane small ^ Q and a larger /--\ Q.)

Any hints?

After scanning over the board several times, I now have confirmed each band to do both addition and subtraction with the same q's, it's just 10db louder, but a exact flat reproduction. I'd checked all around for a wrong 20k. Does each IC 6a,8a,10a,12a add back in gain?

Also on the scematic it says there are 4 5k1 resistors while the board
says they are 1k5 for the imput into these ic's.

There is also a 22u by the insert point that you can't see it's orientation on the pdf, and you can't see it on the pcb either. (course neither way has worked.)

Check if your level boost is after the input debalancer or after the output balancer..

I actually can't remeber what I did wrong, but I think I had put in some resistors with incorrect value...

So, just to respond in this thread too, at the output balancer, if I nullify it's gain, by shorting the 10k for it's IC, everything's peachy.
6a,8a,10a,12a all have equal step gains. I think I did this right, with no scope by:
Running stereo white noise, 1 channel direct, 1 channel through eq completely, attaching balanced portion of direct channel together and testing signal points on eq with direct channel's pin 2 to compare gain with point of the eq running as configured. bypass of course matched at both points. with bal - ic corrected a singal sweep with eq ingaged is -/+ 1db 20-20k.

So am I incorrectly adding or subtracting gain as I go along with 5k1's, or have I made a mistake somewhere, (I will built one more to see if I screw up again.) I'm checked the little balanced piece, there is only 7 things of relivance there right?

again you have to forgive me, I'm a newbie. Usually a bothersome one too.

I have been studying the Calrec EQ circuit topology by entering the schematic into Circuitmaker. So far I have only entered the HI & LO frequency sections because I wanted to explore the shelving action of the circuit.

But much to my surprise when the 10K gain pot for the HI section is cranked fully CW I am seeing 18db gain within the filter passband. When I do the same to the LOW section (HI section at 50%) I get a whopping 27db peak. Is that right?? That sounds like way to much gain to me. I am using the Gyraf website schematic marked as rev #1 and dated 08-10-2002. Has the schematic been updated? I have looked hard to find a mistake in my simulation but as of yet have not found one.

So did anybody figure out this gain thing?

Well, dug are you experienceing the 18+24db gain at unity with the eq engaged?
I asked if anybody else had the problem with their stuff.
mine works great except for this, it can be a pain in the neck.
I can be a nice effect too.
I suspect it's those

I am assuming if we make changes to the 4 summing amps it willl all work out less.

I am probably ignorant of electronics, but the 5k1's before the opamps on each summing opamp isn't in the original from what I can see, and I beleive it was discussed that at some point it was 1k5, but I see 6k8 and other such values before 6a, 8a and 12a on the original and I always see the 5k1 before the opamp in the rev I was trouble shooting before rev 5, so, although that feeback loop value is the same I thought you could adjust gain with the value before it, but again, I am ignorant..

I just know the frequency reponse and everything else is peachy on both of my channels it appears except the additional huge gain when engaging the eq, and the it's still quiet as you could imagine so it seems to be nice analogish gain that way, I've preceived anyway.

[quote author="cwatkins"]
Also on the scematic it says there are 4 5k1 resistors while the board
says they are 1k5 for the imput into these ic's.
[/quote]

Nobody replied by now but I'm currently also confused of that.

The redrawn schematic lists 4 x 5k1 but the parts list only 1 x 5k1. :?

In the original schematic there is one 5k1 on IC6A, a 20k on IC12A.
The values on IC8A/10A are hard to read but I would say 6k8, too.

As the parts list and the PCB layout plan also includes 2 6k8 but I haven't found one in the redrawn schematic I think the original is correct and the redrawn one has an error here.

if you still have gain probs try running the calrec unbalanced.

the pcb is correct but I also had problems with the schem. jakob once said there maybe some mistakes in the redrawn.

alo
i think the gain problem was fixed by jakob.replace the two 10k resistors that are in series in the input,by two 22k resistors.
best regards
pedro