jsteiger

Hello,

I built my LC25 a month back or so. Haven't turned it on in a little while because i've been busy with vacation and life.  It was working totally normal last time I used it, but for some reason the unit is not passing any audio anymore. When I bypass the unit, audio goes through, but once I switch it to active, nothing. I've tried different slots in my box to no avail. I do not have a spare DOA sitting around, should building another DOA and tossing it in be the first step?

Thanks,
Adam
Is your opamp fully seated?
http://capi-gear.com/catalog/DOA_Install.php
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jsteiger

Well, if its not the opamp it could be a bad/cold solder joint somewhere. If things were working fine and then stopped, that's usually the case.
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Well, if its not the opamp it could be a bad/cold solder joint somewhere. If things were working fine and then stopped, that's usually the case.

 I mean I had it on and working for probably 20 or so hours  so it wasn’t just a brief thing.  I’ll order up an op amp today and see if that doesn’t sort it out if not I guess I’ll have to start searching the board for other issues 😐

Hey Jeff,

Ordered a new 2520 and 1731 to see if the op amp helped. My unit is now working, but the 1731 has a very considerable amount less of headroom (something like 8db) before noticeable saturation. Is the normal or do you think I botched something on the 1731? Either way, I'm happy that the unit is working again!

jsteiger

Hey Jeff,

Ordered a new 2520 and 1731 to see if the op amp helped. My unit is now working, but the 1731 has a very considerable amount less of headroom (something like 8db) before noticeable saturation. Is the normal or do you think I botched something on the 1731? Either way, I'm happy that the unit is working again!
This is way not normal. There should be zero difference in headroom between properly built discrete opamps.
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This is way not normal. There should be zero difference in headroom between properly built discrete opamps.

Oops! Reversed the Q7 and Q8. Thanks Jeff!

The 5kHz gyrator is comprised of GR21, GR22, GR24, GC15 and GC16. Also half of A4 which is shared with 2.5kHz. If that is fine I would ASSume the chip is fine.

Hi Jeff,
I resoldered all of the resistors and caps listed above, as well as each point on the 5k knob, and the problem still exists... i might get a dB or two boost or cut at 5k with the knob FULLY cranked. I’m wondering if I should replace the two caps GC15 and GC16? Thoughts?
Thanks again for your time!
Chris

jsteiger

Hi Jeff,
I resoldered all of the resistors and caps listed above, as well as each point on the 5k knob, and the problem still exists... i might get a dB or two boost or cut at 5k with the knob FULLY cranked. I’m wondering if I should replace the two caps GC15 and GC16? Thoughts?
Thanks again for your time!
Chris
Post a pic of that section of the PCB. I wanna check and see that the R's are placed correctly.
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Post a pic of that section of the PCB. I wanna check and see that the R's are placed correctly.

see the photo below.
Thanks Jeff.
- Chris


jsteiger

see the photo below.
Thanks Jeff.
- Chris
Looks like you have GR14 and GR22 mixed up.
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Looks like you have GR14 and GR22 mixed up.
That did the trick! Thanks so much Jeff, I’ve said it many times... but you are “the man”! Cheers,
Chris

Hi. Just completed an LC25. At first power up, PR6 started to smoke, then the green active LED stopped working. Thanks in advance for any help!


Potato Cakes

Hi. Just completed an LC25. At first power up, PR6 started to smoke, then the green active LED stopped working. Thanks in advance for any help!

Read through this thread. You'll find things to check like op amp, solder joints, etc. Did you build the op amp? Did you power it up with no op amps installed? Are all of the ICs oriented correctly? Do you have an extension jig to test voltages?

Thanks!

Paul

duantro

I've built a LC25 and it works, but is distorted and the peak light is on. I'll check for bridges and placement of parts.

edit: I pulled 2520 out and powered up, to see if it was maybe an opamp issue. no clip light, but r17/ 10r  went up in flames!
I inspected gar 2520 and it looks like I misread the "do not bridge/ bridge these pins for support" I must be going colorblind. maybe these circles should be yellow and red, instead of maroon and red! I had bridged the input + pin to c1 on the 2520. I've removed the bridge and will look for another 10r resistor and try it again tomorrow.
« Last Edit: May 10, 2019, 08:36:15 PM by duantro »

Leon

Hey Jeff,

I am eyeing a pair of LC25 and LC40 and am curious about a modification.

Which resistors effect the gain of the grayhills? Would it be possible to modify them for smaller steps?

As in possibly these gain steps:

-9
-6
-3
-2
-1
-0.5
0
+0.5
+1
+2
+3
+6
+9

Could make for a cool mastering eq I think.

Normally this would be simple but looking at how you have the switches on the PCB it looks like they are actually sharing resistors? Is that true?

And if this is possible....can some custom faceplates be ordered? :)

Thanks Jeff!

Hello there. How is the mod going?

I would be interested in the mod also. The large gain step is the only thing that prevents me from ordering a pair of LC25. 

Thanks,
Leon

IanB

Just finished an LC 40 & a 25.
25 = perfect.
40: 40hz & 2.5k are inactive. I re-flowed those parts of the pot board and main pcb  today & just retested; still no dice.
I’m assuming the chips are fine as 80 & 5 work fine.
I’ll swap the pot board with the LC25 tomorrow and see if that works (my a keys are at work! Numpty!).
It also looks (in Q Clone) that 5, 10 & 20 are shelving, not bell curving which is weird, right?
Ian

jsteiger

Just finished an LC 40 & a 25.
25 = perfect.
40: 40hz & 2.5k are inactive. I re-flowed those parts of the pot board and main pcb  today & just retested; still no dice.
I’m assuming the chips are fine as 80 & 5 work fine.
I’ll swap the pot board with the LC25 tomorrow and see if that works (my a keys are at work! Numpty!).
It also looks (in Q Clone) that 5, 10 & 20 are shelving, not bell curving which is weird, right?
Ian
One or 2 things at a time...first like you said swap the switch sub assembly and see about 40Hz and 2k5. If that doesn't do it, post a pica of the gyrator caps and R's for those sections. Its super easy to mix up some R's that are 10x different.
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IanB

A1 section

IanB

A4....