belton brick reverb woes

[pinkjimiphoton]

so, a while back i bought a cheap 40 $ reverb kit on ebay from landtone, went together quick and easy and worked perfectly. sold it to a friend who wanted it, bought another one, it came in yesterday and i built it again. it works, but the "tone <damp?> " pot, when turned down is causing a weird distortion to ring out in the brick above certain input levels.
i looked at schematics til i was blue in the face trying to find a match, but no dice..
the "build doc' that came with it was nothing but a BOM... and i'm not confident, after past experiences, that the brick can be removed safely  to try and trace the circuit. it LOOKS like it connects the wiper of the "tone" control to the input of the dwell control, but i can't seem to find where the other two connections go..i believe they go to a pair of 22n caps on the board.. there isn't much there.
do you think i may have smoked one of these caps? i'm thinking dc is getting thru somehow, and making the brick distort. i've tried reflowing every joint and circuit disturbance <you know, whacking the bejesus out of it against my bench to make it mess up> but no dice.

there really isn't much IN there, its got 4 film caps, 4 electros, and maybe 10 resistors if that. i'm kinda stumped.

i requested a schematic from the vendor, and got 4 lame pictures that are no help. attached.

the tone control is the single pot. the mix and dwell are side by side on the other side of the board.

i'm betting someone else has had this issue, so.... help/advice appreciated!

[vigilante397]

I know it won't have a schematic, but can we have a link to where you bought it from? Somebody may see a hint that would give away what it is, or at least what it's based on.

[pinkjimiphoton]

here ya go, nathan
https://www.ebay.com/itm/192662775787?ul_noapp=true

[vigilante397]

Wow, that had even less information than I expected I'm afraid I may not be much help on this one. But I've done a few different BTDR-2 builds, if you want to post your voltages I can at least take a look there and see if anything sticks out to me.

[Mark Hammer]

here ya go, nathan
https://www.ebay.com/itm/192662775787?ul_noapp=true

I found your problem.  According to the vendor, "Our instruction is on the PBC of the klon."  So apparently you have to buy a klon, or at least a klon kit, and you'll find the instructions there, on the PBC...whatever the heck that is.

[Kipper4]

Two dual op amps. Could be culture jams Box of hall alike?

[pinkjimiphoton]

i messed with it some. thought i had it working, but no, the guitar was turned down a bit.
it distorts badly at a full level guitar signal, like, paf's around 8k. the other one didn't do that.
cursing myself right now for not socketing the 5532's. i suspect therein lies the problem.

it happens when you turn the tone control full clockwise. either pin of the tone control goes to its own 22n cap to ground. the wiper connects to pin 3 of the dwell control. the dwell control works, but as soon as ya turn the tone control up above about 9:00 it starts to distort, very similar sound to a blowing up fender reverb. i'd think blocking cap failure, but there's really only them 22n's, and they're both to ground.
i rewired the whole mess a little cleaner, wondering if that shitty ribbon cable i bought way too much of was to blame, but no difference.
i replaced the two 22ns with chicklets from the red polys that were in there.
the brick seems to be working. the clean signal is strong, the reverb signal too, but that tone control deal is problematic. i don't think  its the pot, i'm thinking a cap somewhere... but there are none other than the electros in the power supply. pretty much it appears to go in a chip, out of it, to the brick/dry then mixed together.

right now, my money is on a bum 5532, as the right side pinout voltages on the two chips are completely different.. the one to the right is reading

5  4.5ish
6  is reading .05ish
7  is reading 9.25ish
8  is reading 9.70ish

the other is reading

4.5ish on pins 5-7, and 9.70ish on pin 8.

i gotta literally hop in the shower and fly out the door, gotta gig tonite. i will get actual voltages tomorrow at some point.

thanks guys.

yes, probably based on CJ's HOF i'd imagine. i gotta look at that one close, thanks for the tip. been trying to find a 3 knob one but i think it may be easier once i sit down with something close and take a hard look at it.

peace

[vigilante397]

Two dual op amps. Could be culture jams Box of hall alike?

That was the first thing I thought as well, but the tone control threw me off, Box of Hall just has Mix and Dwell.

From what you said with those voltages though it looks like you're right Jimi, those are not friendly op-amp voltages. Break out your favorite solder removal device and see if you can get it out

[samhay]

I don't recognise the circuit, but the resitor values suggest a cludge of Belton's stock circuit (39 k's, etc) with a sprinkling of other design elements - probably similar to the Box of Hall with dwell control.

The Belton bricks have AC coupled input and outputs, so I wouldn't worry about feeding DC into them via the dwell or tone control. Worry about the op-amps.
If the tone control is set up conventionally, then one of the lugs will be connected via a cap - 22n is likely - to ground. If the cap is shorted, the tone control will vary the DC into the final op-amp stage and any mixer stage for the brick.
Have you measured the voltage on the op-amp pins while twiddling the tone control?

[anotherjim]

5  4.5ish
6  is reading .05ish
7  is reading 9.25ish
8  is reading 9.70ish

We don't know exactly what that amp is meant to be doing without a schemo, but if the 5532 isn't fried, it looks likely that pin 6 is short to ground somehow.

[pinkjimiphoton]

just got up a few minutes ago... i know, i know, but i didn't get to bed til almost 5.

i will try twiddling the tone knobs and checking voltages. i DID check the pins on the 5532's, no shorts,.. so i'm guessing the one with the weird readings got fried or might have just been a junk one out of the gate.

i'll write voltages down when i'm down there, and scan the bom, too. think the next step is to replace the opamp. the tone and dwell are both part of the same circuit as far as i can tell.. looking at it? i don't understand it at all... but they both do appear to connect to that same opamp on the side thats messed up.

thanks brothers... a little wee bit closer. its a nice sounding reverb when it works, so what the hell, maybe its worthy of a trace, too. ripping off the chinese guy for a change... just kidding. i gotta lot of respect for all us geeks.

but turn around, they say, is fair play, right?

[pinkjimiphoton]

lazyness wins out again. i dicked around with it all nite and finally got it working, went thru a couple changes.

i swapped out the weird opamp for a known good one, no difference. i checked and rechecked everything, re-flowed any suspect joints to make sure i had good penetration thru the holes to both sides even. no dice.

then i was thinkin... in an amp, a blown cap or a TOO BIG cap in a reverb circuit can make this kind of sound..

so i thought, wait a minute, too much bass?

there are two caps in the "tone" control. they basically just feedback to the mix and dwell controls. one is a 22n to ground, the other was a 22n to... beats me where, i couldn't find continuity anywhere on the damn board i THINK it may have gone to one side or the other of the closest 100u cap, but i could'n't get a reading.

anyways.. that cap, i snipped one side of the lead, jack darr style and temporarily grafted in a much smaller cap, 3.9n instead of 22n. bingo. no more noise. too much bass was getting in i guess and overdriving the brick. limiting it made it so the dwell and tone now work great, and even with multiple fuzztones POUNDING that sucker i can't make it overload now.

so i guess this one is cracked for now. i have no doubt i'll end up doing one of these for someone else again, so i'll do the tracing THEN.

if not.. sorry
thanks for the advice and help!