Keeley 1962 clipping switch rebus

[razabri]

So, I've built this one using layout from - https://effectslayouts.blogspot.com/2019/03/keeley-1962.html
No issues in general and the effect sounds well and somewhat close to the original.

The thing is, I can't get my head around the behavior of the clipping, as within the circuit you have two options - hard and soft, switch would send the signal through the led, or through Mosfet for a different "flavor".

Issue I'm having is that there's to much of a difference between the two, for one, and, as I've been trying out different options (diodes, transistors), I've noticed that even when there is nothing in the slots, there's still level difference between the two positions of the switch.

One thing I think I got is that in one position the diode or transistor would go before and on the other after two 1n7000 diodes, if I'm reading it right, but even with that, why would the level change when there's nothing clipping the signal?

I have found a vero layout at a different place, and they have this part wired a bit differently - http://dirtboxlayouts.blogspot.com/2019/09/keeley-19621962x.html

At both of these posts in people's comments there's no consistency on what to expect, some have big differences, some almost none...

[stonerbox]

Hi, the fact that you experience volume difference with the switch in different positions, and with the diodes and MOSFET taken out, suggest the switch or something else is wired up wrong. Could you post your voltages? Two sets of them. One with the switch set to diodes and the other set to MOSFET (with the sockets empty).

Suggestion, bring out a flashlight and magnifying glass / phone camera zoomed in to check for solder blobs/bridges that might connect the socket pins.

Tried to find a schematic and found only this very low resolution schem on a French site. I tried to upscale and clean it up a bit but it is still pretty crunchy on the eyes..

[razabri]

Hey, thanks for reply! I thought so, about the wiring and all, but I've already triple checked everything (going a bit crazy about it), as it seemed logical to me too, that the wiring was off, but so far I can't seem to locate the issue. Thing is, I've noticed that clipping "element" one red led and in the other case MOSFET used as a diode, are coming from different sides of 4001 diodes, so I thought maybe that's the reason, but I know to little about circuitry to know if that makes any sense.

Sending the relevant part of the circuit with illustrations on how the clipping should occur - perhaps that helps...

[razabri]

Ok, something just occurred to me - with the clipping elements gone, we'll still have one of the 4001 diodes in the circuit, but switch would change between them, and as they are differently oriented, change in signal level would be normal, right?

[stonerbox]

If you have any of the diodes ( D1 [LED] , D2 [4001] or D3 [4001] ) left in it will make a connection from R18 (4,7k) to output pin (7) of the opamp and definitely change the volume. The 4001's act as clipping diodes too.

[razabri]

Yup, that's the case - looking at the schematic you provided (thanks), it's the same situation - on it, the switch is in the position to clip through the MOSFET, and if you remove it, still D2 is in the circuit, and other way around D3 remains, oriented differently, thus difference in level. But still, there's a big difference in level with those elements, and clipping through the red led diode is louder. I find them better leveled if I swap them between the slots, minding the polarity, as signal hits them from different side of D2 and D3. Not sure if the circuit is right/original, or someone drawn it from the perf layout and it seems to me that wiring could be done differently so that the signal always approaches from the same side of those diodes... Don't really know how I would change the layout to get there...

[stonerbox]

Why not just try reorienting D3 and see if that fixes it for you? To up the level of the MOSFET clipping. Really strange.. the MOSFET should be louder as is.

[razabri]

I might just try that one, but I wouldn't want to drift from the original, if the perf board layout is close to it to begin with.

[razabri]

Ok, so there's this schematic too, the one actually used to create perf layout - hope it reveals something more, as there are lots of pics of the original too, over at FSB. Perf board guy actually shared the link, somehow I missed it... There are some discussions there and at perf layout page, also at that vero board page, but it all seems a bit dodgy to me, without clear details about this clipping stage and what's happening in there, how close it is to the original, etc.

FSB thread on tracing it - https://tinyurl.com/5n7rnevx

[razabri]

Alright, so after reading few more descriptions, it seems like the MOSFET is mentioned as introduced to the circuit by the switch, so perhaps guys who traced this one made an assumption that clippings are bypassed - only led or only transistor, when it could be that the transistor is added and led remains...

Also, I'm not sure how to read that stage on the schematic from FSB, as clipping has two leads that I assume go to switch, but how?