JHS Kilt Schematic

[rmjlmartin]

Hi everyone, and thanks in advance for your help.

I'm looking for a schematic for the JHS Kilt, preferably the v2. I basically want the distortion circuit, and I don't care about the boost in the v1 Kilt.

I know it's a modified Bixonic Expandora, and I have schematics for that and a couple of diy clones, but I'm trying to find out exactly what changes JHS made, since I have an Expandora EXP-200R (the third, "reissue" version), and the Kilt sounds very different from it.

[thesmokingman]

thinking about this logically, whatever JHS did is covered somewhere else either as an existing expandora mod or rat mod because the rat is the basis for the expandora ...  is there some specific change in the sound vs the expandora that you're trying to reproduce?

[rmjlmartin]

I have a friend who would like me to build him a Kilt clone. There are several diy Expandora clone boards available, and unless JHS did something that significantly alters the circuit, I'm assuming it would be a matter of finding out what component values were used and substituting them in the build.

[somnif]

Unfortunately the only PCB pic I can find is too low res to read part values.

https://cdn.shopify.com/s/files/1/0795/2349/products/Kilt-Circuit.jpg

There appears to be a 10 pin thing on the underside of the board (I'm guessing that's something to do with the "red remote" offboard switching given its tied to the indicator LED), and they're obviously not using LM308s on it, but beyond that I don't see anything super deviant from a bog standard expandora. I'll dig a bit more though.

[rmjlmartin]

Great, thank you!

[Boba7]

I don't think there's much difference between v1 and v2.
Here's a cleaner v1 gutshot. It seems they chose NE5534 instead of LM308n. I imagine the compensation cap must be a much higher value. And an NE5534 in a Rat does sound different that the LM308n.

I really can't imagine JHS inventing anything, so it must be a very standard Expandora with all switches on top and a different chip, and that's about it.

[thesmokingman]

5534 is internally compensated and would be fine if not preferable in the first op amp position, I'd still want the 308 for the "rat" op amp for the way that op amp handles the feedback loop configuration. I'll grab an expandora schematic and go over a few more tweaks:
the diode coming off the first op amp should be the same kind you use for clipping in order for the opto-fet to function the way it is supposed to.
you can increase the size of the 22n between op amp 1 and 2 for a little fuller sound.
the bass switch on the three switch expandora included switching in a huge electrolytic cap in parallel on the output cap ... I believe a 10uf ... speaking of which I believe the output cap on the original was 100n and ended up at 1u on the three switch version.
I'd probably keep the output cap at 1u and make a fat or bass switch that puts in the 6u8 cap in parallel with the 2u2 cap in the feedback loop of the second op amp like the proco fat rat's fat switch
I'd also consider the Timmy's treble control values for the tone control of the expandora.

[rmjlmartin]

Hi again, and thanks for the tips.

I'm sorry to be so slow replying, but my internet has been out.

I also now have access to a Kilt v2 that I can trace, so I'll try to do that and see what I can come up with. I know I won't be able to get values on all of the surface-mount components, so hopefully between that and your suggestions, I can get something together. I'll get some gut shots, too, if the rest of you are interested in seeing them.

I've ordered some NE5534 op amps to start with, and I already have a diy Expandora built, so if there aren't too many differences, I may try modding it. If there are a lot of differences, I'll just start from scratch with another board.

Thanks again!

[rmjlmartin]

Hi again. I've had a chance to do a bit more here.

I've traced the circuit on the Kilt, and it is mostly the same as the Expandora. I'm going to be building it out of a pedalpcb Pandora's box board. I've attached the schematic from that build document for reference.

And here is a gut shot, hopefully clear enough to make out everything- https://www.facebook.com/photo.php?fbid=10210843030630540&set=a.2957504195380&type=3&size=1152%2C2048

As best I can tell, the main differences are the op amps and capacitors. JHS doesn't use the pulldown resistors (R1 and R20 on the pedalpcb schematic) and has a couple of extra capacitors in the power supply section, which I assume doesn't really matter. All of the resistor values seem to be the same, except that the Kilt doesn't have R12 and R14 in the schematic.

The cut/flat switch switches between C5 (C14 on the schematic) and C18.

The 10-pin ic that's on the other side of the board does appear to be associated with the red remote jack and also changes the led color when G2 is turned on.

I can't read any of the values of the small surface mount capacitors, and I'm not exactly sure how to read the electrolytic caps. On the electrolytics, I'm assuming that the middle number is the value, and that it's measured in uf? So C1 and C3 would be 100uf, C5 would be 10 uf, C12 and C15 would be 4.7uf, and C13 would be 2.2uf?

So I guess I'm going to have to experiment with some capacitors. Which ones affect the tone of the pedal? C4 in the schematic was already suggested. Do I just need to be prepared to experiment with all of them in the signal chain? Any thoughts on what the compensation caps (C6 and C8, C2 and C6 in the schematic) should be changed to for the NE5534 op amps?

Again thanks very much for your help!