Electra muddy sound goes away with an input buffer

[nonost]

Hi. I'm building a LaVache (the Madbean project about the Lovepedals' Les Lius, which is an Electra distortion) and I'm having a problem: it sounds dull.





When I put a buffer in front, all the highs come back and I get the tweedy sound you expect from this pedal. I've built a few of them in the past and didn't had that issue. It's really strange...I build them the same, the same wire lenght and everything.

I tried it with an extra really short input wire (like 4cm) without luck. It's driving me nuts.

Cheers!

[anotherjim]

R1 could be a lot less than 1M? That would make the guitar dull and a buffer in front would fix it.

[nonost]

I removed R1 and it didn't make a difference. It's really weird cause I'm testing it with the same guitar+cables+amp as always and didn't had this issue before.

[GibsonGM]

Error in a component value dropping input Z, but still allowing it to work??  Strange symptoms. Gain pot actually 500k?  Shots in the dark.

[anotherjim]

Compare the collector voltage with the one that does work.

[iainpunk]

Compare the collector voltage with the one that does work.

i dont think bias is the issue, as it does work properly with a buffer up front

Error in a component value dropping input Z, but still allowing it to work??  Strange symptoms. Gain pot actually 500k?  Shots in the dark.

an extremely low input impedance can sometimes be an issue wit really low Hfe transistors, or transistors where the C and E are swapped around. i deliberately use it in some fuzz builds, but i could imagine an overdrive sounding like ass.
yours might be turned around 180°, maybe give rotating that transistor a try

cheers

[amptramp]

This doesn't address your problem but the shape control behaviour is weird.  It is shunted by D1 and D2 so the zeners never get to the reverse breakdown voltage.  In the symmetrical position of the shape control, Z1 antiparallel with Z2 do not allow each other to get to their zener voltage and of course, they are shunted by D1 and D2 anyway.

The fact that other builds of the same device have been successful points to either a bad (or reversed) transistor or a wrong part.

[nonost]

Thank you all for your help, guys.

I always measure every component before soldering. I checked every part when debugging and then make another board from scratch and ending up having the same issue.

I don't see the problem with the shape switch. In the stock position there are a couple diodes with the higher Vf (.6v). Then the right position puts a lower Vf diode to ground so you have asymmetrical clipping (.6v & .3v). The left position puts two .3v diodes to ground so the "stock" ones are bypassed since these two have lower Vf.

Pretty weird. With an easy input buffer (either jfet or opamp) there's no issue. Of course I tried many transistors: 2n2222A, BC108B, PN3565 and 2N5088. I used this same transistors in the past.

[duck_arse]

perhaps you would be so good as to post a photograph of that which you have built, just so's we can see what you say is true. not that we don't believe you, but we do like to look anyway.

[iainpunk]

This doesn't address your problem but the shape control behaviour is weird.  It is shunted by D1 and D2 so the zeners never get to the reverse breakdown voltage.  In the symmetrical position of the shape control, Z1 antiparallel with Z2 do not allow each other to get to their zener voltage and of course, they are shunted by D1 and D2 anyway.

The fact that other builds of the same device have been successful points to either a bad (or reversed) transistor or a wrong part.

i think they mean Schottky, not Zener diodes there, atleast, that would make a lot more sense

cheers

[Steben]

With the boost on, input Z is expected to be rather low.