Zen Drive Black Magic issues

[ac30irons]

Hey all,

I have just put together a pcb for the Zen Drive Black Magic. There is little resource available for it other than the attached schematic. Iv subed the ic for a 4558.

Well - it farts, and it’s a bit of a shart in the decay of a note. It all starts well until the note dies off and then it glitches out. Iv been through with an audio probe and the issue begins at the drain of the MOSFET.

Can any one spot anything off with the schematic, it was traced sometime back.

Cheers

 

[jwin615]

No DC bias on the gate?

 

[Robert]

That 15K drain resistor seems awfully high.

 

[ac30irons]

That 15K drain resistor seems awfully high.

So out of pig headed mess I have built another and socketed the drain resistor. Tried everything from 1k to 20k to no avail

 

[jimilee]

If that’s from the tdpri, it’s not verified, if that helps.

 

[Robert]

"I put a BS170 in the schematic but I honestly don't know what it is, the markings are sanded off. Could be a 2N7000 as well, who knows."

https://www.tdpri.com/threads/school-me-on-the-black-magic-zendrive.798622/post-10291868

Considering the values and the biasing arrangement, I'd try a JFET in there.

 

[ac30irons]

If that’s from the tdpri, it’s not verified, if that helps.

I believe it was - and if nothing else, we can verify it unverifiedness !!!

 

[ac30irons]

"I put a BS170 in the schematic but I honestly don't know what it is, the markings are sanded off. Could be a 2N7000 as well, who knows."

https://www.tdpri.com/threads/school-me-on-the-black-magic-zendrive.798622/post-10291868

Considering the values and the biasing arrangement, I'd try a JFET in there.

Thanks my man - it’s past my tinkering time now but I will report back tomorrow.

 

[ac30irons]

So, tried a J201 - Nope, Tried a 5457 - yep.

It every now and then, glitches, is the best way to describe it, mostly if sliding up and down the low strings - really weird, you have to work quite hard to make it happen. It’s a bit like a synth or octave that isn’t quite tracking correctly.

Thanks for all the guidance on this one.