Newbe question on ruby amp

Jump to Latest
P

Planobilly

Member
Joined 2015
#1
Hi guys,

First transistor amp build try not working. How the Ruby Works ( schematic at Rob Robinette.com)

I know next to nothing about solid state. Trying to trouble shoot.

I injected a 1000Hz signal at 250mv. Have correct wave form at gate. Have 9 volts at drain. No signal at source of of j201 JFET. 4K resister to ground from source verified. Schematic calls for 3.9K but I did not have one. I assume 4K will work. There may be other issues but I assume I have to solve the JFET buffer issue first.

The amp produces noise and popping/motor boating and noise is increased with increase of gain and volume control so I assume the LM386 is at least producing some amplification.

I ASSUME JFET is bad. Am I correct n this assumption?

Thanks,

Billy

Sorry to have to ask such basic questions...this is a new world for me.
 
Last edited:
#3
Is there any DC voltage at the Source??

JFET pin-outs can be confusing. Figure out exactly what part you have, find the datasheet, check that sheet for variants, figure out which way is up, and confirm you are wire right. Or use ohm-meter: two pins will be a few hundred ohms apart either way. These are S and D, and for audio it reallt does not matter which is which. The third pin is of course Gate.
 
#4
Yes there is .2 volts at the source. The mfg is indicated on amazon as todiys. everything I can find indicates D,S,G , same as Rob's drawing.

I think I will order some more from Mouser from Fairchild or some one who has a real data sheet.

I am getting a little worn out so I will get back into this tomorrow. Can you take the JFET buffer out f the circuit and have it still work?

Any way thanks and see you guys tomorrow.

Thanks,

Billy
 
You must log in or register to reply here.
Top Bottom