I had lower, but it is all over place
Once settled down, it was just a few mv,
But after playing a while, I got 1.1 volts.
This is in open air, hoping chassis helps.
Otherwise I can't be comfortable...I
Like circuits to be inherently stable. I am sure this one is,
I must have something amiss. Design is solid I am sure.
Russellc
Once settled down, it was just a few mv,
But after playing a while, I got 1.1 volts.
This is in open air, hoping chassis helps.
Otherwise I can't be comfortable...I
Like circuits to be inherently stable. I am sure this one is,
I must have something amiss. Design is solid I am sure.
Russellc
The preamp. I tried a little experiment with regards to offset. Placed a pillow case on top of the wooden board all of this is on, placed the circuit boards back on top of the cloth. Hooked up the multimeter, placed my small cardboard box over the boards, then folded the pillow case up over the whole mess. I figured this would be a little more "wind proof" and indeed the offset seems more stable. Mostly single digit mv, plus or minus. Still moves around bit, but not like before.
Takeaway is that hopefully putting this thing in a case should help out with the offset drift. Hopefully having something to ground things to will stop the hum.
Russellc
Yes, at this stage it looks like having the boards isolated from outside is solving the offset problem, and I believe a chassis may very well provide necessary grounding for the hum.
Really nothing to change, other than what I did as an isolation experiment. Only other thing I would try at this time would be how things are grounded, and this is very limited with no chassis.
Russellc
Really nothing to change, other than what I did as an isolation experiment. Only other thing I would try at this time would be how things are grounded, and this is very limited with no chassis.
Russellc
6L6, I have a question about one of your pictures in post #38. The middle picture ( one of the whole apparatus spread out chassis-less) shows a wire, larger dark wire with red shrink wrap on it, on end nearest the circuit board going underneath the green alligator clip on board closest to camera. It appears to attach onto the ground of that board. The other end of this wire goes past your volume control board and disappears off picture.
What is this wire? Its going to power amp, right?
Russellc
What is this wire? Its going to power amp, right?
Russellc
Last edited:
After much knob fiddling with pots, it seems offset is under control while snuggled in it's pillow case bed.
On fire up, they show around 15 to 40 mV, settling down to 1.2 or so, up to 7 mV and back down, then after a while, 1.1 to 4.5 mV.
Happy with that, now if the hum can be tamed once chassis gets here.
Russellc
On fire up, they show around 15 to 40 mV, settling down to 1.2 or so, up to 7 mV and back down, then after a while, 1.1 to 4.5 mV.
Happy with that, now if the hum can be tamed once chassis gets here.
Russellc
