Posts: 54
Threads: 11
Joined: Sep 2018
Country:
Question: How much residual AC ripple is acceptable for the negative bias supply?
Posts: 522
Threads: 58
Joined: Aug 2018
Location: CANADA
Country:
Hi jmcd
You say my bias supply without a reference to a schematic?
The ones that are actually mine have large filters and extremely low hum as a result, and are tied to the correct points to follow galactic Ground principles.
Every supply node should have the lowest ripple possible, within reason of complexity, cost and circuit context. For an SE amp, cost or complexity must be spent to assure a quiet output, where push-pull has inherent power supply noise rejection when balance and thus the latter can have a noisier PSU but be quieter overall than SE.
Have fun
Posts: 522
Threads: 58
Joined: Aug 2018
Location: CANADA
Country:
Hi jmcd
Note that earlier the Cs were small and now they are large; should be 100uF in all positions.
Have fun
Posts: 176
Threads: 27
Joined: Oct 2018
Location: United States
Bio: I'm 34 years old and work on MI amps and do some cattle ranching.
Country:
Looks interesting! What is the pre-amp design?
Posts: 522
Threads: 58
Joined: Aug 2018
Location: CANADA
Country:
Hi jmcd
Guitar pickups have the usual parasitic elements of inductance and capacitance and these vary with the design and the manufacturing consistency. The latter can manifest itself with how the wire is wrapped - is it neat, tight layers, or does the bulk of turns simply fill the space? neat winding leads to both pickups sounding the same and sounding the same from one guitar to the next. Loose windings may be "vintage" in a way, although I doubt any manufactured pickup was made that way, and definitely gives uniqueness to each pickup and thus to each guitar.
In any case, it seems like a damping resistor would be the simplest fix to employ; just place this across the output of the offending pickup ahead of the volume and tone controls. You could get fancy and use a cap in series with a resistor, but that would be difficult to tune without using a scope. As soon as I write that, I realise doing it by ear is about the same as adding the R and tweaking that by ear.
Posts: 176
Threads: 27
Joined: Oct 2018
Location: United States
Bio: I'm 34 years old and work on MI amps and do some cattle ranching.
Country:
JMCD,
If it has Burstbuckers that's would also explain your troubles. Those pickups are unpotted and purposely wound with uneven coils. I had some at one point and they squealed with high volume and high gain. I liked using them to get feedback at low volumes for recording but eventually tired dealing with the noise.
Most of the of Gibson pickups are well potted and are supposed to have even windings...I'm interested to see how Kevin's suggestion works for you.
Posts: 36
Threads: 7
Joined: Feb 2019
Location: MESA AZ USA
Bio: Having Fun.
Country:
How did you make the front panel? Looks great.
Posts: 54
Threads: 11
Joined: Sep 2018
Country:
Thanks! I get my panels from Mason at TMI Amplification. He's on a tube-amp-builders group on FB.