Hum is a ground loop. It goes away if I unplug one of the inputs, doesn't matter whether L or R channel. How best to eliminate this?
Ground loops can be very difficult to resolve.
I had perhaps a similar issue on D Self's Blameless Class B and ultimately it appeared to be a design issue with the board grounding schemes and what happens when fed from a common supply.
https://www.diyaudio.com/community/threads/3-stage-lin-topology-nfb-tappings.101321/post-1623053
I had perhaps a similar issue on D Self's Blameless Class B and ultimately it appeared to be a design issue with the board grounding schemes and what happens when fed from a common supply.
https://www.diyaudio.com/community/threads/3-stage-lin-topology-nfb-tappings.101321/post-1623053
Don't worry about it, there may be no problem when installed in the owner's system.
In any event, he is not paying you to redesign the amp, just get it working..
In any event, he is not paying you to redesign the amp, just get it working..
I know but... Would lifting the ground line on one of the inputs do any damage?
I do see where the ground wires from the speaker terminals and the transformer attach to the front panel (star ground?). Would it help possibly to run a long ground wire there from the input jacks?
I do see where the ground wires from the speaker terminals and the transformer attach to the front panel (star ground?). Would it help possibly to run a long ground wire there from the input jacks?
Not as such in any normal setup but you must remember that disconnecting the connected input (the RCA lead) will then cause massive hum from the now non grounded but still connected input on the other channel.
Roger that. I guess I'll just do a final cleaning of the chassis and faceplate, button things up, and call it a day.
There's something to be said for getting experience, but I hope you're getting paid for this.
Most techs make $30 to $50 per hour these days, plus parts which are also marked up.
Shops charge twice that to pay the manager, rent etc.
But yes, the schematic (if correct) does show a ground loop. I would not mention this, but wait and see if he says he has hum.
Also there are potential "death caps" C2 and C3 connected from each side of the AC line to the chassis.
If these are not marked in some way as X or Y capacitors, or if they are just regular ceramic discs, those should be removed.
Most techs make $30 to $50 per hour these days, plus parts which are also marked up.
Shops charge twice that to pay the manager, rent etc.
But yes, the schematic (if correct) does show a ground loop. I would not mention this, but wait and see if he says he has hum.
Also there are potential "death caps" C2 and C3 connected from each side of the AC line to the chassis.
If these are not marked in some way as X or Y capacitors, or if they are just regular ceramic discs, those should be removed.
There are caps on the switch (C1,C44) that do appear to be just standard ceramic caps (0.01uF/1.4KV). There are also two ceramic caps where the mains line comes in (C2, C3) that also look to be standard ceramic (AE 0.01M 1kV) Not sure if the AE marking means anything but I have some 0.015uF/1.5KVDC (350VAC) film caps I can replace all of these with (unless the power switch ones dont need replaced).
R1, R2 are 5.6MOhm CC resistors with the special yellow 5th band indicating low noise or very stable (I forget). Lots of the components in the amp were Mil Spec types. I guess Winslow wanted to use the best stuff he could get, whether or not it would potentially bankrupt the company or not.
R1, R2 are 5.6MOhm CC resistors with the special yellow 5th band indicating low noise or very stable (I forget). Lots of the components in the amp were Mil Spec types. I guess Winslow wanted to use the best stuff he could get, whether or not it would potentially bankrupt the company or not.
Not trying to redesign, just to remove dangerous parts that would not be used in new equipment.
If he wants filtering, plug it into a filtered outlet strip.
If he wants filtering, plug it into a filtered outlet strip.
But why not replace with a proper safety cap and get the benefit of the filtering? Not trying to be contrary, but most times I've seen mention of "death" caps it was "replace with the proper type that fail open...X1/Y2".
Won't get involved in redesigning an amp that I've never seen, esp safety related.
But 50 year old ceramic capacitors don't belong on the AC line, if they ever did.
Even some X/Y types will break down at that age.
But 50 year old ceramic capacitors don't belong on the AC line, if they ever did.
Even some X/Y types will break down at that age.
Been researching...lots of info regarding them not being needed in an amp that has a 3 prong plug. Not going to go that route...the amp has only a two prong plug. I suppose I could remove them, see if the hum improves any, and if not, install safety caps in their place, if for no other reason than to keep the amp "schematic" correct, only with modern safety devices vs ceramic...i.e. not redesigning the amp....