60Hz and 120Hz hum and buzz

[dannysgrandpa]

I have a 1970 Fender silverface Bassman 70 that has been modded by means of an effects loop addition. I think this could be a contributing factor, but, the amp is very noisy. I've tried new tubes, some rearanging of the lead dress, and heat shrinking some exposed wire ends. This had very little effect on the noise. I've ordered some shielded coax wire for the preamp circuitry in hopes that I can make this amp usable. The filter caps are fine and voltages are within tolerances. Nothing looks burnt. Just some really crappy work on the effects loop mod. Also, the noise seems to be intensified, or, changed by the volume and tone pots. Any thoughts? Thanks in advance..... Bill

[Structo]

Check your grounding.

Some clear gut shots would help a lot.

[Phil_S]

1) That isn't a picture of a '70 Bassman, is it?
2) Is it 60Hz or 120Hz? 60Hz is roughly A# below the low E on your guitar. You can tune down your E string to match it. 120Hz is roughly A# on the A string.
3) Assuming it is 60Hz (this is a very low frequency, in range for a bass guitar), when was the last time the filter caps were changed? On a 1970 amp, they are likely to be way overdue and this would be my first priority even though I listed it as #3.
4) Shielded wire will suck tone. Try to avoid its use. This amp shouldn't need it. It won't help you with 60Hz hum from bad filter caps.
5) Have you put a patch cable in the effects loop? What happens?

[dannysgrandpa]

Sorry, the pic is my D*mble clone. I thought I was putting that pic in the side bar under my name, but, it wound up where it did. Haven't tried a patch cable in the loop yet, will do today. Will also check the filter caps. So, let me get this right...shielding the inputs and such is not a good idea? My clone amp has shielded preamp wiring and is the best sounding and quiet amp I've ever used. The Dumbles are basically modified Fender circuits with some added bells and whistles. I would think that shielded preamp and input wiring would quiet things down, but, I'll take your advice and leave things be until I check the caps and loop. Thanks, Bill

[dannysgrandpa]

Sorry, the pic is my D*mble clone. I thought I was putting that pic in the side bar under my name, but, it wound up where it did. Haven't tried a patch cable in the loop yet, will do today. Will also check the filter caps. So, let me get this right...shielding the inputs and such is not a good idea? My clone amp has shielded preamp wiring and is the best sounding and quiet amp I've ever used. The Dumbles are basically modified Fender circuits with some added bells and whistles. I would think that shielded preamp and input wiring would quiet things down, but, I'll take your advice and leave things be until I check the caps and loop. Thanks, Bill

[Phil_S]

So, let me get this right...shielding the inputs and such is not a good idea? My clone amp has shielded preamp wiring and is the best sounding and quiet amp I've ever used. The Dumbles are basically modified Fender circuits with some added bells and whistles. I would think that shielded preamp and input wiring would quiet things down, but, I'll take your advice and leave things be until I check the caps and loop. Thanks, Bill

Well, this is the stuff flame wars are built on. There is a small amount of capacitance from shielded cable. In most amps, it's simply not needed, so why get into that? I use it when I can't quench the noise otherwise. Check the caps and the loop first. Don't do stuff that isn't needed.

[Structo]

Yes but shielded cable is great if you want to shave off some top end.

Really I think that 1 foot of 30 pf/ft isn't going to change much and if it does, it's probably for the better.

Matter of choice. IMHO

And everyone knows what opinions are like.......