Peavey Foundation electronics rebuild

[Jordac]

Hi all,

I’m getting ready to rebuild the electronics in early 80s Peavey Foundation Bass. I have the schematic and have read some helpful posts. I have one question at this point; maybe someone can help. There looks to be a small capacitor connected to the output jack. At least I think that’s what it is, labeled M 103. I can’t find this on the schematic, or anywhere...

 

[AudioTaper]

Hi all,

I’m getting ready to rebuild the electronics in early 80s Peavey Foundation Bass. I have the schematic and have read some helpful posts. I have one question at this point; maybe someone can help. There looks to be a small capacitor connected to the output jack. At least I think that’s what it is, labeled M 103. I can’t find this on the schematic, or anywhere...

Are you trying to rebuild it exactly like a factory, using NOS/vintage parts? Or just to the factory specs using new parts?

What diagram are you going off of?
The cap is a 10nF, but I'm not sure what material. I'll post this over on the US Peavey Club page and send some help this way.
U.S. Peavey Club

 

[Jordac]

Thanks so much for your reply. I’m using new parts, matching old specs (mostly). To clarify, the cap in question looks to be between the ground wire from the bridge and the ground of the jack. I’m wondering what it is for...

 

[ctmullins]

I believe its purpose is to act as a fuse of sorts, to protect the player if the venue wiring is defective. Back in the day, older buildings with older wiring could be miswired in a way that could induce a shock to a player who contacted two different circuits, usually when playing a guitar/bass and grabbing a microphone. Nowadays this is much less likely to happen, but still possible.

I usually omit the bridge ground, and only add one if the instrument is unacceptably noisy.

 

[Jordac]

Thanks, that seems to be right. Does it affect the tone, where it is placed?

 

[ctmullins]

Thanks, that seems to be right. Does it affect the tone, where it is placed?

Nope.

 

[Jordac]

Would you think that a lower voltage DC ceramic (.01 uF) would make the most sense? We would want it to blow, if there were a short...

 

[ctmullins]

I would think so, but I’m not an EE.

 

[Tim Skaggs]

Hi all,

I’m getting ready to rebuild the electronics in early 80s Peavey Foundation Bass. I have the schematic and have read some helpful posts. I have one question at this point; maybe someone can help. There looks to be a small capacitor connected to the output jack. At least I think that’s what it is, labeled M 103. I can’t find this on the schematic, or anywhere...

Connected to the output Jack and what else on the other leg? Is it connected to the ground at the output jack? Sure it’s not your tone cap?

 

[Jordac]

It's not the tone cap. It connects between the bridge ground and jack ground.

 

[jmlee]

I believe its purpose is to act as a fuse of sorts, to protect the player if the venue wiring is defective. Back in the day, older buildings with older wiring could be miswired in a way that could induce a shock to a player who contacted two different circuits, usually when playing a guitar/bass and grabbing a microphone. Nowadays this is much less likely to happen, but still possible.

I usually omit the bridge ground, and only add one if the instrument is unacceptably noisy.

I had a Taylor T5 guitar and it actually had a fuse in it to serve the same purpose—and that's in a modern guitar.

 

[Tim Skaggs]

It's not the tone cap. It connects between the bridge ground and jack ground.

I agree that it’s probably an electrical safety item. I wouldn’t worry about replacing. Just use the one you have if it has good leads left

 

[bassbrad]

As an old timer who has more than once suffered a jolt from electrical systems I advise to never ever turn your nose up or back on any prudent precautions. The life you save may be your own.

 

[Crater]

It doesn't protect you by "blowing"...it protects you by limiting the current (mA) that can flow into your hands/body if your amp's hot and neutral wires were reversed. The safety cap still allows AC interference signals to be bled to ground.

 

[Jordac]

Thanks for the replies. I appreciate understanding this better now. The old cap seems fine; easy enough to leave it in.

 

[Jordac]

It doesn't protect you by "blowing"...it protects you by limiting the current (mA) that can flow into your hands/body if your amp's hot and neutral wires were reversed. The safety cap still allows AC interference signals to be bled to ground.

Gotcha; thanks for the explanation. I’m less familiar with how a capacitor is used for this purpose. I do plan to keep the old cap that’s currently there. More generally, how do capacitor values affect the level of protection when used as a safety cap?

 

[bigtone23]

Don't quote me on this, but this is what I remember from another Peavey bridge ground cap discussion from years ago...
I think a larger cap will limit more current, but at the expense of reduced string ground, so the pickup hum could be louder.
I'd stick with the stock value. Peavey already did the homework.