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PostPosted: Tue Jan 16, 2018 7:54 pm 
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I wired the champ primaries and mains so it would hit the fuse first, then the switch. Now, the volume switch acts like a master on/off (which i prefer tbh), and there's some nasty hum from quiet-ish to full loudness. I even connected the main hot to the tip of the fuse holder like Morgan recommended in another thread. In my picture the pen points to the new red wire that connects the black and brown primaries to the switch. The switch turns on with a lot of crunchy static.

I've also included a very, very accurate and to scale layout of what I did. Also, it's worth noting that before i changed it, when plugged in and in standby (switch off) there was an almost buzzing sound coming from the speaker. Either input, or nothing plugged in at all, and nothing changed if i touched the transformer. However as soon as the switch turned on, the noise went completely away, and the amp was dead quiet all the way to 12. What have i done wrong? Thanks in advance for any help!ImageImage


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PostPosted: Tue Jan 16, 2018 9:42 pm 
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I would suggest moving the white wire on the middle lug of the volume pot away from the red wires carrying the AC mains current. I'd switch it over to the other side of the pot, closer to the input jacks, if it will reach. Otherwise, pull the red wires away from the pot toward the turret board. I'd reconnect the cloth-covered red wire on the other side of the white wire, rather than running between it and the chassis.

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PostPosted: Wed Jan 17, 2018 9:53 am 
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Ok sounds like a plan. Since I have to order a couple of things to finish the amp, i think i'll get shielded cable to replace that white wire all together.

Just out of curiosity, why does the switch function differently now, and why wasn't there humming before?

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PostPosted: Wed Jan 17, 2018 10:47 am 
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That's a good question. I'm hoping that Morgan pokes his head in on this thread, since he's much stronger on these vintage Fender circuits than I will ever be. Or maybe Keith/byoc, "the Boss."

One thing I would double-check would be all of your power transformer, output transformer and AC mains wiring, to make sure that all the connections are correct and secure. Also check your chassis ground points and your input and output jack wiring.

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PostPosted: Wed Jan 17, 2018 11:19 am 
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Was there something wrong with the way it was before? If you must do a mod where the fuse connects directly to the mains before a switch, I would suggest connecting the common mains wire to the switch and the neutral mains wire to the fuse, so that the fuse and switch are not in series.

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PostPosted: Wed Jan 17, 2018 12:05 pm 
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It's mostly piece of mind knowing the power is hitting current protection before any other component. But to answer your question, yes there was. With the switch in standby (off but power to the heaters, etc), there was a buzzing type of hum.

The common, neutral, white wire whichever you'd like to call it, is still connected to the primary center taps. So i'm not sure how it would be connected to the hot in series.

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PostPosted: Wed Jan 17, 2018 12:34 pm 
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I've taken DVM's tip and relocated the white signal wire altogether. The hum is mostly gone, but i'll replace it with shielded wire anyway. Thank you for the tip!

The switch is still very scratchy when turning on and off and actually makes a buzzing sound on volume "0". I've checked that my grounds are tight and soldered properly. Bad switch perhaps?Image

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PostPosted: Wed Jan 17, 2018 12:47 pm 
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robgar91 wrote:
The switch is still very scratchy when turning on and off ...Bad switch perhaps?

It's pretty normal to have a little pop or something when turning on these amps. Are you saying the the volume control is scratchy when you turn it? Or are you talking about switch noise when the power is switched on and off?

robgar91 wrote:
...and actually makes a buzzing sound on volume "0".

This could mean there is DC voltage on the volume pot, or you might be getting a ground loop. Check for DC voltage on lugs 2 and 3 when that noise is happening. You might also try moving the ground wire on the volume pot (the black wire on lug 1) from its location near the filter caps to a the ground lug on the closest input jack.

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PostPosted: Wed Jan 17, 2018 1:29 pm 
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Switch noise. I'm not really used to rotary on-off switches so it may be normal.

I'm getting 0.00v DC on the lugs of the volume pot. When i tested the lug on the left that connects to ground, there was a quick bluish flash from the 6v6. That must've been why you didn't mention lug 1 lol.

Since the left lug and the body of the pot both connect to ground, wouldn't that cause a ground loop?

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PostPosted: Wed Jan 17, 2018 1:35 pm 
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Maybe arcing your 6v6 is the secret lol. Now there is no buzz at volume 0 and the noise from on to off is not as bad.

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PostPosted: Wed Jan 17, 2018 6:18 pm 
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robgar91 wrote:
Since the left lug and the body of the pot both connect to ground, wouldn't that cause a ground loop?

Nope. The lugs are isolated from the body.

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