Guitar Amplifier Hum Varies with Volume Knob - Page 3 - diyAudio
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Old 9th September 2013, 03:43 PM   #21
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This is exactly why some guitars come with 250K pots and others have 500K pots, and modern bright players put in 1M or 2M pots.
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Old 9th September 2013, 03:45 PM   #22
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I'm going to have to experiment with this soon for finding a good match for my new Alumitone pickups.
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Old 9th September 2013, 03:56 PM   #23
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Fair point about the "virtual" series resistor being six feet from the actual grid pin - there could be definite issues resulting from the long cable run. I'll try the classic Fender "dark" input wiring with the two 68k resistors forming a voltage divider. The volume pot should be 250k (Squier Classic Vibe 60s Telecaster).
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Old 9th September 2013, 09:53 PM   #24
Enzo is offline Enzo  United States
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So we find the amp is incomplete, and has an input jack hanging by clip wires. Is the amp not enclosed in a chassis?

I can understand how the center position on the pot might maximize noise, but unless we have the pickups collecting it, we shouldn't have the hum. If you have bare wires running to your jack, they act as antennas for hum and noise. Correct that, and I wager your volume pot settings will matter a lot less.
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Old 10th September 2013, 08:14 AM   #25
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Quote:
Originally Posted by Enzo View Post
So we find the amp is incomplete, and has an input jack hanging by clip wires. Is the amp not enclosed in a chassis?
Way back in post #2 I asked him to post a picture, as his problem is most likely due to how he's built it - but he never has.
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Old 10th September 2013, 01:57 PM   #26
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Sorry, I'm not trying to be secretive - my guitar amp photo shoot time is just rather limited during the week. I mentioned in my original post that the wiring is a bit of a rat's nest at this stage. The attached photo shows the chassis prior to rebuilding the 12ax7 stage, for whatever that is worth. It should be noted that the guitar jack is simply posing there for the photo - during my prototyping, the chassis is upside down and the jack is on clip leads on the table. I'll try to be a good OP and follow-up this evening. I do greatly appreciate the help!



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Old 10th September 2013, 06:19 PM   #27
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Quote:
Originally Posted by SlunkBoy View Post
Sorry, I'm not trying to be secretive - my guitar amp photo shoot time is just rather limited during the week. I mentioned in my original post that the wiring is a bit of a rat's nest at this stage. The attached photo shows the chassis prior to rebuilding the 12ax7 stage, for whatever that is worth. It should be noted that the guitar jack is simply posing there for the photo - during my prototyping, the chassis is upside down and the jack is on clip leads on the table. I'll try to be a good OP and follow-up this evening. I do greatly appreciate the help!
It's the other side we need to see!
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Old 14th September 2013, 06:17 AM   #28
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Quote:
Originally Posted by Enzo View Post
I can understand how the center position on the pot might maximize noise,...If you have bare wires running to your jack, they act as antennas for hum and noise. Correct that, and I wager your volume pot settings will matter a lot less.
Yes, a high-resistance volume pot in a high-gain circuit is usually quietest at either extreme of rotation, and noisy in-between where it's not really connected to the pickups or the ground.

Yes make sure you are using high-quality shielded wire for all the wiring in the guitar, high-quality well-shielded guitar cord (not a speaker cord, not a cheap small-diameter soft-vinyl type with molded unshielded plugs and poor noisy braid shield) and use shielded wire from the input jack to the tube grid and put the grid series resistor and resistor to ground near the tube grid.

And replace your pot in the guitar with a lower value pot. The value and the way you wire your tone control in the guitar will also change the resistance from hot to ground and affect the hum.

You can also check whether you have too much gain and too much compression in the amp, which exaggerates front-end noise when there's no noise gate. Toward reducing the gain, consider installing that series grid resistor.
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Old 14th September 2013, 06:37 AM   #29
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so where did you place the volume control?
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Old 14th September 2013, 07:53 AM   #30
tinitus is offline tinitus  Europe
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if using 'onboard' active pickup pre, I suppose you should have DC protect cap on input of your pre/power/combo amp

is your guitar bridge properly grounded ?
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