Hum Pot adjustments [resolved]

ArtnShit · 4701

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Offline ArtnShit

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on: February 23, 2022, 06:19:26 AM
Hi,

Total noob question- Trying to adjust the humpots, but I am getting nothing on my meter. My meter is only capable of reading the lowest scale of AC as 200V, not 200m, is it just not sensitive enough?

Thanks!
« Last Edit: March 01, 2022, 08:16:43 AM by Paul Birkeland »

a&s


Offline Doc B.

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Reply #1 on: February 23, 2022, 06:52:39 AM
Could be that's the issue. Try connecting the amp to speakers and putting your ear right up against one speaker. Trim the hum pot on that channel for lowest noise, then repeat on the other channel.

Dan "Doc B." Schmalle
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Bottlehead Corp.


Offline ArtnShit

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Reply #2 on: February 23, 2022, 07:18:20 AM
I hear only a little hiss from the tweeter in either speaker, nothing my SS amp did not have.

I am only getting sound out of the left channel now, though. Any advice on how to troubleshoot?

Using V1 Klipsch Cornwalls if that changes anything.

a&s


Offline Paul Birkeland

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Reply #3 on: February 23, 2022, 07:19:05 AM
How were your voltage checks? Are both of the trim pots turned all the way up?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline ArtnShit

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Reply #4 on: February 23, 2022, 07:21:02 AM
All voltage checks were in the appropriate ranges. Trim pots were not turned all the way up, they are both all the way left. I cannot discern a difference with changing them.

« Last Edit: February 23, 2022, 07:23:21 AM by ArtnShit »

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Offline ArtnShit

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Reply #5 on: February 23, 2022, 07:23:51 AM
Oops! I meant humpots, both trimpots turned all the way up.

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Offline Paul Birkeland

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Reply #6 on: February 23, 2022, 07:27:04 AM
One common problem that we find sometimes is that some speaker spades don't always fit well into our binding posts, so I would start there. 

Otherwise the path of debugging your issue would involve likely both posting some photos of the build of the non working channel, as well as potentially playing a 60Hz tone into the amp and taking some AC voltage measurements in certain spots to see where the signal isn't making it through.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline ArtnShit

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Reply #7 on: February 23, 2022, 07:39:42 AM
I am not using spades, just putting the speaker wire into the posts, but that has always been fine in the past for me. Here are some pics of the full build I took. I am wondering if my connection to the right input is not so good. When I turn the amp on I hear the low-pop from both speakers if that helps with anything.




a&s


Offline ArtnShit

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Reply #8 on: February 23, 2022, 07:49:33 AM
Also, I can take more in-depth pics if needed.

a&s


Offline ArtnShit

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Reply #9 on: February 23, 2022, 09:25:51 AM
I am preemptively adding some more pictures of the right channel.

a&s


Offline Paul Birkeland

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Reply #10 on: February 23, 2022, 09:37:56 AM
The two things I see are a strand or two of wire hanging around the trim pot that may be shorting the signal out, and possibly the center pin connection to the RCA jack is low enough that it's touching the outside portion of the jack.

What DC resistance do you read across the RCA jack?  Something well below 100K would confirm one or both of the above are causing some problems.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline ArtnShit

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Reply #11 on: February 23, 2022, 09:41:56 AM
What two points would I measure to read across the RCA jack?

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Offline Paul Birkeland

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Reply #12 on: February 23, 2022, 09:49:34 AM
The center pin and the outside.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline ArtnShit

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Reply #13 on: February 23, 2022, 10:04:35 AM
I am getting 100.4 with my meter set to "200K" in the resistance section. Is this normal?

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Offline Paul Birkeland

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Reply #14 on: February 23, 2022, 10:10:37 AM
That is what's expected. 

What I would suggest is picking up a meter with a lower AC voltage setting, an old phone/tablet with an 1/8" headphone out, and an 1/8" to RCA adapter.

Harbor Freight has a meter for about $25 that can resolve low AC voltages.

With these items in hand, we can trace signal through your amp. 

One other thing you could try is to unscrew the C4S board and tilt it up out of the way a bit, then post a picture of the 9 pin socket wiring.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man