6505+ crackling noise

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mark77
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6505+ crackling noise

Post by mark77 » Sun May 01, 2022 4:35 am

Strange crackling noise when the CLEAN channel is selected and the LEAD Pre is up (no crackling if the LEAD Pre is all the way down).
If I switch to the LEAD channel you can still hear the crackling noise, but if I turn the CLEAN Pre all the way down it's even more. :mad:
https://soundcloud.com/vince-skyler/sets/6505-crackling
I cleaned the contacts and replaced the tubes.
I also tested the amp with both a speaker and a load-box.
Same behavior.
Any idea?
Last edited by mark77 on Mon May 02, 2022 2:19 pm, edited 1 time in total.

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Enzo
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Re: 6505+ crackling noise

Post by Enzo » Mon May 02, 2022 12:30 pm

So something is making noise in the lead channel and it leaks into the clean. Fix the lead noise and I bet the issue resolves itself.


First get a good 1AX7 and substitute it for each preamp tube going down the row. ANy change? Just refreshing tube pin contacts might help. Other ideas, ribbon cable contacts might be iffy.

mark77
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Re: 6505+ crackling noise

Post by mark77 » Tue May 03, 2022 4:04 am

I asked the technician to check the plate resistors first, because I have a problem like this: https://www.youtube.com/watch?v=wcorr4JQC80.
But even on the Clean channel the sound is strange, at least at low gain levels.
Very thin and almost fragmented, as if the amp was having trouble to reproduce it.

mark77
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Re: 6505+ crackling noise

Post by mark77 » Wed May 25, 2022 3:46 am

Resistors checked. They are ok.
Did anyone have a similar problem?
Any solution...? or the tech has to check everything...

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Enzo
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Re: 6505+ crackling noise

Post by Enzo » Wed May 25, 2022 7:28 pm

Only way to check resistors for noise is to put them in operating circuits at voltage. measuring their resistance tells us nothing about noise.

I suggested a number of things earlier, did your technician try them? They are the way we generally start to narrow down the problem. The entire circuit is involved with amplifying the sound, noises can come into it most anywhere. We use techniques like turning down the volume to see if the crackling also turns down, that means the noise is coming from BEFORE the volume control. Alternatively if the volume control has no effect on the noise, then the noise comes from after it.

A technician doesn't just "check everything", he uses a systematic approach to find the source of the noise in your amp. It could be a tube, it could be a resistor, it could be a cap, it could be a poor solder connection, it could be a cracked or broken copper trace on the board, it could be a connector, etc.

mark77
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Re: 6505+ crackling noise

Post by mark77 » Thu May 26, 2022 4:25 pm

I cleaned the contacts and tried different tubes (as I wrote in the first post).
The technician has also considered the case of the ribbon cables and will check them.
As you said, it can be anything.
That's why I posted the audio files; because I was hoping someone had a similar problem and could tell me how to solve it.

mark77
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Re: 6505+ crackling noise

Post by mark77 » Tue May 31, 2022 9:56 am

After the technician checked the amp without detecting any problems, it was clear that the issue was the electrical system or an interference (EMI/RFI).
I tested the amp on every electrical outlet in the house, and the further I went from my room the more the crackling was reduced until it disappeared in the room farthest from mine.
And the problem was ...? Powerline (WIFI).

Now my question is ... since they all work on the same frequencies (2.4 and 5 Ghz), is it possible to shield the amp?
Because my electrical system is old and the conduits are very narrow and I can only pass an ethernet cable externally.
And then if the one who lives above or below me decides to use powerline, what do I do ...? :lol:

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