Peavey 6505MH hum problem at low voltage

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AntonioFinn
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Peavey 6505MH hum problem at low voltage

Post by AntonioFinn » Thu Mar 19, 2020 10:20 am

Hello!

AMP: Peavey 6505MH

The problem:

After few seconds, when I switch on my amp, it begins to hum (50HZ). The hum is emitted by outputs (speaker, and headphones), but not by „send”.
- The hum isn’t there above 230V, but if the voltage is lower than 230V
- The hum is stronger if the voltage is decreasing.
- At 220V the amp is useless, because of the hum loudness.
- The „resonance” level inluences the loudness of the hum.
- The switch on of the „Crunch” increases the noise too.
- The hum is not depend on volume level, gain level, and channelI tried…
- to replace power tubes
- different outlet, it works fine above constant 230V
- reharsal room outlet with constant 228V, it makes the humming noise. There is some Peavey amps, but these work properly.
- in my house the voltage is fluctuating between ~220-233V, when the voltage is above 230V, it works fine

The noise is stronger after ~30-40 sec usage.

Why can’t my amp „tolerate” low voltage?
What should I do?

martinadolfi
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Re: Peavey 6505MH hum problem at low voltage

Post by martinadolfi » Fri Jun 18, 2021 1:56 pm

Exactly the same happens to me. I didn't notice it was the voltage since I almost always have around 218v, so it's almost always humming. Everything else exactly the same. Seems to be on the poweramp section. Changing tubes didn't work either.
So ok, I'm not being off much help here, but it's good to know you're not alone :D

M.

NakajimaYusuke
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Joined: Tue Apr 18, 2017 5:48 am

Re: Peavey 6505MH hum problem at low voltage

Post by NakajimaYusuke » Sun Aug 15, 2021 2:48 am

Hi, my 6505mh has exactly the same problems as you guys.
Is there any news about this issue?

My 6505mh is a 100v version (for Japan).
I have confirmed that hum occurs at 101V and 98V and 95V.
When I tried it at 117V with an up transformer, the ham disappeared.
So, as reported in this thread, hum seems to occur only at low voltages.
But my 6505mh is designed for Japanese voltage. (100V)
So normally 101V shouldn't be a low voltage for my 6505mh.
Actually, there was no problem for 4 years.

My 6505mh is about 5 years old.
And ham started to occur when it was about 4 years old.
It may be due to aging of some parts.

WrldEatr9
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Joined: Wed Jan 02, 2019 9:35 pm

Re: Peavey 6505MH hum problem at low voltage

Post by WrldEatr9 » Mon Aug 16, 2021 9:37 am

Anyone tried replacing the preamp tubes?

NakajimaYusuke
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Posts: 12
Joined: Tue Apr 18, 2017 5:48 am

Re: Peavey 6505MH hum problem at low voltage

Post by NakajimaYusuke » Wed Oct 06, 2021 11:58 pm

I have replaced the 1st pre-tube with various types, but I haven't seen any change in the ham problem. :(

I don't think this is a problem near the pretubes.
This is because when I cut off (mute) the signal between the Send and Return terminals, there was no change in the hum noise problem.
:x
In other words, even if the preamp signal was not sent to the power amp, the problem did not go away.
So I expect this problem to be caused by something other than the preamp side.

NakajimaYusuke
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Joined: Tue Apr 18, 2017 5:48 am

Re: Peavey 6505MH hum problem at low voltage

Post by NakajimaYusuke » Sun Apr 03, 2022 9:15 am

Hi, I replaced the power tubes with new ones.
However, the hum noise did not go away. :(

What should I do next?

arqe
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Joined: Sat Mar 11, 2023 8:13 am

Re: Peavey 6505MH hum problem at low voltage

Post by arqe » Sat Mar 11, 2023 8:23 am

Hi, the very same problem here with 6505MH. The hum noise seems to be 100% correlated with power input voltage. I measured the voltage continuously - No hum for 230 V and higher, below 230 V the hum is always present (no cables plugged in to the input or fx loop send/return jacks).
Not at all sensitive to channel selection, pre or post gain volumes or power amp settings. The only thing that alters the hum to some level is the crunch switch.

Is there any advice as to what may be checked/replaced? I am not gonna replace all tubes just to see no change though.

NakajimaYusuke
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Joined: Tue Apr 18, 2017 5:48 am

Re: Peavey 6505MH hum problem at low voltage

Post by NakajimaYusuke » Wed Mar 15, 2023 4:28 am

Hi, I am glad that you are interested in this issue. :D
I haven't solved this problem yet. I live every day with a hum.

This problem seems to occur not only on the 6505MH but also on other 6505 series as well.
https://www.youtube.com/watch?v=4RGFrObwnxM

And as you point out, the CRNCH switch is known to reduce this hum a bit.
Even if the 6505MH's preamp section is disabled.
I find this a bit of a strange phenomenon. :?:
I feel like this hum is a problem in the power amp section.
So it's strange that a switch in the preamp section would affect the hum.
This makes it even more difficult for me to determine the cause of the problem. :cry:

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