Noise in one channel

tagomago · 2899

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Offline tagomago

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on: October 02, 2022, 09:30:32 PM
Hi all

Since I built the Eros 2 some time ago I had an issue with noise in one channel. It is pretty low but it kinda bugs me.
I measured the output of the preamp with the inputs short cutted. In the right channel I get about 80mVAC noise, in the left channel it's about 4mVAC.
I used shielded cables and a good Fluke 45 meter to measure this.
The issue does not change channel when I switch the EF86 tubes.

My voltages are:
IA: 218.8V
IB: 220.4V
OA:166.3V
OB: 164V
OC: 95.3V
OD: 95.9V
OkA: 96.3V
OkB: 97.1V
OkC: 1.62V
OkD: 1.54V


Offline Paul Joppa

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Reply #1 on: October 03, 2022, 03:52:46 AM
Can you describe the noise? hiss/roar,hum/bus/squealing/beeps/etc?

Paul Joppa

Offline tagomago

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Reply #2 on: October 03, 2022, 04:02:26 AM
Hi Paul

It's like a storm far away. Rumble.


Offline Doc B.

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Reply #3 on: October 03, 2022, 04:09:27 AM
I'd be inclined to try a different 6922 before I took anything apart.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline tagomago

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Reply #4 on: October 03, 2022, 04:19:40 AM
I just measured the noise with an oszilloskope. It's weird that I'm measuring a 50Hz / 80mVrms sinus on the right channel that is causing the measured noise.
But it does not sound like a 50Hz signal at all.
The rumble I hear is very instable, sometimes it is not there at all.
I will try a different 6922


Offline Paul Birkeland

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Reply #5 on: October 03, 2022, 04:28:08 AM
I would also be inclined to suggest powering down nearby equipment, as you may be picking up some magnetically induced hum.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline mediumgrade

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Reply #6 on: October 18, 2022, 11:14:10 AM
Quote from: Paul Birkeland on October 03, 2022, 04:28:08 AM
I would also be inclined to suggest powering down nearby equipment, as you may be picking up some magnetically induced hum.

I second this. I had a similar low, garbled noise issue with mine which turned out to be a wireless headset receive that was too close. Moving the device further back fixed the issue for me.


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