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AB528 Microphone preamplifier
Noisy/Clicky
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Topic: Noisy/Clicky
August 19, 2023, 05:14:18 PM
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Perry
Newbie
Posts: 4
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Noisy/Clicky
I just finished my second ab528.
There is a crackling, irregularly noise.
The diode on the front panel is lit solid green.
I have done all other tests, changing cables, changing slot in my 500- rack. but still there.
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August 21, 2023, 05:26:58 PM
Reply #1
JPK
Administrator
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Posts: 1085
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Re: Noisy/Clicky
Does the preamp work apart from the noise?
Does the noise level depend on the position of the pot?
Does it depend on the gain switch position?
What is the DC voltage on Q5 collector, taken on the heatsink? Should be about -0.5V.
Check that all your electrolytic caps are in the correct direction.
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JPK
September 04, 2023, 11:46:54 AM
Reply #2
Perry
Newbie
Posts: 4
Karma: +0/-0
Re: Noisy/Clicky
Thank you for your reply!
After more testing of the AB528, the noise/crackling only appears when the v48 is on.
Does the preamp work apart from the noise? - Yes
Does the noise level depend on the position of the pot? - Yes
Does it depend on the gain switch position? -
Yes, the noise increase when the gain is increasing
What is the DC voltage on Q5 collector, taken on the heatsink? Should be about -0.5V. - The DCV is 0.
Check that all your electrolytic caps are in the correct direction. - All are correct.
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September 06, 2023, 10:15:06 AM
Reply #3
JPK
Administrator
Hero Member
Posts: 1085
Karma: +35/-0
Re: Noisy/Clicky
Check that the 48V is present on both microphone balanced lines (input XLR pin2 and pin3), against lunchbox chassis.
Check the solder joints on R1, R2, C1, SW1, RLY1, RLY2, RLY3.
Try removing C1, in case it is damaged.
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JPK
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AB528 Microphone preamplifier
Noisy/Clicky
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