Audio Research SP9 guilty of screeching sounds! - diyAudio
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Old 6th February 2003, 10:47 PM   #1
Eric116 is offline Eric116  United States
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Default Audio Research SP9 guilty of screeching sounds!

Hi all,

First of all, please pardon me of my ignorance in all tube matters, as my understanding and manipulation of the Audio Research SP9 Mark II preamplifier that sits in my living room has to this date been limited to turning buttons and flipping switches located on the front of this device.

However, thanks to the help of the speakers people (the "other" forum), I have come to the conclusion that the preamplifier is responsible for screeeeching sounds when the volume is turned up or down As background, the preamplifier is linked to a McCormack Power Drive DNA 0.5 amplifier, and finally to a pair of B&W Nautilus 804 speakers. Current hypotheses on the cause of this problem are (1) the volume knob and (2) the tubes.

Has anyone encountered a similar issue? Is this an "easy" fix or is it a major project? Also, any input on troubleshooting would be greatly appreciated!

Thanks for your help!

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Old 6th February 2003, 11:47 PM   #2
SY is offline SY  United States
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If this is happening when you *change* the volume setting, I'd start the troubleshooting process by looking at offset voltages, especially if this is isolated to one channel. And stick a scope on the power supply rails to see if something is oscillating.
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Old 6th February 2003, 11:53 PM   #3
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Default SP9.


A tube has its' voltage to cathode insulation surpassed and has gone south.

Typical for this circuit really...

Sillly design if you ask me,

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Old 3rd January 2007, 09:46 AM   #4
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Default ok!

Hi ! You sent me circuit 6h30 (6n6p) please?
I want it! thank you!
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