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Scott 222D Phono Stage-Intense oscillation
Scott 222D Phono Stage-Intense oscillation
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Old 9th November 2018, 02:38 AM   #21
sisyphus51 is offline sisyphus51  United States
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I used to be able to turn up to MAX level with the tonearm lifted to guage noise/hum. Now 12:00 causes the output to burst into approx. 500 hz. heavily distorted oscillation even with input shorted. There is something wrong with the phono EQ that is generating feedback.
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Old 9th November 2018, 02:46 AM   #22
sisyphus51 is offline sisyphus51  United States
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I actually prefer the sound of my Schiit Mani into the Scott Line-Level input!
It gives me a very rich and powerful sound! :-)
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Old 9th November 2018, 02:59 AM   #23
Chris Hornbeck is offline Chris Hornbeck  United States
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Quote:
Originally Posted by sisyphus51 View Post
I used to be able to turn up to MAX level with the tonearm lifted to guage noise/hum. Now 12:00 causes the output to burst into approx. 500 hz. heavily distorted oscillation even with input shorted. There is something wrong with the phono EQ that is generating feedback.

First, clean all the switches and controls. Seriously, you'll thank me later.

Next, it's time to check all the power supply electrolytic caps. Originals are old enough to be grandparents, and about half a century past their design age.


All good fortune,
Chris
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Old 10th November 2018, 01:07 AM   #24
sisyphus51 is offline sisyphus51  United States
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Originally Posted by stocktrader200 View Post
bypass the RIAA/NAB switch to permanently be in the RIAA position.
NAB eq is not needed anymore as reel to reel tape is not common.
Check ground connections on 12AX7's
I needed a break from worrying about this thing so, I just bypassed the whole Phono stage with an external Phono Amp/EQ. However, I like your suggestion to by-pass the NAB/RIAA Switch! * There is a slow 'motor-boating' oscillation audible in the speakers when I switch to the Scott Phono Input before All Hell breaks loose at about 12:00 on the Volume Knob. I know something is messed-up in that area but, I need to get a scope probe in there!
I see a decent Tektronix Scope for sale locally and will look into it. And my friend, in L.A., who gifted me the Scott will send me a probe, or two - and some other tools - I don't want to "boldly go" ripping-up the original circuit without further insight into the defect. ;-)
Thanks to you, and the others, for all the interest and advice! :-)
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