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More on KT-8300 op amp upgrades


newaag
 

This is for Ryan, and others upgrading op amps in the KT-8300

If you are experiencing problems with new high speed op-amps, you may
want to try this. Problems could be ringing, whirring, high
frequesncy hardness, etc.
Locate the area around the the audio opamps. What you need to find
are the feedback resistors. On one they are Rg63,Rg64 - 47kohm, on
the other they are Rg133, Rg134 - 120kohm. You want to try soldering
a 10 to 100 pF cap directly across the leads of these 4 feedback
resistors listed above. For experimenting, use any cap available,
even ceramic. If this improves the sound, you have eliminated a high
frequency problem, most likely oscillation. I would use thre smallest
cap possible that fixes the problem. Of course, if you have a 100MHz
scope, your job is a lot easier, as you can see the oscillation, and
the cure when the caps are installed.

cheers,
Bob


Mike Zuccaro
 

In a message dated 4/4/02 10:14:48 PM Pacific Standard Time, newaag@yahoo.com
writes:

<< 20kohm. You want to try soldering
a 10 to 100 pF cap directly across the leads of these 4 feedback
resistors listed above. For experimenting, use any cap available,
even ceramic. If this improves the sound, you have eliminated a high
frequency problem, most likely oscill >>
And very short leads- at 100mc even small caps can be resonant. Bad news.
Use the smallest micas you can find.
MZ