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Old 30th November 2002, 11:58 PM   #1
diyAudio Member
Join Date: Oct 2002
Location: Winnipeg MB Canada
Default Feedback Loop help

Hello Everyone,

I have a Rotel RA930AX integrated amplifier. I have completed numerous upgrades such as:

-discreet bridge built with soft recovery diodes.

-bypassed all tone controls and hardwired with Nordost cable from input to volume control. (now only one source can be used).

-replaced all applicable caps with Elna Cerafine.

-added 22000uf Elna Cerafine caps to power supply.

-Changed op-amp to AD827.

-Replaced all resistors with Roederstein metal film.

-Paralled .1UF Solen and .01 Teflon(russian) cap in power supply.

-Removed plastic covers from all caps including the 22000uf ones and put a damping material on the caps.

-Replaced speaker outputs with better Vampire units (hard wired to board with Nordost cable. Also replaced RCA inputs.

That is about the extent of the upgrades so far.

I plan on upgrading the volume control.

What I want help with is identifying which components are in the feedback loop. I want to replace these components with better resistors/capacitors.

Does anybody have a schematic and can help me identify them?.

I am not too good with circuit topology.

Also, what would be the next logical upgrade to do to this amp.

Thanks for reading all this.

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Old 1st December 2002, 12:16 AM   #2
halojoy is offline halojoy  Sweden
On Hiatus
Join Date: Nov 2002
Default Feedback localisation

Feedback always comes from the output.
Usually before the output relay
and between the output transistors.
But I guess you can not see the bottom side of the circuit.
So a schematic would be best.
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Old 1st December 2002, 12:23 AM   #3
diyAudio Member
Join Date: Oct 2002
Location: Winnipeg MB Canada
Thanks Halajoy.

My amp does not have relays.

I can trace the circuit if you can help me with what I am looking for.

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Old 1st December 2002, 01:36 AM   #4
halojoy is offline halojoy  Sweden
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Join Date: Nov 2002
From the output point,
there should be 1 or two small resistors going
in direction to the input transistors.
Often is a small capacitor right beside the resistor.
They are in parallell.

It can also be a track that goes halfway from the output
back towards the input.
and then the resistor/cap is closer to the input.
The input is mostly one or two pairs of transistors,
with close body contact to eachother.
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Old 1st December 2002, 01:39 AM   #5
diyAudio Member
Join Date: Oct 2002
Location: Winnipeg MB Canada
Thanks again halajoy!

I will check it out and let you know how I made out.

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