Here's a list of the tests run today to isolate the exact conditions/setup under which the buzzing can be created (the short answer is, interaction between the amp and DSP is causing it):

Test #1 (all amp inputs removed; isolating the amp):
With all RCA, DC trigger, or any other input connections removed from the AMP (speaker wire outputs still attached to the speakers of course), there is NO buzz. That means the amp by itself alone is not creating the buzz.

Test #2 (only RIGHT channel amp inputs removed; isolating amp by channel to see if any RCA input to the amp causes all channels to buzz or if the buzz becomes channel specific)
I removed TWO of the RCA inputs from the Axiom DSP to the amp (the Right Rear and Right Front inputs).
With the two LEFT input connections hooked up from the DSP to the amp (LEFT Front and LEFT Rear), those two LEFT channels both have buzz, the RIGHT channels had no sound similar to Test #1.
The centre channel had no buzzing (note that the centre channel RCA input to the amp comes directly from the Denon AVR).
As such, the buzz becomes channel specific to the DSP-RCA input (LEFT or RIGHT but not CENTRE) into the amp.

Test #3 (removing RCA input to the DSP from the AVR to remove the AVR as the source of the electrical interference)
All RCA inputs for all channels from the Axiom DSP were plugged back into the amp.
I removed a single input (RIGHT channel) going from the Denon AVR to the Axiom DSP (Note that the Axiom DSP is turned on).
Still get buzzing but from ALL channels INCLUDING buzzing in the right speaker channels even though the Denon AVR is not connected to the Axiom DSP for the right channel.

Test #4 (remove the Denon to DSP connections completely to isolate the DSP and amp alone)
Removed all RCA inputs from the Denon AVR to the Axiom DSP. Removed the centre channel RCA input from Denon AVR to amp.
All DSP outputs to the amp are still connected.
Buzzing occurs in all channels which means the source of the buzz is coming from the DSP (or DSP-amp combination)!

Test #5 (shut off Axiom DSP power to eliminate concept of ground loop hum from wall power)
With the same conditions as in Test #4, I then completely unplugged the Axiom DSP from the wall.
So all DSP RCA outputs are plugged into the amp. There are no inputs from the AVR into the DSP. There are no inputs from the AVR to the amp. The DSP is receiving zero power and the ADA amp turned on.
Result: buzzing in all channels

Summary

The buzz condition comes under the conditions when:
  • Axiom ADA amp is turned on
  • Speaker wires are running to any speakers
  • The Axiom DSP has an RCA connection going from itself to the amp.
  • Axiom DSP power cord completely disconnected from any power socket.
  • There are no connections of any kind from the AVR into the DSP or the amp (however even when the Denon is connected to the amp with the centre channel input, it did not change the results of the buzzing, connected or disconnected).


Whichever channel left or right that is connected from the DSP to the amp will create the buzz in that channel. If the left channel from the DSP to the amp is not hooked up there is no buzzing in the left channel but if the right channel is hooked up at the same time there is buzzing in the right channel. As such, when both the left and right inputs from the DSP go to the amp then there is buzzing in all channels. When there are no RCA cables from the Axiom DSP to the amp there is no buzzing in any channel.
The only clean sounding channel is for the centre speaker. Under any or all of the previous conditions, the centre channel made no buzzing. The Denon AVR supplies the amp directly with a RCA input.

The bottom line is that when the ADA1500 amp is connected to the Axiom DSP, even when the DSP has no power and no source inputs, the mere RCA connection between the two causes a buzzing through the speakers when the amp is powered up.

Last edited by chesseroo; 10/24/22 07:10 PM.
"Those who preach the myths of audio are ignorant of truth."