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PPA and Denon D7000 issue.

post #1 of 5
2/23/10 at 4:30pm
Thread Starter 
HI all,

I am currently having a problem with my PPA V1. I recently purchased a pair of Denon D7000 headphones which have a 25 ohm load. I initially built the amp with a gain of 10, but with the Denon's I had hardly any volume control. I then changed the gain to 5, which gave me more volume control, but I m having another issue.
Whenever I listen to music, the llouder I make it, the signal clips, I get distortion in the music. The amp is using the OPA627 op-amps and is wall powered by a steps power supply I also put together. Are these headphones too much for the amp, or could there be something wrong with the amp itself?

I have ruled out the headphones by plugging them into different sources.

Thank you for any help you can give.

Tim
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post #2 of 5
2/23/10 at 4:41pm
PPAv1 with monolithic or discrete buffers? Low impedance = easier to make amp less stable. Also, can you confirm OPA627 and not OPA637 on Left/Right channels as OPA637 isn't stable at gain of 5x.
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post #3 of 5
2/23/10 at 4:49pm
Thread Starter 
Thanks for the response,

It has OPA 627AP's on all three channels. The buffers is the Laroccc Audio Triad board setup.

Tim
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post #4 of 5
2/23/10 at 4:54pm
Maybe diamond buffers getting unstable with low impedance load - measure current draw on amp, check for DC offset and see if any of the buffers run more current through output resistors than they should (which may need to be replaced with slightly larger ones)
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post #5 of 5
3/1/10 at 11:44am
Quote:
Originally Posted by TimG View Post
Thanks for the response,

It has OPA 627AP's on all three channels. The buffers is the Laroccc Audio Triad board setup.

Tim
Try adjusting the bias higher in addition to the checks Recommended in previous posts. BTW the PPA V2 Discrete Buffer and the LA Buffer Module you have are the same circuit however due to the module platform the parts and layout are more compact. If you have the Dyn-O-Bias LA Buffer and this instability results not only will the bias have to be increasing but in addition the input resistor on the PPA board will need to be changed. if however you have the standard LA Buffer then this should be stable with simply a bias adjustment.

In any event You should not be having stability issues with a LA standard buffer or a PPA V2 with your Dennon's unless something is defective in the PPA and or buffer proper. The LA Dyn-O-Bias version is extremely sensitive toi its environment and that is why it is not used in the PPA V2. While the Dyn-O-Bias buffer will sound better than the standard buffer it is far more picky about its workload than the standard buffer is.

Good search terms are PPA Dyn-o-Bias, Dyno-Bias, Larocco Audio Dyn-O-Bias stability issues, LaRocco Audio Dyn-O-Bias Buffer
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