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In Reply to: RE: Please re-read my post carefully posted by Fitzcaraldo215 on January 25, 2014 at 09:11:19
...when I saw yours. The frequency range possible from SACD goes out in the ultrasonic range to ~50kHz. Some amplifier topologies appear to have trouble with ultrasonic frequencies, causing distortion and oscillation. I remember reading a caution when I had the Sony SCD-777 SACD player that one shouldn't use the switch on the back in the "full range" position (or something like that) unless you were sure that your amps behaved nicely with the ultrasonics present in the output. I never had any problems running "full range" with the tube amps I was using during the time I had the SCD-777. This reason also explains why RBCD is fine - brick wall filters take out the ultrasonic info.
Follow Ups:
At least Sony is willing to admit there is a 'potential' problem. I use an outboard low pass filter and I sleep well.
-reub
I can't solve the problem of the Ayre making the Beveridge amplifier oscillate, can you say where you got the low-pass filter or if you built it yourself, can you supply instructions? Thanks.
My low pass filter is homemade, and the basic schematic is on page 11 of the linked application note. A 'full' schematic can be seen in the gain vs frequency plot on page 15, 'with RC'.
I'm no guru, but after repeatedly beating my head against the wall I came up with a filter that works for me. If you want to try one like it, send me an email for more info.
best regards,
reub
I think I can build that with the info provided. What cut-off frequency did you choose?
50KHz - Enjoy the journey!
I and my local guru pretty much agree with your explanation(s). He also mentioned the VHF noise that comes with DSD. We took pains to make the amps stable prior to setting up the Bev system, and the first thing I need to do is to figure out whether we treated the two amplifiers differently in any way. It's quite possible that that is the case. For example, I built a shield out of "TI Shield" that runs between the input and driver stages of each of the two amplifiers (which is all solid state) and the very high voltage tube output stage. Each of the two amps has the shielding, but maybe one shield is working better than the other, due to better grounding or to slight differences in how the shields were located. Similarly, there are ferrite beads here and there on leads that connect the solid state circuit to the output stage.
In retrospect, I had been experiencing moments when the R channel would sound a bit lower in gain compared to the left, but it is a very momentary phenomenon, and nothing else elicited the white noise. Possibly those fleeting changes in gain characteristic represent an episode of oscillation as well.
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