2. amps-preamps
  3. 1068854374

Help, is it clipping? or cables? or...feedback.

Here is my problem....on loud transients the treble moves forward and becomes harsh. If I add negative feedback on amp, this seems to help. But, negative feedback sounds closed in. So, what is "choking system?

AMP is VAC 70/70 driving Diapason adamantes II. Cable Mapleshade double golden helix. Is it the cable? Amp / speaker match? Or, is it upstream...theta data II, VAC DAC tube DAC? preamp does not seem to be issue as I have tested several.

Or, is this just plain digital? I am using what I consider to be best recordings....

Any thoughts? I am considering a cable redo...I have a mish mash of them in system.

Thanks!
scotty333
5 responses Add your response
alrau1's avatar
alrau1
56 posts
 
Scotty,

Sounds like clipping to me. The giveaway is that the negative feedback helps--this lowers the gain of the amp. I assume you'll note further improvement upon lowering the volume control--if you do, you've been pushing the amp too hard.

--Al
Post removed 
kkursula
95 posts
 
I do not think speakers are too much for 70/70. 6ohm and 91dB, is very easy load. Check your tubes in your amp.
scotty333 OP
79 posts
 
Thanks for the great feedback. I beleive you are right on. My tubes in the amp are VERY old. Perhaps its like the frog being boiled in water - start with nice water and heat slowly...I will have new tubes to try soon and update.

Any other thoughts would be greatly appreciated.

Thanks again. Scott
marakanetz's avatar
marakanetz
5,473 posts
 
It seems like a self-oscillation to me!
Oscillation may be from the following reasons:
1. RF interfearance(less-likely in tube amps)
2. Heavy speakers with wide swings of impedance up or down arn't a good match to the output transformer of tube amplifier.
3. Cables with high capacitance(be aware that very often high-end speaker cables have worse reactance parameters than a regular cheap speaker wire!). Check if the problem still percist with cheap RadioShack or Home Depot speaker wires
4. Deeper negative feedback helps to reduce or stop self-oscillations.
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