Help, is it clipping? or cables?

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.


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.

Do those speakers suck up watts? To clip that amp you must play at ear splitting levels. I also have the vac tube dac and wonder if your tubes are in good condition? One bit dacs do compress at high volumes, and sound harsh.
I do not think speakers are too much for 70/70. 6ohm and 91dB, is very easy load. Check your tubes in your amp.
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
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.