WTF? Sporadic distortion on amp

[pabbi1]

This is the 'new' McAlister EA-6, freshly returned from Peter, with a better than new rework of the circuit... tube compliment is:

1x 12BQ6

1x 6BQ6

2x 12AU7

4x 6CG7

4x 17GW6

This is with the Eastsound E5 and the HE60.

Good news: This amp is great, if not spectacular when playing acoustic (Allison Krauss), classical, and some rock (Jane's Addiction, Who Ultimate Collection, and Hoobastank). Just superb.

Bad news: On saturated and distorted rock (Tool '10k Days' and 'Lateralus', Jett 'Get Born' and 'Shine On', and even Velvet Revolver), I catch a raft of fuzzy distortion (almost static) in the upper guitar band and the top of percussion (cymbals)... BUT, ONLY on certain CDs / bands (/producers???). WTF?

Vocals and any acoustic instruments are universally outstanding. The only thing I can come up with is the 'Even order harmonics' (good albums) vs 'odd order harmonics' (bad albums ?) that Peter says he is after - can exploring that single minded signal processing objective be causing this bizarre behavior? Honestly, I have never had any amp behavior quite like this. Even some heavily distorted guitar is great (Neli Young - 'Down by the River, Cowgirl in the Sand, Cinnamon Girl)... just bizarre.

This is NOT a function of volume - noticeable cranked up, and down low. It is not crappy CDs - they sound GREAT on the Blue Hawaii.

For the moment, let's put aside the 'ugly innards' part - it still does a LOT of things in spectacular fashion... regardless of it's price.

[Guest sacd lover]

This is the 'new' McAlister EA-6, freshly returned from Peter, with a better than new rework of the circuit... tube compliment is:

1x 12BQ6

1x 6BQ6

2x 12AU7

4x 6CG7

4x 17GW6

This is with the Eastsound E5 and the HE60.

Good news: This amp is great, if not spectacular when playing acoustic (Allison Krauss), classical, and some rock (Jane's Addiction, Who Ultimate Collection, and Hoobastank). Just superb.

Bad news: On saturated and distorted rock (Tool '10k Days' and 'Lateralus', Jett 'Get Born' and 'Shine On', and even Velvet Revolver), I catch a raft of fuzzy distortion (almost static) in the upper guitar band and the top of percussion (cymbals)... BUT, ONLY on certain CDs / bands (/producers???). WTF?

Vocals and any acoustic instruments are universally outstanding. The only thing I can come up with is the 'Even order harmonics' (good albums) vs 'odd order harmonics' (bad albums ?) that Peter says he is after - can exploring that single minded signal processing objective be causing this bizarre behavior? Honestly, I have never had any amp behavior quite like this. Even some heavily distorted guitar is great (Neli Young - 'Down by the River, Cowgirl in the Sand, Cinnamon Girl)... just bizarre.

This is NOT a function of volume - noticeable cranked up, and down low. It is not crappy CDs - they sound GREAT on the Blue Hawaii.

For the moment, let's put aside the 'ugly innards' part - it still does a LOT of things in spectacular fashion... regardless of it's price.

I would say a bad tube or the amp is oscillating.

[pabbi1]

Would this make sense, as it seems spot on:

Originally Posted by derekbmn

If i'm not mistaken(and I very well could be) the McAlister amps have very low maximum output voltage.As in not a whole lot of voltage swing. Are you sure it's not simply clipping on complex passages ? Running out of steam so to speak on temporary but sustained peaks.(ie: guitar) Personally I think that may be what it is.

[Guest sacd lover]

Would this make sense, as it seems spot on:

Originally Posted by derekbmn

If i'm not mistaken(and I very well could be) the McAlister amps have very low maximum output voltage.As in not a whole lot of voltage swing. Are you sure it's not simply clipping on complex passages ? Running out of steam so to speak on temporary but sustained peaks.(ie: guitar) Personally I think that may be what it is.

I didnt pay enough attention to the fact this is an electrostatic amp. None of the tubes you list would have a lot of voltage swing so I would tend to agree possible clipping makes sense.

[JBLoudG20]

Sounds like poor engineering to me.

[deepak]

On saturated and distorted rock (Tool '10k Days' and 'Lateralus', Jett 'Get Born' and 'Shine On', and even Velvet Revolver), I catch a raft of fuzzy distortion (almost static) in the upper guitar band and the top of percussion (cymbals)... BUT, ONLY on certain CDs / bands (/producers???). WTF?

I noticed this too with my Stax SR-404. It was worse on really badly mastered CDs. Particularly bad on a Coldplay album that I had to stop listening to after a few minutes into it. The Stax just couldn't handle most modern rock. Any sort of heavy distorting guitar caused this crackling/static sound.

This was with an SRM-313 amp.

edit: also heard this in an Omega 2/KGSS at one meet.

[pabbi1]

May well just be poor design - but, I have never heard any clipping on the BH...

[Iron_Dreamer]

Well, the BH is the highest voltage swing amp out there AFAIK!