AVA product specifications question

warnerwh · « **on:** 29 Apr 2006, 04:41 am »

I'd like to know all the parameters used in measuring all the AVA amps, preamps and dacs. Also what parts have been used to build them and why. The website only has minimal information.

The only reason I want this information is so that I can help you guys make them better. I know essentially nothing about engineering electronics but that doesn't seem to bother other people. I've read many times people making recommendations to engineers of electronics and speakers on how to do something or how it must work that have never done it themselves so I figure I can help Frank and his team and maybe some others who know nothing either can also help us.

The AVA 550exr rev. 5 I recently purchased is so good it amazes me. I've owned many very good and acclaimed amps and this amp simply trounces them running my Rm 40's which are very revealing of anything upstream. Upon examining the innards the build quality is also excellent.

The sound though must be experienced. No tube or SS amp has sounded near this real. We have zero SS sound and no noise or mushies like most tube amps. Most amps I've not heard but this one is so good that I'd be willling to put it up against anything, even amps costing 5 figures. This is no exaggeration. Maybe Frank learned something in the last few decades. I'm very impressed!

I've been telling people that AVA gear would probably be worth trying for some time now. Been in the hobby since the early 70's so know the Van Alstine name has been in business longer than many audiophiles have been alive.

A friend (gongos) took my advice and bought this 550 off of Audiogon and was also way impressed but felt he couldn't afford it just to run the top part of his VMPS RM 2's so I bought it from him and am glad I took my own advice.

I don't know how someone could improve on the amp I have but am willing to mod the Fetvalve amps with my own ideas for 500.00. These mods to AVA gear that will no doubt do nothing to improve the sound and may(probably) cause damage to your component are a must have. I have plenty of experience as I've soldered speaker wire several times now. My references are to short to list btw. PM for more detailed info. Thank You

Tweaker · « **Reply #1 on:** 29 Apr 2006, 05:28 am »

warnerwh,
Interesting way of making a point. Seems as though a lit bit of Frank has rubbed of off the amp onto you. I own two of his amps. I should really be crotchety!
Well , I gotta say I am very envious of your fet-valve. I have Omegastar solid state amps and as good as they are I can imagine how insanely good the 550 must be. I never want to hear one though. I have to learn to be satisfied with what I have. Makes me kinda sad.

avahifi · « **Reply #2 on:** 29 Apr 2006, 09:57 pm »

It would probably be a good idea for you to call me at 651-330-9871 before starting to make any changes to that Fet Valve 550exr rev 5 amplifier.

There are some things we can do usefully, such as the biasing and other circuit changes to bring it to an Ultra specification, but we must work on the audio boards themselves, and have the equipment to bring the amp up slowly on a variac with a square wave generator, dual trace scope, high power load bank, and a meter to make final bias current adjustments. Mistakes would be VERY, VERY expensive for an amateur.

I think the circuit changes that could be done on the original boards would likely be very risky for someone to attempt without "hands on" guidance at the bench the first time.

Changes to things like power cords, capacitor brands, wire brands , fast diodes, etc. without making the useful engineering changes first will not be very useful. The rule is fix the worse case problems first. Other things probably will not be very cost effective.

Frank Van Alstine

warnerwh · « **Reply #3 on:** 30 Apr 2006, 01:07 am »

Frank: Only Kidding! Last thing I'd do is change something. The odds of me doing any good are the same as the sun burning out in the next 5 seconds.

Last thing anybody else would want is me working on their electronics even if I would. If someone needs help replacing tubes then that's something I can handle

TomW16 · « **Reply #4 on:** 30 Apr 2006, 02:05 am »

Hey warnerwh.

Even tube rolling isn't as easy as it seems with the FetValve amps since it may require rebiasing the amp, which, if I remember correctly, Frank doesn't recommend that an amateur try without guidance.

I have the 350 EXR and I think that it sounds great too.

Tom

warnerwh · « **Reply #5 on:** 30 Apr 2006, 03:11 am »

Is it absolutely necessary to rebias the amp if you try different tubes? I can understand that tubes must have different electrical characteristics but within a family I'd think they shouldn't be so far off as to damage anything. I could live happily with the JJ's in there though.

Maybe ideally it should be rebiased. I'd like to hear what Frank has to say on the subject. Is biasing something that's easy to do?

eico1 · « **Reply #6 on:** 30 Apr 2006, 03:25 am »

Frank has told me personally and in person that all ava equip is designed, tested, and rejected using test signal generated by galvanic conduction for measurements and a Theremin for listening evaluations. Just kidding.

steve

avahifi · « **Reply #7 on:** 30 Apr 2006, 11:21 am »

Rebiasing, kind of a crap shoot, staying with the same brand of replacement tube does not change the bias setting enough to worry about, but some brand changes will require bias resetting

Its 75 ma per positive output device measured with an ammeter replacing the B+ fuse, for what it is worth. Trim pot is near the bottom of the audio board, don't kill yourself trying to adust it.

Frank

zybar · « **Reply #8 on:** 30 Apr 2006, 12:38 pm »

Quote from: warnerwh

I'd like to know all the parameters used in measuring all the AVA amps, preamps and dacs. Also what parts have been used to build them and why. The website only has minimal information.

The only reason I want this information is so that I can help you guys make them better. I know essentially nothing about engineering electronics but that doesn't seem to bother other people. I've read many times people making recommendations to engineers of electronics and speakers on how to do something or how it must ...

Are you just running the mids and tweeter or full range?

George

warnerwh · « **Reply #9 on:** 1 May 2006, 01:16 am »

George: I'm only running the mids/tweeters with the AVA.

Frank: You stated in an earlier thread:

"Fet Valve amplifiers: 2 x 12AT7/ECC81. Re-bias if making changes to tubes with significantly different gain characteristics (call us for details). Older series Fet Valve amplifiers (Fet Valve 500/300 and older) use 12AX7 tubes. "

Can you list tubes that are known to be within safe parameters and those you know for a fact that aren't please? Or would you rather I call? Thanks

avahifi · « **Reply #10 on:** 1 May 2006, 10:46 am »

I do not have a good data base on this. We always rebias on amps here for upgrade. Usually changes are minimal when sticking with the same tube brand (unless circuit changes were not minimal) with bigger bias changes noted when changing tube brands, but we have not seen very many of the NOS or so called premium brands (very happy with our experience with JJ Tesla tubes).

Frank

ricmon · « **Reply #11 on:** 2 May 2006, 02:16 pm »

You guys may want to check out this thread on tubes in the fetvalve amps

http://www.audiocircle.com/index.php?topic=25207&postdays=0&postorder=asc&start=0