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Best Solid State for Avalon Isis

I would appreciate informed comments regarding best solid-state synergy with Avalon Isis. I’m looking for an amp that will maintain absolute control of deep bass, while maintaining a rich and dynamic mid-range, and clarity without sacrificing musicality. It should be transparent, and allow a vast and layered soundstage to appear. Although the Isis appear relatively efficient (90db at 4ohm), the paired 13” woofers are going to need an amp with muscle.

Source is a Wadia 9 series. It runs direct. It does not need a pre-amp.

I listen to big, loud, congested orchestral music (ie. Mahler, Bruckner, Wagner). I like to hear all the detail, including the musician's technique and subtle alterations in tempo. Orchestral sections need to have mass. I want to feel the bass at low in addition to high volumes.

My room is 20 x 30 ft, and has plaster walls/ceiling with wood floors and padded area rugs. Tubes are not an option. Because of the room and source, I am not looking for an amp that is artificially fast or tipped toward the higher frequencies.

A company which is solvent, established, reliable, and with good customer support is important, with preference for an American manufacturer. I plan on trying to home demo some of these, but need advice on where to concentrate and expend my efforts.

These are some I'm considering, and additional suggestions are welcome:
Pass Labs XA200.5
Boulder 1050 Monoblocks
Halcro DM78
Spectral DMA 360
Edge NL Sig One
Hovland Stratos

Thank you,
Rob
rtn1
dev's avatar
dev
832 posts
 
Hi Rob,

first congrats again on your new amps.

what power cords are you using? Do you have the amps on their own designated lines?

Are the amps ontop of any type of isolation? (Sistrum) if they are have you done any comparison and what did you notice.We both at one time owned PASS X-600.5 mono's so we know what they are all about including the difference once put ontop of the SP-101's.

Referring to the Pass amps did you try those on your Isis? if so what is the difference between them and the Karan 1200's.

Some new pics of your system would be nice.
dev's avatar
dev
832 posts
 
Hi Rtn1 (Rob)

I was just wanting to bring this thread back to life, kindly refer to my above questions to you thanks.

You have had the amps for a while now so any further thoughts.
tuboo
93 posts
 
there is a lot of misconception about 'pure class A'.
there are not much pure class A amps around. the old Pass Alephs were pure class A and they had not many watts.
most (almost all) amps are class AB.
it is all about bias. as an example if an amp has 600 watts into 8 ohm and the manufacturer claims 'pure class A' this amp should draw about 4 times 600 watt out of the wall. not very likely.
many tube amps manufaturers claim pure class A too.
you only have to look at the continuent current draw, ie if a tube amp draws say 400 watt continuely it will have about 100 watts pure class A. this is not an exact math figure.

i see another statement like 'this amp has big watts so it does bass well'. most of times this will work out, but i have experienced 50 watters which can put ashame any 1200 watter. watts never claim bass alone on amount of watts. its all in the powersupply..

Nelson Pass has a great article concerning pure class A at his website. check it out.
one of the heavy class A contenders are indeed the big Gryphons. boy they get HOT.
bombaywalla's avatar
bombaywalla
1,958 posts
 
Tuboo,
good comments re. class-A. I agree with you - there's a LOT of marketing hype. The more the consumers do not understand, the more the manuf seem to take advantage playing the spec game. I see this more in the USA than in Europe, Asia or Australia.

One comment from my side - an amp can also be biased in sliding class-A (rather than in full power class-A such as the Alephs). A sliding class-A amp can support only a very small output signal - one that would probably not create an acceptable SPL for listening - but has no x-over distortion characteristic of a class-A output stage. As the input signal increases, the bias for the output transistors increases (slides up).

>> one of the heavy class A contenders are indeed the big
>> Gryphons. boy they get HOT.
Indeed they do!
A couple of more contenters - the Plinius SA-250 Mk4 when switched into class-A mode. The Threshold T200. These amps get HOT too! I measured the fins of the T200: 54 deg C when stabilized.
rtn1 OP
535 posts
 
I think this is a good discussion. The Karan slides the bias to achieve class A, but is touted to be unique in the way this is accomplished. I am not an engineer, so I cannot speak to whether this makes sense. Milan Karan designed the amplifier to use balanced power (+60, -60), and has designed a circuit to send a signal to increase the bias prior to the main signal. Thus, the claim is that the bias is increased fully and proportionally to the main signal before the main signal passes through. So maybe the argument is how effectively the bias can be increased ahead of time.

Is there anyway to measure class A power other than the continuous power it draws from the wall?

Of course, all this is beside the point when considering what the amplifier actually sounds like. However, I do believe that in general an amplifier should sound better in class A than in class AB, with all other things held constant.

Does any of this make sense?
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