What to look for in a power amp?

Greg - i just set up my Q5s this past weekend (as well as my amps and TT). Not an easy assignment given the weight of these beasts combined with being on the top floor of a four story walk up (we had to use a crane to bring the speakers in). I will start listening this coming weekend as i was too tired to finish everything yesterday (and the contractors aren't fully out of the apt). I will start a new post which shows my gut renovation of the apartment and what i have done to the listening room ('area' as it doubles for our living area).
For my amps, i spent a lot of time choosing, but must caveat that i chose for the M5, which i had on order before switching to the Q5 in January. I looked at the Spectral, Boulder, Soulution Burmeister, VTL and Zanden. I ruled out tubes for practical reasons, the biggest one being A/C bills in New York during the summer. I chose the Soulution 700s, but was equally as impressed with the 710 Stereo amp. I would definitely audition them if i were you or you are welcome to come by my place once i am running at full speed.

my pleasure - it is enjoyment after all that we are supposed to be seeking

thanks eas47 - i am really excited...i will get pictures uploaded this weekend (i have kept a picture log of the whole renovation). regarding the joy of music in NYC, this was a huge issue for me. nothing like investing some serious $$$ only to have your neighbor complain at anything over 70 dB. I live in an old warehouse in the lower east side (10th street between Avenue C and D). the building was constructed in 1874 and converted to a residential space in 1978. the prior tenants did little-to-no work and the worst part is that flooring was nailed directly into the structural beams in my apartment and the sheetrock was nailed directly into the structural beams in the apartment below me with zero insulation between the two (i am on the top floor so no problems to the north.

As you can imagine i had a big challenge on my hands. I did a total gut renovation (i was able to recover the flooring to use for my cabinet millwork) and started by leveling the floors. The GC then built an isolated (floating) floor:
- put insulation in the 14 inch cavity between my floor and neighbors ceiling
- laid two layers of 1 5/8" plywood, separated by acoustic glue (doesn't squeak)
- laid down an isolation pad - basically insulation that is broken up by fiberglass blocks every two feet to support the overlaying floor
- laid one layer of 1 5/8" plywood (but this layer does not touch anything structural, not the posts or walls) to create the isolation affect
- laid 1 5/8" flooring down (which also does not touch anything structural)

The system is not up an running yet, but the sound isolation seems to be working well as the neighbors haven't complained about the construction work since the flooring was complete.

Steve tried to push me to get two JL Gothams - i don't think the floor system is that good, but i am hoping it stands up to the challenge of isolating reasonable listening levels. the floor also adds isolation for the system itself (still to be proven when i fire the system up this weekend).

I have also had to find some interesting sound absorption solutions due to the irregular shape of the listening room (btw - has anyone seen the pictures from RH house of TAS - one side of the room is fully open and he said it measures very well, i am curious to understand this better as it is the same challenge that i am trying to solve).

i will do a post under 'member systems' - it has been a fun process and everyone here has taught me a lot about room treatments. i do think my room will have over absorption issues, but i have a potential diffusion fix to help that (i am hoping it is not necessary given the aesthetic impact)

Congrats Brian

I was only suggesting twin Gotham subs because of your very large room which IIRC has a very high ceiling

Shoot, Brian, I'm as interested in the millwork from the reclaimed flooring as I am in the audio system. I've seen some spectacular examples of this. What's the wood - oak or ???

Hi Ken, I did the floor in a wide white oak - 10" to 16" - i looked at doing this all in reclaimed but it became price prohibitive for me. I went with a group called Ebony (they are Ireland based but with several locations in the US) - they did a beautiful job. I was able to save the wood from my flooring prior to the renovation (the original slow growth pine). i reclaimed that wood and used it for all of the cabinetry millwork. my stereo rack and LP shelves are also built from reclaimed posts and beams - pictures to come this weekend.

and it has their proprietary RC. Wonder how they handle sub crossover - unless I'm missing it, it's not described in the cut sheet. Is it me, or is 200 amps a tonne of current? My amp is 50.

Amps +/- usually means it will source and sink 200 A, which any good (symmetrical) amp should do. It is a marketing ploy to my mind, as it does not actually put out 400 A but sort of implies it if you don't know better.

That said, 200 A is a heckuva' lot of current!!!

Gregadd said:

Ken you might also be intereted in the companion CD player with DIY tube output statge.
http://www.head-fi.org/forum/thread/85561/post-pics-of-your-builds/4875#post_5631908

Click to expand...

Greg, already have a terrific uni-player with tube output, but it's mothballed since I'm currently using a transport-only, feeding digital into a TacT preamp.

Gregadd said:

Ken I don't know how Harmon does it. Here is how it's done on the Aesthetix Atlas that has a similar feature:

separate high-pass crossover input with 6dB/octave filter slope and selectable crossover frequency.....

Click to expand...

Selectable Xover is nice, but the fixed 6dB slope is not. Still, it's nice to see Harmon producing a 2.x product incorporating RC. That's a rarity.

Quick comments: SS amps almost invariably have lower output impedance and thus higher damping factor due to a combination of no transformer and lower output-impedance devices. An output impedance of 0.1 ohms is a DF of 80 into 8 ohms and that's fairly typical for SS amps; tubes do well to hit 10 - 15 generally speaking. I think the main problem with transformers are their relatively high output impedance and their nonlinear response as power goes up and the core begins to saturate. Another significant problem isn't really the transformer itself but is related: transformers are designed for impedance-matched systems, and most speakers' impedance is all over the map, varying with frequency and power level.

The thing that "muddies" bass is not just (or just "not") the rise time; the high output impedance means the amp cannot control the speaker, and it (the speaker) rings after a transient step.

Of course, all these "problems" are "benefits" if you like the sound, and in some cases help compensate other flaws in the system (e.g. transformer HF roll-off can help tame a bright speaker/room).

FWIWFM - Don

DonH50 said:

Quick comments: SS amps almost invariably have lower output impedance and thus higher damping factor due to a combination of no transformer and lower output-impedance devices. An output impedance of 0.1 ohms is a DF of 80 into 8 ohms and that's fairly typical for SS amps; tubes do well to hit 10 - 15 generally speaking. I think the main problem with transformers are their relatively high output impedance and their nonlinear response as power goes up and the core begins to saturate. Another significant problem isn't really the transformer itself but is related: transformers are designed for impedance-matched systems, and most speakers' impedance is all over the map, varying with frequency and power level.

The thing that "muddies" bass is not just (or just "not") the rise time; the high output impedance means the amp cannot control the speaker, and it (the speaker) rings after a transient step.

Of course, all these "problems" are "benefits" if you like the sound, and in some cases help compensate other flaws in the system (e.g. transformer HF roll-off can help tame a bright speaker/room).

FWIWFM - Don

Click to expand...

Yes and negative feedback plays a big role in how an amp responds to the imposed speaker load eg. high NFB amps will deal with impedance dips/peaks better than a no NFB amp. OTOH, there's a penalty to be paid for using high NFB