Tube Amp for Green Mountain Audio Callisto


i'm considering switching to a tube amp to drive my GMA Callisto speakers and hoping to get recommendations from folks that have done so. What tube amps would pair well with the callistos?

The speakers have the following specs:
Impedance: 4.8 Ohms, +/- 0.75 Ohms from 100Hz to 20kHz
Sensitivity: 90dB

What would be the minimum power i can get by with? i don't listen at ear bleeding levels... maybe 80 db 12 feet from the speakers.

thanks in advance for any suggestions!

-Scott
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Do you have a decibel meter (like a Radio Shack)?

If you do, turn up the volume to your normal listening level at the listening position, then measure the decibel level from a distance of 1 meter directly in front of each speaker (left then right, or vice versa).

This will provide you with the decibel level at 1 meter when the volume is at your normal listening level. Try to measure a couple of volume peaks as well to get an idea of decibel level at loud points in the music.

For your speakers, 1 watt of power produces 90dB measured at 1 meter. Each doubling of power will produce an additional 3dB. So...2 watts will produce 93dB, 4 watts will produce 96dB, 8 watts will produce 99dB and so forth.

Using this info, you can determine how much power you will require to produce the volumes you prefer.
Why not ask Roy at GMA what his minimum power recommendation is?
With requirements like that you could get by happily with a 3W 2A3 SET amp. You would lose a little bit in dynamics, though.

With an 8W 300B, you'd have plenty of dynamics. (SETs, with their class-A operation and frequently overbuilt power supplies, and ability to swing much higher voltage than their wattage rating suggests for brief periods, usually have excellent dynamics within their power capabilities.)

Roy's speakers are an extremely easy load and SET-friendly despite the moderate sensitivity rating.
Scott,
Tho' I not owned the exact speaker you own, I did own the Green Mtn C1.5i 3-way floor-stander. My speaker was a 6-Ohm load just as benign as your stand-mount. I was quite successful driving my floor-standers using 2 very modest amps - the Jolida 502A, which was/is 60W/ch in ultra-linear mode & the AES/Cary Sixpac, which was/is also 60W/ch (because I had an upgraded power xformer) but this time in triode mode using EL34.
Both tube amps created beautiful, seductive music. My personal favourite was the AES/Cary Sixpac.
I believe that you could try either tube amp for not much money (considering the times). FWIW. Good luck!
thanks for all the excellent responses.

using a radio shack SPL meter, i turned the music on as loud as i care to listen with the following results:

~88-90db from the listening position (the big peaks sometimes hit 95), which correllated to ~90-92db 1m from the driver (big peaks hitting 97).

on paper it would seem that i could get by with around 8 watts, as that would equate to 99db.

i also called Roy - he so amicable - and he confirmed that with as little as 15 watts, the callistos will sound great.

i was thinking an atma-sphere S-30 would not have enough juice to get my speakers singing, looks like i was wrong. i'll also look into the 300B, Jolida and Cary options.

thanks for all the suggestions!
Consider also the Atma-Sphere M-60 monos...

Also, a VAC Renaissance 30/30 or 70/70 would be incredibly sweet.

There are used versions of all of these presently for sale.
Blue Circle gear has great synergy with GMA speakers. Disclosure: I am a Blue Circle and GMA retailer, Departure Audio. The DAR and FtTH ate hybrid integrated amps in the Blue Circle line. The new GDC integrated, while not a tube piece, is a terrific value at less than 2K and also a great match with GMA speakers. All of these have more than enough power to get everything out of the Callisto's. Blue Circle is one of the few lines GMA enthusiastically endorses with their speakers. Roy and I will be demonstrating these systems at some upcoming shows.
Srosenberg,

95 dB peaks at that distance is a far different story than 80 dB - in fact, you need about 32 times the power! So, forget what I said about a 300B and definitely forget about the 2A3! :)

(I know you didn't indicate you were looking at SET specifically but I thought I'd throw that out there.)

IF you are interested in SET, an 845 or 805 design would still serve you well. Or, actually paralleled 300Bs for around 20W.
I have a Response Audio/JoLida 60 wpc tube amp, as well as a Mapleshade-modded 18 wpc Scott. Both sound fantastic with my Callisto. With it's 90 dB rating, most any amp over 10 watts will drive it. Basically, it comes down to quality versus quantity with this speaker- although more power is always good for speakers IMHO. enjoy!!!
I would make sure whatever amps you choose have a "zero-negative feedback" option or are simply "zero-negative feedback" amps. Roy's design is both time and phase-aligned, so, personally, I'd only put hardware in front of my Callistos that also maintain the time-domain integrity of the audio signal.

I have only use Ayre hardware with my Callistos, but I have owned a set of AES Sixpacs and thought they sounded great. You can run these amps with zero-negative feedback. They only have a couple of drawbacks - they produce a bit of heat and with 12 EL-34 power tubes, they ain't cheap to re-tube. That being said, if I was in the market for tube monoblocks, the AES Sixpacs would be on my shortlist.
but I have owned a set of AES Sixpacs and thought they sounded great. You can run these amps with zero-negative feedback. They only have a couple of drawbacks - they produce a bit of heat and with 12 EL-34 power tubes, they ain't cheap to re-tube. That being said, if I was in the market for tube monoblocks, the AES Sixpacs would be on my shortlist.
Nrenter
Amen! I too owned a pair that drove my Green Mtn C1.5i floorstanders & I too can say that I really liked the sound of the combination.

If the originator of this thread is looking for tube monos this is one amp that he should short-list.
In my fantasy world where I have a system in each and every room of my house, one system would contain a fully tricked-out Cary SLP-98P and a custom set of Sixpacs painted to compltely match the pre-amp. I think that would be a cool setup.

One more thing to note about the Sixpacs: There is a lot of iron in each monoblock. If you've not lifted one, you'll be surprised exactly how heavy each amp is. New they are a bargain. Used they are a steal. Make sure they are packed *really* well.

If you decided to consider SS integrated, put the Ayre on your short list.
Wow...sorry for another post.

Sixpacs are on sale at MusicDirect.com for $1,750.00
I've had three different pairs of GMA speakers including the Continuum 3. Six Pacs were great amps on them but an 845 SET was even better.

(The Pacs are the best push-pull amps I've heard; triode operation with 0 NFB is a great way to do P-P!)
triode operation with 0 NFB is a great way to do P-P!
Paulfolbrecht (Reviews | Threads | Answers)

Agreed. My VAC Phi 110/110 sounded superb in this mode.
I would have expected this as well, but tried an Carissa Signature 845 amp with my GMA Eos HDs,and didn't like the synergy at all. I had fantastic success, on the other hand, with a VAC Avatar Super, as well as Eico HF-81. Both velvety full and lush. The Carissa Sig was thin and hard by comparison.