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In Reply to: RE: Tympani IVs in a 12x 22 x9 room posted by neolith on May 15, 2017 at 11:24:31
Thank you for the informative response. It re-emphasizes how much more I have to learn. There is another Adcom GFA-555 available now. What are your thoughts of biamping with a pair of them?
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FWIW, for several years I had no trouble and enjoyed listening to my T IV-As using 2 of the original bridged GFA 555s, (as if each were a monoblock). I could played the speakers loud with no blown fuses, nor any other difficulty. I also did use the Adcom 555s to bi-amp the speakers to no advantage but requires a lot of nasty extra cables and speaker wiring (in addition to Magnepan's X-O). I also used a restored Adcom GFP 565 pre-amp, which I still use today. There wasn't anything wrong with this 565, but having it recapped provided some peace of mind, even though I couldn't detect a difference, (as if I added a $350 Tice Clock to my system).
Would you consider using the GFA-555 and GFA-555 II together as monoblocks? Or is there some sort of difference between the two that makes that undesirable?
IMO it's a try, (the 555 and 555II bridged consideration), as it couldn't do any harm, paying attention to learn if both speakers are performing similarly (both levels and sound quality) perhaps playing a 'mono' recording or if available engaging a 'mono' switch on a pre-amp even with a 'stereo' recording. I would swap the amps as well.
They will not do well with the 4 ohm load in bridged mono operation. It is better to biamp with the two amps instead. One amp per mid/tweeters and one for the bass . If the slight differences between them are not something that bothers you then you can vertically biamp one amp per speaker and save on a load of speaker cable.
Satie,There is a Crown Macro Reference available on Audiogon now. Would that be sufficient to power all six panels? Or is the Odyssey Kahartago and Adcom GFA-555 bi-amp a better option?
Edits: 05/16/17 05/18/17
The Crown Macro Reference can power up the whole speaker. better than the Khartago+ Adcom 555. But the Macro is hard a bit bright and thin sounding on top though it is transparent and detailed. The Odyssey amps are richer and fuller sounding. Using the Crown on top would make it necessary to match it with a tube preamp and/or solid core copper wiring..
The Crown would make for a terrific bass amp though. I use a Crown 5002 for my bass panels.
It seems then that the options are:1) Bi-amp with Odyssey Khartago on MT and Adcom GFA-555 on bass
2) Power all six panels with the Crown Macro Reference.
3) Bi-amp with the Adcom on MT and the Crown on bass?
There is an Audio by Van Alstine PAS 4i all tube preamp on audiogon for $439. Would be a good match with the Crown Macro Reference?
Please share your thoughts.
Edits: 05/17/17
Yes, the Van Alstine PAS mods are very good with tighter bass and more extended treble than the original Dyna pre. It will do fine driving a 10K input impedance but noticeably better into 50K.
The Van Alstine PAS tube pre-amp will be a real good match with any solid state amp, as long as it's output impedance isn't too high for the amp's input impedance (observing the old 10-to-1 ratio rule. A 1k output with a 10k input, for instance.). I had one years ago, and it's a nice pre, not too warm (without the Van Alstine mod, the PAS has the old classic tube sound).
Each Tympani panel is 16" wide, so a 3-panel array is actually 48"/4' wide, a pair taking up "only" 8' of room width. Still a lot, but less than 9'!
Turns out the second Adcom is a GFA-555 II and the matching preamp
Edits: 05/15/17
I prefer to biamp with two identical amps. It solves the problem of matching gain and I think the integration across the audio spectrum is better.
BTW, there are two ways to actively biamp - vertically and horizontally. In vertical biamping, there is one stereo amp for each speaker, similar to monoblocks - stereoblocks if you will. With horizontal biamping one amp handles the two bass channels, and the other handles the two treble channels. In order to vertically biamp, the amplifiers need to be identical. The advantage of horizontal biamping is that you can use two different amps. As I said, I prefer using identical amps and vertically biamping. This allowed me to place the amps right behind the speakers and use eight 2' pieces of 16 AWG magnet wire for the speaker cables. The IC's were balanced and unaffected by the long runs. Balanced IC's are much less affected by materials and construction compared to unbalanced and consequently much cheaper.
I married the perfect woman. The downside is everything that goes wrong is my fault.
Edits: 05/15/17
Be careful with the 555. I've had three, and they are notorious for their power supply capacitors leaking, and for blowing up, taking the speakers they are hooked to with them.
Either you have had some bad luck or I, some good luck. I have two of the original Adcom GFA-555s, and neither has even been recapped but both are in service today. I've used them to drive top/bottoms when bi-amping, and as bridged 'mono blocks' to drive Tympani 1Cs, IV-As and MMGs.
Admittedly long ago I showed some poor judgement and set one afire while playing the canons on a Telarc 1812 LP too loud. (CD weren't even around at that time.) It happened while I was driving Tympani 1Cs and Adcom was kind enough to replace it at no charge with yet another original GFA-555.
I don't know if your experience with 555's is more typical than mine, Norman, or visa versa. What I do know is that the 555 was a lot of amplifier for not a lot of money, a clear best buy. Anthony Cordesman's Stereophile review of it was, as usual for him, a bit over-enthusiastic (he was always trying to "scoop" all the other hi-end reviewers), as Stereophile owners/editors Gordon Holt and Larry Archibald stated in their follow-up comments.The amp was designed by Nelson Pass, but built to a price point. I don't know what causes some power supply capacitors to dry out (as mine had, I being the at least second owner) and others not to, but before hooking up a 555 to a valued set of speakers and turning it on, have it checked out on a test bench.
I bought one 555 to use for the bass columns of my Infinity RS-1b's, and a PS Audio 200C for the m/t panels, a good combination. As a 200C can be had for around the same price as a 555, I would much prefer the 200C. I actually still have mine, the 555's long gone.
Edits: 05/17/17 05/17/17
'If it ain't broke, don't fix it.' I myself have been on the "test bench" and most likely will continue to be there again in the near future (if I allow myself to be placed there), but my 2 Adcom 555s, NOT.
Ha! True, for one already having and using a 555 or two, no need to bench test. I was talking to anyone considering getting a 555.
The speakers have been purchased. A pair of Wyred4Sound mAmp monoblocks are now available at the same price point as the Crown Macrotech Reference. These would allow for vertical bi-amping of the Tympani IVs (not IVas). Wyred4Sound is well reviewed with Magnepans, but I wonder if there is any issue with mixing older and newer technology. Please comment.
Edits: 05/17/17
In a word, no problem mixing a class D and AB amp. Especially not a problem on the tympani where slight time domain variations between the amps can be easily compensated with tiny changes to relative distances between the drivers..
I had no problem obtaining coherent performance and great imaging using a blend of class AB, tubes and class D amplification in triamping and biamping my Tympani IV and with its modified Neo8 mids..
I am leaning towards the Wyred4Sound mAmps with the Tympani IVs, in a vertical bi-amp arrangement. I'll hang on to the Adcom and MMGs for a while until I get used to the Tympani Sound.
Very highly regarded little amps at their price point. Very convenient form factor.
Satie,Two Wyred$Sound mAmps or one Crown Macrotech Reference for the same cost?
Edits: 05/18/17
I would take the Crown Macro Ref. since it can do over 1KW into 4 ohms and has a deep bass that is very impressive. It is fairly easy to get around its thin high end signature with a tube preamp. And it drives anything while the mAmp is going to have problems below 3 ohms and has only 1/3rd the power.
It will be useful to have the extra power.
Thank you. I was leaning toward the Wyred4Sound as newer pieces, but the dealer was being difficult, so I will pursue the Crown.
The other thing that you would care about in owning a vintage amp is that there is a pro audio repair shop that can rebuild/service a Crown amp in practically every town.
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