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Colin Dunn
Reply with quote  #1 
I know Transcendent hasn't designed or built one of these yet, but I think the world needs a multi-channel tube amp for home theater and surround music applications.

There is a Chi-Fi 5-channel tube amp, the Meixing MC5S. They're not widely available, though I did find one on-line reseller that quoted the price at about $1,350. This amp has five channels at 70 watts per channel. The amp takes 20 tubes! Five 12AX7s, five 12AU7s, and 10 KT90s.

Maybe it's a tremendously small niche, but I'm surprised no one has designed and built a 5- or 7-channel tube amp with about 25 watts per channel. After all, 70 watts will get you only 3-4 dB more headroom than 25. Tube fans likely have efficient speakers as it is. I'd think the lower power would be an acceptable trade-off if smaller, less expensive power tubes could be used. A 25-watt amp is quite practical for home theaters with horn-loaded speakers. With normal dynamic speakers with an 88-90dB sensitivity rating, such an amp would fall about 5-10dB short of full reference levels, but who listens to movies that loud in their home?
PetrL
Reply with quote  #2 
Look at the Son of Beast - most power per standard chassis volume and it is only 15 Watts/channel. Your idea is not viable with OTL, in my opinion. Not to mention that the PSU etc. would have to be too much of compromise for Transcendent (it actually is for virtually all multichannel amps).

What would be possible is a multichannel preamp, maybe 300Bs for main channels and some 12A?7 for the rest... Then hook whatever power amps you prefer.
CharlieM
Reply with quote  #3 

Almost reluctant to respond, but as I have the experience.

I had a 7.1 all tube, almost all OTL surround set up.  The beastz driving the fronts, the Mini Beast driving the sides, the CFA driving the rears, and a Dynaco ST70 driving the center and ".1" bass channels. Four GGs driving each amp.  An Oppo Blue Ray DVD 7.1 player as the source.  The following are my impressions and things I believe anyone should consider.  

First, a space suffcient to encompass everything and for the sound to disseminate.   Mine was 4 meters by 9 meters.  I had a dedicated 20 amp outlet which powered everything, and it was at its limits.  I had to custom make a display case to place everything on, and with that much gear it could look ostentatious if not presented properly.  The heat generated, even in the middle of the winter, meant opening a window or two.  If I had it to do again the case would be enclosed with its own dedicated cooling source.

Front, side, center, .1 and  rear speakers where carefully chosen and assembled or modified.  Unless it is for just one listener or viewer in a focused seat, movie viewing or even 5.1 SACD listening, IMO should lean towards a wider/off axis speaker.  These are usually of lower efficiency and a bit harder to drive by a low powered OTL than the high efficiency full rangers we often use with OTLs that have a pronounced beam and are therefore unsuitable for surround sound systems.  It is entirely possible to put together two and even three way systems with 91 to 93 SPL drivers that cover the spectrum while throwing wide dispersion, and are still small enough to mount on walls for the sides and rears.  Then, even the 4 watt CFA or Mini are powerful enough as side and rear power amps.

It takes a while, using 4 GGs, to balance the sound front to rear and side to side. For that reason it is also necessary IMO that each and every channel have its own dedicated attenuator.   (One could eliminate the preamps and have the volume controls on the amps and take the DVD player directly into the amps.  There are a number of small tranny-coupled two-tube power amps out there that could be fitted on a chassis that although larger than the standard, still small enough to fit in a number of rooms.)

Besides being very expensive as compared to a Bose “out of the Box” all in one 7.1 system for example, it is not really practical.  More often than not I would just listen in stereo rather than fire everything up.   There's the old adage that you only have two ears and so you shouldn't need more than two channels.  Yes, IMO this works entirely well for listening to recorded music, which is usually, even live, presented in front of you. 

However, movie watching and its subsequent surround soundtrack are a whole other world. And although impractical, the sound quality of the above system took movie viewing into not just another level, but into another realm.   Much more three dimensional and immersive, as compared to an out of the box 7.1 all in one system, or even as compared to a THX digital extreme system in a commercial theatre.  The only thing that could be improved upon is the replacement of the GGs with MPs. There is no comparison, OTL amplification does to movie soundtrack playback what it does to recorded music playback.   And TS OTLs are by far the best.

Colin Dunn
Reply with quote  #4 
I would agree that OTL is probably not the most practical design for HT applications. My question wasn't so much about Transcendent's current emphasis on OTLs, so much as why no one is designing or selling a multi-channel tube amp in general.

I would think that for HT applications, a simple class-AB design at 25W/channel would be the most likely route to having a usable 5-channel amp.

Years ago, I read "Audio Reality," so I know Transcendent has designed some amps that are not OTLs, though it seems that in the time since, they've found a niche selling this design.
sailor
Reply with quote  #5 
I know Bruce said that as good as the CFA amp was it didn't sell that well as he is known for OTL amps. I still own a CFA and it is a good sounding amp. But the power draw would be my greatest concern. I listen to DVD and Blueray at 2.1 and happy with the outcome.
Colin Dunn
Reply with quote  #6 
What was the CFA? The discontinued Super-Compact 100W amp?

As for power draw, the traditional solid state theater guys need a couple or three circuits to run seven channels of 200+ watt amps from the likes of Emotiva or Outlaw. The opposite school of thought from OTL but similar power requirements. So building a theater with 2-3 110V circuits to power the gear is not unusual.

Too bad the Super-Compact kit is no longer sold...
ed schilling
Reply with quote  #7 
The CFA........ "Cathode Follower Amp"

It was/is excellent and Sailor is correct. It just did not sell well but that had absolutely nothing to do with sound quality! Buce's "homeys" are after OTL. It's why we are here!
Ed
sailor
Reply with quote  #8 
Need to correct one thing after reading my post. As Ed said the CFA is a 3 watt transformer SE and an idle current of about 95 watts input. The power draw  of an idling MINI  is in the 280 area. The Beast is around 190/ channel for 8 tubes and probably about 260 per channel for 16 tubes. A 5.1 or 7.1 system would add up to a fairly high draw but not impossible. For comparison, My old Dyanco stereo El84 tube amp is around 12 watts output [claims 15] and idles at about 75 watts. Most not all 5.1 systems use inefficient speakers and is where most systems would have a problem as bluray is very dynamic and has massive power swings with special effects requiring large watts to drive.
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