2. amps-preamps
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Power output of tube amps compared to solid states

I'm having a hard time trying to figure out how tube amp power output relates to solid state power output. I've been looking at the classifieds for tube amps and I see lots of tube amps with 50w or 60w output, but nothing close to the 250w output typical of solid state amps.

So I have no idea what type of tube amp is required for my set up, right now I'm using totem forests with a required power rating of 150w-200w at 8ohms. The bass is so powerful on these that I have the sub crossover set to 40hz.

My question is, are tube amps so efficient that 50w from a tube sounds like 150w from a solid state? Or will 50w output from a tube severely limit how loud I can play my speakers? If so, are tubes usually meant to be driving super-high efficiency speakers?

I had previously tried a tube pre-amp with a solid state power amp (both musical fidelity) and didn't like the results because the imaging suffered greatly, even though the music sounded nicer from a distance. Now I want to try a solid state pre-amp (bryston) with a tube power amp (no idea which brand to look at), but I don't know how much power output I need or if it will even be possible with my speakers. Does anyone know what I would require?
acrossley
atmasphere's avatar
atmasphere
11,958 posts
 
Myles, the mbl has an impedance peak of about 8-9 ohms in the midrange driver. The designer is expecting the amp to reduce power by 3 db through this range. An amplifier with feedback will do it, one without will not. A good number of tube amps tend to sound shrill on this speaker even though otherwise they have plenty of power. So Michael was probably using an amp with a lot of feedback.

The problem here is that IMO, amps with feedback sound somewhat shrill out of the box, IOW its my opinion that a speaker that requires this will never sound like real music.

Kirkus, I know about the TIM articles but obviously amps designed to overcome that 'issue' were horrendous.

IMO the issue with feedback boils down to open loop propagation delay in the amplifier- IOW its a timing issue. The feedback signal simply does not arrive back at the input in time to make the correction. With a steady-state signal, the amp locks in pretty well over a few iterations, but with a constantly-changing waveform the amp will be chaotic. This is an interesting subject and I agree- a topic for another thread.
emorrisiv
313 posts
 
What a incredible collection of very high-tech posts! You guys lost me at the first page of the string.I guess all the music I have been listening to while trying to follow along has put me into a brain overload.
I own Acoustat 2s with a really old tube preamp and a old ss power amp.This seems to be a pretty good combination, though I have to say I look forward trying out a tube mono block setup.
I will say that my experience is that tubes sound more alive and real to me.IMHO goes without saying,s
ince I have no where near the knowledge of you guys.I bow to your expertise.

Ralph: Will your 60watt OTLs work (with zeros) or do I need to save up more for your 140watt monsters?

e
pubul57
3,712 posts
 
Always thought the Acoustats were designed around the "current" paradigm. I would be surprised if the M60s would do it, Zeros or not. Always seemed like SS was the way to go with that speaker, but....
emorrisiv
313 posts
 
I have heard them with tubes and they make magic.SS is surely the norm, but I have used a 60 watt Arcam SS amp and they were not bad,not as good as with the 120 watt Hafler but not bad. This made me wonder about the 60 watt tube OTL with zeros.
What I have found with these speakers is;the better you feed them (quality that is not quantity)the better they sound.

cheers

e
atmasphere's avatar
atmasphere
11,958 posts
 
Emorrisiv, I've heard the Acoustats sound great with a set of M-60s and a set of ZEROs. The guy that had them also had an ARC Classic 60, and he had to use the ZEROs with that amp also. They seemed to otherwise present a challenging load for a tube amp, but my guess is that they were doing what a lot of ESL manufacturers do, which is to set the impedance low to try to get transistors to work with them.

At any rate Acoustats and tubes are a great combo if you can overcome the impedance issue, and ZEROs do that quite well.
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