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In Reply to: RE: how much power do you need? posted by Russ57 on January 22, 2015 at 14:57:52
Well I thought I'd use these speaker I bought from the second hand store.
DENON SC-M51 not the most efficient speaker for this plan (I think 88db) but they were 16.00 for the pair :). I thought there might be something wrong with them. I got them home and they sound great through my old Adcom gfa-545 and Apt Holman preamp that I've had forever. Like I say I have built guitar amps but never Hifi.I was always kinda intimidated. When I look at the schematics many of them seem simple enough. Thanks for all the suggestions so far really appreciate the feedback/help.
https://www.youtube.com/watch?v=IGDsZh3mMqc
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Tube watts are precious. To get more forces you into pentode, ultralinear, or tetrode mode. Doing that forces you into feedback. All of that forces you into a much greater understanding of electonics and the need for better measuring devices. If you can avoid all of that it is much simpler to build something that sounds good (IMHO).
Speaker efficency is the key to that goal. If you can put together something that presents a constant impedance at a reasonable XXdb/watt then you can forego feedback and high wattage. I have found that looking at pro audio speaker offerings is the ticket. I also think it pays to consider an active crossover and and bi-amping. Real bass takes serious wattage best served by a solid state amp.
Just my 2 cents based on what I have discovered over the years. Certainly you can build a higher wattage amp and use more traditional speakers but I find that a harder way to to go.
Russ stated a fundamental truth. Regardless of technology, proper mating of amps and speakers is crucial to obtaining a good result.
Paul Joppa has provided the 'phile community with a useful rule of thumb, for mating amps and speakers. Joppa's Rule states that in an "average" listening space an amp/speaker combo should be capable of producing 102 dB. SPL peaks at a 1 M. distance. Even if the Denon speakers are honestly rated and "tube amp friendly", they are not suitable for use with any amp you can make using the "iron" already in your possession. To make matters worse, many commercial speakers need to be rerated, when combined with tubed power amplification. A nominal 8 Ω speaker that exhibits substantial dips in its impedance curve, especially in the bass region, has to be treated as being 4 Ω, when mated to a tube amp. Another "gotcha" is a speaker that is 4 Ω and rated at nn dB. for 2.83 V. of drive needs derating by 3 dB., as 2.83 V. into 4 Ω is 2 W. Tube power amps, with their O/P trafos, produce the same power on all the speaker taps.
Eli D.
Thank you for that very informative reply. This is going to take some thought and planning and I'm up for it :)
Most of them are wide range and efficent. Could make the start of a good set of speakers. We all know a 6v6 guitar amp can play pretty loud.
Yeah what you say makes sense. What started this was my signal tracing of a el84 guitar amp while I lay on my bed. I fixed the problem then laid there listening to my ipod through the guitar amp and a single Reverend Alltone 12 inch speaker.Maybe it was the glow between my ears and satisfaction of getting that amp going, but i really enjoyed the music while i drifted off for a "little nap"
Edits: 01/22/15
A fellow once made a remark to the effect that a tubed HIFI amp is a guitar amp gussied up in lipstick and nylons. It's a bit more complicated than that, but many circuit elements are common to both applications.
While a guitar amp is a distortion machine controlled by the player, a HIFI amp is supposed to reproduce that which the performer(s) laid down.
Eli D.
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