I used to think I needed 30+ Watt but then I did the math. I backed it up with measurements. I found that typical listening levels were in the mW region. Hence, I question the need for power.
I think it's a perfectly legitimate question to ask.
~Tom
I run 80W/channel amps on half watt per channel average in order to get nice loud picks on forte-fortissimo. However, my listening room is big and well damped.
Well, plus some more watts on woofers and subwoofer, some much more...
Main speakers have 16 of 13W drivers, 2 inch high, 6 inch wide, with one tweeter in the middle, per side. They create cylindrical wave so stereo is well heard from wide angles. Nearfield is long, distortions are very low due to tiny excursion of individual cones needed to create equal to the single cone sound pressure...
Perception of loudness is highly affected by distortions of speakers. For example, we were watching a movie. Heroes spoke softly, then they entered a disco club... My wife complained: "Too loud!"
I did rewind the movie a little back and asked her to watch carefully indicators.. The level was almost the same, but ears reacted as if it was increased many times!
Hi Tom,
I've done the math too and have concluded like you that that first watt is the most important (hmm sounds vaguely familiar..
), but I suspect I like the occasional foray into the higher spl levels more than you do - which is OK since my very infrequent exposure levels to such sound levels are well with OSHA guidelines, but I am in the process of building a 20W per channel SE amp to replace the 7-8W a channel SE amplifier I am currently using because it will give me somewhat cleaner reproduction at the high end of my normal listening range and give me a few more dB for the times I want to go really LOUD.. (A few seconds at best.) I have found that with my speakers the 8W amp sounds much more dynamic than my 5W amp which sounds a lot more dynamic than my 2W amp.. You get the picture, the usual guidelines are 10 - 20dB of headroom over normal listening levels for peaks - the 10dB criteria is well satisfied with 30W and his speakers.. Of course it is also true that well designed tube amps clip much more gracefully than the typical solid state amp and in some instances you may not even be aware of a brief clip..My car also has a bit of additional headroom for the times I want or need it..
I designed a 30W 300B based PP amplifier project which was published in VTV about 12yrs ago. A fair number of people have built them.
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Perception of loudness is highly affected by distortions of speakers. For example, we were watching a movie. Heroes spoke softly, then they entered a disco club... My wife complained: "Too loud!"
I did rewind the movie a little back and asked her to watch carefully indicators.. The level was almost the same, but ears reacted as if it was increased many times!
Like you I have also observed this both with movies on the HT and in the car - only I suspect it is human perception and not the speaker at any reasonable Spls. (NPR dialog followed by musical clips which has me scrambling for the volume control in the car - Spls measured were comparable based on my crappy RS Spl meter..) My conclusion is that the ear/brain processes band limited sounds like speech and wideband material like music quite differently.. I have done measurements where the peak and average spls were very similar on speech and music, and I perceived that the music was much louder even though my measurement set up (audiotester or Arta, mic pre and mic) indicated there was not much difference at all.
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Aha!
Details still not completely rethought out, a couple of years ago I thought i knew exactly what I was building..
Currently I think I am building a two stage IT coupled GM70 amp.. The OPT is a custom Electra-Print 7K/150mA/40W monster, the IT a Lundahl with relatively low primary inductance (30H) is giving me concerns. Currently the plan is to drive it with a D3A triode connected with fixed bias to get the rp as low as possible (even leds increase the rp too much) - I may use 5842 for its even lower rp, but the concern here is whether or not I can even get enough linear swing for full power in plain old class A.. I'm no longer aiming for A2 although the OPT and chosen operating point make it possible (1kV/120mA). I may end up making the driver stage modular so that upgrades/swaps are easy. The only other thing that is nailed down is that the GM70s will be heated by Rod Coleman's CCS boards. (I figured why reinvent the wheel - his designs are sophisticated and excellently executed.) So that's it nutshell.
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1) PP or PSE
2) fixed bias by means of DC-coupled 6SN7 cathode follower (+/- 170-180V and 15K cathode resistor)
3) 250/60 mA to 270V/55mA about 4K for PP or 1.5K for PSE
First try a PSE or a PP like that.
DC filament supply or AC using a good 22R pot per pair. Buy selected Golden Dragon 2A3's. You can get good quality caps given the low voltage at reasonable prices. You don't need to swing tons of volts to drive 2A3's....lot of choicie for the front-end.
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thank you!
I think that for my needs I cant use PSE.. I want something like 30Watt
so I don't like the idea of paralleling so much 2A3's..
ppp is the way I was thinking..
I hadnt started to think abut the driver and phase splitter but I dont think there will be 6SN7 in it..
what abut 300V/50mA? i had seen some schematics that even exceeds this.. (I know, 300V max for 2A3..) what is the difference in sonic?
This starts getting you into class AB1 territory unless you use the 2A3-40 tube, but with this tube you can go up to 400 volts. The 2A3-40 is really a 300B type tube with a 2.5 volt filament.
Remember, as Kevin said, A pair of 2A3_40's will give you 30 watts.
I think there is some contradiction in your requests. You want 30W from 2A3's but don't want to parallel too many.
A PSE is 2 valves per channel. With a proper driver you will get more than typical amps both for PSE and PP.
6SN7 is spot on for that job. 6CG7 is as good as 6SN7 if you want a full glass tube.
The main advantage of 2A3 is high efficiency with low anode voltage and less voltage drive in comparison to other popular triodes. Anyway if you want to go higher then consider the Russian 6C4C which is specified for 360V. DC filament supply only. The sonic result is never dependent on the output stage only.
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P.S.
Another excellent choice for the DC coupled cathode follower is the 5687
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If I want something like 30Watts. if I go for PSE I will have to parallel a lot of them.. so it looks like PPP will be better for that
I think I'm satled on a the output stage..
as for the driver, I tried to understand how to design it, but i still dont fully understand.
how do I calculate the voltage swing to drive 4 PPP 2A3?
how do I calculate the input impadence of the output stage?
what else is matter for driving the output stag?
I know that there a lot of thing that I have to befor I start to billd this project, but this is my way of lernning those thing, I jump to the deep water..
so I'm sorry for all the nuby qustions...
so thank's for all the information, I'm learning a lot from this forum (not only from my post..)
I ment:
I know that there a lot of thing that I have to understand befor I start to billd this project
PSE is usually 2 valves per channel. With the 6SN7 (or 6CG7 or 5687) DC coupled cathode follower you will get no less than 9W. With good 2A3's and low loss OPT's you can get more, around 11W!!
In PP, with the same driver, no less than 14W. I think you should try one of these with normal efficiency speakers (84 to 90 dB's).....first!!
If you want 30W make a PPP. Use the same driver (dual supply of +/- 170-to-180V and 15 K cathode resistor for each section). You can bias the 2A3's individually or in pairs. If you bias in pairs then parallel the two sections of the driver, too. There is no difference between individual biasing and pair biasing, IMHO. Basically you just need to duplicate driver and output stage from a normal PP....
Half primary impedance (about 2K), of course.
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