Class A Should Be Called Class E(xpensive)....
I learned this lesson years ago.....I ran a relatively high bias current, high power PA amplifier as my only music source during my waking hours, and then discovered the difference to my power bill....😱 .
500W+500W is big fun when called upon, at normal/low levels the effectively infinite headroom and absence of distortions is a delight, however the power costs go against my wallet, and especially the 'greenhouse' costs go against my principles.....most of my listening nowadays is on a pocket portable AM radio running rechargable AA batteries !.
I am getting around to building setting up a solar/battery powered +/-12V or +/_24V audio system for the design exercise and to see what can be achieved, and for the 'greenhouse' guilt free listening 😉.
Anybody here have experience of running chip amps (TDA7294 etc, or others) on +/-12V or +/-24V battery supply ?.
Dan.
I learned this lesson years ago.....I ran a relatively high bias current, high power PA amplifier as my only music source during my waking hours, and then discovered the difference to my power bill....😱 .
500W+500W is big fun when called upon, at normal/low levels the effectively infinite headroom and absence of distortions is a delight, however the power costs go against my wallet, and especially the 'greenhouse' costs go against my principles.....most of my listening nowadays is on a pocket portable AM radio running rechargable AA batteries !.
I am getting around to building setting up a solar/battery powered +/-12V or +/_24V audio system for the design exercise and to see what can be achieved, and for the 'greenhouse' guilt free listening 😉.
Anybody here have experience of running chip amps (TDA7294 etc, or others) on +/-12V or +/-24V battery supply ?.
Dan.
My experience is that class A can really sound very good. I've built 2 very similar amps recently with nearly identical CFA topology. One version is a 15W full class A amp, and the other is a 100W Class AB.
I listened to both of them on a pair of B&W703's and a small set of book shelf speakers of local Taiwan design. I know that both amps are perfectly stable, can drive difficult loads without any stability issues etc. The class A has about 28 dB of feedback while the AB has about 40 dB of feedback.
They do sound different, and on certain types of music, the class A definitely has the edge.
So, if you have some efficient speakers and all the goods to build the Hiraga's, I would go ahead and do it - If you do a good job I am sure you will be rewarded with a wonderful sound. For the Hiraga (20W class A design), you will need a very substantial heatsink. My class A runs at 1.4A bias current, and uses 0.4C/W h/sinks - the temp is up at 60-70C, which is a bit on the hot side.
Here's a link to my class A amp Ovation sx-Amplifier
I listened to both of them on a pair of B&W703's and a small set of book shelf speakers of local Taiwan design. I know that both amps are perfectly stable, can drive difficult loads without any stability issues etc. The class A has about 28 dB of feedback while the AB has about 40 dB of feedback.
They do sound different, and on certain types of music, the class A definitely has the edge.
So, if you have some efficient speakers and all the goods to build the Hiraga's, I would go ahead and do it - If you do a good job I am sure you will be rewarded with a wonderful sound. For the Hiraga (20W class A design), you will need a very substantial heatsink. My class A runs at 1.4A bias current, and uses 0.4C/W h/sinks - the temp is up at 60-70C, which is a bit on the hot side.
Here's a link to my class A amp Ovation sx-Amplifier
Hehe exactly my reason to avoid class-A. Because my amplifier has to run 24 hours per day when I'm at home. My class-A has never been as high as PA amps, only 60W of Moskido and a variation of Aleph amps. But I keep a few low power ones (around 25W).
Imo, the benefit of class-A is the absence of the fatigue due to distortions. When class-B is a must, then I will not rely on THD, but I will rely on the simplicity of the circuit while capable of delivering "acceptable" THD and other performance.
Yes, simplicity often brings "unmeasurable" merits. That's why I have Lazy Cat's/Shaan's VSSA and similar higher power circuit.
Of course. But what story to be told? Even conventional power supply is preferable than a battery 😀
But 7294 requires higher voltage. Car chip amps are the most suitable.
Going by andersonics calcs a 50w class a amp burns approx 6 cents per hour. I'm ok with that. I don't think class a amps are responsible for much more than good sound 🙂.
and one can run a low bias high voltage class A push pull amp. or call it a high bias class A/B amp if you wish. +/-55V and 1.3A bias. that will give you a good 25W class A at 8ohm. and 130W class A/B at 8ohm. around 13W class A at 4ohm and 250W class A/B at 4ohm. given the PSU is up for the task.
then you have the clean good class A sound. AND you get plenty of headroom.
then you have the clean good class A sound. AND you get plenty of headroom.
I was talking class A/B, but it still chewed appreciable power at any output, including idling...the cooling fan switched in and out at idle.
I don't leave 200W of lamps on for no reason, much less an audio amplifier.
Hmmm, I have repaired Krells and others, and I am not totally 'sold' on the sound....Doug Self has good things to say about pure class B done correctly, but then again it maybe that he has 'engineers' ears.
Ok, I need to read up on these.
I am ok with limited power output in this application....tv/radio/background music with some 'audiophile' listening, albeit not at AC/DC concert levels...I have had that and it was big fun, but not necessary in this instance as I get to work/hear plenty of big live shows.
With decent lead/acid battery supply decoupling, what's wrong with running +/-24v ?.
Dan.
Nearly on topic.
If an amplifier is left in the quiescent state and it is a type that has been arranged to have a low current draw, i.e. ClassB, or quasi complementary, or high Re complementary, or CFP output, then is it usual for the mains to see a very high load impedance?
If this is the case, could a "standby" feature which mutes the input to the amplifier take advantage of that high load impedance?
I am wondering if a capacitor placed in series with the primary feed, while the standby mute is in operation could reduce the transformer resistive losses?
The capacitor would place a lossless dropper in the mains feed, but still keep the amplifier warm and ready for instant start up. Or am I wrong?
If an amplifier is left in the quiescent state and it is a type that has been arranged to have a low current draw, i.e. ClassB, or quasi complementary, or high Re complementary, or CFP output, then is it usual for the mains to see a very high load impedance?
If this is the case, could a "standby" feature which mutes the input to the amplifier take advantage of that high load impedance?
I am wondering if a capacitor placed in series with the primary feed, while the standby mute is in operation could reduce the transformer resistive losses?
The capacitor would place a lossless dropper in the mains feed, but still keep the amplifier warm and ready for instant start up. Or am I wrong?
You have about 140W of quiescent dissipation. You will need some very good heat sinking to deal with that.
Krell had a scheme that kept the output stage quiescent at low levels (I.e class AB levels). When the signal exceeded a certain level, the bias was switched to class A levels with a long delay time ( seconds) after the signal dropped back below the threshold. This type of circuit is very easy to arrange and on a big class A amp can bring some substantial benefits in terms of energy saving.
130W pr ch. thats not much more then my 25W class A amp. and you also get the class A/B headroom. when you pass 250W pr ch. then you can talk about serious cooling🙂
I don't have extremely expensive speakers. I use JBL 4412 and 4425 and a pair of Dynaudio nearfields. I listen mostly to music from CDs. While the KSA is less fatiguing, the Sysasym has a more open sound and is more detailed. If I just want music playing in the background while I work, I prefer the KSA but if I want to sit and do critical listing to a piece of music, the Symasym is where I go. It just reveals more of what is there. YMMV
Agreed on the Krell....nice enjoyable listening overall but a little too smoothed and lack of fine detail.
Nice enough to live with, but ultimately uninvolving really.
No experience of the Symasym, but I should do some reading.
Dan.
Class Distinction.....
Could you please provide quotes of his findings of Class A ?.
Dan.
If I recall correctly he reckons his tri-modal design exhibits very little change according to operational mode.
Could you please provide quotes of his findings of Class A ?.
Dan.
Yes, Self's tri-modal looked interesting as a way to keep one's class A amp warm while in "stand-by" (class B) mode. But book went back to library, so no quotes...
Could resonance be a problem/or advantage here ?
Just thinking that something like a 5H primary inductance and a series cap of say 1.5uf with 230 volts rms applies would generate over 1Kv rms across the inductance.
That's just a theoretical example and a real transformer with secondary and loading is very different. Maybe some combination of cap and tranny could be useful.
Often designers like Shelf or Pass forget that there is people that listen or better word will be enjoy techno or house music
Often posters of the forum post an opinion that makes god of class A based on their private and favorite music
Often many amplifiers of the past was designed in a piece of paper and a simple 1USD calculator and then got refined and re-visioned only by LISTENING resulting audio equipment with an aspect based on the listening criteria of the designer
HUGE example and easy to read article is the Hafler DH101 preamp that after launched in the market had a quick revision in the RIAA and the curve was corrected Now if you look at the corrected curve from the graph you will easily realize that the wrong response will actually enhance classic rock music which speaks on its own Classic American guy( David ) at the 70's is not expected to listen to Disco music for example 99% is expected to listen to Eric Clapton or Elvis or something like that
Try to listen techno music with small First Watt amplifier or with the Mark Houston amplifier or with an Aleph I dare to say also with a HAfler DH 200 it will not work !!!
The bottom line is always drawn by the listener , Down under it will say :
That's the way i Like it !!!
Learn to live with that !!
Kind regards
Sakis
Often posters of the forum post an opinion that makes god of class A based on their private and favorite music
Often many amplifiers of the past was designed in a piece of paper and a simple 1USD calculator and then got refined and re-visioned only by LISTENING resulting audio equipment with an aspect based on the listening criteria of the designer
HUGE example and easy to read article is the Hafler DH101 preamp that after launched in the market had a quick revision in the RIAA and the curve was corrected Now if you look at the corrected curve from the graph you will easily realize that the wrong response will actually enhance classic rock music which speaks on its own Classic American guy( David ) at the 70's is not expected to listen to Disco music for example 99% is expected to listen to Eric Clapton or Elvis or something like that
Try to listen techno music with small First Watt amplifier or with the Mark Houston amplifier or with an Aleph I dare to say also with a HAfler DH 200 it will not work !!!
The bottom line is always drawn by the listener , Down under it will say :
That's the way i Like it !!!
Learn to live with that !!
Kind regards
Sakis
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