Making amplifiers more efficient

[keantoken]

I have started to understand amplifiers more and to get a general, yet feeble, understanding of how biasing works. I have found an old circuit that I was playing around with a while ago and while I was refining it, I found an interesting piece of logic. I had found two ways to fix the overdriving problem on Q1: lower R1, or increase R7 (the original values are not shown). I figured out that it would be more efficient to increase R7 but the amp would give more power if R1 was lowered . I opted for the more efficient method because this unit didn't work good for a higher-power design anyways. About the circuit, if something isn't right, then remember that this is what my simulator told me. I am wondering if R6 could function as maybe a volume control. If I was trying to make a hi-fi preamp I would definitely change Q1 and Q2 but I am not planning to do anything with this circuit unless it turns out to be the only one that will work out of my idea stack. Anyways, I was thinking that people could post efficient biasing ideas and maybe ways they found to make their amplifiers more efficient with virtually no loss in amplification. Heres the schematic:

[sreten]

Hi,

I can't make head nor tail of that circuit, simply it doesn't work in
any sensible fashion that I'm used to, so pointless to analyse it.

This is more like it :



from : http://www.zen22142.zen.co.uk/Circuits/Audio/audio.html

/sreten.

edit : bypassing PR1 with ~ 4.7uF will improve switch-off speed,
and ideally R4 should be bootstrapped form the output and ......
could go on, checkout :

http://sound.westhost.com/index.html

[keantoken]

Darn... My analyzation of the circuit is that the signal is injected at Q2's base which is connected to Q1 in a complementary darlington (of course you know that). Feedback is via R6 and C3. The only way I could get a speaker in there where it wouldn't create a phase shift in the feedback chain was to just connect it across the power supply . What seems wrong to you? Is it because of the way I have the schematic set up? The simulator is telling me that everything works, that both transistors are biased correctly... I couldn't connect the speaker to any of the emitters or collecters without having to worry about shifting the phase in the feedback circuit, and worse, the phase shift would change with frequency. The way I see it, any time you have a phase shift other than 180 or 0, you have got a capacitor or inductor filtering the details out of the input! I need a few more details .
I know that this isn't a symmetrical design, but you don't always need a symmetrical design for small-signal amplification.

[poobah]

Kean,

sreten has given an excellent circuit for building and experimenting with!

Put that in your simulator!

[EWorkshop1708]

You can't connect the speaker to the power supply.

Also, you need a transistor for the positive part of the music signal, and another one for the negative part.

Use the circuit he put on here, or visit sound.westhost.com

And to answer your question about biasing.......

To bias an output stage means to set how much current that the amp uses while on, but not playing music. Without biasing, the amp will play distorted music.

[keantoken]

nonetheless... Please post your ideas for making amplifiers more efficient! I know that this thread started out bad, but if I could delete the first few posts (of course, being OK'ed by the posters), then I would. I am hoping for this to be a reference for anyone who wishes to lower their energy bill a couple hundred dollars...

[poobah]

Efficiency is a measure of how much of the total power is applied to the amplifier's output. Class A amplifiers are very inefficient, in the range of 10–20% with a max efficiency of 25%.

Class AB and B amps are commonly between 35–55% efficient with a theoretical maximum of 78.5%.

Class D amplifiers can run as high as 97%.

BTW... don't even think about Class D just yet... REALLY.

So the "Class" of amp you build really sets the limits for you.

[sreten]

Originally posted by keantoken
nonetheless... Please post your ideas for making amplifiers more efficient! I know that this thread started out bad, but if I could delete the first few posts (of course, being OK'ed by the posters), then I would. I am hoping for this to be a reference for anyone who wishes to lower their energy bill a couple hundred dollars...

Hi,

Ideas ? the subject is beyond discussion, every configuration known to man has already
been analysed to death and is available in all the usual reference books on the subject.

/sreten.

[CBS240]

Actual components being used has a significant effect on any amp topology. Even the best design can perform poorly if poor components are used. Take fake output transistors for example. Just about all of us here has been shafted in this way by cheap knock offs. However, there are few SS designs out there that have not been thoroughly discussed.

[janneman]

Originally posted by CBS240
[snip] However, there are few SS designs out there that have not been thoroughly discussed.

... such as... ?

Jan Didden