Switching current source for Class A?

[QED047]

Originally Posted by Lumba Ogir

Hi,
considering the aggressive nature of this circuit architecture, it would most certainly be less painful to live with the crossover distortion of the output devices.

I understand what you mean, however there is a definite listening pleasure to be had from a single-ended output. Class A-o-philes will happily argue that point all day.

The price of heatsink is far higher than the cost of parts needed to replace it using the current switching circuit we have here and although it may look rather foreign in an amplifier, if you take everything from the sense resistor down and put it in a "black box" labelled "current sink" it does no violence to the purity of a single-ended o/p stage. In fact, this is literally how I would recommend configuring a practical implementation of the idea.

[Lumba Ogir]

QED047,

there is a definite listening pleasure to be had from a single-ended output

That`s aiming far too high. Seemingly, you are cheerfully unaware of the difficulties associated with this kind of attempt. As for now, the damages are in all probability greater than the benefits.

[QED047]

Lumba Ogir, you seem to be determined to discourage us. if you're talking from experience then it would only be fair to let us know what practical issues you are referring to. My own experience is that switch-mode can deliver highly worthwhile audio amplification and that it can be both fun and profitable to experiment with these readily accessible techniques.

[payloadde]

Well, speaking for myself, for me this is just playing around. Proof of concept kind of thing.

I actually found a solution to adjust the standing current with my current mode PWM regulator chip. For that purpose I increased the gain of the sense amp to 30x and added a variable voltage devider to it's output with a range 1/1 ... 1/3. This gives a standing current variation between 0.7A ... 2A. This potentiometer is mechanically coupled with the volume control. Needs a 4-way pot for stereo then. The DC servo perfectly keeps the midpoint voltage, no need for a cap at the output.

Again, just a demonstrator. For a serious project this would need to be scaled up a bit. 60 volts +, 5 amps +, SMPS power supply, output filter, pre-amp.

[payloadde]

Sorry, there was a mistake in this drawing. Here's the corrected version.

[Lumba Ogir]

QED047,

Lumba Ogir, you seem to be determined to discourage us.

Not at all, on the contrary. You should pay greater attention to signal integrity. Every part will effect (harm) the audio signal. You should also think more in the time dimension. Every diode junction introduces a time delay, precluding accuracy.

My own experience is that switch-mode can deliver highly worthwhile audio amplification

It depends on the definition of worthwhile. If you mean efficient audio amplification, I can agree.

[QED047]

Originally Posted by payloadde

Well, speaking for myself, for me this is just playing around. Proof of concept kind of thing.

That's the spirit I hope you're getting a big kick out of seeing a heatsink-less transistor doing the job down below! But what are your impressions about the sound you get? I've done some critical blind listening tests using QED junior's *very sensitive* hearing equipment and there were no significant correlations to be had!

[payloadde]

What about the sound ?
Well, it seems that this little (s)witching devil fools me into believing that
a) I hear all the music there is
b) I cannot hear any of the artifacts from the rude treatment in the cellar.
After all we are chopping several amps of current 400,000 times a second into pieces and then of course I've got this terrible pain in all the diodes down my left-hand side ... ;-)
so where's the catch ? there must be ! THD could be terrible if we decided to measure it.

In one of your previous posts you wrote:
the four resistors around the sense amp (10k & 1K) need to be matched to within 1% or better to ensure proper behaviour...
May I ask what were the symptoms before matching them ?

[payloadde]

Preliminary Final Version

[ontoaba]

Originally Posted by payloadde

Preliminary Final Version

Nice, you made it with safer Vgs area from ripple when compared to that original schematic at page 1.

Look at here, just for references. Another liear+switching mixture

Class-AB meets Class-D: Yamaha's EEEngine Topology - where are this Diy Projects?