Cascading diamond buffers - a cheap low THD 10W amp with TIP41C

[suzyj]

Edit: I just figured out the first post is a editable, so is a good place to keep up-to-date design docs without forcing people to wade through pages of guff.

Post # 151 (Cascading diamond buffers - a cheap low THD 10W amp with TIP41C) has attached current (as of 13 Jan 2018) design for a super-cheap low distortion amplifier using BD179 & BD180 output drivers. I'm rating it for 5W into 8 ohms, a little more into 4 ohms. It's just the ticket for driving tweeters and little full-range speakers. I'm thinking it'll be a useful 50 ohm line driver too.

I've attached .asc file, .zip of KiCAD source and gerbers, screen shots showing where everything is on the PCB, schematic screenshot, simulated behaviour pushing 10V pk into 8 ohms, simulated square wave response, simulated clipping, open loop gain and closed loop gain.

I've got the real thing sitting on my desk as I type playing music through a little 4" PC speaker, and it sounds like an amp that's not adding anything to the music.

[globalplayer]

Nice. Love the symmetry.
How does it sound?

[Oldvinylplayer]

Oh dear. Now I just have to get a move on with the line arrays.

Given that this is a ground up design, is there any advantage in making a higher voltage amplifier to drive more than one TC9 in series?

Graham.

[moschfet]

Yes very nice circuit, but why do you take the poor TIP?
Why don't you take some of the old known IRF-Mosfets? They are also cheap, but much better...I think.

[globalplayer]

I would be interested in a 300W 8 Ohm version.

[suzyj]

Originally Posted by Oldvinylplayer

Oh dear. Now I just have to get a move on with the line arrays.

Given that this is a ground up design, is there any advantage in making a higher voltage amplifier to drive more than one TC9 in series?

Graham.

Higher voltage means I have to ditch the 2N3904/3906 & 2N2222/2907 in favour of higher voltage parts - say MPSA06/56...

I'll have a play. Parallel might be easier, as it can be accomplished with more output devices.

I'm also playing with 3 sets of BD179/180 in lieu of the TIP41/42, simply because it allows me to spread the current source load across 3 transistors, and I can then use 2N3904/3906 rather than the BD139 there (higher gain), which in turn reduces current requirement for my reference.

[suzyj]

Originally Posted by globalplayer

I would be interested in a 300W 8 Ohm version.

That's not at all what this amplifier is.

[suzyj]

Originally Posted by moschfet

Yes very nice circuit, but why do you take the poor TIP?
Why don't you take some of the old known IRF-Mosfets? They are also cheap, but much better...I think.

Vgs on a MOSFET is ~2-4V, vs Vbe for a bipolar of ~0.6V. MOSFETs will need higher supplies.

[globalplayer]

Higher voltage, change some Rs, high power output transistors...

[DPH]

Series with higher voltage benefits class-b (ab, what have you) biasing conditions as you stretch/smooth out the crossover region*. Plus you can double your budget per amp.

*Distortion In Power Amplifiers Figures 15-23