Amp Camp Amp - ACA

[kpsthakur]

The classic ACA but new kits and configuration and price should be available about BAF time.



The mystery new amp should be revealed at BAF also.

Waiting eagerly...ACA has been a “Superhit” at my place

 

[opa1]

Ok Pico, I have it finished. I have 22.7vdc under load. Set bias at 11.42. This is after 1/2 hr. warm up and connected to 8 ohm speakers. Nothing on input.

 

[2 picoDumbs]

Increase Vds across Q1 to around 12V. That's a good guess to start with.
I will take measurements tomorrow to confirm.

 

[opa1]

OK will do. Thanks!

 

[ZacharyP]

Looking good!

 

[xrk971]

Has anyone made a micro ACA with all SMT, BF862, and SOT223 n-channel MOSFETs yet? That might be a fun small desktop amp or possibly headphone amp.

 

[2 picoDumbs]

OK will do. Thanks!

Ran out of time today, I was testing a new amp idea I had F4 Beast Builders

I will test your amp first thing tomorrow.

 

[2 picoDumbs]

OK will do. Thanks!

For 22.7V power supply
Anything between 11.4 and 12V across Q1 seems good. Outside of that you start seeing higher order harmonics being introduced.

Here it is at 11.6V Vds across Q1

 

[opa1]

For 22.7V power supply
Anything between 11.4 and 12V across Q1 seems good.

Here it is at 11.6V Vds across Q1

Good deal. Thanks for checking this. I have them set at 11.92. Seems to like it there. Runs cool for class a. I can hold my hand on the heatsinks after a hour warm up. I'm also glad I went with the linear supply. These sound better than the first set I built with the switching supply.

 

[ZacharyP]

Whats the highest voltage you can safely run an ACA?

 

[2 picoDumbs]

You could probably go to 30V, but it will require bigger heatsinks.

 

[moppy]

Can I use this?

My friend gave me his unwanted transformer rated at 12v-0-12v 50VA.

Can I use this underrated transformer for this ACA?

 

[kpsthakur]

Yup

 

[moppy]

Yup

Ok. Thanks. I'm worrying is under power.

 

[kpsthakur]

It is, may have to use it unregulated to achieve ~17V, but heavily filtered for noise

 

[ernesternest]

My friend gave me his unwanted transformer rated at 12v-0-12v 50VA.

Can I use this underrated transformer for this ACA?

As I remember, a rule of thumb is to take a transformer rated at least twice the needed power. My 19V ACA dissipated 25 W per side. My high power 24V ACA dissipates 35W per side.

So your tranformer might be good for a single side 16V ACA. 16V might be not enough for good sound.

My stereo 24V ACA relys on a 250W, 2x18V trafo (which I had unused laying around) and I would not go below 150 W.

Best

Ernst

 

[2 picoDumbs]

I think if you are going to deviate away from stock at least try and improve on the original design otherwise just use the 19V switch mode supplies.

 

[moppy]

Oh thanks.

Anyway, I have ordered this one. I think should be enough. I can't get a 14v, perhaps 15v I guess should be fine too, right?

 

[ernesternest]

Seems to be a good choice and bring you close enough to the wanted 19V. The few more you will get won't degrade the sound.

 

[moppy]

Seems to be a good choice and bring you close enough to the wanted 19V. The few more you will get won't degrade the sound.

Yes, I wish I could get the best sound of it.

By the way, according to original design, without modification like increasing the voltage and bias, how hot the heatsink will be? I ordered a heatsink from RS UK which rated at 0.29degC/W and the size is 150x200x15. I have ordered 2 pieces of this. Do you think I can fit 2 boards (left anf right channel) into 1 piece, so that I could save another piece.