Amp Camp Amp - ACA

[opa1]

I have my linear supply wired up. 18-18 200va to two BR's and four 50v 22000uf caps with two 3.3k resistors at output per side. I'm getting 25.3volts DC unloaded from the PS. Is this voltage going to be too high for the ACA?

 

[kpsthakur]

Yup

 

[Zen Mod]

it'll be good ..... just take care to have output node biased on proper DC potential , same ratio as with regular PSU

 

[opa1]

So set bias at 12.5v for the 25v supply?

 

[ZacharyP]

Yes

 

[opa1]

Cool! Thanks for the help!

 

[Variac]

There is a new amp kit but it's not an ACA and will be more expensive.
The ACA will continue at what we hope will be a lower price!

Don't know if anyone else saw this, but Nelson has announced on First Watt
that ACA #2 is in the pipeline. He wrote that it will be released at Burning Amp on November 12.

 

[kpsthakur]

There is a new amp kit but it's not an ACA and will be more expensive.

The ACA will continue at what we hope will be a lower price!

:Cramps:

Any ETA in them??

 

[2 picoDumbs]

So set bias at 12.5v for the 25v supply?

Go back and check my results. I think I mentioned the value for 24V supply.
All my settings were made measuring across Vds of Q1 using a distortion analyzer for best results.
13V might be a better setting for 25V supply. 12.5V might be considered good enough.

 

[ZacharyP]

it'll be good ..... just take care to have output node biased on proper DC potential , same ratio as with regular PSU

Why do you recommend 14v bias?

 

[2 picoDumbs]

Why do you recommend 14v bias?

There is a sweetspot of about +/- 0.1V outside of that you start seeing much higher levels of undesirable harmonic products.
14V may or may not be the sweetspot for 25V. I can't remember but if you look you can see what the sweetspot was for 24V.

 

[opa1]

I looked back in the thread. @2 picoDumbs 24v supply was running at 12.5v.

I pulled out a decent lab supply and set it at 24V

THD is roughly the same but higher order harmonics have been reduced compared with 19V supply as previously observed with the 26.6V supply.

Vds across Q1 was set at 12.5 V

Bias is around 1.35A with Papa mod.

 

[2 picoDumbs]

So maybe around 13V might be a good starting point for a 25V supply or a bit higher.

 

[2 picoDumbs]

I could possibly measure it when I go back to work if you really want to see the effect of varying the voltage

 

[opa1]

I should have mine finished in a few days. I don't have test equipment to check. All I can do is set the bias. My linear supply puts out 25.3vdc without a load to each board. If you could check that out it would be great!

 

[2 picoDumbs]

What is the loaded voltage?
Are you using 2.2K across b and e of the bipolar transistor.
What mosfets are you using?

 

[opa1]

What is the loaded voltage?

Don't know yet. I just powered up the supply to check its operation. Its the second gen pcb. Has the 2.21k R15 built in. the MosFets are
IRFP240PBF

 

[2 picoDumbs]

Ok good.
I'll wait till you're finished to confirm the loaded supply voltage.

 

[Variac]

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.

:Cramps:

Any ETA in them??

 

[2 picoDumbs]

Cool.