Amp Camp Amp - ACA

[leonski66]

Over my Pay Grade but I wish you the best.

Anything in the schematic looking like it won't take the higher voltage?

What voltage is the stock wall-wart? I'm up against a similar problem right now with a stereo piece WW is 12v 2a but I'd love to change to 8x Alkalines for experiment......Should work, right?

 

[6L6]

The modifications should consist of;

1) Unplugging the 19v bricks and attaching the 24v bricks.

2) Readjust for 12v at the test point.

3) Enjoy the music.

 

[TonyTecson]

moving from 19 volts to 24 volts, i found that in my build the voltage adjusted to the half of the b+ automatically....at least that is what i found, but you can see for yourself too....

 

[jerryo]

Really? No modifications at all required other than re-setting the test voltage to 12v
I read in the Build guide something about readjusting R12 from 68k to 39.2k for ACA version 1.0b! Is this not related to the increased voltage then?

Cheers

 

[TonyTecson]

ah, that has nothing to do with bias, that is all about voltage gains....you can change the 68k to half and the voltage gain is halved....

 

[invaderzim]

does this BOM look correct?

 

[Skylar88]

Where's 2SK170/LSK170?
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[invaderzim]

woops, those are kind of important. And I just noticed the pairs are sold out..

 

[Skylar88]

No need for a matched pair 170's for the ACA. But it is important is to get the 'BL' type for Idss between 6mA and 10mA.
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[invaderzim]

good to know. So the matching is only important if they are going in an amp where it uses two in the same board?

 

[osscar]

Looks like I also need to build an ACA - I got such a nice aluminum chassis. 0.5m radiators (consists of two parts - can be placed on both sides possible). The decorative front, side and top wood panels still need to be cut, but the chassis and radiators look suitable for ACA. I think it will be dual mono.

 

[thomasnadeau]

Where's 2SK170/LSK170?
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I just checked the store and they are in stock:

Linear Systems Matched JFETs – diyAudio Store

 

[Variac]

The JFETS only need to be matched if they are a pair in the same channel. So matching isn’t necessary for ACA. A really smart move of Nelson’s!

Some people like to use matched JFETS, one in each channel but it isn’t necessary.

 

[Variac]

B grade is what you want.

 

[invaderzim]

I just checked the store and they are in stock:

Linear Systems Matched JFETs – diyAudio Store

quads are showing available but pairs aren't. punkydawgs shows the 2SK170 on ebay and that is supposed to be a good source

 

[TonyTecson]

the bias trimpots take care of those, all the time....

 

[TonyTecson]

matching jfets

a 0-20 ma current meter like this one puts you in business....https://shopee.ph/product/238365398/4626734896

An externally hosted image should be here but it was not working when we last tested it.

 

[avitkauskas]

What would happen if you connect 4 ohm speakers to ACA? Would it run hotter? Use more power? Is it bad to ACA?

 

[Mooly]

Four ohm loading will not harm the ACA but it will lower both the maximum available output voltage and it will also lower any given signal voltage at the output terminals more than would an 8 ohm load because of the high-ish output impedance of the ACA.

What matters most is the impedance curve of the 4 ohm speaker because it is the peaks and troughs of that curve that will alter the voltage output of the ACA vs frequency.

The ACA runs hottest when it is idling with no signal.

 

[mraudioguru]

"The ACA runs hottest when it is idling with no signal."

Really? I did not know that. Please explain.