Amp Camp Amp - ACA

[Variac]

In fact some of the kits have 50v caps because we had them.
Your substitution would be a tiny upgrade!

Originally Posted by bcmbob

Hi, I'm an Amp-Camp nubee who just received two PCBs and am placing a parts order. This may have been answered earlier in the thread but I haven't read it all yet. I have several 3300uf 50V caps from a mis-order. Can I use these instead of the 35V spec on the BOM?

[BertW]

Does anyone know the source for the Amp Camp's
surplus aluminum? or an alternate surplus Al source?

[bcmbob]

Check out Metals Depot

[Loudthud]

Originally Posted by Congo5

Hi all, new here. I ordered boards and parts from Mouser today. I want to use this for headpones, othodynamic Fostex T-50's. I am new to DIY amps, but have read this thread, have built several CMOY's and have some background with electricity. HVAC, automotive, computers. These phones are rated at 3000mw. I measured a 1k sine wave from BK Precision 3020 modded t-50's....3.23v=104db * ** 4.14v = 110db so if math is correct 3.2v squared divided by 50ohms is 204mw .. 4.14v would be 342mw. If I understand the formula.... I can double R1,R2,R3,R4 and have enough power and a lot less heat. So I ordered extra 3W 1ohm and 1.3ohm resistors. If there is interest I can document the build and post it. I have an oscilloscope but can only do basic things so far... Thanks

You could just leave off R1 and R3 and that would cut the current in half. I suspect the distortion would increase because Q1 would be farther into it's non-linear zone and open loop gain would be reduced. The distortion will be low order, you might actually like the sound. I like listening to mine with the feedback disconnected. Just remove R12. My latest build (#6) has a pair of IRF520s. They have a flatter distortion at 1W graph.

[Congo5]

Thank You Loudthud...leave off R1 and R3..so obvious...now. Are you using this for headphones? I could try the IRF510 as I have them, I read the data sheets, just don't always know what it means... I also have a lot of IRFZ46N.....

[bcmbob]

Like most folks, I have a box full of wall warts and bricks, several surplus PC power supplies and a couple spare 22 V toroids. I understand that NP designed the ACA with simple PS requirements - but I'm curious if anything has shown itself to be preferred/optimum for this amp.

Also, as PC PSs provide primarily 5 and 12 volts, are there any mods necessary them match it up with the ACA?

[Variac]

The ACA is designed to operate with 19v and 2A per channel. Lots of laptop bricks are rated at 19v, anything over 2 amps is fine, or, obviously 19v, 4a for 2 ch. Conventional PC power supplies that go in a PC chassis aren't too useful for this.
If you haven't read his article in the articles menu in the blue band at the top of every page I'd suggest loking it over. It's full of good info.

Originally Posted by bcmbob

Like most folks, I have a box full of wall warts and bricks, several surplus PC power supplies and a couple spare 22 V toroids. I understand that NP designed the ACA with simple PS requirements - but I'm curious if anything has shown itself to be preferred/optimum for this amp.

Also, as PC PSs provide primarily 5 and 12 volts, are there any mods necessary them match it up with the ACA?

[Variac]

A surplus scrapyard in Santa Rosa , California. If you live close to there PM me.. the heatsinks are from http://www.heatsinkusa.com/
8.460 x 5" was more than enough per channel

Originally Posted by BertW

Does anyone know the source for the Amp Camp's
surplus aluminum? or an alternate surplus Al source?

[bcmbob]

Originally Posted by Variac

The ACA is designed to operate with 19v and 2A per channel.

Conventional PC power supplies that go in a PC chassis aren't too useful for this.

That's what I thought but I noticed this reference by waam68 in an earlier post. I have read just about everything but that post caught my eye.

[Loudthud]

Originally Posted by Congo5

Thank You Loudthud...leave off R1 and R3..so obvious...now. Are you using this for headphones? I could try the IRF510 as I have them, I read the data sheets, just don't always know what it means... I also have a lot of IRFZ46N.....

I had a pair of IRF120s with 1980 date codes from the Carter administration. The anti-static foam had caused corrosion on the bottom surface. I was committed to a TO-3 heatsink so I just scraped the rust off with a wire brush and installed them. They worked! The next amp used IRF520s (not IRF510) and it worked about the same. With the IRFZ46N you have somewhat higher input capacitance (than IRFP240) and higher transconductance. Probably a slight downgrade in sound quality without some changes to the circuit. The IRF520 gives a cleaner and smoother high end but slightly more LF distortion, probably because of the lower gain.

I'm using a smallish bookshelf two way reflex speaker with a first order crossover. The low damping factor of the ACA gives a nice bass boost to the 4 inch woofer. I don't know what to expect with headphones except a loud turnoff thump.

Playing with R1-R2/R3-R4 resistors changes the distortion quite a bit. It also changes the gain. It's a lot like the PLH amp. Nelson discusses the tradeoffs in his article. Link: http://www.passdiy.com/pdf/PLH_amplifier.pdf

Note: IRF120, IRF520 and IRFZ46 won't fit the ACA PCBs, you'll have to improvise.