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ACA-Nelson Pass's Amp Camp Amp


The Dude
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@CECAA850 you were correct, fun project and went off without a hitch. 

 

Currently running with a Schitt Modi DAC and my Heresys in my office.  I have tried different caps and different crossovers before and didn't really hear a difference.  Switched from one solid state to another AVR and never really heard a difference.  This time went from Yamaha Integrated receiver to ACA and am amazed at the difference it made.  Going to hook up a line stage/phono pre amp later today and see how that turns out.  Really impressed with this little guy.  May end up down a rabbit hole in years to come trying different Class A amps, maybe something for the K402's at home. 

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Just now, The Dude said:

@CECAA850 you were correct, fun project and went off without a hitch. 

 

Currently running with a Schitt Modi DAC and my Heresys in my office.  I have tried different caps and different crossovers before and didn't really hear a difference.  Switched from one solid state to another AVR and never really heard a difference.  This time went from Yamaha Integrated receiver to ACA and am amazed at the difference it made.  Going to hook up a line stage/phono pre amp later today and see how that turns out.  Really impressed with this little guy.  May end up down a rabbit hole in years to come trying different Class A amps, maybe something for the K402's at home. 

There was one issue, I didn't test the LEDs correctly and ended up with one good blue and one good red, oh well. 

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If you like the ACA, you would love some of the other Pass DIY amps. I have built an F5 and an M2x. IMHO, the M2x is an end game amp as long as 25 WPC is enough. I am using mine on the mids with BMS 4592ND drivers on K-402 horns and the sound is very good.

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8 hours ago, The Dude said:

@CECAA850 you were correct, fun project and went off without a hitch. 

 

This time went from Yamaha Integrated receiver to ACA and am amazed at the difference it made. 

What Yamaha integrated were you using? I'm really curious about the ACA.

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If you like the ACA, you would love some of the other Pass DIY amps. I have built an F5 and an M2x. IMHO, the M2x is an end game amp as long as 25 WPC is enough. I am using mine on the mids with BMS 4592ND drivers on K-402 horns and the sound is very good.
Maybe I need to spend the next year collecting parts? Transformers are somewhere in the garage.

2260f388cc0216ea1897136104f9c221.jpg

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14 hours ago, henry4841 said:

There is a newer version called the ACA mini that should be ready for sale in the next few weeks that is much cheaper to build not needing an expensive case. https://www.diyaudio.com/community/threads/diy-aca-mini.379037/

 

I checked out some of the early "clones" people have completed. Pretty cool stuff. Since they are all pretty recent, it will be interesting to see what they think after a little time.

 

There are getting to be just too many choices in this world. Low cost Class A or low cost Class D? 😱

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1 hour ago, CWelsh said:

I checked out some of the early "clones" people have completed. Pretty cool stuff. Since they are all pretty recent, it will be interesting to see what they think after a little time.

 

There are getting to be just too many choices in this world. Low cost Class A or low cost Class D? 😱

Class A is still class A, the most linear of all the choices. This is not to say other forms do not sound good but technically still class A is class A. In other words it is the standard to compare other forms of amplification. 

 

I have not followed the thread too much on the new ACA mini but unless I am mistaken it is a PP and the older ACA is SE. I did build an ACA a few years back and it did sound really good considering it's cost. Tube sound in a SS amplifier is the best way I know to call many of Nelson's designs. 

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16 hours ago, henry4841 said:

There is a newer version called the ACA mini that should be ready for sale in the next few weeks that is much cheaper to build not needing an expensive case. https://www.diyaudio.com/community/threads/diy-aca-mini.379037/

 

Did some reading there and by now there should be some feedback given. Cool looking kit. Just read 5 pages so...

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1 hour ago, The Dude said:

Nothing fancy, the RS-300 natural sound. 

I wondered if you were coming from something modestly powered or something with triple-digit wattage. And, you're running a single ACA in stereo mode?

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  • 1 month later...

I've built most all the Firstwatt clones including the Nelson Pass' projects for diy'ers. This little ACA sounds remarkable good considering you are getting the SE class A sound for little money. Class A amplifiers are not cheap to build or buy. The sound of the ACA is much like the sound of my SE BA-1 project I built many years ago. Not a power house but for many plenty enough. The BA-1 and BA-2 projects are not cheap to build requiring matching of the multiple output devices for best sound. Big powerful power supply section and expensive case with large heatsinks to cool those mosfets running in class A. The ACA is a very nice cheap project rewarding the builder with an excellent sounding little amplifier. Great project for those wanting to get into diy. 

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The ACA amps are very similar to my favorite SS topology, single ended Class A, current source loaded Mosfet output taken from drain. It was based off the Zen amplifiers which are also very cool if people have not tried them. Some use light bulbs as drain loads instead of a CCS which is neat. But they are not great at driving tough loads and have fairly high distortion. Back to the ACA amps, the third version is the best in my opinion which has several additions including feedback to improve upon the design and making it more speaker friendly for people with speakers that present tough loads. Many of Klipsch speakers are easy to drive in regard to power but as for impedance and reactive nature of the loads they can be tough on amplifiers. The mini ACA is two stage push pull complimentary amplifier. It does have feedback which is good but the fact it's a push pull design puts me on the I will most likely never build the amp list. Still looks very promising and I am certain it will be a great amp for people to build and get great results. If I did go SS push pull I'd do something like the mini for sure.

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On 1/12/2022 at 10:01 AM, The Dude said:

  Really impressed with this little guy.  May end up down a rabbit hole in years to come trying different Class A amps, maybe something for the K402's at home. 

Been there, done that, works great on K402's with TADs.

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