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ACA-Nelson Pass's Amp Camp Amp


The Dude

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2 hours ago, The Dude said:

I have not, still in the hunting and gathering part in regards to components.  Since I have other projects that take priority, this is on the back burner until fall/winter.  

 

Have you considered the SP14?

Hi have, but the price increase is substantial to get the SP14 with a remote and I haven't gotten beyond my bang-for-the-buck tendencies. Especially since I plan to buy a second ACA.

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  • 4 weeks later...
  • 2 weeks later...

The new ACA is up and running! In each of the available options (bi-amp, bridged mono and parallel mono) there is an improvement over the single ACA. The essence of the sound doesn't change, but there is more detail, the sound stage seems to have greater depth, and the bass is tighter. What I found with the parallel mono mode, is how all the improvements are very noticeable at lower volumes. This is a pretty big change from the single amp.

 

These things seem to be made for Klipsch speakers. For less than $750, I have 15 wpc of single ended pure class A amplification. Not too shabby, if you ask me.

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8 hours ago, CWelsh said:

The new ACA is up and running! In each of the available options (bi-amp, bridged mono and parallel mono) there is an improvement over the single ACA. The essence of the sound doesn't change, but there is more detail, the sound stage seems to have greater depth, and the bass is tighter. What I found with the parallel mono mode, is how all the improvements are very noticeable at lower volumes. This is a pretty big change from the single amp.

 

These things seem to be made for Klipsch speakers. For less than $750, I have 15 wpc of single ended pure class A amplification. Not too shabby, if you ask me.

That's good to know, I'd be interested to know how one would handle gain matching each channel to insure accurate levels out of each amp. I know some of the Tubes4Hifi pre amps have individual channel gains, so I assume one could accomplish it by that means.

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13 hours ago, The Dude said:

That's good to know, I'd be interested to know how one would handle gain matching each channel to insure accurate levels out of each amp. I know some of the Tubes4Hifi pre amps have individual channel gains, so I assume one could accomplish it by that means.

That's a good question. I spent a fair amount of time doing an A B comparison to make sure there were no glowing differences, but that isn't the same as taking measurements. Maybe someone with more technical know how that I have will chime in with a suggestion. Do you suppose measuring voltage at the speaker terminals might do it?

 

At some point, I intend to build and try the DIY Audio active bi-amp crossover, which I believe should offer the same capabilities for individual channel gain adjustments. In the amp itself, I think minor tweaks to the bias pots might do it. I'm guessing, here.

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2 hours ago, geezin' said:

Recently looked on ASR to see how the Pass ACA fared. Not well by his standards. What am I not (hearing) seeing?

It just shows that something can measure poorly but still sound pleasing. I used "pleasing" intentionally, to emphasize subjectivity.

 

@The Dude, ASR is Audio Science Review.

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2 hours ago, geezin' said:

Recently looked on ASR to see how the Pass ACA fared. Not well by his standards. What am I not (hearing) seeing?

You're comparing a $300 diy kit to $4000 commercially built amplifier. I'm not an engineer, but I'd guess it's more than $300 in parts to get to high fidelity.  That being said, having the enjoyment of building one and still having it sound pretty good regardless how it measures is something I am ok with.

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3 minutes ago, The Dude said:

That being said, having the enjoyment of building one and still having it sound pretty good regardless how it measures is something I am ok with.

It used to be that one could build things more cheaply than buying them. Modern economies of scale have pretty much ended that. For example, I'm currently building a set of speakers that roughly compare to the Klipsch Chorus, in terms of components. Because I have to purchase them at retail prices, the cost of components is a significant fraction the price of the Chorus itself. In other words, I'm not really saving much by building them myself. However, what I end up with is mine, both in design and in execution.

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11 hours ago, geezin' said:

Recently looked on ASR to see how the Pass ACA fared. Not well by his standards. What am I not (hearing) seeing?

I did read the ASR review, but it has been a couple of years or so. My memory is, he didn't like it because of the high distortion ratings using his measurement tool. Even Nelson Pass acknowledges that it has second order harmonic distortion numbers that look high. Apparently, the same is true of virtually every tube amp in existence. Whatever the case, I can tell you the thing sounds pretty freaking amazing through high efficiency speakers.

 

I watched another reviewer on YouTube absolutely trash the ACA. However, what he was really testing was a Chinese clone he picked up on Ebay for cheep and playing it thorough not terribly efficient speakers. Crazy people!

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9 hours ago, Edgar said:

It just shows that something can measure poorly but still sound pleasing. I used "pleasing" intentionally, to emphasize subjectivity.

 

@The Dude, ASR is Audio Science Review.

You make an excellent point. My enjoyment of the amp is subjective. Others may find it less pleasing than I do. And, I will admit that the cost and the fact that I assembled the kit contribute to my evaluation. Still, for less than $750, I don't know that you can beat it. I've tried some Class D amps and agree that they sound great, especially for the price, but the ACA has something I really like, and that makes me happy.

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