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Amp Camp Amp - ACA
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Old 28th February 2019, 04:23 AM   #7181
RafaPolit is offline RafaPolit  Ecuador
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Oh, I fully agree! And I think the answer may be on the fact that, when flipping absolute phase you change the 'sign' of the even harmonics: second harmonic distortion is changed from positive to negative and the other way around, meaning you get different 'flavors', specially with amps that have more prominent 2nd harmonics.

There's an interesting parragraph about that in Papa Nelson's new article in First Watt.

So yeah, I'm sure it's worth testing. I was just mentioning that, in theory, absolute phasewould be reversed. That some recordings would be better served by positive 2nd harmonics while others by negative, I'm also sure.

So many things to try out! That's the beauty of this hobby! Big hug,
Rafa.
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Old 28th February 2019, 04:31 AM   #7182
RafaPolit is offline RafaPolit  Ecuador
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Ps. To keep the external connections consistent, what I would recommend is soldering pin 2 to the left channel and pin 3 to the right. That way, if you switch from bridged to Balanced, you won't have to invert the speaker cables to preserve polarity.

Obviously, you can always invert the polarity anyway for these shifts in harmonics!
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Old 28th February 2019, 08:36 AM   #7183
indra1 is offline indra1  Indonesia
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Quote:
Originally Posted by 6L6 View Post
.. But here's the thing... Absolute phase is best tested in your system, and you choose what sounds best to you. I had a friend over recently, listening to his new factory-made SIT-3 (fantastic amp, as good as you can possibly imagine) and then we switched to the M2x with Norwood buffer -- it sounded really good, enjoying it immensely, holding its own against the SIT-3 quite well. But I was listening to a recording I've known since I was a child (and never get tired of) and thought something wasn't quite in the right spot... So I reached down, inverted the speaker wires, and immediately my friend shouted out "Wow! What did you do??" because it sounded about 98% as good as the SIT-3. ...
Jim, if it is not too much of a bother, could you kindly share with us your impression between a regular non bridged ACA and the M2X w/Norwood, both at the inverted speaker polarity (inverted absolute phase) for that particular recording?
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Old 28th February 2019, 11:15 AM   #7184
RCV is offline RCV
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Has anyone tried bi-amping a set of two-way speakers with the ACA? I am using the ACA as a bridged monoblock, not have tried yet using it as a bi-amp.
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Old 28th February 2019, 03:42 PM   #7185
6L6 is offline 6L6  United States
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Amp Camp Amp - ACA
indra1 - Let the salesmen of poetry and prose at the audio magazines write words about sound. I don't do that because I know better than to try to describe what my ears are hearing, in my room, with my speakers, with my other equipment, etc... because that will not be anything like what you will perceive with your ears, in your room, with your stuff, etc... You get the point.

The ACA is an absolutely wonderful amp and I listen to mine daily, I sincerely love it. M2x, however, is in a completely different league.
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Old 28th February 2019, 04:12 PM   #7186
indra1 is offline indra1  Indonesia
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Allright Jim, no problem. My request was actually rather technical, something to do with perception on the phase of H2, which (as NP mentioned) not everyone is able to hear. Your #7188 post show your ability to perceive H2 phase on a H3 dominated amp, quite rare actually. I think that what you can share will help to remind ACA users to try listening to both polarities at least once.
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Old 28th February 2019, 04:14 PM   #7187
6L6 is offline 6L6  United States
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Yes - my real point was to just try it yourself. Both of the amps in that situation were non-inverting so, in theory, flipping phase shouldn't have made a difference. But it did.

As it takes little time, is reversible if you don't like it, and can be done by everybody, try it and see what you think.
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Old 28th February 2019, 04:25 PM   #7188
indra1 is offline indra1  Indonesia
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Yes Jim, since many years ago listening to both speaker polarities on a newly encountered system has become second nature for me. If you check, I reminded others to do so many times in Pass forum alone. But I defer to the eloquent way you express the experience, way more impact than I could ever hope to do.
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Old 28th February 2019, 06:34 PM   #7189
RafaPolit is offline RafaPolit  Ecuador
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Well, even if the amp in non-inverting, switching the polarity of the speakers will offset the even-order harmonics peak-to-valley relationships, so you would hear a difference on a revealingly system (or with revealing ears!).
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Old 28th February 2019, 07:00 PM   #7190
laserscrape is offline laserscrape
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The ACA page explains the trick to bridging but is it really a good idea with standard ACAs?

I know the amps will see half the load each, its recommended to double the bias current (meaning standard supply heatsink and supply needs an upgrade). without you have double the watts but each amp has to deliver twice the current so what do you actually gain from that?

User loudthud also mentioned in post #458 the distortion spectrum will shift fro second to third order and recommended doubling supply voltage to retain the 2nd order distortion... it sounds like you want a bridged ACA that still sounds like an ACA (sweet) you need 38V supply.
Would bias current automatically double with 38V supply?
if so then higher watt bias resistors are needed also.

its seems a bridged aca is better treated as a different amp than converting standard ACAs to bridged

Last edited by laserscrape; 28th February 2019 at 07:03 PM.
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