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Old 17th July 2010, 12:05 AM   #1
jkeny is offline jkeny  Ireland
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Default New Aksa Amplifier build pics - Naksa

I recently bought this new amplifier offering from Hugh dean at Aksa because I liked the philosophy behind it's design & also the initial reports of the sound impressed me immensely striking many bells (forgive the pun) & ringing through with my experiences along my own audio journey. here's the main thread on this : New Naksa Amplifier! Quick Initial Impression......

This is a 70W per channel amplifier designed with sonics in mind. It's design is single ended where possible & it has a unique THD spectrum which intrigues me & I'm hoping will prove itself to be exemplary in the area of sonics. The design philosophy that Hugh has followed is to reduce the sonically offending higher odd order harmonics at the expense of some extra even order harmonics - a philosophy that I see adopted by well respected designers such as Gary Pimm in his SS Tabor amplifier "There is more second harmonic but the higher order distortion is way down. This is a case where I would glady take an increase in second harmonic distortion in trade for virtually getting rid of high order harmonics."

The pcb arrived in about a week from Oz to Ireland and they look stunning - two channels & the PS on one board - just supply a 30-0-30 transformer & a 300mm long heatsink (I ordered mine without heatsink to save on postage).

Now I happened to have a perfect donor amplifier case to house this Naksa - it's a Samson servo 550 studio amplifier. Heatsink is 300mm long & was serving a 275 watt per channel amp so suitable for this 70watt amplifier.

I've only started the fitting of this pcb into the case but here are some pics of my progress so far.

Inside of Samson amp & Naksa pcb in the background
Click the image to open in full size.

Pcb mounted on heatsink & outputs wired to speaker connections - inputs (at the top) wired but not yet connected to vol pot (I'll be using some lightspeed vol units)
Click the image to open in full size.
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Old 17th July 2010, 01:31 AM   #2
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by jkeny View Post
...because I liked the philosophy behind it's design...

This is a 70W per channel amplifier designed with sonics in mind. It's design is single ended where possible & it has a unique THD spectrum which intrigues me & I'm hoping will prove itself to be exemplary in the area of sonics. The design philosophy that Hugh has followed is to reduce the sonically offending higher odd order harmonics at the expense of some extra even order harmonics - a philosophy that I see adopted by well respected designers such as Gary Pimm in his SS Tabor amplifier "There is more second harmonic but the higher order distortion is way down. This is a case where I would glady take an increase in second harmonic distortion in trade for virtually getting rid of high order harmonics."
The philosophy is not the best one (There is better philosophy). The most important thing is that the designer can differentiate a subjectively good sound from a subjectively bad sound. This is a skill that I found correlate highly with "tweaker"-type designers than the theoretically oriented designers.

I believe that the best amp should have low distortion, both high order and second order, no exception. And because single ended topology always correlate highly with second order harmonics, it is hardly the best topology either.

The problem is, can anybody show me an amp that is low in distortion (including the second order of course) but sound subjectively good/better? (I know it will be hard to build without oscilloscope at minimum)

The problem IMHO is not simply about low order or high order harmonics, there must be something else. When you try hard pushing the (second order) harmonics down, you seem to mess up with something else.

The perfect or better amp is possible, but where is the circuit? Somebody may have designed it for his own personal use, but if it is not approved by the majority (hopefully the golden eared audiophiles), no need to debate that his is the better one
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Old 17th July 2010, 01:49 AM   #3
jkeny is offline jkeny  Ireland
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Jay, if I can understand your post you are saying that this is not the best design philosophy but are voting for a low distortion as a better sounding amp? Have you not followed the numerous discussions along these lines - there are plenty of examples that show that vanishingly low distortion has no correlation with an amp sounding good!

You do realise that we like the distortions that emanate from musical instruments, don't you?

Have you looked at the distortion spectrum of the Naksa & have specific points to make about it?

I don't wish to get into a debate about distortion spectra at this time - the amp will either survive or not my best instrument that I have in my lab - my ears/brain as this is what I use to listen to music & this is the reason I bought this amp!

I hope you understand my predilection to this habit I have of listening to music rather than looking at THD spectra but if the spectra & the sound both make sense then I'm doubly happy. I haven't fired it up yet so it could sound like rubbish & if so, I'll say so, with apologies to Hugh
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Old 17th July 2010, 02:24 AM   #4
jkeny is offline jkeny  Ireland
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I hope I haven't picked you up wrong but you seem to be dismissing the approach rather too quickly rather than spending some time reading the links & analysing the spectra. AFAIK, Hugh is a designer who uses both measurements & his ears - he's no slave (or stranger) to measurements but tries to also correlate what he sees in his measurements with what he hears - a very difficult investigation & one that intrigues me!
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Old 17th July 2010, 02:31 AM   #5
Jay is offline Jay  Indonesia
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Originally Posted by jkeny View Post
Jay, if I can understand your post you are saying that this is not the best design philosophy but are voting for a low distortion as a better sounding amp? Have you not followed the numerous discussions along these lines - there are plenty of examples that show that vanishingly low distortion has no correlation with an amp sounding good!

You do realise that we like the distortions that emanate from musical instruments, don't you?

Have you looked at the distortion spectrum of the Naksa & have specific points to make about it?

I don't wish to get into a debate about distortion spectra at this time - the amp will either survive or not my best instrument that I have in my lab - my ears/brain as this is what I use to listen to music & this is the reason I bought this amp!

I hope you understand my predilection to this habit I have of listening to music rather than looking at THD spectra but if the spectra & the sound both make sense then I'm doubly happy. I haven't fired it up yet so it could sound like rubbish & if so, I'll say so, with apologies to Hugh
Nooo, actually I'm agree with you If later, IF, you found that this amp sound like rubbish, don't forget to tell me which one doesn't.

Actually, I want those whose ears I can trust (I think I can believe Hugh and may be you) can show me the best sounding lateral mosfet amp he/you has ever heard. I'm ready to expect that those people will have bipolar as better reference. Surprised me though, that Rod Elliot uses his mosfet P101 as his "reference". That is if he is "honest" enough about it.
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Old 17th July 2010, 02:36 AM   #6
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Quote:
Originally Posted by jkeny View Post
I hope I haven't picked you up wrong but you seem to be dismissing the approach rather too quickly rather than spending some time reading the links & analysing the spectra.
I only looked at the first page of that thread you linked, but in that its only simmed distortion figures which are quoted. Is there anywhere some measurements?

Also you said:

The design philosophy that Hugh has followed is to reduce the sonically offending higher odd order harmonics at the expense of some extra even order harmonics

Is there anywhere a technical treatment of how this trade-off occurs? The only place I've seen it is in the argument against using low levels of NFB, so is this a 'no feedback' design?
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Old 17th July 2010, 03:03 AM   #7
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by jkeny View Post
I hope I haven't picked you up wrong but you seem to be dismissing the approach rather too quickly rather than spending some time reading the links & analysing the spectra. AFAIK, Hugh is a designer who uses both measurements & his ears - he's no slave (or stranger) to measurements but tries to also correlate what he sees in his measurements with what he hears - a very difficult investigation & one that intrigues me!
I think you have picked up me wrong, because of my poor English.

I don't know about Hugh electronics background, but he is intelligent and I suppose has very good ears. But there are others with better electronic knowledge, BUT, often with poorer ears (usually related to poor hands-on experience), and worse, less intelligent

What I'm saying is, there is better philosophy than you mentioned. Single ended is probably not the best if you want to get rid of those second harmonics. But I believe that to get a good result sound wise from that theoretical concept requires good ears, not EE degree.

I feel lucky that to enjoy the music I have a high dependency with the speaker, and only little with the amplifier. If I have to build Hugh's amp for my reference system, I will use Sanken 2SC2922 for it's output (tho the amp is not designed specifically for that transistor). But because I have plenty of lateral mosfets (and I like them) I'm not interested with the best bipolar amp, but I'm interested with the best lateral mosfet amp. And because Hugh encouraged me to build the Mooly Amp, then that is what I built and listened
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Old 17th July 2010, 03:04 AM   #8
AKSA is offline AKSA  Australia
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Yes, keep reading..... actual measured distortion has been presented.

It is a commercial product, there is no so-called 'technical description', merely a guarded comment about the philosophy and a description of the actual measurements at both 1W and 25W. What would you expect, my friend?
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Old 17th July 2010, 03:21 AM   #9
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Yes, keep reading..... actual measured distortion has been presented.
Thanks.

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What would you expect, my friend?
No one expects the Spanish Inquisition As it happens I live without expectations - no expectation means no disappointment and definitely no expectation bias. Now, that turns out to be quite valuable when listening to modifications of audio kit...
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Old 17th July 2010, 03:25 AM   #10
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Originally Posted by abraxalito View Post
I only looked at the first page of that thread you linked, but in that its only simmed distortion figures which are quoted. Is there anywhere some measurements?

Also you said:

The design philosophy that Hugh has followed is to reduce the sonically offending higher odd order harmonics at the expense of some extra even order harmonics

Is there anywhere a technical treatment of how this trade-off occurs? The only place I've seen it is in the argument against using low levels of NFB, so is this a 'no feedback' design?

Hugh's philosophy is right on for a better sounding amp. In my reverse engineering of the symasym , I have found that the loading of the VAS , while increasing total THD , will give that "magical sound" . Investigating further , I saw that the 2nd increases with load while 3rd-5th decreased. You do pay a price with increased heat (dissipation) and distortion in the VAS , but the heck with .003% if it does not sound better than .02% with the "right" harmonic content.

Another factor is speed , some compensate for amazing slew rates and 100khz perfect square waves. My amps can do this , but we listen to audio , not 100khz SW's. I have found that careful attention to the different compensations (the main Cdom , lead ) and the right compensation for different devices also determines amp "character". Another is bias... MJW21193/4's not only sound different than 2SA1943/2SC5200's but need a hotter bias. There is no "perfect amp" ,all is just a big trade-off . Now that I am building a new amp , I will allow for all these tweaks to be done without any redesign , worst case with separate Current /voltage boards is just another board swap. Is not DIY great !!!
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