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Old 1st June 2007, 10:48 AM   #21
Did it Himself
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Thanks both, that's a help.
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Old 1st June 2007, 01:19 PM   #22
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Default And Hugh says that this emitter resistance value is critical and cannot be replaced

For other values without losses.

I just cannot tell the value Hugh selected... for sure it is a commercial normal value, not special order made by Hugh...value can be found everywere.

There are a lot of small things that were founded during reseaches.

You know...very small increase here in the emitter resistances... another small increase int he feedback line.. other increase in the stop resistances...other increase in this, that and those....those things altogether are unbeatable.

Hugh is very rich related those details.... and they result special, as i could not beat his amplifier without use the same sub-circuits and parts he sent me.

My Dx amplifier turns much better using Hugh subcircuits and parts...but, of course, will be another Aksa Nirvana plus 55.....and not more Dx amplifier, not more a simple and cheap amplifier.

I have perceived bass worst using emitter resistances.... worst in level, ..but quality is another thing, very subjective and very hard to describe.

The first idea i had was that i was impressed because i have enormous respect by Hugh...also i know that i am not so experienced as he is...because he spent less years than i spent searching for perfect sonics...but he is much more organized into colecting informs and select them to tests and comparisons....i was very lost and confused doing that.

I made A to B testings.... the Aksa eated my Dx amplifier without too much problems.... loose in bass (quantity) but winned in treble, voices and sound stage...had lower distortions and overall sonics were very, very, very different.

I strongly recomend Aksa...go to listen one...and them return to tell me if i am wrong.

My dream was that Hugh, when finished the Lifeforce design, would say to me:

- "Well Carlos, this one is superated by Lifeforce and then i decided to give you all the old Nirvana board i have, as people will not order than anymore"

Ahahahah...not only he did not made that, but also he asked the Nirvana boards back as a pre condition to sell the Lifeforce...he do not want to see Nirvanas free to speculations.

regards,

Carlos
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Old 1st June 2007, 01:42 PM   #23
AKSA is offline AKSA  Australia
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Richie,

I mount 0R47 emitter resistors on the outputs UNDER the pcb. They are mounted a couple of mm below the pcb and enjoy good air circulation. This is, of course, rather important at high power.

If you do the math on the optimum bias for an AB, you find the emitter resistor should drop 26mV, which is a significant figure related directly to the Bolzmann constant.

If you use a 0.22R resistor, this assumes a bias of 120mA. If you use 0.47R, the bias is 55mA. Since mosfets require at least 100mA of quiescent to place them in a reasonably linear portion of the parabolic transfer function, and I choose to use bipolars, I go for the lower bias.

You can see that to achieve high efficiency, important in this Class D switching world with low quiescent dissipation, the larger emitter resistor is preferable, BUT it costs rail efficiency, which is not so good.

OTOH, the larger resistor promotes quiescent stability, improves current sharing between parallel pairs AND linearises the output device, no bad thing either. I go for a quiescent variation of no more than 3% between complementary pairs, since I match carefully. Since we are designing for maximum sound quality, linearity is crucial and too important to pass up, so I choose 0R47. I have had no problems since the domestic situation, unlike pro-audio, is not too concerned if we drop a few watts from max power. A nice stiff power supply avoids the usual sag of the rails anyway, and largely makes up for this loss of rail efficiency.

Cheers,

Hugh
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Old 1st June 2007, 02:02 PM   #24
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Thanks very much for the details Hugh. I had gleaned from Self that Vbias rather than Iq was the critical factor, but you've nailed it down better.
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Old 1st June 2007, 10:42 PM   #25
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Quote:
Originally posted by AKSA


OTOH, the larger resistor promotes quiescent stability, improves current sharing between parallel pairs AND linearises the output device, no bad thing either. I go for a quiescent variation of no more than 3% between complementary pairs, since I match carefully. Since we are designing for maximum sound quality, linearity is crucial and too important to pass up, so I choose 0R47. Cheers,

Hugh
Hugh, not understanding your comment that a larger resistor improves linearity. This is contrary to what I've read. A lower value supposedly reduces higher order harmonics of crossover distortion, and lessens gm-doubling aberations. Also, a few weeks ago, Curl stated, if I recall correctly, that higher quiescent current in the output transsistors reduced higher order harmonics (I presumed that the subject distortion was due to the transistor, per se, as opposed to crossover distortion.)
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Old 1st June 2007, 11:24 PM   #26
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hi pooge,

What have you found to be the best?

regards
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Old 2nd June 2007, 12:47 AM   #27
AKSA is offline AKSA  Australia
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Hi Pooge,

I've found this gives very good sound. I can't argue too much about this, because such debates become interminable and people soon loose interest in the finer academic points, but a larger emitter resistor constitutes degeneration, reduces transconductance, and to my understanding always improves linearity by dwarfing the non-linear b/e junction with ohmic resistance.

There is some controversy on this point, with proponents invoking higher math to prove a point of some conjecture.....

gm doubling is a function of both transistors being on at the same time during crossover, and its effect is to rob very low level detail, the bane of Class AB. It can be reduced by better controlling the output of the voltage amplifier.

Cheers,

Hugh
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Old 2nd June 2007, 03:13 AM   #28
pooge is offline pooge  United States
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Greg and Hugh,

I have not personally found any value to be the best. I have not personally tried different values and listened to them yet (or read any other subjective reports), although I just ordered new values last night to try just that. As I opted for going lower, Hugh's comment about going higher gave me a tweak.

I've been studying the situation lately just to decide what to use (and order), and opted for .22 ohm based on going as low as practical without going too low to compromize output sharing.

I was just struck by Hugh's comment that raising the value linearizes the output. Didn't know if that was a subjective or objective observation, and it struck my curiousity.

Hugh responded by stating that larger gives more degeneration. This may be true if standing currents were the same, but it is the voltage across the resistor that is fed back, and this is made virtually the same by adjustment in bias current.

As to "dwarfing the non-linear b/e junction", the intrinsic emitter resistance is an inverse function of Ic, so if the bias current is doubled, the intrinsic emitter resistance is halved. So along with a halving of emitter resistance from say, .47 to .22, the relative proportion of added resistance to intrinsic would appear to be the same, with a lower intrinsic resistance to modulate in the case of .22 ohms with higher bias.

As to gm-doubling being reduced by better controlling the output of the voltage amplifier, I can not follow this with any available knowledge. It is my understanding that lower Re reduces this.

Not holding Hugh to the fire for a rock solid explanation of cause of why he thinks the larger resistor sounds better. It's just that I can't tell when Hugh makes a statement about such things as linearity, whether it is subjective or objective, because he wears both hats (a good thing). But I never know what hat he is wearing when he makes such a statement.

If there is another explanation of why larger resistance might sound better, I am all ears, because I am happier when my right brain gets along with my left.
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Old 2nd June 2007, 06:42 AM   #29
AKSA is offline AKSA  Australia
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Aha,

But you want explanations!! I just want better sound, and my prevarications register my reluctance to enter these debates.....

Cheers,

Hugh
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Old 2nd June 2007, 06:57 AM   #30
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Default Those debates finishes normally very bad.... we have some bricks that use to enter

behaving very unkindly.

It is a pitty, but, i have learned a lot reading those debates.

I have colected many informs during those things, you have gave me those secrets for free during conversations and because of negotiations we have made about some Aksa 55......but i could perceive that some forum readers, having attention, could receive nice informs about your circuit.

During the massacre they use to make.... some clever guys had insigths and clear nice informs that pop out during the hot argumentation.

We have to leave the experience to learn things... theories and conclusions about are not enougth in audio sonics.

My amplifier had emitter resistances removed, clearly i had more "punch" in the bass...so... to reduce parts count, to make it more simple and more cheap, the emitter resistances do not exist anymore.

But finishing the unit, i have apreciated the sonics, but comparing with mine Aksas, my units loose into the comparison....so.... i conclude that researches made by Hugh, related many things, including this emitter resistances, altogether, made the difference.

There are a lot of things that do not make any sense... and sometimes those non sense things are very near us... around us....a nice man can married a very bad and crazy woman.... that's love... non sense too.

Input differential, in every theories, works better using costant current sources and line voltage regulators... some schematics using sophisticaded methods to drain charges can be used too...using Fets transistors and many other interesting parts...... the problem is that theories do not produce sound.... the amplifier with simple differential sound even better.... very strange those things...and only the A to B comparative testing, using the same circuit with both aproaches can show you how strange those things are.

You have to use Blind testings, because our "beliefs" will influence the result...not knowing what is playing (ask some help) you will be fair...cannot detect, conclude, discover, what circuit is playing...decision must be only because of sonics.

Levels must be the same...same power, same speaker, same music, same effects, same place...dark place...cannot see nothing..confortable place and repeat tests to see if they make sense....... also change letters of reference.... invert signals... try to confuse every clever brain not to discover what is A ...and what is B.

Also do not loose time searching because or curiosity...only Aksa owners knows those circuits, subcircuits and values...and they will not publish so gratefull they are related Hugh.... well...Hugh proved his amplifier is the best for customers...they are happy because Hugh gave them the chance to use the best possible...they perceived that, as they have other equipments to compare...so..they do not talk about....only personally, and with another one that has Aksa for sure.

That P61 have not the subcircuits... was a very early circuit and the critical parts were not published those early days.

regards,

Carlos
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