AKSA 55, 100 - Listening impressions

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Tube_Dude said:



I was talking about, the performance of the addiction of a resistor to a CCS , in the tail of a LTP in an amplifier and not of the analysis of a perfomance of a CCS per si.

And in a amp, the rail is the greatest source of noise , with many harmonics , from the swithing of the output devices and from the rectifiers .

Yes, I realized that after your previous post. However, as I said the improvements are small, and there are other ways get much better performance. On the other hand, the resistor won't do much harm either, except for adding a bit of thermal noise, which probably doesn't matter for line level amps.


But in the simulations the rails are pure DC. ;)

Only if you forget to add a signal source to them to use for PSRR simulations. ;)
 
Tube_Dude said:


That is the crux!!

When the residual of the null test is only thermal noise , you don't listen to the amp anymore , you listen only to the music that pass trough the amp without alteration. The amp come out of the equation. ;)

Yes, but both I and mastertech (I think) was jokingly referring to listening to the actual result of the null test.
 
Tube_Dude said:


And how you simulate a signal with spikes and wideband spectral noise , as we find in a rail of a power amplifier? ;)

AC sweep and trusting Monsieur Fourier. ;)

Of course, simulations have their limitations, but sweeping the frequency gives you PSRR vs. frequency graph. You can also do transient analysis using pulses or other curve forms, and you can of course add several signal sources if you want to study IM effects etc.

As usual, no simulation is better than its models. Measurements can tell you some things the simulator can't tell you, but the simulator can also tell you some things you would fail to see if trying to measure them, at least without fancy state-of-the art test equipment.
 
lineup said:
A resistor from differential pair emitters to set current
is in fact not a constant current source.

Of course not, but resistors have been used as approximations of current sources since the early days of electronics. The lower the AC to DC ratio, the better the approximation.

LTPs originally used a resistor only, and many textbooks present them that way. The use of a CCS was a later invention to improve the CMRR and with todays cheap transistors, is probably the most common method.

Some seem, however, to prefer the sound of using a resistor. Somebody recently mentioned in some other thread that there was an amp (McIntosh, HK, ...?) that had an extra winding on the transformer just to provide a -100 V supply for the LTP tail resistors.
 
NULL Tests

If you want to do null tests, here is a way:

http://sound.westhost.com/sim.htm

http://sound.westhost.com/project57.htm


How revealing this is will depend on what tortue you feed it.

It may reveal speaker interactions as well.

Good for gross distortions but how will it reveal problems in ambience, imaging, decay etc and how will we interpret these?

Useful but no cigar I think. Our main problem is that way have no scale to evaluate the importance of differences when we find them. In isolation they can be seen in magnitude but not importance.

Our ears listening to actual presented music still remain the most sensitive and reliable instruments we have in evaluating the qualities of this music.

Yes, we can be fooled but if we are, over time we either fall out of love or remain happily fooled ;-) Tubes continue to happily fool me!



cheers
 
Christer said:
, but resistors have been used as approximations of current sources since the early days of electronics

Christer
I think you miss what I am trying to say with my post.

CCS always makes other transistor decrease its current
with same amount as input transistor increase.

While using a resistor it may happen
that
both transistors increase +0.1 mA at input of +1 Volt
this is because the increase across emitter resistor
is 0.2 mA

And to me this is a clear difference, when using constant current source versus resistor.
And CMRR, whatever this is - most of us dont know and use these words, was not my issue.

---------------------
sometimes I dont understand how people read:
they miss the main message
and add a sidenote comment on some remote detail you used to give your message
or they even 'reply' by start talking of something else

if someone quote your post
you would expect a response to your main message
Wouldnt you?

:)

another example:
when you want to explore an amplifier, subjectively and obejctively
people can be allwoed to sabotage a whole page (10 posts)
by compete who can make most funny post about beer

this is clearly not what we want :whazzat: :whazzat:
Do you want such response?


my advice:
those who wants to discuss beer in diyaudio.com
should start threads in Off Topic
instead of polluting other peoples discussions.
This is what will benefit diyaudio.com
and keep this a respectable website for exploring DIY audio
 
Resistor CCS

I experimented that in average DIY amps (not all), resistor do sounds better as CCS. The question is why, how come?
Lineup gives an explenation that R is not working so good as CCS (for differential pair). But what makes it "seems" to sound better?

I think the answer is not as simple as "it gives harmonic distortion bloom". It has to be a technical explenation why. (I'm not EE here :D)

The schematic that Christer mentioned maybe this one http://www.diyaudio.com/forums/showthread.php?postid=752768#post752768
Why that amp makes the difficult+expensive way of making additional high-voltage rail just to feed plain R as CCS? It is more easier for them to make 2 transistor based CCS with the same rail.

I ask a question in this thread http://www.diyaudio.com/forums/showthread.php?s=&threadid=70309&highlight=
The answer seems lies in the transistor itself. Transistor is not all "real number" device. It has capacitance, so its properties and behavior has to be expressed in complex number (i+jw).
But since the capacitance properties is so small, this (i+jw) behavior appears at frequencies sweep above 100khz-Mhz region. In this high frequency sweep, this (i+jw) does makes a difference.
(There are 2 very good papers in this thread, one pointed by Dimitri and one pointed by JCX)

The question is : Audio is below 20khz, so what is the importance of Mhz behavior there? I have tried transistors with higher fT, usually they do sounds better. Again, what is the relation of Mhz behavior to below 20khz reproduction? It seems intermodulation is the answer
http://www.diyaudio.com/forums/showthread.php?s=&threadid=65028&highlight=


But I have an opinion (for myself) that transistor based CCS sounds different than plain R because of this Mhz behavior, which is more important than the drawback of using R as CCS (like Lineup pointed).
Input-output properties of transistor based CCS (like impedance, etc) in 1khz will not be the same with those properties in 1Mhz or 10Mhz.
In the other side, Resistor is the same at 1khz or 1Mhz or 10Mhz, it only follows Ohm law V=IxR, no (i+jw) there.

This maybe still the missing link. What is the corelation of Mhz behavior to below 20khz reproduction properties?
 
lineup said:


I think you miss waht i am trying to say with my post.

CCS always makes other transistor decrease its current
with same amount as input transistor increase.

While using a resistor it may happen
that
both transistors increase +0.1 mA at input of +1 Volt
this is because the increase across emitter resistor
is 0.2 mA

And to me this is a clear difference, when using CCS versus resistor.
And CMRR, whatever this is, was not my issue.
-


To the contrary, CMRR is exactly what you are talking about. ;)

CMRR stands for Common Mode Rejection Ratio and tells how well the LTP surpresses a common-mode voltage, that is, a voltage of the type you describe. If you input +1 mV to one input and - 1 mV to the other input, you get a differential voltage of 2 mV, and the voltage at the common emitter node will not change. If you instead input +1 mV to both inputs, you have what is called a common mode voltage, and the common emitter node will also increase by approximately +1 mV. For arbitrary input signals, you can decompose them into a differential mode part and a common mode part. You want to surpress common mode voltages as much as possible, since they cause distorsion, ie. you want a high CMRR.

Pleas note two things.:
1) If you use a resistor, the rejection of common mode voltages, that is how much the tail current changes from common mode voltages, will be better the larger the value of the resistor. That is, it is good to have a high negative rail voltage so you can use a large resistor.
2) Ideal CCSs don't exist in reality. Any implementation of a CCS will have an output impedance, and thus behave approximately like a resistor for AC signals. The advantage of a CCS is that you can simulate a high AC resistance withouth having the correspondingly high rail voltage you would need with a real resistor.
 
Re: Resistor CCS

lumanauw said:
Lineup gives an explenation that R is not working so good as CCS (for differential pair). But what makes it "seems" to sound better?

On the contrary.
I try to explain why a resistor could possibly be better than a constant current source.

In my mind:
two transistors increasing their currents with approximate same current
have a more similiar behavior

than

one transistor increase current
while the other decrease with same amount
 
On the contrary.
I try to explain why a resistor could possibly be better than a constant current source.

In my mind:
two transistors increasing their currents with approximate same current
have a more similiar behavior

than

one transistor increase current
while the other decrease with same amount

Hi, Lineup,

Sorry, I did not read your post carefully :D. I tought you emphasizes that R gives worse CMRR than transistor based CCS (which is true).
R is worse than transistor CCS in CMRR, but there is something else (I think) that is more important than this CMRR, that is the Mhz behavior of both. I still don't know for sure what is the explenation of Mhz behavior with audio reproduction, towards the sonics
 
Re: Re: Resistor CCS

lineup said:


On the contrary.
I try to explain why a resistor could possibly be better than a constant current source.

In my mind:
two transistors increasing their currents with approximate same current
have a more similiar behavior

than

one transistor increase current
while the other decrease with same amount

I see your point now, but unfortunately I am afraid you have entirely missed how a diff pair works and why it is used. There is a reason it is called a differential pair; it is used to amplify differential voltagas and reject common mode voltages, as I explained in the previous post. So unfortunately you can't get the effect you wish for. However, diff pairs do have another very nice property. For small differential voltages, they are much more linear than a single BJT is. unfortunately they get heavily non-linear for larger voltages. Adding emitter degenration resistors extends the linear region.
 
Here is the Thread about Hugh showing basic schematic

The thread was moved, or cancelled....do not remember....but i remember that disappeared from our eyes.

We have to search to find it...so....not something to see easy.

hehe

here is the link:

http://www.diyaudio.com/forums/showthread.php?postid=415297#post415297

Schematics (basic) was published, and other details and discussions are there.... this new thread was opened, because the one that opened, could not have the original thread....so, information is now partially duplicated....forum rules do not accept duplication.... some exception i think.

regards,

Carlos
 

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Re: Here is the Thread about Hugh showing basic schematic

destroyer X said:
here is the link:

http://www.diyaudio.com/forums/showthread.php?postid=415297#post415297

Schematics (basic) was published, and other details and discussions are there....
....

thanks, Carlos
:)

I dont know if this is same as an original AKSA of today.
I would most certainly think it is not.
Some basic things may however be the same.
Here is link to this old AKSA schematic attachment:
attachment.php



What is remarkable is it uses only 8 transistors.
Idea seems to be: Keep it simple as possible!
Do not add an active component (transistor) if you can find another good solution.
 
Here is the basic schematic, showing reference numbers

This may be helpfull for discussion.

The real AKSA kit is not exactly this way...this is the basic schematic, some values had changed with improovements made, also some condensers were included, and resistors too.

So, this is the basic circuit, a base to development...and this do not sound very impressive...sounds just reasonable.

The parts makes enormous difference, the selection and some added components, and those are protected by copyrigth and customers agreed not to publish or let people copy.

regards,

Carlos
 

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just could not resist,spank me for laughing

pmkap said:
Spectral SS which reminds me of having an ice pick driven into my ears

Not only very funny, but by far the best description.
The worst i can imagine to give me the shivers and goose skin is a combo of a Spectral and an Apogee metal plate.

But that stuff is/was built, sold and well rated.
And on the technical side, the level of a Spectral is amazing.

Which is a good example of the same apparent on this thread.
The theme was to post how well the AKSA55 sounds, if it is worth the pecunia, and what are the reasons that it performs so well

Instead, half of the thread is filled with posts on how the circuit can be improved, the difference between a resistor and a CCS, the importance of Self, and that by the simplicity of the circuit it can not be good.
With added comment that posts should not include talk about beer that distracts the eye of the main theme, and continuous copying of the previous post for mental retards or resthome droolers.
I've never met anyone smart enough to tell me how something will sound by merely looking at the schematic.
 
Re: just could not resist,spank me for laughing

jacco vermeulen said:
The theme was to post how well the AKSA55 sounds, if it is worth the pecunia,
and what are the reasons that it performs so well

Instead
... the difference between a resistor and a CCS
... by the simplicity of the circuit it can not be good.
... posts should not include talk about beer

What is the reason it performs well?
Can it be the use of resistor and not CCS?

I said idea seems to be: Keep it simple as possible!
Note: I did not not say: simple=bad
Because sometimes in my experience, simple=good
If you read into my saying simplicity is bad, it is your subjective opinion.
Not mine.


I think one post or two may mention beer,
but personally I prefer the discussion is, as you stated:
- how well does the AKSA55 sound?
- what can be reason it does?
 
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