First version Aleph 0 (Null, ZERO, O, Os, 0s) versus later Aleph versions

[tiefbassuebertr]

Both models of first Aleph version ("O", "0s") basicly consits two voltage gain stages (second stage even cascode version) and one unity gain stage (single ended power follower respective common drain) - simplefield schematic see my pdf

All later versions (US patent 5710522) only used two gain stages; one voltage stage and one power stage (not power buffer), i. e. voltage gain and current gain at the same time (single ended power gain stage respective common source) - schematic see about
http://www.kk-pcb.com/mini-a.html and
http://prbetech.myweb.hinet.net/Alep...Aleph1.2-1.htm

I have heard both versions, but unfortunately never at the same time for making A / B comparison at different loudspeakers.

According to the circuits, the "Aleph 0" could have the better properties in the low frequency range through their higher damping factor resp. the lower output resistance (power follower stage instead of common source)

Maybe one of you is owner of both Aleph versions and can tell me about his impressions of the individual differences in sonic character. I think, Mr. Pass have heard both versions by a widest range of different loudspeakers.

Thank you very much for your comments

[Nelson Pass]

There are a number of practical differences.

The Aleph 0 will drive low impedance loads without a grunt. You
can overlay the distortion vs power curves for 8, 4, and 2 ohms
and they are the same curve.

It also measures lower distortion vs power, distortion vs frequency
and has a higher damping factor.

The later Alephs have only two stages, and lower feedback. The
measured performance is not as good, but they have a charming
characteristic into many of the more efficient loudspeakers. They
also have no adjustments, and cannot be blown up.

The Aleph 0 is not easy to damage, either, but we did lose a couple
of Aleph 0s units into dead shorts over the history of that amp.

[tiefbassuebertr]

Thank you for these explanations, Mr. Pass. Do you know about publishing serious distortion measurements from a HiFi magazine on the web?
Then I can investigate and compare this one by pSpice (circuitmaker)

[Nelson Pass]

I recall that Stereophile did a review of the Aleph 0 and
other Alephs. I don't recall what they did for measurements.

[Blues]

Here are Aleph 3 and 1.2. The Aleph 0 is not in their on-line archive.

http://www.stereophile.com/solidpowe...ss/index4.html

http://www.stereophile.com/solidpowe...74/index9.html

[tiefbassuebertr]

thanks for this advices. I have make a simulation of Aleph 3 accordingly the IM plot by
http://www.stereophile.com/solidpowe...74/index9.html
and schematic according service manual
http://peufeu.free.fr/audio/schemas/Pass_Aleph_3.pdf

Some resistor value I have slightly changed to get the mentioned 10 mA for each half of diff input amp and 2,2 A for the output stage - according the circuit describtion in the above mentioned service manual.

Unfortunately, I have difficulties by understanding with in the "Stereophile" mentioned measurement conditions - quatation of http://www.stereophile.com/solidpowe...74/index9.html :
================================================== ===============
Fig.7 shows the spectrum resulting from a combined 19+20kHz signal - the intermodulation products resulting from an input signal consisting of an equal combination of these two frequencies - at 26.7W into 4 ohms (the highest output power available with this signal without visible signs of clipping).
================================================== =====================
Means this now 26,7Wpeak or 26,7Weff into 4 ohms load resistance?. Therefore I have choise for both sine wave generators the two individual values 1Vss in first case so as 1,1Vss in the second case (see schematic of pdf fig. 1) - this creates max. output voltages 10V5ss and in the second case 11V6ss by the simulation at the points, where is max signal addition.

11V6ss was here the highest possible value of signal without visible signs of clipping. If I calculate stereophiles watt-number 27,6 x 1,414 x 4ohms = 156 and square root of this = 12,5Vss (that means close to the number of me, named 11V6ss) then I guess 26,7W eff is the right value of Stereophile. The results there are to see in pdf fig. 2 and fig. 3
.
If you can see by the graphs from simulation of me, it is not extremely close to the measured values from "Stereophile". But on the other hand tend it to a sufficient accordance, especially the fig. 3.

Unfortunately the other measurements that carried out in "Stereophile" are not of interest for me, since even bad sounding amplifiers deliver good results here. Even by 19 and 20 KHz IM check I get satisfactory results by the most of amplifiers from the world marked.

My favorit measurement for IM there is basicly the same, but I choise the frequencies 199KHz and 200KHz. The measurement conditions then are very hard. By most of commonly circuits from audio amplifiers, both mainstream and "Ultimate High End", especially such with two voltage gain stages, push pull true complementary buffer stage and low idle current for class A/B mode so as NFB I get only a lot of disaster but not useable simulation results cause the high frequencies. Only circuits with real first class engeneering release (sometimes good) simulation results by such difficult conditions.

I am very inquisitive whether this is possible by the Aleph 3 circuit in this manner, since it sounds so much better than most other audio amplifier devices in the same price class. The results I will show at next time so I have succes to get it from "circuitmaker".
By the circuits from X-series it was possible up to 1MHz without trouble because there are only one voltage cascode gain stage - look this about
http://www.diyaudio.com/forums/showt...postid=1884675
(some simulations of X-circuit variations)

[Nelson Pass]

I wouldn't count on much performance of the Aleph 3 at 199/200 KHz
IM tests. The amplifier is not designed to have any bandwidth to that
frequency

[tiefbassuebertr]

For me not the bandwidth is crucial. Much more important is for me, what kind of behavior is to observe at higher frequencies, far above the audible spectrum.
If the amplifier behaves as a clean low pass filter, no audible distortion are to be expected
If the amplifier go to a triangle resp. saw tooth generator - even with high bandwidth - is always assumed that a harsh playback will be observed through TIM
The latter is above a certain frequency basicly always present when two voltage gain stages have overall NFB. If there are only one voltage gain stage, I get only low pass character,
but never the conversion from a sine wave in a saw tooth wave, even by highest frequencies arround 1 MHz
To minimize this in cases of two voltage gain stages with NFB, I reduce the open loop gain of the first gain stage (most performed modification step of me by amplifier service).

[tiefbassuebertr]

Independent of the describtion and graphs in stereophile I discover one thing in the circuit of Aleph 3, that I don't like. That is the feedback capacitor of 1 nF between the output and input of the output stage (voltage/current gain stage). This capacitor is the so called Cdom (C for dominant pole) Let us see what happens by IM check with the follow frequencies: 199 KHz so as 200 KHz - one of my favorite measuring method, but very difficult to handle from all commercial audio amplifiers with more than one voltage gain stage.
But I note, that the message "Access Violation" from Circuitmaker prevent the creating of the expected diagrams
I put back the original parameters to investigate at first the frequency response with this capacitor of 1 nF (pdf fig. 1) and without (pdf fig. 2). Without this capacitor there are clearly an oscillator around 3MHz, typical for two voltage gain stage and NFB without compensation. But even by the diagram of fig. 1, (this capacitor is inside), there are to observe a slightly peak arround 800 KHz like a 2db ripple chebyscheff low pass. But I think, this is because the tolerances between modelling and real life parameters by the MOSFETs.

Now I put in this 1nF capacitor again and by the third try I get suddenly IM results (Fig. 5 - there are very heavy intermodulation products)

At next step I try to get better results without this capacitor Cdom, this typical source for transient intermodulation distortion (sine wave input results in a saw tooth output signal, independend of the load resistance, mostly arround 20 - 200 KHz).

My favorit step in such cases is to reduce the open loop gain in the first gain stage. In the case of the circuit from Aleph 3 the frequency response is also flat by introduce 33 Ohm in the wires of source from Q101/101 and remove Cdom ( Fig. 3 and schem. Fig. 4).

This IM result is very good with respect to such high frequencies, and is clearly better compare to Fig. 5 (see Fig. 6). This result only surpassed by the circuits of the X-Series.

The last IM measurement, that I do, is the same as done at begin, but now also with the new constellation, i. e. without Cdom and with 33 ohms source resistors. By 19KHz and 20KHz now the results not so good. What is the reason for this? Because the open loop gain arround this frequencies was reduced though this step?
The frequency response of damping factor (inverse frequency response of open loop gain) please refer Fig. 7 (with Cdom, 1nF) and Fig. 8 (with R-source, 33R)
there are to see follow damping factor :
arround 20 KHz = -48 db by Fig. 7 and -34,5 db at Fig 8
arround 200 KHz = -41 db by Fig. 7 and -32,5 db at Fig 8
According this values there isn't verify the reason for this IM behaviour.
But the reason for the very bad results of IM measurement of Fig 5 (in opposite to Fig. 6) by 199/200 KHz is
clearly understand by looking the results (visual check) of the 200 KHz sine waves, that are to see by Fig. 9 (with Cdom, actually a triangle wave) and Fig. 10 (without Cdom and with R-source of 33 0hms - nearly perfectly sine wave).

But what could be the audible effect by Aleph 3 and the other Aleph devices through this step compare to the first circuit? I haven't tested it by the Aleph devices, but in many other cases (mostly additional buffer push pull output stages with idle current around 30-100 mA) I get mostly better results as before. Only by subwoofer applications I observe sometimes a disadvantage; the bass reproduction was less tight and clear as before, especially by such with low cabinets, heavy membrane cones and optimize versions for use by car hifi. In this case high open loop gain and strong NFB is more important than low TIM at high frequencies.

Professional electrician (not beginners !! ) with oszilloscope, scope spectrum analyzer and HF generator can easily find it out this by their own Aleph devices, because this steps are easy to make - but please note, 33 ohms of source resistors are based of the modelling MOSFETs parts in "circuitmaker" - in real life it could be more or less. If you can perform ac analysis with your spectrum analyzer, you can tune a max flat response arround 1 MHz (use dummy resp shunt as load resistor and not your speakers for the aim of dummy to avoid blown away noiselessly your tweeters). If there are a residual peak, you must additional enhance the values of both source resistors. If the frequency response is flat with and without load resistance, no risk of residual oscillation and other unstable HF effects are present.

I'm really sure that most of the music lovers prefer music reproduction with a reduced open loop gain (and certainly those with aleph amplifiers for tweeter in bi-amping systems).

At next I will investigate the Aleph O (mono device) and Aleph 0s (s = stereo). service manuals now download not by www.passlabs.com but by the follow URLs:
http://vidar.hallais.no/media/downlo...y/Aleph%200%20(75w).pdf (Aleph 0)
http://vidar.hallais.no/media/downlo.../Aleph%200s%20(40w).pdf (Aleph 0s)

PDF of Fig. 1-10 Aleph 3 analysis - frequency response - 199/200 KHz IM - 200 KHz sine wave
fig. 1: frequency response with Cdom 1nF, source resistors 0R (original circuit)
fig. 2 frequency response without Cdom 1nF, source resistors 0R
fig. 3 frequency response without Cdom 1nF and additional source resistors 33R
fig. 4 schematic
fig. 5 IM 199/200 KHz with Cdom 1nF, source resistors 0R (original circuit)
Please note: fig 5 has been shown twice - unfortunately happened by creating of this pdf file
fig. 6 IM 199/200 KHz without Cdom 1nF and additional source resistors 33R
fig 7: frequency response of damping factor with Cdom 1nF, source resistors 0R (original circuit)
fig 8: frequency response of damping factor without Cdom 1nF and additional source resistors 33R
fig 9 200 KHz sine wave (actually triangle wave) with Cdom 1nF, source resistors 0R (original circuit)
fig 10 200 KHz sine wave without Cdom 1nF and additional source resistors 33R

[ctong]

The download links for Aleph 0 and 0s are invalid. I am curious to see the difference between the 0 and 0s. Thanks.