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Old 1st July 2004, 02:52 AM   #1
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Default Aleph with 40db gain?

Just learn something from Mr.Pass. Simplicity.
Advoid even single transistor, if possible.
So, got this question. If I wanted to get rid of preamp, take signal straight from the CD player, go into 1 volume potentio and direct to aleph, is it possible?
Aleph has gain only 20db (10x). I will be needing gain about 40db(100x).
What happens if the feedback resistors are modified to have gain about 100X? What will be going wrong? Is that distortions will go enormous?
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Old 1st July 2004, 03:24 AM   #2
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It should work, although you want to adjust the frequency
compensation values.

The Aleph doesn't have much more open loop than that, so
you will be running with little or no feedback, and you might
not quite reach that figure.

And yes, you should expect more distortion.

However if you replace the load resistor off the input diff pair
with a current source, it will give you more gain, at least at
lower frequencies.

Try getting by with 30 dB or maybe a pot on the feedback loop
so that instead of adjusting the volume control you adjust the
amp's gain.

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Old 1st July 2004, 04:08 AM   #3
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Quote:
It should work, although you want to adjust the frequency compensation values.
Yes, understand that.
Quote:
The Aleph doesn't have much more open loop than that, so you will be running with little or no feedback, and you might
not quite reach that figure.
If the gain cannot reach 100x while feedback resistors are 100x, is the DC offset still good, or wandering around?
Quote:
And yes, you should expect more distortion.
I dont like this. Loves the normal aleph sound.
Quote:
However if you replace the load resistor off the input diff pair with a current source, it will give you more gain, at least at
lower frequencies.
Why is that? I think the nice sound of aleph also contributed by single 392R. You said about "Little 2nd harmonic". Changing this will change the sound?
Quote:
Try getting by with 30 dB or maybe a pot on the feedback loop so that instead of adjusting the volume control you adjust the amp's gain.
So this is "Do-able". Wonder why it is not popular approach. Input volume pots have their lack, if the volume is set low, the R and C inside mosfets will form LP filter. This idea should be better than having input volume potentio.

I get impression 40db gain is not a good idea with single aleph design. How about making preamp like the inverting block in aleph-ONO, feed it to aleph power amp, each have gain 10x, while the preamp is adjustable in its feedback (like 1x to 10x). Will this maintain the sound of aleph?

Mr. Pass, what is your personal comparison between aleph and X generation amps from passlab? You have discontinued aleph generation, turning to X generation. So it must be something better with X generation. Or they are different things, but you have decided to discontinued aleph?
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Old 1st July 2004, 04:22 AM   #4
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I think you appreciate that after you have sold maybe
10-20,000 Alephs, everybody who wants one either has
bought it already or can get it cheaper on the used market.

A 10 year run would be considered very very good.

Every product has an "arc" to its sales, and before we
perceived the decline in sales of Alephs, we had the X
design ready. We sold them side by side for a couple of
years, but finally Alephs declined to about 10% of sales,
so we concentrated on X products.

Sonically the X amps tend to be more accurate and dynamic,
while the Alephs are warmer. Depending on the speaker
you use or your personal taste, preferences could go either
way. I still use Alephs all the time in listening tests.
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Old 1st July 2004, 04:49 AM   #5
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Quote:
I still use Alephs all the time in listening tests.
No wonder my ears prefers alephs. I tought my ears are not right, but here I have the truth from the master.
How about XA? Are they more aleph or more X?
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Old 1st July 2004, 05:13 AM   #6
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Another option would be to use transistors with more gain in the front end. The "raw" open loop gain of the front end is approximately 20 dB if I recall correctly. (The back end also provides gain...something not commonly seen, given that most outputs are followers with roughly unity gain.)
A MOSFET with more transconductance or a low beta bipolar would do the trick. Another possibility would be to run two MOSFETs in parallel on each side of the differential--yes, all four would have to be matched. If you jiggle your parts choices correctly, you can set the open loop gain a little higher than it is now, say about 50-60 dB, then set the closed loop gain to 30 or 40 dB. This way you won't be pushing huge amounts of gain that get turned into huge amounts of feedback, hence changing the sound of the amplifier any more than necessary.
However, when all is said and done, you will find that the sound of the amplifier has changed. If you lower the amount of feedback in the amplifier as it is, then it'll probably decrease the bandwidth somewhat and will definitely have higher distortion, as well as lower damping factor. If you follow the path I outlined above, the amplifier will have lower distortion and better damping factor...but sound somewhat more "hi-fi" and less like an Aleph.
Nelson's suggestion of 30 dB overall gain is reasonable, given that you're using a CD player. I wouldn't go so far as 40 dB unless you were using a low gain phono stage. For that matter, 25 dB might be enough, depending on your CD player.
Your choice.

Grey
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Old 1st July 2004, 08:39 AM   #7
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From the papers by Mr. Pass, I created my own imagination about what happened. This is amateur imagination, big chance all are wrong.

Why alephs have warm sound? Because the final stage is single ended. Only the bottom transistor sucks little or big current from aleph CCS above. The 1 side action like this will give big 2nd harmonic. This is what create its warm sound. Hot mosfets sure gives its part. Does anyone has made aleph design wholy by bipolars? Wondering what will be the sound like, inspite Mr. Pass said he pities ones who makes cold mosfet amp (or hot bipolars?)

Susy designs are different. They stressed on the ability of susy to cancel each others distortion, so the speakers will experience minimum distortion. This is why makes it sounds clean, because the right and left side of amps will produce exact distortion that cancel each other, in the eyes of speakers.

If we make 2 alephs back to back, like XA backengineered, they will cancel the distortions to each other, including those nice 2nd harmonics. I don't know. What is the sound of this? I think it will be more X than aleph.

Still about the master's design. I liked the concept of folded cascode like in the x100 backengineered. It performs only 1 stage with folded cascode. The second stage is only current booster, formed by complementary N and P, like totem pole configuration. It makes the whole system 2 stages, like the master said. The full swing already in the folded cascode.

If we only make half of susy patent, and take the - from ground, will it sound like aleph? But with greater efficiency.
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Old 1st July 2004, 12:50 PM   #8
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Every CD-player put my hands on over the last years delivered around 2 Vrms output level at 0 dB. This amplified by 40 dB gives you 200 Volts and 10000 Watts on a 4 Ohm load...
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Old 1st July 2004, 01:51 PM   #9
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by Nelson Pass
It should work, although you want to adjust the frequency
compensation values.

........................


Try getting by with 30 dB or maybe a pot on the feedback loop
so that instead of adjusting the volume control you adjust the
amp's gain.

As far I'm aware this implies the feedback loop pot is a very
bad idea, at low volume levels the amplifier will almost certainly
oscillate, unless it is compensated for unity gain stability.

For an amplifier with dominant pole compensation if you increase
gain and reduce the compensation capacitor the amount of
effective feedback at high frequencies remains constant,
however for adjusting the volume via the feedback loop you
need to increase the capacitor for unity gain, running it then
at say 30dB gain = no high frequency feedback at all.

X33 (30dB) gain and reducing compensation values with an
input pot sounds the best option to me for direct CD connection.

Its also possible to set the gain and compensation for say X20
(26dB) and have a switch in the feedback loop for higher gain
when its ocassionally needed. This could be a potentiometer
but it would only have say 6dB range, general volume level
control would have to be done elsewhere so a switch is easier.

sreten.
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Old 1st July 2004, 01:57 PM   #10
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Hi !

Holger is right. Almost all CD players have 2V on output.
We need rather attenuator not amplifier. Fortunately, I have
yamaha CDX-593 when output signal is regulated and I have connected it directly to Aleph3. If CD model of "lumanauw" has enough small output impedance utilizing 1K potentiometer may be simple good solution. Taking into account that only small part of Aleph power will be utilized by listener , effective signal source resistance visible from Aleph input will be much less than 1K. If we assume that enough output power is 2W/8Ohm ( it is enough for me ) than needed input signal is about 0.5Vp( 1Vp-p ).
CD gives about 2.8p so source signal has to be attenuated about 5 times. Part of potentiometer visible by Aleph input will have about 200 Ohms. It will have no any bad influence on Aleph sound.

Regards
Jacek
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