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Old 25th June 2003, 03:46 AM   #1
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Default Aleph-4 Questions

A few questions....
How critical is input and output fet matching ?, and what are the effects of mismatching.
What is the effect of reducing the 3 amp bias current ?.
What is the effect of reducing supply voltages for lower level listening ?.
Recomended output fets ?.

Thanks,
Eric.
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Old 25th June 2003, 05:03 AM   #2
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Although it goes against the grain of our perfectionist
orientation, the answer is: not as much as you might think.

It's nice to have some matching, as you get lower DC offset
on input diff pairs, and maybe a little less distortion. On outputs,
you get better current sharing (so the dissipation is distributed
more evenly) and maybe a little less distortion.

So I like to match, after all it's easy enough to do, but I don't
lose any sleep over it.

You may have previously seen posts by me to the effect that the
best results I get is when I have the time and energy to insert
different devices into the actual circuit until I get the best
performance (by whatever criteria you care to choose) and then
solder in the best set.

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Old 25th June 2003, 07:40 AM   #3
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Default Re: Aleph-4 Questions

Quote:
Originally posted by mrfeedback

What is the effect of reducing the 3 amp bias current ?.
What is the effect of reducing supply voltages for lower level listening ?.
For a less maximum output power, I reduce the bias current.
The sound remains the same at best, but, I normally hear it getting worse.

For a less maximum output power, I also reduce the supply voltages.
The sound remains the same at best, but I again normaly hear it getting worse.

I look forward to other opinions.

JH
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Old 25th June 2003, 09:54 AM   #4
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Default Moer Questions....

Hi Nelson, and thanks for your reply.
I read that 0.1 V Vgs is specified and 0.01 Vgs is typical in your products - what is the typical spread in a batch of fets - IOW how many fets does one typically need to buy in order to get a suitable set for a stereo Aleph-4.

As a further question, you make mention in the Aleph-4 literature of non-linearity of air and single-ended output stages being similar.
How does the Aleph-X presumably lesser distortion fit sonically with this observation ?.
Does this also mean that AP of the signal input and polarity of the speaker WRT the output are important, or audible - IOW for correct in room acoustic AP, is the amplifier throughput polarity important or discernable ?.
Efficiency considerations aside, which is the better sounding circuit - Aleph-4 or Aleph-X ?.

Thanks, Eric.
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Old 25th June 2003, 09:58 AM   #5
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Default Variable Room Heating.

Hi JH, it sounds like you have tried reduced bias current and supply voltages - what sonic changes do you notice ?.

I am asking this to ascertain if it is sonically acceptable to use a variac and/or variable bias current when using the amplifier in low level applications which is most of the time in order to save energy costs.

Eric.
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Old 25th June 2003, 10:48 AM   #6
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Default Re: Variable Room Heating.

Quote:
Originally posted by mrfeedback

... you have tried reduced bias current and supply voltages ... to save energy costs.

Ni Hao!

Actually in order to cool down the heat sinks rather than to save energy costs, I have tried them with my Zen V2 and XSOZV2 (both having the Aleph current sources)--sorry, not directly with Alephs.

Sonic changes to be drier and to lose smoothness in pitch definition. For your info, mine are finally at 1.3A-bias, which is less than the original 2A, and subjectively within acceptable sonic changes.

It's intersting. Nelson Pass always advocates greater bias.

JH
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Old 27th June 2003, 09:33 PM   #7
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Default Re: Moer Questions....

Quote:
Originally posted by mrfeedback
I read that 0.1 V Vgs is specified and 0.01 Vgs is typical in your products - what is the typical spread in a batch of fets - IOW how many fets does one typically need to buy in order to get a suitable set for a stereo Aleph-4.

As a further question, you make mention in the Aleph-4 literature of non-linearity of air and single-ended output stages being similar.

How does the Aleph-X presumably lesser distortion fit sonically with this observation ?.

Does this also mean that AP of the signal input and polarity of the speaker WRT the output are important, or audible - IOW for correct in room acoustic AP, is the amplifier throughput polarity important or discernable ?.

Efficiency considerations aside, which is the better sounding circuit - Aleph-4 or Aleph-X ?.
"You ask a lot of questions...." (quote from the George Pal
version of the movie The Time Machine)

Since matching need only occur in parallel banks, if you are
building 2 channels of Aleph 4 you need 4 sets of matched
devices, and this makes things easier as they only need to
match within a set. I would figure on buying 25% extra.

The value of the observation of the single-ended nature of air
is still speculation. But certainly each Aleph sounds different,
and how much is ascribable to this phenomenon is unkown.

This does indeed imply that absolute polarity would be important
so far as there are even harmonics in the reproducing equipment.
Can you hear this? Anecdotally this seems to be the case, but I
personally don't have good enough ears to call it reliably.

My preferences? Depends on the material, other equipment,
time of day, what wine I'm drinking, and who I'm drinking it with.

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Old 28th June 2003, 04:55 AM   #8
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Quote:
This does indeed imply that absolute polarity would be important so far as there are even harmonics in the reproducing equipment.
Can you hear this? Anecdotally this seems to be the case, but I
personally don't have good enough ears to call it reliably.

My preferences? Depends on the material, other equipment,
time of day, what wine I'm drinking, and who I'm drinking it with.
Hi Nelson, in my experience according to throughput polarity, (for the same in-room acoustic AP) this even harmonic characteristic does affect the in-room sound when listening attentively.

Likewise I have to be in the mood to listen for it.
Good wine and good company and those cares can go out the window.

Eric.
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Old 28th June 2003, 04:57 AM   #9
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Quote:
This does indeed imply that absolute polarity would be important so far as there are even harmonics in the reproducing equipment.
Can you hear this? Anecdotally this seems to be the case, but I
personally don't have good enough ears to call it reliably.

My preferences? Depends on the material, other equipment,
time of day, what wine I'm drinking, and who I'm drinking it with.
Hi Nelson, in my experience according to throughput polarity, (for the same in-room acoustic AP) this even harmonic characteristic does affect the in-room sound when listening attentively.

Likewise I have to be in the mood to listen for it.
Good wine and good company and those cares can go out the window.

You say that eack Aleph sounds different - can you give some idea of the differences ?.
Is the Aleph-X improved efficiency the only advantage of this design ?.

Thanks, Eric.
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