Aleph5. More bias-worse sound. - diyAudio
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Old 7th April 2004, 09:46 AM   #1
masfe is offline masfe  Spain
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Question Aleph5. More bias-worse sound.

First of all, I am new in this forum and I would like to say hello to everyone.

Second, as you can see, my english is not too good. So I hope that you will forgive me if I am not able to explain the question clearly.

Recently I have build a pair of aleph 5 monoblocks with 1,5 amp bias (0,5 each mosfet). The sound with this level of bias is very good: open, very detailed, airy, maybe with a little excessive presence of highs and a little poor bass, but in general amazing.

But according wiht the experience of most of other owners of alephs and the affirmations of Mr. Pass, with more bias the sound of the amplifier is better. So I have changed R21 for a pot and raised the bias to 0,66 Amp each mosfet (my heatsinks doesn't admit much more). And that is the problem. The sound now is worse (in my opinion): More bass and less highs, but goodbye to details, more compressed, confused. It seem that the sound is inside the speakers.

The monoblocs are conected to an Audiolab 8000S working as preamp (no banlanced outputs) and to a pair of B&W CDM7.

So I would like to know if everyone else have the same experience or if this is a problem of my alephs or of my configuration or what...

Thank you.
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Old 7th April 2004, 10:27 AM   #2
piewie is offline piewie  Belgium
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I think you should replace R19 by a pot and not R21 if you only want to increase bias.
I left R19 out to get maximum bias current. I think R21 had something to do with current gain or so.
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Old 7th April 2004, 10:51 AM   #3
masfe is offline masfe  Spain
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Default number error

I have make a mistake with the number of the resistor. I wanted to say R19. You're right.

Thank you.
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Old 7th April 2004, 03:42 PM   #4
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Refer to this thread. It might give you some hints:

Passion to mod Aleph-5

Thomas
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Old 7th April 2004, 04:59 PM   #5
masfe is offline masfe  Spain
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What I want to say is that the changes in the sound increasing the bias of my alephs not only afect the ratio between highs and lows, but all the nature of the sound.

Maybe I have a problem with the amps.

Or maybe, it got to do with other parameters. Maybe there is a level of bias that match with a type of speaker or a type of room or a type of preamp and other bias doesn't match.

masfe
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Old 7th April 2004, 09:02 PM   #6
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Quote:
Originally posted by masfe
What I want to say is that the changes in the sound increasing the bias of my alephs not only afect the ratio between highs and lows, but all the nature of the sound.

Maybe I have a problem with the amps.

Or maybe, it got to do with other parameters. Maybe there is a level of bias that match with a type of speaker or a type of room or a type of preamp and other bias doesn't match.

masfe

Reading your description about the changes in sound increasing the bias I tend to think to the transformers and/or passive filtering . If the transformers power rating are not adeguate to the bias changing , the results in audio compressions and spectral unbalance are, from my point of view and experience ,quite audible as you report .


For the matter try download and read the article
Power Supplies by Nelson Pass .
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Old 9th April 2004, 08:34 AM   #7
masfe is offline masfe  Spain
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Each monoblock has a 300VA, 25 V toroid and six 22.000 uf caps, bypassed with 0,47 uF polyester cap (no inductor).

I have removed the pot and placed again R19. Now the sound is great, as before, and there will be less heat.

I have readed the article about power supplies: very interesting. Maybe, as you suggest, passive filtering is not good enough.

thank you.
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Old 9th April 2004, 09:55 AM   #8
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You may wish to measure the Aleph current share of the ccs and negative side. Do a search for details.


Odds on its move of 50/50 % if the sound balance is weird.

macka
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Old 10th April 2004, 03:43 AM   #9
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msafe

I assume that you had too much current source gain when you tried the 0.66A. I would try the 0.66A with R19 of about 1K-1.2K.

JH
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Old 10th April 2004, 09:40 AM   #10
masfe is offline masfe  Spain
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Really, I must tell you that my Knowledge in electronics is very poor. Recently I have understood how a transistor works. I'm still learnig, but in the last years my brain works slow and slow and I think that in a couple of years it will refuse to work at all.

So, I have built the aleph 5 with a little idea of what I was doing. I know more or less what are ccs and the components invoved. I will investigate the matter and search about it in the forum.

When I raised the bias to 0,66A the pot was setted at 1 Kohm, and with this configuration I didn't like the sound.

For the moment I'm not going to do any more until I learn more and know what I'm doing. The alephs are working and the sound now is very good to me. I only was wondering if the rule: more bias-better sound is correct in any case or if it can depend on other external factors.

I'm very grateful for your kindness and for sharing your knowledge with me.

masfe
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