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Old 29th November 2005, 10:32 AM   #1
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Default Changing my mind.

Dear all,

For a long time i had the idea to build a Aleph2, becouse my speakers are not the easiest to drive.
But as it takes me to long to build my amp my speakers beginning to get older, and need replacement.

Mi wife likes smaller speakers, so i dont need 100w power anymore.

The speakers i am building are the Hatt mkIII from Tony Gee.

So i changed my mind, and like to build an A3 or A30, and have some quistions about them.

To do so i need to rewind the secondary from my transformer to match the lower voltage of the amp.

1. Which one is better and why?

2. Can i use a higher rail voltage, and what will be the benefit of it?

3. If i bias the amp higher, what will be the sonic benefit.

4. What will be the best way to up the bias?

5. Is there a optimum between the railvoltage and the amount of bias (dont mind the heatsinking, i have plenty).

I hope you can give me some answers.

Regards.

Edwin.
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Old 29th November 2005, 05:10 PM   #2
Buhl is offline Buhl  Denmark
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Default Re: Changing my mind.

Quote:
Originally posted by E. Pardaans
Dear all,

For a long time i had the idea to build a Aleph2, becouse my speakers are not the easiest to drive.
But as it takes me to long to build my amp my speakers beginning to get older, and need replacement.

Mi wife likes smaller speakers, so i dont need 100w power anymore.

The speakers i am building are the Hatt mkIII from Tony Gee.

So i changed my mind, and like to build an A3 or A30, and have some quistions about them.

To do so i need to rewind the secondary from my transformer to match the lower voltage of the amp.

1. Which one is better and why?

2. Can i use a higher rail voltage, and what will be the benefit of it?

3. If i bias the amp higher, what will be the sonic benefit.

4. What will be the best way to up the bias?

5. Is there a optimum between the railvoltage and the amount of bias (dont mind the heatsinking, i have plenty).

I hope you can give me some answers.

Regards.

Edwin.
1. I have been told by an engineer working in a company that makes transformers, that serious rewinding is not a good idea, because toroids are designed after specific parameters, giving the vindings on the primary and secondary side, wire gauge and so on. Just revinding causes the magnetic flux to change unpredictable, and you could have strange problems.
A better way would be big coils on the primary side, but I dont think it would be enogh. Putting two Aleph 2 trannies in series would bring the secondary voltage down to half, thus reach a level suitable for a A3/A30 - about 18-20 volts AC unregulated.

2. yes, you can use higher rail voltage, but without higher bias, your amp will work wery poorly in normal impedances.

3. I notice a large increase in details, and the soundstage opens up, expanding in depth and width.

4. Remove R19 from the circuit.

5. You can't have to much BIAS - almost true, but at some point you begin to strain you mosfets, caused by lack of cooling, or by reaching their ratings. The sonic signature changes by the amount of bias added, and with my Zen 4 the sound is more soft with high bias, so its also a question of your preferences, apart from the question of heatsinking and rating of the devices.

Try and search for the excel scheme that illustrates the relationship between voltage, bias, power and a lot of other things. I think its made by Wuffwaff ?

Cheers !
Buhl
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Old 30th November 2005, 04:02 AM   #3
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Hello Buhl,

Thank you for your reaction.

As i understand you correctly it is no good idea to rewind my toroid for half the voltage.
I assume winding an extra secondary for 20-25V will have the same problems.
The reason i liked to rewind the toroids is they are 2000W a piece, and i dont want throw to them away or sell them.

My idea was to feed two A3-A30 amplifiers from them with half the voltage so i could also have speakers in another room.


I have read on this forum that an Aleph is not really suitable for difficult loads.
As far as my understanding goes parallelling speakers is an heavy load on an amplifier correct me if i am wrong.
Is it possible for an Aleph2 to drive 4 speakers without any problems?


I have seen that spreadsheet but it is for an AlephX.

Regards.
Edwin.
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Old 30th November 2005, 05:32 AM   #4
Stocker is offline Stocker  United States
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I have heard WAY more success stories (including my own) of rewinding all sorts of transformers than stories of wierd problems. I have even seen "kit" toroid transformers that let you wind the secondary to whatever you need, with only the primary pre-wound. I vote for rewinding as required.
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Old 30th November 2005, 06:56 AM   #5
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If you rewind your toroid isnt it more important to use the full 360 degrees of the toroid then just rewind it for the requierd voltage?

Edwin.
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Old 1st December 2005, 01:28 PM   #6
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I made up my mind.
I will make a A30 and rewind my transformer for the requierd voltage.
I also want to set the bias to 3A at 25V rails.

Will this get me more power with lower impendances?
I assume i can up the bias by lowering the value of the source resistors.
Is this be calculated with ohms law?
Is there anything else in the circuit that needs to be changed when you change the source resistors?
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Old 1st December 2005, 02:38 PM   #7
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Hi,

there a spreadsheet out there somewhere for calculating Aleph power. I cant find it on my PC so I will have to download it myself.......
3A bias at 50% ac-current-gain will give 6A peak current.

Yes Ohms law also works in an Aleph although R19 will bend it a bit.

You also need to change the resistors feeding the active current source through the 220uF cap to get the active-current-gain right.

William (who will look for his sheet)

NEW Aleph-X calculation sheet: AXE-1

found it!
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Old 2nd December 2005, 10:53 AM   #8
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Thank you William,

I will play with this for a while and try different bias levels and rails voltages until i got what i want.

In the meantime i got another question about current gain.

Does the amplifier deliver more power when you set the current gain higher (50-80%) at the cost of leaving class A?

Regards
Edwin
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Old 2nd December 2005, 02:48 PM   #9
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Hi,

yes it will deliver more current as you can see in the spreadsheet. During negative peaks the current source will shut off.
Ive played my Aleph5 with around 63% into my Thiels cause at 50% and 2.4A of bias it would distort at high playback levels.

You will also change the character of the bass a bit. It is very easy to experiment with (you could even use a pot) this setting.

At the moment the A5 sits at 52% into some Dynaudio W42s

William
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Old 12th December 2005, 10:47 AM   #10
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After fiddling with the spreadsheet another question is bubbling in my mind.

Everybody talks about higher bias for the output fets, but i didnt find anything about biassing the input fets (irf9610).
The differential input pair is biassed at 20mA if i am correct.

Does biassing the inputpair higher bring any improvements?

Edwin.
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