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-   -   Aleph 5 versus Aleph 30 / Panos29 (http://www.diyaudio.com/forums/pass-labs/20741-aleph-5-versus-aleph-30-panos29.html)

Alois 25th September 2003 12:28 PM

Aleph 5 versus Aleph 30 / Panos29
 
I currently (still) have a too hot running Aleph 4 that I would like to convert either into an Aleph 5 or Aleph 30.

What is the difference in sound between the two? Hopefully panos29 could comment on this because I know that he has changed an A5 into an A30. As I would use the amp for bi-amping I think I could live with the power of an Aleph 30 consuming 200W (only).

I would like to use a 800Va 24-0-24 volt transformer and a pi filter what would give me around 29 Volt of rail voltage (34V without pi) instead of the official 25V. Would I have to do any other changes further down the line in order to compensate for the 4 Volt difference?

Tanks and regards, Alois

joensd 25th September 2003 01:13 PM

Hi Alois,
I guess the 800VA is what you have on hand.
Otherwise Id go for a lower voltage one and do something about the 5V lost in the pi-filter.
Wanting to get your amp cooler and burning about 4A*5V=20W just in the filter is a bit contradictional.
Which coils are you using that can withstand the heat?

Ill be building an Aleph3 soon and have chosen for a 2*18V/500VA. Probably will put in some coils as well but only loose about a volt or so.

Cheers
Jens

Andypairo 25th September 2003 01:17 PM

My Aleph 30 runs at about 29V per rail, but IMHO if you deal with a difficult load is better to have lower rails and higher current.
Mine sounds wonderful but don't ask it to play too loud on lo-Z speakers, it just hasn't enough current...

But in a bi-amped system (for the mid-high I suppose) it will be a great choice.

Cheers

Andrea

Alois 25th September 2003 02:01 PM

Hi Jens

Yes, I just have an 800VA on hand. To explain the difference of 5V please note that as general rule the factor 1.41 is used to calculate the DC value (24*1.41= 33.84). How ever I have seen a lot of people calculating with 1.2 to 1.3 especially if you are using a coil (please refer to the following link http://web.vip.hr/pcb-design.vip/power-3.html This guy uses 21V * 1.2 to get the desired 25V.

Further more the following link gives a certain hint as well http://www.users.bigpond.net.au/mefi...nstruction.htm
1. When choosing the AC secondary voltage you need to allow for voltage drop across the rectifier bridge, plus the internal resistance of the windings, etc. "Rules-of-thumb" vary, but you should not use the ideal value of VDC = 1.414 x VAC. Nelson recommends between 1.2-1.3, as do most other designers / engineers.

Conclusion: 0.2 * 24V = 4.8V so with your 18V you will more likely get 22V than 25V.


Greetz Alois

Alois 25th September 2003 02:02 PM

Hi Andrea
What changes have you made to the official version to be able to run the A30 with 29V?

Greetz Alois

Andypairo 25th September 2003 02:13 PM

As far as I remember almost nothing, just keep an eye on the AC gain (there are a number of threads about it) and on the bias, which is mosfet-dependent.
I had to increase the compensation cap cause I had a "bump" on the waveform at high levels but this might not be your case.

My trafo is 2*22 Vac, CRC filter.

Cheers

Andrea

joensd 25th September 2003 02:40 PM

Sorry Alois,
was a bit fast with my calculations.
Of course it depends on the coils youre using and the regulation of the transformer (which should be quite OK with 800VA for Aleph30).
But still 5V loss over the PI-filter?

And yes Im not necessarily aiming at 25V and definitely will be below with the coils.

IMO you dont have to change anything for the circuit.


Cheers
Jens


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