Aleph 5 versus Aleph 30 / Panos29

[Alois]

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]

Hi Alois,
I guess the 800VA is what you have on hand.
Otherwise I´d 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?

I´ll 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]

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]

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]

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

Greetz Alois

[Andypairo]

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]

Sorry Alois,
was a bit fast with my calculations.
Of course it depends on the coils you´re 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 I´m not necessarily aiming at 25V and definitely will be below with the coils.

IMO you don´t have to change anything for the circuit.


Cheers
Jens