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-   -   transformer with 43VAC secontary for an allef 2 (http://www.diyaudio.com/forums/pass-labs/82451-transformer-43vac-secontary-allef-2-a.html)

nikosgr 1st July 2006 06:11 PM

transformer with 43VAC secontary for an allef 2
 
Hi to all

I am in the process of building an allef 2
I have two transformers that I want to use 1500 VA secondary 2 X 43VAC
After rectification close to 59 VDC on air and under load I assume 55 volts
In the schematics of allef 2 we have 45 volts
Is it ok if I use those transformers?
Please advice

Mark A. Gulbrandsen 2nd July 2006 01:42 PM

That is too high of secodary voltage. This is getting into Aleph-1.2 terriitory. You need to be around 33 to 35 volts ac secondary for Aleph 2.

Mark

nikosgr 3rd July 2006 08:34 AM

Hi to all

Thanks for the replay

Watt if I use a CRC filter bank , I assume that I will loose sum volts there depending
On the value of the resistor

Please advice

jh6you 3rd July 2006 09:07 AM

Unless your speakers require high current, I think that you could use the 55V with a reduced bias current by adjusting R19, e.g. down to 0.4A/FET instead of the original 0.5A/FET, keeping the same power consumption of the amp. Of course, the reduced bias might affect the output power rating fairly much, though.

Mark A. Gulbrandsen 3rd July 2006 10:54 AM

The reduced bias will also affect how the amp sounds. It won't sond like an Aleph 2.. thats for sure. Burning up 10 volts in a CRC will make alot of extra heat... but if you don't mind the heat then go for it. Keep in mind that the Aleph 2 runs very hot as it is.. also incresing the bias is generally more effective towards even better sound than decreasing it... at higher bias levels it gets way hotter! Once you decide on the heat sinks then double that amount and you might have enough!

Mark

xr000 3rd July 2006 11:04 AM

up
 
:smash:

jh6you 3rd July 2006 12:56 PM

Mark,

I do not deny your claim about the sound. I just thought about using the existing transformer as Nikosgr wishes. If a new investment to a new transformer has a good money value for the sound, that could be better. :)

In my opinion, the total current with the reduced bias is still more than Aleph 3 and more over the rail voltage is much higher with a positive effect. If the shared bias current 0.4A/FET is considered too low, we could increase the bias/FET by reducing number of paralleled FETs, e.g. 0.6A/FET * 4 (total 2.4A) instead of 0.5A/FET *6 (total 3A). Of course, the amount of bias is adjusted by changing size of R19.

Regards


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