Transformer rating for Aleph 4

Status
Not open for further replies.
Jump to Latest
#3
ok - maybe I'm not doing the maths right...

I get 35 * 1.414 (close enough 2^.5) - 2 (say, for diode losses) = 47.5 volts.

Am I not allowing enough for diode (rectifier) losses?

Let the audio elders illuminate me!!

Merbert
 
#4
you've got to allow for mains fluctuations, transformer regulation etc. Vac x 1.2 is a more typical loaded voltage.... you may get more than this but never rely on Vac x 1.4142 as this assumes zero supply resistance, zero mains fluctuation and infinite capacitance.... none of which we are able to obtain. secondaries around 38-42V are likely to be more suitable. 2V for diode drop is standard.
 
#5
What about Aleph 2?

I can get my hands on some Ulveco 990VA with secondaries rating at 32V nominal and 33.2V idle.

The voltage rails of an Aleph 2 are to be 45V and I was wondering if I can use this thoroid?
Should I use nominal or idle for my calculations?

Would a slightly lower value for the voltage rails be a problem, say 42 - 44 volts?

What would the effect be in such a case?

Thank you.

Axel
 
#7
I am getting a custom toroid made for my aleph 4 that I am working on, would 1000VA 40+40 suffice? Would that account for the losses, or would that be too voltage on the rails? I was planning on getting 35+35. The guy said he could make any voltage necessary, with the power rating that I want.

Also, is it better to get two seperate 500VA toroids for the aleph 4, and have a seperate one for each channel? What is the optimal VA rating for each channel?

Thanks,

--
Brian
gte619j@prism.gatech.edu
 
#8
i would tend to use secondaries between 38 and 42V for +/-48V so 40V should be fine... separate transformers/rectifiers/caps for each channel is certainly better. most ppl consider average DC x 2 a good minimum for transformers so 500VA per channel would be the minimum .... personally i dont like anything below average DC x 4 in highly biased or class A amps which would equate to 1000VA per channel but you could get away with 500VA just with more voltage drop.
 
#12
I wrote to Mark Finnis before:
His reply:-
At 12:50 AM 13/12/2001 +0800, you wrote:


Can you let me know what is the spec of the transformer for Aleph 4, the ampere and the secondary voltage? I have one 30v+30v transformer and I wonder if I can use it to built Aleph 4.

35-0-35
7 amps per channel

cheers

mark
 
#13
Transformer specifications

You may wish to trying Duncan supply simulation software to check voltages, currents and ripply (see previous thread - Duncans amp tools PSU 11)

Prior to downloading the simulator I emailed my local toroidal manufacturer Harbuch Electronics Pty Ltd in Sydney for the specification to suit the Aleph 2 and their response was :

For 2x45V/3A with +/- 0.75V P-P ripple with +/- 90,000uF you require a 625VA transformer 2x36V/8.7A part # J2423 freight

I then ran the simulator and and after sorting out how to use it, the simulator result is very close to their spec and suggest you try it.

For a no load voltage of 36 volts (ac) @ 8.70 amps the secondary impediance is about 0.20 ohms with 5 % regulation(there is a handy help menu with formulae to workout no/loan and impediance).

You then select the bridge, capacitor and loan resistance(15 ohms is correct for 45 volts DC @ 3 amps)

The rms voltage is 45.09 volts and the transformer sags to about 35 volts AC.

I ran several values of capacitance, 40,000 uf @ 20 milliohms ie two large can in parrellel gives a ripple of 750 millivolts.

Parrelleling more capacitors to say 90,000 uf @ 7 milli ohms reduces the ripple to 312 millivolts and increased the DC rms Voltage slightly to 45.29.

For the Aleph 4 @ 48 volts DC the simulator suggests about 37.75 volts AC (no Load) for the same conditions except I have allowed for the reduced bias current of 2.5 amps for the Aleph 4 (240 watts or 120 watts per bank @ 48 volts @ 19.20 ohms load ).The transformer sags to about 37 volts rms.

The ripple for 90,000 uf was 271 milli volts and increases to about 650 millivolts for 40,000 uf.

I reality of course the standing Dc voltage under load could be a bit higher for either the Aleph 2 or 4 without any penalty, and the master himself has indicated the design a quite tolerant of supply variations.

I though this was fun and sort of makes progression through the project more interesting as you get to undertand more about various aspects of the amplifier.


best regards

macka
 
#16
ALEPH 1,2 +/- 60 V
ALEPH 2 +/- 45 V
ALEPH 3 +/- 25 V
ALEPH 4 +/- 48 V
ALEPH 5 +/- 34 V

That´s for the power supply voltages

For the transformers I only can tell what is minimum required, I don´t know what Nelson Pass uses
ALEPH 1,2 1000VA
ALEPH 2 600 VA
ALEPH 3 400 VA
ALEPH 4 1000 VA
ALEPH 5 600 VA
 
#17
Contrary to hints above, I do not know what voltages Nelson used ..... however, I can tell you what I used ..... and what I get under load 🙂

Remember I found my toroids surplus, so "took what I could", I did not choose according to theory!

They are 35-0-35VAC, the cap bank is 4x 80,000uF in a Pi filter arrangement (there is a 1.5V drop across the chokes, which are large, gapped iron core types wound with braided wire .... don't know the exact value as they were attached to the heat-sinks when I bought them).

And the amp sees .... 44.5VDC

This doesn't bother me, as I don't need the 100W anyway and the amp is not worried by minor variations in rail voltage. I could remove the chokes and get another volt or so, but I'd rather keep the filter.

I do seem to recall Nelson using the x1.2 "rule-of-thumb" in some piece of correspondence, just don't ask me to remember where !

cheers

mark

PS: BTW ..... All thanks go to Nelson
 
#19
Power Supplies

Nicolas,

I would suggest the meaty 1000 va transformer will work very nicely.

I e-mailed Mr Pass a little while ago and he indicated "The design is quite tolerant of supply variation."


Have you deciced on you filter capacitors yet?

I thought about this for a while wondered if so called Audio grade capacitors were worth the silly prices they charge.

Anyway my curiosity got the better of me and I emailed the Master himself.

Aparently the Aleph design is somewhat insensitive to capacitors for the power supply and he suggested normal grade capacitors if parrelled will produce a similar result of special quality capacitors.

They can then be by passed with film capacitors for reduced impedance at high frequencies.

I ended up buy a quantity of 70 15000uf capacitors from a trader in the USA, they are NOS but for about US$40, I thought well why not!

regards

macka
 
#20
Wow, how are you going to put 70 1500uf capacitors into the amp? Are they very small in size? What value of film capacitors are you using?
For Aleph 4 that I am in process of building slowly( well, because $$$- MOSFET MATCHING-thinking of 80 pcs). I thought of using wima for C103, C12, C4 and black gate or panasonic for C11. The rest, I will be using panasonic from Digikey.
Because they don't have 25000uf, I am thinking of dual mono power supply using 8 2200uf capacitors. They are the cheapest I can find, but still expensive compared with yours.
Presently, I have bought only the transformer and the heatsink, The transfomer arrived in spoilt condition (cut by the fixing hardware, and Avel send me another one). I hope this time it will arrive in good condition.

70 pcs for $40 is real cheap? What is"NOS"?

Have you done your layout yet?

What preamp are you planning to use for your Aleph?
 
Status
Not open for further replies.
Top Bottom