PSU question for A30

[Buhl]

In the phase of collectiong the pieces for my A30 amp, im a bit confused about what PSU design I should go for - a resistor in the area of 0,47 ohm in a CRC filter, or just a simple big old C ?
My rough calculations gives me that a 0,47 ohm resistor will drop the voltage about 1,88 volts, and at approx. 2 amps pr. channel dispatch some 7-8 watts - not that much - and thus i will incorporate the secondary drop in the design, and use a 20 volt tranny, and thus end up around 24 volts - that is if I use a 1,3 instead of square root of 2 (witch I recall nelson suggested to use, for more life like calculations)

In the haze of the post returned to me by the schearch machine, when entering CLC or CRC i found a thread that stated that CLC or LC was the only way to go....

Is the effort and heat of the R worth it ? I saw that Nelson uses it in the FW amp - or should i just go with with the C of about 220.000uF / channel, like the original alephs ?

If I should use a resistor, is 0,1 ohm enough, or is 0,47 better ?

Any other tips, besides the use of small polypropylenes acros the big C's ? Im not a fan of CAD-software, more the "better big than sorry" type of apporach.......

And just a short 2. Q: the voltage ratings of the 220uF caps in the A30 - is 35 volts ok, or should I use 63 volts ?


Cheers !
Hans

[wuffwaff]

Hi,

since your bias won´t be that high I would go for a CLC approach. It wastes less energy and is much more effective. For example something like 44000-2.2mH-66000.........
You can have a look at the effects of resistors and chokes with PSU Designer II (no CAD!)

The 220uF caps can even be 25V without a problem (the coupling caps in the input and current source could even be 6,3V BG NX)

William

[Nelson Pass]

I have built them successfully using a .47 ohm value per
channel, which isolates the two channels and give a 1 volt
drop across the resistor. This gives a reduction in the supply
ripple by a factor of about 10.

[Buhl]

Wuffwaff and Nelson - thnx for the answers - I would like to use R's instead of L's - as they are somewhat harder to get for me, and to be frank - i dont mind the extra heat.... ;-)
I suspect that the the cap at the current source is C9 close to Q5 - or is it C10 ?? Wuff - you mention the use of BG caps here - is this location and the input coupling cap a good place to spend some extra $$$ in trade of quality ? I plan on using Panasonic FC, as I have them lying in my "box O'goodies".

Nelson, the use of Resistors that you mention to give isolation, as well as a factor 10 in reduced ripple (sounds as it is worth to include ??) - is that the "normal" use whare you place the resistor in the positive and negative rail between two banks of Caps ? How could this isolate the channels - is that because that you use a seperate cap bank for each channel ? and finally ( as if I didnt ask enough questions...) are there any pros by using a cap bank for each channel, with its own bridge ?(or two bridges, but I would like to thy and use one, as this i whats used in the A30 schematics)

Thank you for taking the time to answer and contribute to my knowledge increase ;-)

Cheers !
Hans

[wuffwaff]

Hi,

the cap at the current source is the one connected to the base of Q5.
BG NX 220uF 6,3V are not very expensive and I used them in my Aleph5. There is another thread "coupling cap in Aleph" were these caps are discussed at lenght ending with a bunch of BG´s used for the input cap and a panasonic FC + 10nF at the other position.

William

[Buhl]

Hi again
as I read the schematic, the only cap attached to the base of Q5 is C7, witch is 0.001uF ?
C9 is connected acros the collector and emitter, and C10 to emitter, and to base via the R21@820 ohms - R9&R10 is 220uF ?
I a bit confused now - ??

Cheers!
Hans

[wuffwaff]

it´s the one connected to R21. Insome Alephs the cap comes first then the resistor. Here it seems to be the other way round.......

sorry,

William

[jh6you]

I think that 220uF of 35V grade is ok for C9 and C10.
If you use 63V grade, the life of the caps could be vertually permanent.

Regards

[Buhl]

OK, good to know - I'll stick with the 35 volt - permanent is almost to good for me

But still Im a bit confused about the use of resistors (or inductors) in the PSU - I suspect that nelson uses it in the FW amps because they have to drive very sensetive speakers, and/or the circuit itself is more prone to pick up noise from the supply ? I recall that some have said that they did not think that further regulation beyond a simple C of the aleph supply gave any improvement ?

Ups, and another thing - I want to be able to play with BIAS (dont we all ??) and thus want to calculate for the greater current draw when ordering my toroid - how much does the A30 draw when R19 is removed - its about 2 amps/channel when not removed ?

Cheers !
Hans

[wuffwaff]

Hi Hans,

with 0,47 Ohm source resistors this will probably be over 3A / Channel. Instead of removing it you could also change it to a higher value. You will need a pot in this position anyway to set the amp up in the first place. Just change the setting and measure the pot so you´ll know what resistor you need for a given bias.

All the Aleph´s were without C-R-C or C-L-C so this will work just fine.
The nice thing about DIY is that you can try other things too without having to worry too much about cost or customers.
A nice C-L-C supply will give you far less ripple. Why don´t you just try with and without. Measure the ripple voltage and listen to the changes in sound.

William