power supply for f6 or other

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fwt1712

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#1
Is there any advantage to vary what appears to be the 'standard' 60,000uf per channel and 300 - 400 va transformers with 18v x 2 secondaries?

In particular there are 18,000uf and 22,000uf caps in the same series as the 15,000uf caps I am considering i.e. CDE slpx or Nichicon LGU etc. that would fit on the Diyaudio psu that I will be using. For a few extra dollars I could get 88,000uf per channel in the same form factor as 60,000uf.

Similarly are there any real benefits in going from a 300va to 330va to 400va or larger transformer.

Are there any dependencies here i.e. would it make no sense to increase uf but not va?

I am open to suggestions but want to be able to use a cl60 (in 240v) for in rush control i.e. don't want to go to a soft start.

thanks,
Nigel.
 
#3
As a more generalized answer I would argue that the power-supply is a very important part for a push pull amplifier. A single end amp with a constant current source only needs a reasonable quite power-supply, but a push-pull amp like the F6 usually sounds much better with a low noise, very low output impedance power-supply. I want to argue that the power-supply constitutes at least 50% of the total sound-quality of an push-pull amp.

Simple active capacitance-multiplier power-supplies with very low total resistance in the preceding filtering will add a lot of dynamic vitality and firm control to the sound compared to passive resistive CRC filtering. This is at least my experience with power-supplies.

Cheers,
Johannes
 
#4
kapacitans-multi.png

L1 and L2 should be 20 turns of very thick cable around a small former of some kind. It will smooth the peak loading current pulses from the rectifier bridges and prevent or at least damp the constant pulses of intense RF noise that otherwise plague normal power-supplies based on rectifiers under heavy load.

Feel free to increase the capacitance values. The 100 ohm resistors connected to the source-pins of the fets are to bias them and avoid letting them close and enter the very non-linear region at very low currents. It might not seem very important with class A amplifiers, but you can definitely hear a difference with or without them.

Cheers,
Johannes
 
#7
I consider myself a noob. So even if you explain me too much technical details of the working principles of SMPS, I might not be able to understand.

But, lately I found people are getting interested in low noise smps like connexelectronic.

I was wondering whether they are good for class a amps as well?

Thanks,
Saikat

Sent from my Nexus 5 using Tapatalk
 
#8
fwt1712 said:
Is there any advantage to vary what appears to be the 'standard' 60,000uf per channel and 300 - 400 va transformers with 18v x 2 secondaries?
thanks,
Nigel.
Click to expand...

Dunno.. I followed the "recipe" and it's Wonderous in my ears.
I'd think on building it stock.. then dick around with adlib variations, should you then/still feel the need.
Unless you have extensive electrowizardy knowledge?
In which case it's improbable that you'd be asking.
 
#9
Zen Mod said:
my approach -fuse, CL60,250VA Donut , two bridges, 4 x 33mF,CL60 from GND to case

per channel
Click to expand...

Ever since I built my Aleph J clone using two separate PSUs, I have adopted a similar approach for my other First Watt clones. To fit the two PSUs in a moderately sized case I stack the transformers and use compact PCBs. Each uses 4 Cornell Dubilier 380LX series 33mF capacitors.

attachment.php


The CL-60 thermistor is also mounted on the PCB and connects to the 4 mounting holes.

attachment.php
 
#10
I have found that with the f5 more capacitance makes for a bigger, tighter sound with more depth. I am currently using 6x33,000uf with 10uf poly bypass on each cap. The poly bypass caps actually made a big difference. I am using a 600VA transformer. No softstart, just CL60.

I replaced the "R" in the CRC filter with a 2.5mh choke. Improvement, but not huge.

I'd say buy as much transformer and capacitance as you can afford. It's the basis of the amplifier and something that's hard (and expensive) to change once you have it built.
 
#11
There's more than a few Pass designs with a pass transistor/cap multiplier setup on the power supply (Zen V9 for instance)

For a dual rail, I believe the F5x project here on diy audio had a regulated setup that might be of interest...
 
#12
fwt1712 said:
...........
I am open to suggestions but want to be able to use a cl60 (in 240v) for in rush control i.e. don't want to go to a soft start.

thanks,
Nigel.
Click to expand...
Inserting a Power Thermistor in the transformer Primary circuit IS implementing a soft start.
Not bypassing that added resistance is bad practice.

the 10r of a CL60 does too little in the way of current limiting to be of much value on 240Vac mains supplies.

The CL60 works well on 110/120Vac mains supplies.
Hikari1 said:
......... No softstart, just CL60. .......
Click to expand...
you are making the same inaccurate claim.
 
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#15
Hikari and Andrew, yes I was referring to using a CL60 as a 'soft start' device (rather than using a soft start board/kit). From what I understand, a cl60 is used to effectively play this role in the commercial First Watt amps using a 300va transformer and a total of 120,000uf i.e. 8 x 15,000uf. My question is/was if I go to 400va (at 240v) and a total of 216,000uf i.e. 8 x 27,000uf is a cl60 sufficient to deal with in rush or should I get a soft start board/kit such as those available from the diyaudio store, or consider another cl variant. Thanks all, Nigel.
 
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