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-   -   The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB (https://www.diyaudio.com/forums/group-buys/336479-slb-smooth-butter-active-rect-crc-cap-mx-class-power-supply-gb.html)

xrk971 13th April 2019 06:01 AM

One PCB is dual rail and can provide up to 5A continuous current. Depending on your rail voltage, may be enough for much more than a 25w amp. I use just single rail at 37v and 4.35A for a 50w SE Class A amp.

For the typical +/-24v At 1.25amp PSU needed for 25w Class A amps out there, this supply will not even break a sweat. For lowest noise and to minimize chances for ground loop hum noise, I highly recommend one dual rail per trafo per channel for monoblock operation. Having left and right channels share a common PSU often results in ground loop hum.

jameshillj 13th April 2019 09:27 AM

Just a strange query, 'X', but could you try moving the R5 (0.1R) to the 'ground track' between the C7 and C13 for the +ve reg supply in a SIM, or actual proto board?

xrk971 13th April 2019 09:35 AM

Jhofland and I have had numerous discussions around the subject of where to put the R in a CRC. I normally split them with one across the positive and one across negative terminals. The sims show that it makes no difference where they are placed as the return current has to form a loop.

gary s 13th April 2019 09:41 PM

Another question X, for the usual +/- 24VDC supply to feed the power amp from the output of this design, what is your recommended transformer secondary voltage feeding the board?

I also assume that the transformer must have dual secondary windings and not a centre tapped winding?

Do you think there would be any added advantage in slotting in a separate CRC or CLC board between the output of this board and the power amp for extra supply stiffness.

For the schematic you have shown, what is the equivalent total capacitance the amp would see using the cap multiplier as shown on the PCB?

xrk971 13th April 2019 09:56 PM

The cap multiplier really is a ripple eater so comparison of equivalent “capacitance” is not of real value since real capacitors provide a storage of energy, whereas the cap Mx or ripple eater acts as if it is a very large C in a CRC filter but has no storage of energy. You could calculate what the equivalent C would be needed to give a 3.6mV ripple for 37.5v at 4.35A. It would be pretty big. So capacitance multipliers really are suited for Class A amps where the current is steady. So “stiffness” isn’t needed and doesn’t really apply like it would in a Class AB amp where the current is changing with the music.

This supply is all you need, no more CLC or CRC needed in addition. When used with my SE Class A amp, it is so quiet I can’t tell the amp is even turned on with my ear pressed to the speaker cone.

How to size the trafo? Depends on the brand a bit. I would size the VA rating at 3x nominal requirement to reduce sag and saturation. So for +/-24v at 1.25A that’s 48v x 1.25A that’s about 200VA and voltage at required rails plus 3v for the cap Mx and probably 4-5v more for sag. So 24v +3v + 4v = 31v. Now divide by 1.4 and you get 22v. So for the typical 25w Class A amp, use dual 200VA 22v trafos one per channel. Note that some brands like Antek sag more than others so step up one more notch to 24v. But maybe a Talema or Toroidy is fine at 22V. Yes, dual secondaries not center tapped. One more thing, it never hurts to go up one more notch in VA rating either so dual 300VA would assure you of even better performance.

gary s 13th April 2019 11:10 PM

Thanks X for that comprehensive reply.

gary s 14th April 2019 12:26 AM

SLB Group Buy List
baswamin - 2 boards
meanie - 2 boards
jwjarch - 2 boards
gary s - 2 boards

Total = 8 boards.

Looking forward to using these to mate with your Alpha 20 PCB's received recently, which I will build as dual mono designs. Very interested to see how they will compare to the MX2.

Any anticipated pricing yet or when they will be available?

Mark Johnson 14th April 2019 12:43 AM

Quote:

Originally Posted by xrk971 (https://www.diyaudio.com/forums/group-buys/336479-slb-smooth-butter-active-rect-crc-cap-mx-class-power-supply-gb-post5759241.html#post5759241)
Jhofland and I have had numerous discussions around the subject of where to put the R in a CRC. I normally split them with one across the positive and one across negative terminals. The sims show that it makes no difference where they are placed as the return current has to form a loop.

However it does prevent at least one type of disastrous PCB layout.

xrk971 14th April 2019 12:53 AM

I am about to order a set of verification pcbs. Will build it and verify that it all works. Then order final set. So probably 3wks away at least. Boards will be 2mm thick, 2oz copper, ENIG finish and blue solder mask. Probably about $23ea. Usual shipping charges of $5 in US, $10 in CAN and $15 everywhere else. I am not sure how heavy they will be, so above shipping is approximate and might be a little more.

jhofland 14th April 2019 02:18 AM

where to put the R in the CRC
 
Quote:

Originally Posted by Mark Johnson (https://www.diyaudio.com/forums/group-buys/336479-slb-smooth-butter-active-rect-crc-cap-mx-class-power-supply-gb-post5759829.html#post5759829)
However it does prevent at least one type of disastrous PCB layout.

Putting them in the low side and the high side does have a practical problem, at least for the layouts I do. The resistors themselves dissipate enough power to get pretty toasty. So you want to place them where they can get some reasonable air flow. Those in the low side tend to get trapped between the large filter caps which restricts cooling somewhat and the added space between the caps increases board area and ripple current loop area.


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