diyAudio (
-   Group Buys (
-   -   The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB (

xrk971 26th January 2020 01:03 AM

Hi Aljordan,


1) I did read through the SLB thread and the Alpha 20 thread but that was at least a few months back. The thought of looking through the Alpha 20 thread again makes me want to cry, as that thing is a monster. Is there something more I should be checking on the SLB boards or the Alpha 20 boards to make sure they are functioning optimally?

Measure voltage across the big Source resistors on output and calculate bias current. Should be around 1.25 to 1.3A.

2) You will notice in the picture that I didn't twist the DC power and ground lines from the power supply to the Alpha boards. Is there an advantage of doing so?

Twisting it reduces emitted 60Hz/120Hz/180Hz EMI hum noise that might get picked up by other stuff like your input cables.

3) What the heck are those female adapters called that go into the audio inputs on the Alpha 20 boards? I'd like to order some to do it properly.

It’s in the BOM, but JPS64 typically specifies Molex KK 2-pin female shell and crimp connectors. You need a Molex crimp tool too.

4) What do the pots adjust on the Alpha 20 boards?

The LTP bias current and DC offset to certain extent. We realized after making the boards that you can skip all the pots and put fixed resistors there. One of the schematics in the Alpha GB thread is redlined to show what values to put where the pots are.

jameshillj 26th January 2020 01:23 AM

Do those rather long wires between the pcbs and the power fets on the heatsinks create any loss of filter performance, stability or increased noise levels?

It looks rather compromised from the point of view about optimizing the pcb layout and designing short tracks between components, etc.

… just asking.

xrk971 26th January 2020 01:39 AM

Those long flying leads are for the power pass-BJTs on the SLB cap Mx. as long as they don’t oscillate, the cap Mx can do its 1mV ripple job and no sonic effects are passed though to the amp.

In the Alpha Nirvana and ABBB that do have power MOSFETs remotely located, we have the snubber and gate stoppers mounted as close to the pins as possible. We have not see any detrimental effects of doing this.

drpro 26th January 2020 01:46 AM

Quick question X, working on the ABBB just soldered the 47R and 220pf SMD parts on the mother board. Should I be placing them on the flying lead boards instead?

aljordan 26th January 2020 02:06 AM

Hi X,

I assume you are talking about R131 from this schematic. On one channel I measure .584 volts across R131 and on the other channel I measure .583 volts. R131 in my build is 0R33 ohms. I don't measure any voltage drop across the other big power resistors (R132). I couldn't find the right size so I paralleled two 0.33R resistors at R132 to get me close to the value on the schematic.

I am probably screwing something up here because wouldn't that put my current at 1.77 amps across R131? (I really don't know anything about this stuff). I am using the really big DIY Audio Store chassis, and my heat sinks are not very warm.

My power supply, loaded, is putting out about 25.3 volts.

drpro 26th January 2020 02:07 AM

I should have posted this on the ABBB forum as it's not applicable to the SLB.

xrk971 26th January 2020 02:51 AM

It’s 1.3A for 0.47R and 1.7A for 0.33R. You are fine.

Vunce 26th January 2020 04:10 AM


Congrats on a successful drama free power up!!
Iíve just a couple of tweaks you can try.
Turn the each SLB board 90į so they are perpendicular to the heat sinks. Doing so will position the SLB power output directly under the Alpha inputs for a very short distance your DC power wires need to travel. Also, that will enable you to better position the BJTís on either side of the Alpha board (left and right).
Run the Alpha Board speaker return to one of the SLB ground fastons, then from SLB ground faston to the binding post. Do this for both channels, that should eliminate the faint hum.

Hope this helps, Enjoy!!!

andyr 30th January 2020 05:17 AM


Originally Posted by xrk971 (

I seem to recall when reading through this thread - or the AN GB thread - that you (or Vunce) said a heatsink like you've got in the above pic ... is not in fact necessary. It's OK to mount Q10 & Q12 0n the PCB with a 'normal' finned heatsink bolted to each device?

Am I correct here? :confused:


Vunce 30th January 2020 05:26 AM

Q9 & Q11 will be fine with small finned extruded aluminum HS.

The BJTís (Q10 & Q12) definitely need to be mated to heatsinks capable of dissipating the heat they generate from the voltage drop across them.

All times are GMT. The time now is 10:25 PM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 17.65%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio