Edit Jan 23, 2020: Connection diagram for single trafo and dual rail SLB with M2X amp
The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB
Edit June 16, 2019: Error on Q5 orientation on Single Rail (SR) board. Please install Q5, BD139 with pin 1 to the square pad (as customary) but this will have front of part in contact with HS1. Ok to use smaller stamped aluminum finned heatsink here for back mounting. More info here:
The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB
Edit June 12, 2019: in an effort to reduce my logistical overhead and efforts to pack and ship as track - I will be handling the GB2 via my Etsy shop. The SLB can be found here:
Smooth Like Buttah SLB Class A PSU | Etsy
I have been working on the development of a new power supply for Class A amps that really is quite a big leap forward from current designs used for so long. It utilizes an active bridge rectifier provided by the LT4320 and MOSFETs, followed by a precisely engineered CRC filter designed to match the load, and finally followed by a capacitance multiplier. The advantages that such a power supply will have include:
1. Almost no heat dissipation or loss through the rectifier
2. Improved voltage headroom since no 0.6v drop across the silicon rectifiers
3. Smoother inherent ripple from the rectifier since switching is active and time phased to occur at zero crossing
4. More compact since fewer and smaller bulk caps are needed
5. Lower overall cost since fewer large bulk caps are used (and we all know this is one of the most expensive parts of a Class A amp aside from the case)
6. Most importantly, improved performance relative to a traditional CRC supply with lower ripple and higher current capability.
7. The SLB provides a smooth and slower (1 second) ramp that may reduce speaker turn on thump. However, current in rush from the transformer being turned on is not prevented and a suitable soft start circuit such as the Soft as a Feather Pillow (SFP) SSR soft start can be used for a soft start.
You may say that the downside is that it’s more complicated - but for those of you going through the trouble of using 8 x MUR TO220 diodes with their requisite heatsink, insulator pad, bolt, screw, insulated bushing, snubber film cap, and tight spacing that makes assembly difficult - I am not so sure anymore.
Here is a photo of a single rail SLB portion of the amp (we integrated it as part of the amp for testing). You can see how small it is when using SMT variant of the active MOSFETs (mounted underside). Those are 15,000uF 50v bulk capacitors. Compare that to how usual Class A CRC or CRCRC supplies are using 22,000uF or 33,000uF caps. The large 3pin Molex connector allows us to place the cap Mx pass transistor anywhere we like and allows snappy assembly/disassembly from the chassis or heatsink:
Jhofland, Aksa, Vunce and myself have been working on a single rail prototype of this PSU which we are calling the SLB. The name says it all - Smooth Like Butter. Jhofland has been leading the layout and electrical design, Vunce and myself are doing the verification builds and testing of the performance and listening to the resulting music, and Aksa has been instrumental in providing insight and guidance, plus overal cap Mx topology design. It’s been a great collaboration and I feel that we have arrived at something really special and useful.
The design requirement was that it can flow 5 or more amps and have ripple in the single mV range (we are looking for about -60dB to -70dB ripple rejection) with a simple hookup of a secondaries from a power trafo. You then get clean mV ripple (sine like and not sawtooth) with a small adjustable output voltage range based on how much drop you want across the cap multiplier.
Regarding capacitance multipliers, we are testing 3 different topologies: Darlington, LTP differential (similar to the MrEvil design), and a new complementary feedback (CFP) pair with BJT’s. Work is on going but we are getting close to a downselect.
Here is the measured ripple (1.4mV rms) from the Darlington cap Mx with 4.35A load (37.5vdc output) with an 8ohm resistive load:
Under a real SE Class A amplifier load, the ripple is a bit higher at about 6mV rms with the Darlington topology, but still very respectable given a 4.35A current:
Our simulations show that the CFP topology should be even better. The LTP differential topology will be tested soon (tonight perhaps).
I thought it is now a good time to share the initial developments to get everyone ready for the SLB PSU. I hope that this compact little supply will be a useful new tool in your toolbox of Class A amps. It certainly provides some of the cleanest power Inhabe ever measured or heard.
Edit - here is layout:
Update May 5, 2019: Verification build test with 4.4A and 35.4v out and 3.1v drop gives about 1mVrms ripple with the SLB (with R17/18 replaced by jumper):
Here is the SLB vero build (v1):
Update May 6, 2019: Schematic and BOM of v2 (May 3, 2019) Production version of SLB here.. Pricing of SLB is $22.50ea (2mm thick FRP, 2oz Cu, ENIG finish, blue mask):
Edit May 6, 2019: Here is the SLB-SR (single rail version). BOM and Schematics here. Pricing on SLB-SR is $18ea (also 2mm thick FRP, 2oz Cu, ENIG finish, blue mask):
Edit May 9, 2019: Here is the pereformance of the SLB in single rail form as used on an actual SE Class A amp with 37.4v rail and 4A current. The top red trace is for a 10R value on R117 and bottom yellow one is 1.5R for R117:
Edit May 23. 2019: Production PCBs arrived.
Dual Rail
Single Rail
Edit June 5, 2019: Md_Stryker made a Mouser shopping vart/BOM for SLB v1.2 here. Please do not modify it - copy to your own project first!
The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB
Edit Jan 23, 2020:
Connection Digram for a No-Hum M2X PSU with SLB and single trafo:
Connection Diagram for no-hum Alpha Nirvana:
The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB
Edit June 16, 2019: Error on Q5 orientation on Single Rail (SR) board. Please install Q5, BD139 with pin 1 to the square pad (as customary) but this will have front of part in contact with HS1. Ok to use smaller stamped aluminum finned heatsink here for back mounting. More info here:
The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB
Edit June 12, 2019: in an effort to reduce my logistical overhead and efforts to pack and ship as track - I will be handling the GB2 via my Etsy shop. The SLB can be found here:
Smooth Like Buttah SLB Class A PSU | Etsy
I have been working on the development of a new power supply for Class A amps that really is quite a big leap forward from current designs used for so long. It utilizes an active bridge rectifier provided by the LT4320 and MOSFETs, followed by a precisely engineered CRC filter designed to match the load, and finally followed by a capacitance multiplier. The advantages that such a power supply will have include:
1. Almost no heat dissipation or loss through the rectifier
2. Improved voltage headroom since no 0.6v drop across the silicon rectifiers
3. Smoother inherent ripple from the rectifier since switching is active and time phased to occur at zero crossing
4. More compact since fewer and smaller bulk caps are needed
5. Lower overall cost since fewer large bulk caps are used (and we all know this is one of the most expensive parts of a Class A amp aside from the case)
6. Most importantly, improved performance relative to a traditional CRC supply with lower ripple and higher current capability.
7. The SLB provides a smooth and slower (1 second) ramp that may reduce speaker turn on thump. However, current in rush from the transformer being turned on is not prevented and a suitable soft start circuit such as the Soft as a Feather Pillow (SFP) SSR soft start can be used for a soft start.
You may say that the downside is that it’s more complicated - but for those of you going through the trouble of using 8 x MUR TO220 diodes with their requisite heatsink, insulator pad, bolt, screw, insulated bushing, snubber film cap, and tight spacing that makes assembly difficult - I am not so sure anymore.
Here is a photo of a single rail SLB portion of the amp (we integrated it as part of the amp for testing). You can see how small it is when using SMT variant of the active MOSFETs (mounted underside). Those are 15,000uF 50v bulk capacitors. Compare that to how usual Class A CRC or CRCRC supplies are using 22,000uF or 33,000uF caps. The large 3pin Molex connector allows us to place the cap Mx pass transistor anywhere we like and allows snappy assembly/disassembly from the chassis or heatsink:
Jhofland, Aksa, Vunce and myself have been working on a single rail prototype of this PSU which we are calling the SLB. The name says it all - Smooth Like Butter. Jhofland has been leading the layout and electrical design, Vunce and myself are doing the verification builds and testing of the performance and listening to the resulting music, and Aksa has been instrumental in providing insight and guidance, plus overal cap Mx topology design. It’s been a great collaboration and I feel that we have arrived at something really special and useful.
The design requirement was that it can flow 5 or more amps and have ripple in the single mV range (we are looking for about -60dB to -70dB ripple rejection) with a simple hookup of a secondaries from a power trafo. You then get clean mV ripple (sine like and not sawtooth) with a small adjustable output voltage range based on how much drop you want across the cap multiplier.
Regarding capacitance multipliers, we are testing 3 different topologies: Darlington, LTP differential (similar to the MrEvil design), and a new complementary feedback (CFP) pair with BJT’s. Work is on going but we are getting close to a downselect.
Here is the measured ripple (1.4mV rms) from the Darlington cap Mx with 4.35A load (37.5vdc output) with an 8ohm resistive load:
Under a real SE Class A amplifier load, the ripple is a bit higher at about 6mV rms with the Darlington topology, but still very respectable given a 4.35A current:
Our simulations show that the CFP topology should be even better. The LTP differential topology will be tested soon (tonight perhaps).
I thought it is now a good time to share the initial developments to get everyone ready for the SLB PSU. I hope that this compact little supply will be a useful new tool in your toolbox of Class A amps. It certainly provides some of the cleanest power Inhabe ever measured or heard.
Edit - here is layout:
Update May 5, 2019: Verification build test with 4.4A and 35.4v out and 3.1v drop gives about 1mVrms ripple with the SLB (with R17/18 replaced by jumper):
Here is the SLB vero build (v1):
Update May 6, 2019: Schematic and BOM of v2 (May 3, 2019) Production version of SLB here.. Pricing of SLB is $22.50ea (2mm thick FRP, 2oz Cu, ENIG finish, blue mask):
Edit May 6, 2019: Here is the SLB-SR (single rail version). BOM and Schematics here. Pricing on SLB-SR is $18ea (also 2mm thick FRP, 2oz Cu, ENIG finish, blue mask):
Edit May 9, 2019: Here is the pereformance of the SLB in single rail form as used on an actual SE Class A amp with 37.4v rail and 4A current. The top red trace is for a 10R value on R117 and bottom yellow one is 1.5R for R117:
Edit May 23. 2019: Production PCBs arrived.
Dual Rail
Single Rail
Edit June 5, 2019: Md_Stryker made a Mouser shopping vart/BOM for SLB v1.2 here. Please do not modify it - copy to your own project first!
The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB
Edit Jan 23, 2020:
Connection Digram for a No-Hum M2X PSU with SLB and single trafo:

Connection Diagram for no-hum Alpha Nirvana:
Attachments
Last edited: