Mini Aleph Power Supply

[Jack Tupp]

Hello to all. I am a long time lurker and I finally decided to take the plunge into making a class A speaker amp, the Mini Aleph in particular.

I am a noob. I have trouble building from a schematic and I have no background in electronics other than the experience gained from building projects. I have built numerous AMB kits such as Mini3's, M3's Gamma2's and Sigma11 power supplies. The hallmark of Ti's projects are his excellent documentation and personal support.

I would like to go through the Mini Aleph build, sort through the various questions and lay down a solid, updated BOM and document the process so that subsequent builders like myself can get into the world of class A amplifiers.

I've already been in touch with jleaman and he has been very gracious. His enthusiasm is contagious. He was nice enough to dig through his archives and dig up a BOM for the power supply. I would like to edit the BOM to include only the parts for the Mini Aleph in order to keep the scope limited to this type of build. Also some of the parts seem to be deprecated or unavailable, so updated part numbers are needed.

I have no idea what CRC is. Basically, I need someone to tell me what part numbers to stick in where to make a power supply to run a Mini Aleph. Once the details and BOM are hashed out and updated and posted here then pretty much anyone who wants to build one has a good shot at making a Mini Aleph power supply.

Of course, the Mini Aleph BOM is next. One thing at a time.

[Beftus]

There's no single BOM that is the "right one". You can use a lot of different rectifier diodes for instance. Most of them will work... Some prefer slow rectifier diodes, others prefer ultrafast rectifier diodes. Which one do you choose and why? Also bear in mind that some parts are difficult to find in other parts of the world. Many of us will have to make a few changes to the BOM.

The PSU BOM is a good starting point though. But feel free to make some changes as you see fit. For those not very knowledgeable, read the mini-Aleph threads first then ask your question.

A CRC PSU is used to attenuate mains hum.

Oh, and congrats on your choice, the mini Aleph is great amp!

[Jack Tupp]

Originally Posted by Beftus

There's no single BOM that is the "right one". You can use a lot of different rectifier diodes for instance. Most of them will work... Some prefer slow rectifier diodes, others prefer ultrafast rectifier diodes. Which one do you choose and why? Also bear in mind that some parts are difficult to find in other parts of the world. Many of us will have to make a few changes to the BOM. The PSU BOM is a good starting point though. But feel free to make some changes as you see fit. For those not very knowledgeable, read the mini-Aleph threads first then ask your question.

We could list part numbers for instance, from Mouser, Digikey, and Farnell. I suppose options and footnotes are inevitable but as long as they are organized on the BOM/build instructions instead of scattered over 1000 pages of forum threads it will facilitate successful builds with a minimum of hassles for everybody and end repetitive noob questions.

Good documentation will only be a good thing. I can't see any downside to it.


The part number for the heatsinks has changed to HS351-ND at Digikey.

The diodes MUR2020CT-ND are not available at Digikey. I did read someone using MUR860's Digikey part number MUR860GOS-ND

Are those diodes a good all around choice?

[Beftus]

Originally Posted by Jack Tupp

Good documentation will only be a good thing. I can't see any downside to it.

Jack I'm with you on this thing. I totally agree. However it might not be easy to reach an agreement with regard to parts to be used. We all have our preferences.

Originally Posted by Jack Tupp

The part number for the heatsinks has changed to HS351-ND at Digikey.

Better use taller heatsinks than these 1" tall ones... I used 1.5" tall ones and now wish I would have used 2". Class A amps run hot. Pick your parts with that in mind.

Originally Posted by Jack Tupp

I did read someone using MUR860's

MUR860's would work, MUR820's too. I used HFA08TB60's, could have used RHRP1560's too. I'm prettty sure someone can suggest another twenty TO220 diodes that would work too.

[Jack Tupp]

Originally Posted by Beftus

Jack I'm with you on this thing. I totally agree. However it might not be easy to reach an agreement with regard to parts to be used. We all have our preferences.

I understand. Getting engineer types to agree on minutia is difficult. My intention however, is not perfection, rather, a BOM somebody can use with currently available parts they can use with confidence so that if they order these parts and stick the power supply together that it will work. The original threads and the BOM appear to be from circa 2005...5 years ago.

Originally Posted by Beftus

Better use taller heatsinks than these 1" tall ones... I used 1.5" tall ones and now wish I would have used 2". Class A amps run hot. Pick your parts with that in mind.

Excellent tip. Digikey part number HS132-ND

Originally Posted by Beftus

MUR860's would work, MUR820's too. I used HFA08TB60's, could have used RHRP1560's too. I'm prettty sure someone can suggest another twenty TO220 diodes that would work too.

Here's an excellent example. The parts you used are not available at Digikey or Mouser. The second one you mentioned has 3 leads...confusing to me as a noob because there's only 2 holes. The 860 and 820's are both available (and only have 2 leads )

MUR860's Mouser part number : 863-MUR860G
MUR860's Digikey part number : MUR860GOS-ND


jleaman suggested this transformer:

15Vx2 300VA Toroidal Transformer DIY HiFi Power Amp Kit - eBay (item 370271247500 end time Apr-04-10 20:20:05 PDT)

Antek AN-3215

I guess I should make it clear I intend to build a standard Mini Aleph using the IRFP240's mounted to a plate heatsink.

[Jack Tupp]

Ok. A few detail questions on the PCB D0, R0 and C0 are the same as D5, C9 and R5 on the original BOM correct?

As far as the "bleeder resistors" R1 and R2...those are required correct? What about all the other resistor spots on the board?

[Beftus]

Originally Posted by Jack Tupp

Ok. A few detail questions on the PCB D0, R0 and C0 are the same as D5, C9 and R5 on the original BOM correct?

I take it you're referring to the PSU PCB that's available @ chipamp.com? If so then yes.

Originally Posted by Jack Tupp

As far as the "bleeder resistors" R1 and R2...those are required correct?

Bleeder resistors are a safety measure, they drain off the charge after switching off. The PSU will work without these installed, just bear in mind that when you're gonna do some maintenance the capacitors still hold a charge.

Originally Posted by Jack Tupp

What about all the other resistor spots on the board?

The other resistors form a first order RC filter with the final PSU cap. Example: With a 1 ohm resistor and a 10000uF cap in C3 you get a cut-off frequency of 15.92 Hz using this formula: 1 / (2*Pi*R*C)

The five resistors you can place are in parallel, choose a combined value for R, then calculate which values you have to place in parallel to get your value for R. You will want to use four or five 3Watt resistors in parallel so they share the load. Mount these resistors at least 0.25" off the board, they will get hot.

[jtktam]

Originally Posted by Beftus

The other resistors form a first order RC filter with the final PSU cap. Example: With a 1 ohm resistor and a 10000uF cap in C3 you get a cut-off frequency of 15.92 Hz using this formula: 1 / (2*Pi*R*C)

The five resistors you can place are in parallel, choose a combined value for R, then calculate which values you have to place in parallel to get your value for R. You will want to use four or five 3Watt resistors in parallel so they share the load. Mount these resistors at least 0.25" off the board, they will get hot.

I am using R = 0.47,, 5 in parallel and 15000 aps

1 / (2 * pi * 0.094 * 15 000) = 0.000112875846

is that right?!?!

-joe

[Jack Tupp]

Originally Posted by Beftus

then calculate which values you have to place in parallel to get your value for R.

Thanks Beftus, you're helping me a lot. I don't understand what "my" R value is or should be. What is a good all around set up here with these resistors that's going to produce acceptable power supply results?

So I am assuming that if we fill the resistor slots then this line from the original BOM is not necessary:

2, none, short circuit jumper, R3,R4, for the standard CRC configuration, no R is needed


As far as the LED I used this calculator

Calculate Resistors for LEDs


to get @500 ohms PPC499XCT-ND (Digikey) for a 604-WP7104GD (Mouser)

Do those values look like it will make an indicator light and not a flashlight?

[Beftus]

Originally Posted by jtktam

I am using R = 0.47,, 5 in parallel and 15000 aps

1 / (2 * pi * 0.094 * 15 000) = 0.000112875846

is that right?!?!

-joe

No. Capacitance is in Farads, so 15000uF = 0.015F

Equation becomes: 1 / (2*Pi* 0.094 * 0.015) = 112.88 Hz