class A amp project for Mark

[Ian Mackenzie]

I am not sure if this is the right forums (not Lansing diy) but here is a link to a project I am helping build with Mark (pasadena)

http://www.diyaudio.com/forums/showt...0&pagenumber=1

Most of the technical stuff will no doubt be boring for you guys so I will post a few pics as well

The amp is rated at 100 watts rms nominal into 8 ohms per mono block.

This design is a diy version of the AX Passlabs amp series and uses the Pass Labs Super Symmetry and Aleph current source patents. This is a diy exercise so there is no infringment of the patent.

It is intended that this amp will ultimately be used to drive a set of XPL200's in biamp mode.

To start with there are some concept images.

[Ian Mackenzie]

I decided on a square box for weight reduction and structural integrity. The square design also avoids the large rectangular box typical of this type of amp.

It measures about 260mm cubed or there abouts. The heatsinks are 100mm x 150 mm x 44 mm and are rated at 0.61 c / watt each. In use the amp will idle at about 45c in at an ambient temperature of 25c and draw about 250 watts off the mains

The transformer was specially made and is rated at over 625Va and has two 21 volt secondaries rate at 11.9 amps

This is over 264,000 uf (12 x 22,000 50 volt Panasonic) of filter capacitors used in a CRCRC smoothed DC supply.

There will be 16 IRF240 power fets per channel, in use each fet is biased to about 0.7 of an amp for a total of about 5.6 amps of bias.

I must say what seemed like a neat idea has turned out rather complex and a long job in the making. Numerous tools and jig and been either purchased or made for this type of fabrication.

The material is aluminium sheet (4mm angle), 3mm & 4mm plate and bar stock size of 12 x 20mm and lots and lots of drilled and tapped M4 and M3 holes.

[Ian Mackenzie]

Here is the control pcb and associated mounting hardware.

Also some images of the pcb etching process, the powersupply simulation... and construction in progress.

Questions from interested posters welcome.

Ian

[Uncle Paul]

Ian,
This is fascinating stuff for me. As always, you planning and execution is first class.

I'm planning a bi or tri amped 4344 inspired DIY using the MOX crossover and Aleph amps. Not sure if the LF amp will be Aleph, or if I want to use a different class there.

I'd go 4345, but have to unfortunately compromize due to size. Cabinet drawings are finished, parts are sourced, and construction has begun.

Electronics are phase 2 of the project. I have enough amps and crossovers to keep them playing while I complete the DIY electronics.

I've been pouring though the threads (including yours) in the Pass Labs forum at DIYaudio trying to make sense out of all the various versions and variants to determine which is/are the best for my application. It seems that the Aleph X, though 5 years old, is still pretty tough to beat. I'd appreciate any input you have on this.

I plan on integrating the crossovers into the amp pcbs to reduce the number of cross connects and related woes.

I learn something new everytime I read one of your posts, here or there.

Thanks,
Paul

[Ian Mackenzie]

Hi Paul,

Enjoy your loudspeaker project.

The Mox sounds like a good plan if you are going the Aleph route.

It always brings out the most natural sound.

I will be incorporating a Mox in a Pass diy preamp as a followup to this project.

The std Aleph is a nice choice and is easier to build.

They have a more romantic presentation and work well with JBL's.

The X Aleph brings excitement and revelation from the energy and spatial detail in the presentation

Because of size and heat issues consider one of the better class A/B amps for the woofer.

If you are going diy have a look at the SKA GB 300 for the woofers or one the Anthony Holton aussiamps. Some of the class D amps are also interesting.

Ian

[Guido]

The std Aleph is a nice choice and is easier to build.
They have a more romantic presentation and work well with JBL's.
Ian

Yes, Yes and Yes!!!

[Ian Mackenzie]

I find it ironic there are no Yanks to speak of (except one) around here that use them.

The seem to prefer road re surfacing machines for amps by comparison...the yanks do love their roads I guess!
http://www.freepatentsonline.com/5080524.html


http://www.freefoto.com/preview/21-8...d+%2F+USA+road

[Hoerninger]

Ian,

please go on and choose your own road, I would be pleased to follow.
Class As are real fine (and pretty warm ).
___________
Peter

[JBLRaiser]

It was a joke and a hint but speaks volumes for the demographics and VALS of this forum versus the enormous following over on diyaudio.com forums. I few soldering tips and your own your way.....

From a practical point of view (see 30 watt Aleph thead that won't break the bank so) anyone here can enjoy Hi end amplification versus the junk we so often see on Ebay. Franky I would never own an aged mains appliance, its just too dangerous.

I use a Dynaco ST400 for the low end, coupled with a Dynaco ST35 for the horns to my model 19's. Almost 40 year old gear. Any thoughts or comparisons with what you are doing. I'm considering something more technologically advanced.

[Ian Mackenzie]

JBL Raiser,

I have never used the ST35 model so I can't comment.

But if the comments in these links are anything to go by the Model 19's horn compression drivers maybe the limiting factor. Might be worth looking at the newer versions on Great Plains Audio (Iconic)

At any rate the Aleph 60 or Aleph 4/2 would be a nice upgrade from the ST400. The bass response from these amps is quite amazing. You might even get away with running them full range and get a better result than attempting to bi amp (unless you are using an simple RC passive filter)

See Guido's Aleph 2 project.

Thanks for your post

http://www.tnt-audio.com/ampli/dynaco-st35_e.html

http://home.indy.net/~gregdunn/dynac...T35/index.html

[Ian Mackenzie]

Today I did some more construction of the power supply smoothing filter banks.

This is quite a fiddly aspect of the project and I am pioneering as I go so its slow but steady progress.

Things have to be made to fit a certain way and there are numerous considerations. Temperature was only 5 degrees this morning before the heating at Area 51 kicked in. The aluminium almost to cold to touch.

Here we have the first two stages of the CRCRC filter nearly complete.

The 22,0000 uf 50 volt Panasonic capacitors are soldered and hot melt glued to a large pcb that will be supported by nylon stand offs on 20mm x 6mm bar stock with M3 hardware drilled and tapped throughout.

This construction forms a support frame that bolts to the heatinks on each side and provides further structural rigidity.

On the outside of the filter bank are the mini fin heatsinks that are attached by L section to the bar stock.

They draw heat from the power resisters. About 5 watts per heatsink. The power resisters will be thermally bonded and bolted in place with M3 hardware & tapped holes in the heatsinks.

The third stage of the CRCRC network will be located adjacent the main circuit pcb as shown and will be arranged using similar construction as above. This will be complete next week

A close up of the main pcb.

Deceptively simple but very elegant in execution.

Some of you may think this is overkill but as a result of the class A operation the power supply must sustain the voltage and current continously and be very reliable over the long term.

This power supply also has very low noise from the mains and ripple from rectification to ensure the best performance from class A operation.

I anticipate initial testing in about 2 - 3weeks

[Uncle Paul]

Thanks, Ian. Looking forward to your update!

[Ian Mackenzie]

Some more progress yesterday.

Here the intended view of the PS and main pcb.

I intend to test and match the power fets tomorrow and have it ready for testing within a fortnight.

Ian

[pasadena]

Hey Ian,

Wow......That looks undoubtedly fantastic work. The innards look complex and meticulous.

I can see when you mean this beast is going to end up weighing a ton.

Shipping's going to be a challenge I must say.

Waiting for that blue light to flick into action.

Cheers
Mark.

[Ian Mackenzie]

http://www.diyaudio.com/forums/showt...45#post1244445