My "ExtremA" is Built. Whew.

[lgreen]

Well I finally finished my ExtremA. (Link to Original Article on diyaudio.com.)

Parts.



Amp.



I believe with 1.3 ohm emitter resistors and plus/minus 19.6VDC, I'm getting about 79 WPC class A power.
Please correct me if I did the math wrong, I'm tired.

Here it is currently being tested it with a portable CD player into my differential buffer, then into ExtremA.
Power supplies are steady at 19.6 VDC, heat sink temperature settled down after an hour to 52 C on each.

I'm sitting in the garage listening to it, sounds ok with my little test speakers.
Will try on some real speakers soon. If someone comes over and helps me move it. It must be over 100 lbs.

It seems I always finish these things in the middle of the night, stay up late listening and post a few pics.

[lgreen]

Here are a few more pics.

Front without faceplate so you can see the front panel LEDs and the layout.



Side View.



Those Sanken's can make some heat.
You see a copper bar holding in a transistor. Why?
I snapped a tap inside the hole while threading it and could not get it out.
Sometimes you just have to build, not plan or make it perfect. Just build and get it done.

A lot of large parts like in a Pass amp.

2 transformers 16 VCT at 700 VA.
2 IXYS fast recovery bridge rectifiers- high power and high $ but I forget just how high.
Each channel has two 60,000 uF caps and four 22,000 uF caps.
Yet the current draw is so high I only get 19.6 VDC.
Adding caps will not increase the rails, you need to change transformers.
Got the huge case from somone here at diyaudio a few years back.

My soft start uses two CL-60 thermisters (10 ohms each if cold) in series with the primary for turn-on.
...Then after 4 seconds bypasses them using a 15A relay.

This is a fully balanced amp so it has XLR connectors.
A rear panel DPDT switch will ground the "negative" XLR input with RCA Ground so that
the amp can be used with unbalanced RCA sources. Simply flip switch and use RCA (but forgo benefits of balanced operation).
That is what the blue wires are for on the back panel.

The main filter caps have bleeding resistors across them as well as "snubberized" RC with film caps.
I forget the values I did this so long ago for another amp, an Aleph.
At the time people were saying to use brass screws to make connections on the
power caps because they conduct better. So I had some and used them then and still have them in there.

[Leeuwarden]

Cool amp!

[lgreen]

After about 2 hours the heatsinks are holding at 54C. Very hot! I consider 60C too hot but I am ok with anything less.

I was worried that the heat sinking was insufficient but it just might work out after all.
The fins have little micro-serrations in them. Makes it tough on your fingers.

With a Class A amplifier I like to watch the temperature to make sure things are not getting crazy.

LEDs-

There is a green power LED in the center of the front panel that is always on.
The lower part of each side has a single green LED which illuminates when the nearby heat sink reach a preset temp.
At 45C on left and at 57C on right. Took about 15 minutes for the 45C LED to come on.
A Red LED on each side above the green one illuminates if either heat sink hits 68C, meaning - turn off!
So far only the 45 C on the left side has come on. Good news but not a symmetrical display!

[Luke]

Congratulations, youve perservered for a while. How does it sound, can you compare it to any diy amps?

[TheShaman]

Congrats!
If I'm not mistaken this is the first ExtremA up and running (other than the one Sander had built for the original article).

[AKSA]

Warm congratulations, Lgreen, huge undertaking.

How's the sound quality? (we won't ask about the power bill!)

Hugh

[EchoWars]

Massive job!

Is the hum problem solved?

Originally Posted by lgreen

You see a copper bar holding in a transistor. Why?
I snapped a tap inside the hole while threading it and could not get it out.
Sometimes you just have to build, not plan or make it perfect. Just build and get it done.

A good machine shop could have gotten it out. Ask how I know.

[SSassen]

Lgreen,

Okay, we need to go over a bunch of things, some stuff really needs to be changed. For starters.

1) You do have isolation between the BD139/140 on the heatsink do you?
2) Twist all primary and secondary transformer leads.
3) Twist all leads coming from the bridge rectifiers/PSU PCB/buffer caps.
4) Don't use crimp connectors, unless you first crimp and then solder them.
5) Clean up the wiring, twist all wires that carry AC current, route them clear of DC/signal wires.

I'd need more detail pics to give some more pointers, but these are recommended.

Cheers,

Sander.

[lgreen]

Here is what I used for parts (mostly, some things are just for full information).
The ExtremA Parts List (Nov. 2009). This is the most recent list.

I see in the original article the BD139/140 transistors are on thermal pads, I was wondering why, perhaps the packaging is different? Mine are not isolated from the heatsink (well they are-- just not necessary to use pads I don't think). They have a plastic encapsulation on both sides and in the through hole. The exact part is in my parts list.

While I tried to braid (twist) all the wires, keeping AC separate and apart from DC, this will be rechecked and things altered after I play with the amp. I always have messy wiring, I am just not that good at making stuff with a clean layout. Its an art. But I cannot hear any hum from the amp (speakers), there is some low mechanical hum from the big power transformers. I don't pretend to be a pro so lets not kid ourselves- I am lucky it works at all.

The original design uses about 16 crimp terminals per channel/ 32 per amp, I had to use a lot of crimp connectors. But I tried to solder the wire to the connector as well as physically crimp where I could.

The amplifier has a lot of wiring because of the thermal activacted LEDs, soft start, dual mono power supplies and separate PS/ Amp boards. Heck I put the on/off switch on the back panel to reduce wiring and its still messy.

Then again, this is the only known fully self contained ExtremA that I could find, so I am happy that it works. I'm always happy when they work!