There will be two options: you can run the standard +/-24v rails and 25w amp, or go with the higher 39w option which will require use of IXYS TO-264 package capable of 600w and mounted with CPU cooler with heatpipe and PWM fan like how we did it with the Alpha BB amp. 75w or even 100w is no problem with the CPU cooler and fan.
There is also Fairchild FDA38N30 N channel (TO-3P) rated for 312w and less expensive than the IXIS. With FQA36P15 rated for 294w P-channel. I have used these on Hugh's Omega 35w amp with solid Al CPU coolers (no heatpipes) and fans and works well too.
Lots of ideas on how to cool things in this thread:
Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier
I meant just to remind you to include proper notes to prevent expensive mistakes by newbee builders of your design.
Great advise, but I think the message will be lost here.
The flavour of the day is CPU coolers, PWM controllers, silent fans, etc., etc.
Which is all good and a valid approach, but misses the point that most people want a simple, reliable way of dealing with heat dissipation in audio amplifiers, especially Class A.
Most people do not want to get that deep into electronics, this is an audio forum after all.
And what drives all this is Music, Glorious Music.
So, my humble advise to all new builders of Class A amps, being that First Watt clones, AKSA, BA, and so on is this (the Brute Force approach):
-calculate the heat in Watts that needs to be dissipated for your chosen project
-double that number
-now go and find, buy, steal or manufacture if you can the biggest aluminium heatsink possible (no copper please) that will satisfy that number.
-it's even better if the H/S you found, stole or manufactured is slightly bigger, or way bigger
-now go ahead and build your project and sleep soundly knowing that your amp will survive all the abuse you'll inflict on it.
Now, I hear people say:
but big heatsinks are very expensive.
No, they are not.
They are a safe investment and very good insurance.
They are simple and reliable, like a sledgehammer.
Always doing their job, no complaints, no hiccups, no nasty surprises.
So, these are my 2 cents on the subject.
Happy building.
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why dont you integrate the bias network of the output mosfets with the current preamplifier formed from the mosfet and bjt in the original aksa lender schematic?
So that you can direct couple and keep the 600ohm capable driving stage
taking inspiration from this amp:
https://www.diyaudio.com/forums/att...18519237-gyrator-loaded-son-zv9-f3-gf3amp-jpg
So that you can direct couple and keep the 600ohm capable driving stage
taking inspiration from this amp:
https://www.diyaudio.com/forums/att...18519237-gyrator-loaded-son-zv9-f3-gf3amp-jpg
The amp will be one PCB but offer several ways of building following different schematics. Sure, leave off the bootstrap cap and preserve the original profile.
You can also keep it at +/-24v and still have the original 25w amp, but that will still take a higher rail on the front end to avoid clipping of the bottom side of the Aksa Lender front.
If you want to keep it as a Aksa Lender driving a 600ohm load, then use the M2X PCB and get the Melbourne daughterboard. Keep the Edcor or bypass it, either way it will work but at reduced power without Edcor and 24v rails for input stage. The Edcor transformer has nice ability to go above the rails given sufficient front end power to push a 600ohm load. I am not sure that a 2sK170 and 2SJ74 front end can drive 600ohms?
That's exactly what is inside the original First Watt M2 amplifier, and M2 owners don't appear to be complaining very much.
I suppose if you're dying to find out you could ask Nelson Pass. He's the one who designed that circuit and he's the one who wrote post #27 in which he actually measured the input impedance of the (Edcor transformer + M2 MOSFET output stage) while driving it from his 2SK170/2SJ74 circuit. link to post #27
Here is a helpful post, complete with photographs, which begins with an encouragingly relevant remark: If you're going to engineer an input stage daughter card, you'll need a test fixture. (link) . Once you've got a test fixture you can drop in an Ishikawa board (2SK170 + 2SJ74), set the load to 600 ohms, and do some measurements of your own. This way you can find out the answers yourself without bothering Nelson Pass.
M2X Melbourne TH Daughterboards v2
Update: JPS64 finally had time to rework the error I had on the Melbourne daughterboard for the M2X. Here is what it will look like. Some stuff has been moved around for more optimum placement of parts. The heatsinks will now have more room to breathe and stay cool.
Update: JPS64 finally had time to rework the error I had on the Melbourne daughterboard for the M2X. Here is what it will look like. Some stuff has been moved around for more optimum placement of parts. The heatsinks will now have more room to breathe and stay cool.
Attachments
GB Thread for the Melbourne is here:
https://www.diyaudio.com/forums/group-buys/333653-melbourne-daughterboard-m2x.html#post5690033
https://www.diyaudio.com/forums/group-buys/333653-melbourne-daughterboard-m2x.html#post5690033
Measurements are here:
The Melbourne Class A Headphone Amp and Pre-amp
It sounds great as a premp on other amps and great as a headphone amp. I have not had a chance to really try it on the M2X except briefly because the pinouts were incorrect. However, I did manage to try it on the M2 (Teabag layout) by connecting an external Aksa Lender and bypassing the Edcor - and that sounded excellent. More here:
AKSA Lender Pass Hybrid M2 (ALPH-M2) Amp
Here is 2Vpp into a 240ohm load:
Here is 4Vpp into a 2k2 ohm load:
You can even drive a 50ohm load at 1Vpp:
An Edcor is 600ohms so much easier to drive and gives 6x gain - so 4Vpp into the Edcor would be about 9w into 8ohms.
The Melbourne Class A Headphone Amp and Pre-amp
It sounds great as a premp on other amps and great as a headphone amp. I have not had a chance to really try it on the M2X except briefly because the pinouts were incorrect. However, I did manage to try it on the M2 (Teabag layout) by connecting an external Aksa Lender and bypassing the Edcor - and that sounded excellent. More here:
AKSA Lender Pass Hybrid M2 (ALPH-M2) Amp
Here is 2Vpp into a 240ohm load:
Here is 4Vpp into a 2k2 ohm load:
You can even drive a 50ohm load at 1Vpp:
An Edcor is 600ohms so much easier to drive and gives 6x gain - so 4Vpp into the Edcor would be about 9w into 8ohms.
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The Melbourne has now been officially tested with the M2X and it sounds great!
Melbourne Daughterboard for M2X
The M2X also benefits from an SLB PSU. Super quiet 100uV rms output noise now.
Melbourne Daughterboard for M2X
The M2X also benefits from an SLB PSU. Super quiet 100uV rms output noise now.
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