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Old 10th April 2001, 12:30 AM   #1
grataku is offline grataku  United States
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I am an heretic and I am going to hell because I want to built a class A amp that is not a Pass project!
Having admitted to that, does anyone know anything about the Hiraga 20W class A amp? The somewhat incomplete schematic is posted in several sites so someone must have seen it and have some comments about it. It could be an interesting little project that distances itself from the usual crowd and that, most of all, does not involve buying mosfets, which I don't have.

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Old 10th April 2001, 12:45 AM   #2
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Wink How could you Pass it up?

I've seen that amp. It looks simple. How's it sound??

[Edited by vdi_nenna on 04-09-2001 at 07:49 PM]
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Old 10th April 2001, 01:18 AM   #3
hifi is offline hifi  Sweden
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well... I once built the 8W hiraga "Monster" refering to the 2F and battery operated powersupply....it was quite marvelous... i havent compared it to any passaps so i wouldent now how they compare...

But anyway i think the first thing to do is try to find the output transisors or suitable equivalents...(Good luck!)

I have also tried to find the layout of the 20W i know of one who has it but the "#Q# wont send it to me....=//

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Old 10th April 2001, 01:20 AM   #4
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Given the heat produced, I think anywhere a class A amplifier is operating could be rezoned as an annex to hell.
In my case--to have both class A solid state and tube circuits running in the same household (in the southeastern United States, mind you, and with summer coming on) would surely qualify as more than a mere annex. Free ticket to an insane asylum, most likely.
Given that the Mark Levinson ML-2 may rise from the grave, we'll at least have company. (Note that the ML-2 schematic showed bipolars, too.)
I once ran my tube circuit at class A for a few weeks, but it dropped the power down to something like 30 or 40W. The sound was glorious, though. Sometimes I think about going back to that circuit.
If you follow through and build it, report on the sound, please. I've seen schematics here and there, myself, but never quite managed to catch fire on the circuit.

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Old 10th April 2001, 02:31 AM   #5
arnach is offline arnach  United States
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Default Other Designs

Pass is a great designer, and wonderful to the DIY community.

Dosen't mean that other designs aren't just as good or better in ways, and that they shouldn't be discussed and built. Also dosen't mean this his trounce other designs too.. the moral? Discuss and build it all!
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Old 10th April 2001, 03:53 AM   #6
Asen is offline Asen  Bulgaria
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Here is an address with some info:
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Old 10th April 2001, 01:56 PM   #7
grataku is offline grataku  United States
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that was the link I was looking for thank you very much! On the original schematic there were several mistakes and no output transistors. Nothing major really but somewhat bothersome.
What attracted me to this circuit is it's symmetry and the simplicity. And the fact that I got a bunch of large caps rated at 40V that I don't know what to do with!
I don't know if it will help but I am going to make the layout and post it here.
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Old 15th April 2001, 01:17 PM   #8
rmgvs is offline rmgvs  Netherlands
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I've build several Hiraga's 20 Watt amplifiers (and Le Monstres too). The 20 Watter is one of the best transistor amplifiers in the world, the sound is very smooth and airy, almost tube-like. On the net the schematics can be found. The original transistors used by Hiraga are no longer available. Try 2SD718/2SB688 as power transistors and 2SA968/2SC2238 as drivers. The remaining little transistors are easily available.

Then for a joke: try build the amplifier with 3055/2955 and BD139/140 and a simple power supply, you can even use a lower voltage supply (around 16Volts DC, cheaper capacitors with high capactitance possible): it still sounds better than most of the stuff in the shops.

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Old 18th April 2001, 05:35 PM   #9
grataku is offline grataku  United States
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I would like to design the board for this amp. Is anyone interested in sharing the setup costs of the Express PCB service? The way I see it: I design the PCB, send the interested party the layout so that cost can be personally verified by loading the free software on your computer and computing the board costs. I can accomodate requests for some specific type of connectors, or special components with different layout. Then, I can put the order thru on my credit card after I get the share of the payment.
I use express PCB before and the quality of the boards is absolutely incredible.
Also, if someone has a PCB to make, the layout can be added to my design and the board can be cut out after the board is made.
I make the PCB with the components at hand so there are no surprises at the end with components that don't fit. I don't mean to brag, but so far I have designed 100% error free boards.
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Old 18th April 2001, 06:37 PM   #10
rmgvs is offline rmgvs  Netherlands
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Remember there exist a proven lay-out (though I guess the boards themselves are no longer available). Better check whether this lay-out is still usable for today's components (I anticipate it is). The lay-out has been published in the French magazine L'Audiophile and in a French book that contained reprints of a number of articles.
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