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Hiraga 20W class A
Hiraga 20W class A
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Old 27th April 2001, 01:21 PM   #21
argo is offline argo  Estonia
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I am puzzled. Then where there is the 20W version? Or are we talking about the same schematic but with different rail voltage and bias current?

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Old 27th April 2001, 02:56 PM   #22
grataku is offline grataku  United States
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I don't know where you got this idea of the 30W, as far as I know there is NO 30W version of "le Classe A". Hiraga made the simplified 8w Monstre and the 20W versions. If you have some links to substantiate your claim please let us know.
Of the 20W "le Classe A" I have seen the classic schematic on Bonavolta's site and this newer, slightly modified one, that some very helpful and informed guy provided earlier:
Maybe we can all try and persuade Geoff to run some simulations and tell us what are the major differences.
I am in the process of collecting the components at the moment I will probably stick to the original version unless someone tells me that the mods make everything sound better.
On to the next point, transistors:
All but the power trans (see HIRAGA.gif in the link above) are still in production and therefore someone should have them, and they do: MCM electronics (i-mcm.com).
As far as the power trans I am going to overkill it and use some 2sa1216-2sc2922 for no other reason other than the fact that I have them.
Power supply, I need some feedback on this one, please:
I got this surplus transformer, its huge, its dirt cheap but its 2 X (2 X 21.5 V) secondary (yes, ther are two center tapped secondaries), which brings the rectified and filtered voltage up to 2 X 30V DC, so six or seven volts need to go, or do they?
I am thinking I could:
1) stabilize the voltage (independently for each channel of course).
2) use a Pi filter using power resistors.
3) use the 2 X 30V and modify the circuit (increase the collector resistors and the voltage drop resistors to the pilots) the power trans should be able to handle that.

I could make a dual mono version but I have only this two huge 76000 uF 40V caps and I am on the cheap so for the moment I will parallel the secondaries.

What do you think?

[Edited by grataku on 04-27-2001 at 09:58 AM]
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Old 27th April 2001, 05:51 PM   #23
rmgvs is offline rmgvs  Netherlands
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Certainly there are 2 versions available of the Hiraga. Commercially they are marketed under the names of 'Hiraga classe A' (20 W) and 'Le Classe-A' (30 W).

Both contain exactly the same circuit. Differences are:

1. Supply voltage of plus en minus 24 Volts for the 30 Watter.

2. Current becomes 1,5 Amperes.

3. Dissipation now is at the limit of the possible (assuming the original power transistors are used, the TO-3 ones).

4. Total capacitor-value for the 30 Watter is over one Farad (in stead of 408.000 mF for the 20 Watter).

5. Some resistors have a slightly different value (to take care of new voltage and current settings).

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Old 27th April 2001, 06:35 PM   #24
tvi is offline tvi  Australia
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I have an old photo copy from original article in L'Audiophile, its mainly about the "AMPLIFICATEUR 20W HIRAGA" this is the schematic on the stigerik link.

On the last page I have the exact picture used on the bonavolt site, the page is headed "NOUVEAU SCHEMA SUPER 30 W

under the schema on my copy

"Les paires de drivers des amplificateurs 20W et Super 30W ne sont plus disponibles, ces transistors, mis sur le marché japonais depuis plus de dix ans, ont été remplacés par une nouvelle paire encore plus performante, aussi bein aux mesures qu'à l'écoute.

Bein que de caractéristiques proches, il a été nécessaire de modifier légèrement (uniquement dans le cas du Super 30W) Les valeurs de certains résistances, de façon à réduire encore le taux de distortion ainsi que le courant de repos, Pour des raisons de copyright avec L'étranger, nous avons été obligés de suppimer les éférences de ces transistors, Le transistors de couleur noire correspond au 2SC1096, celui de couleur verte au 2SA634; la brocharge rest identique."

I always thought
1.5A x 24V = 36W
1A x 21V = 21W
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Old 27th April 2001, 07:47 PM   #25
babarceles is offline babarceles
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Well in fact I saw the same shematic with 2 kind of transistors : the one that exists when Jean Hiraga draw his 20W amplifier (many years ago)TP2788... and the other one with C1775
D188 a627 c1096 a872 transistors.
Thant for the reply.
But what are the diferents between toroidal transformer and the other kind.
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Old 27th April 2001, 07:49 PM   #26
babarceles is offline babarceles
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I meant what are the differents between the sound of a power supplied Class A amp inclueding a toroidal transformer and another transformer.
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Old 27th April 2001, 07:51 PM   #27
babarceles is offline babarceles
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My project is to biamplifing (??? I'm not so good in english) 2ways DIY speakers (SEAS) in a home theater set.
And I'M also looking for active crossover schematics...if you can help me...
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Old 27th April 2001, 09:46 PM   #28
grataku is offline grataku  United States
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Thanks for clearing that up, sort of. I am going to say nothing more until I see the actual article.
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Old 27th April 2001, 10:03 PM   #29
Geoff is offline Geoff  United Kingdom
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I ran a few quick simulations on the Hiraga some time ago. Unfortunately, I didn't make any notes at the time but, from memory, the original circuit seemed OK but I was less happy with the later, modified circuit. I can't for the life of me remember why now. When I've made more progress with my JLH site I'll repeat the exercise and let you know my findings (give me a reminder in a week or so if you haven't heard from me).


There is a good, phase coherent, active crossover project at the ESP Audio Pages:


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Old 28th April 2001, 01:32 PM   #30
grataku is offline grataku  United States
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Is Hiraga really using two different values for the resistance coming off the emitter of the first input pair or that's just a mistake on the circuit? If it's a mistake can you suggest which value I should pick? 180 ohm, 240ohm, or an average of the two?
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