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Old 2nd October 2009, 08:57 PM   #1
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Default HIRAGA 'le class a'

le class a- 4 ohms driving capability?

hi all,
reference: the class a amplifier site; jean hiraga's super class a;
i was running the 30 watts amp. with microcap7 simulation, this configuration can't drive more then 6 ohms, did some one succeed to increase the driving to lower loads like 4 ohms?
any help is very much appreciated
best regards
Williams
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Old 2nd October 2009, 09:33 PM   #2
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Williams,
what is the problem according to microcap7?
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Old 2nd October 2009, 10:07 PM   #3
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Try increasing the bias current
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Old 3rd October 2009, 06:17 AM   #4
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hi all,
1- i did increase the bias and it didn't help
2- i don't have the original transistors in my library so i had to use western replacements; the problem is that is very sensitive when driving high current because of high Vin (in order to get 30 watts output at 8 ohms), then the distortion of the VAS the 2SA634 and 2SC1096 is very high, the result is a summing a sine wave at the output that is very none linear.
3- the circuit is so simple that every thing is influencing every thing, but if you will follow the shapes of the wave forms at each base/collector, can see the problem
4- even that the output looks clean of distortions it is feed with distorted input (at high levels)
When the Vin is 1.4Vp the amp should deliver 30 watts at this point; all ready the VAS is totally distorted, I will like this amp to be able to drive 4 ohms as well, do you think it is possible, but 8 ohms looks as a big task.
5- it should be an amp that can drive 4 ohms and is very disappointed that is not
Best regards,
Williams
PS: if you like to take a look I can mail you the schematics
Williams
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Old 3rd October 2009, 01:30 PM   #5
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Hi Williams,
it is very important to use output devices with high DC current transfer ratio in order to keep the VAS distortion low, (will inevitably be pretty high, I`m afraid).
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Old 3rd October 2009, 08:16 PM   #6
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hi lumba,
thanks for the answers, what do you think about this amp particularly?
is it worth to build it. Did someone you know built it? It is very simple and challenging
see the schematic from the site, I will like to get your opinion
best regards,
Williams
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Old 3rd October 2009, 08:46 PM   #7
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Yes it is worth it. But given the choice I would build an F5. It is basically a Jean Hiraga amp with two gain stages.
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Old 3rd October 2009, 09:35 PM   #8
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hi,
what is F5 never seen one, where can find it
Williams
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Old 3rd October 2009, 09:47 PM   #9
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F5 power amplifier

http://www.firstwatt.com/downloads/F5-om_sm-080527.pdf

Last edited by Melon Head; 3rd October 2009 at 09:50 PM.
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Old 4th October 2009, 01:08 AM   #10
tinitus is offline tinitus  Europe
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Wonder if this is original or modified

I built it many years ago and it was quite good and stable
No problem with big low ohm fullrange ribbons

Sold around here as a kit
I still have the manual and detailed spec sheets on transistors
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