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Question of the amplifier circuit Jean Hiraga's Class-A
http://diyaudioprojects.com/Forum/viewtopic.php?f=10&t=1044
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Author:  Dan [ 20 Nov 2016, 17:46 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

Well Done Sadik,

Your measurements all seem to be within the normal range.

I would suggest the hum can be reduced using the Pi filter similar to the original design with appropriate voltage caps.

The power you achieve will depend on how much your transformer can handle with both channels running with 1.5A bias (if that is your chosen amount)

Regarding the fluctuation in bias, this will improve once you have the unit in a metal case covering the pcb components.

I hope this helps,

Feel free to ask if you want any more help.

-Dan

Author:  sadik [ 01 Dec 2016, 13:02 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

Hi Dan,

Once again i am bothering you. Can i use Capacitance Multiplier as a Power Supply for this Amplifier. I have made a CM as per this link http://sound.whsites.net/project15.htm

If we cannot use CM then can you please specify the reason for same in detail, like what will be the sound quality at high volume, will there will be some lack of frequencies specially in Bass. and there may be some other points too...

Regards,
Sadik Bhatkar

Author:  Yungman [ 26 Dec 2016, 04:03 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

Hi
I am looking at a few pages on this thread, one thing I am puzzled. I saw the OP using +/-35V rail and the schematic on page 10 use +/-35V also. My understanding is this design is class A. Most of the ones I've seen run on +/-18 or +/-20V. It's a lot of power if you run +/-35V. Can you do Class A with one pair of 2SC5200/2SA1943 with this high rail voltage even if you really pump so much current?

Assuming you swing +/-32V into 8ohm, that is 4A peak and you have to bias the idle current at 2A. That is burning 140W at idle if you use +/-35V rail for class A.

Author:  Yungman [ 02 Jan 2017, 02:49 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

I did simulation with LTSpice, as expected, distortion is very high even with 8ohm load, It's over 0.1%. I know this is a very popular amp and is highly praised. I want to know how the sound of this amp stack up with high quality amps like Threshold, Bryston etal. What make this amp stand out?

Author:  djestro [ 16 Feb 2017, 16:04 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

Hi,

I finaly had some time too change the bias resistors. I'm now at 27K and running at 1,3A. The heatsink go around +/-90°C. Should I go for bigger heatsinks or will the output transistors survive it ?

Thanks! And keep building :)

Author:  KochiyaYamato [ 23 Feb 2017, 02:10 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

djestro wrote:
Hi,

I finaly had some time too change the bias resistors. I'm now at 27K and running at 1,3A. The heatsink go around +/-90°C. Should I go for bigger heatsinks or will the output transistors survive it ?

Thanks! And keep building :)

Do some calculations, thermal resistance junction to transitor case. and monitor your transistor case temp with a accurate thermistor.
You should operate below the maximum rating 40C or more.
Example your cooling temp is 90C, transtistor case temp is 100C
Your dumping 31Watts of heat. and your datasheet has a rating of 1C/W
This means that the junction temperature is 31X1+100C= 131C. If your transitor max junction temp is rated for 150C this is risky. But with a rating of 200C this should be safe.

Author:  michel2711 [ 23 Feb 2017, 06:59 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

Hi,
I am starting to build a 2x20W version of the Jean Hiraga amplifier and I have some difficulties finding a good quality toroidal transformer. I have been searching a 2x20V / 300VA. Plitron has one, but doesn't sell less than $200. I have found some in the UK, but they want $150 for shipping!!, Part Express has some , but not this output voltage. Can you give me a few pointers in the US?

Thanks!
Michel

Author:  KochiyaYamato [ 23 Feb 2017, 16:56 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

You may consider using two pices of switch mode 24 or 36Volt power supply, they may be cheaper.

Maybe look for some second hand ones to and you may be able to get power supplies from broken amps

Author:  michel2711 [ 24 Feb 2017, 08:52 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

Quote:
You may consider using two pices of switch mode 24 or 36Volt power supply, they may be cheaper.


I thought that switched power supplies were not an appropriate choice for class A amplifiers, or maybe I misunderstood what you meant.

Author:  KochiyaYamato [ 25 Feb 2017, 17:25 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

You can use Switched power supplies for any amplifier.
Allot of audiophiles just don't like the idea of switched psu so they stick with the classic. Its like amplifieir heat sinks, with a small cooling fan the cooling perfomance improves allot but audiophilies don't like them and want to keep it classic.
They have a smaller form factor and can output higher powers and should be cheaper than transformors.

They have better ripple regulation too which means less capacitors are needed for same regulation perfomance. Due to they operate at higher frequncies.

Less components and capacitors and less size should mean they are cheaper in general.

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