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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:  JamesSQ [ 16 May 2016, 20:29 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

Found this kit! http://www.ebay.com/itm/Hiraga-super-30 ... 4ade24ff07

Author:  djestro [ 08 Oct 2016, 11:20 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

Hi all,

More than one year later I have found some time to proceed with the build of this amplifier. Today I finished the first channel BUT:
The amplifier stays in class B, I'm not able to draw (any) bias current. I changed the 1.8K to about 1K in small steps but nothing changes at all.

I attached the schematic, board layout, and a scope image (Channel 1: OUTPUT STAGE, Channel 2:Base of the 2SC5200).

Attachment:
Schematic.jpg

Attachment:
Board.jpg

Attachment:
TEK0000.JPG


Attachment:
DSC_0116 (Large).JPG

Attachment:
DSC_0114 (Large).JPG


Thanks in advance!

Author:  Dan [ 08 Oct 2016, 18:43 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

Did you change both R18 and R19 at the same time ?

Author:  suztek [ 10 Oct 2016, 05:31 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

Have successfully build this amplifier and using it for almost 2 years now and still enjoying the sound quality.Refer to post Hiraga equivalent transistors.
Leave the two 1.8k R 18 and R19. To adjust the bias current, you must adjust the two 47 k resistors R 16 and R 17. Using a 35 v supply i got it right at 33 k for each resistor.The current will be around 1 to 1.3 amps.
Good luck
William

Author:  djestro [ 10 Oct 2016, 14:16 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

Dan, suztek,

Thanks for the fast response!
Yesterday I searched a bit further on the forum and indeed in the subsection of the equivalent transistors I read I had to change the 47k resistors. So I changed them to 33k. Now the bias current is +- 0,5A. Tomorrow, I wil buy a stereo 47k potmeter and look what value I need for a correct bias current. (I want to stick to carbon resistors so I will have to search for some parallel/series combinations).

I'm very curious how the bias is set with both 47k and 1.8k resistors. Are the 47k resistors bias setting for the voltage and transconductance stage ? Or am I completely wrong ?

Thanks for teaching me the basics ;)

Author:  suztek [ 11 Oct 2016, 05:00 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

These resistors R16,17 adjust the gain and quiescent current in the output stages.
Regards

Author:  Dan [ 11 Oct 2016, 06:19 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

Be prepared for some heat in your heat sinks !

Author:  Tony M [ 15 Oct 2016, 06:40 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

Hi All,

New member. Always wanted to build my own amps. Have done the JLH 15W ones now onto the Hiraga :D

I have purchased 30W Hiraga boards from EBay (Jim's Audio)
I'm using MJE15034G/15035G drivers (supplied with kit) along with 2SA1295/2SC3264 output transistors (As I have in my supplies)
Other components are as per the original Hiraga 30W design.
Powering from an 18 - 0 - 18 160 VA transformer the 'no load' (no amp attached) is around 24V from the PSU but this drops to around 22V (or slightly less) when one of the Amps is connected.
What I'm finding is that the current through the 0.33 ohm resistors increases to around 2.5 Amps :eek: during testing - at which stage I turned it off. (Have a large 'trial' heat sink which should be OK for the heat running one amp at a time on the 'test bed'))
According to the 'build notes' (PCB supplier) they say that the 1k5 collector resistors should be decreased (1k2 or 1k0) to reduce the output current. (I'm guessing that the 2SA/2SC's are to blame for the high current).
However I note that on this topic it's suggested that the 33k base resistors should be increased to 47k to reduce the output current?
Which is the better option? - or a combination of both?
I've tried running an LT Spice simulation using 2SC5200/2SA1943 (don't have the Spice Models for the 2SA1295/2SC3264) but this indicates an output current but this would suggest only 227ma output current 'as built' using 24V lines :confused:

I'm hoping that reducing the output power will also bring up the supply voltage - otherwise the 22V zeners are not much use ..

Thanks for any advice/comments :)

Author:  Dan [ 17 Oct 2016, 03:35 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

Change both the 33k to 47k first and see what the bias change looks like. Lt spice is not real world and does not factor in all the parameters of the actual components and layout you have.

Author:  sadik [ 19 Nov 2016, 11:06 ]
Post subject:  Re: Question of the amplifier circuit Jean Hiraga's Class-A

Hi Dan,

First of all i would like you to thank for your wonderful job and passing the same to DIY community.

My First Question is
In your article you have mentioned "Various measurements of the amplifier on an oscilloscope are shown in the photographs below. The amplifier is down -3dB at 208kHz and can deliver 58W at full power"
Is it 58 Watts of class A output for single Channel?

My Second question
Why there is need of such a huge Power Supply. If i am using 8200uf Caps x 10 Nos for Each Channel what will be the Problem?

Further i would like to inform you that I have had already made the PCB as per your schematic (using equivalent transistors, the transistors i am using are KSA992, KSC1845, KSA940 & KSC2073), The PCB is tested, I had to change the 47K resistors to 22K to set the Bias to 1.5 Amp, I am measuring around 480 to 500 mV across the 0.33 ohms resistors. I had tested the PCB for about 3 Hours today everything is fine, Even at output the DC offset is around 5 to 15 mV which keeps on changing. There is a slight humm noise in speakers which can be heared only when the ears are at distance of 5 to 6 inches from speakers. The testing was done with 250 va transformer, the output Voltage I measured was 31-0-31 Volts DC for single channel with Power Bank having 8200 uf x 10 Nos Capacitors. The Sound was very sweet and till date this was the Best amplifier i have ever heard. And i am very happy with the Sonic results.

I would also like to mention in detail about the Bias, When i started the Testing the voltage across the 0.33 ohm resistor was about 375 to 380mv after 10 Minutes it went upto 500 mv and was increasing, then i powered on the Ceiling Fan and the Bias again came down to 470 to 480 mV which was stable during my 3 Hour run. Second thing is i measure different voltage across both the resistors, the Voltage difference is about 15 mV. is it OK?

Below is the Photo of my PCB layout, In this layout i have made provisions to use the equivalent transistors with different pin layout also.
Image

Below Photo is of PCB testing. the Heat sink is Horizontally placed on Ground but i turned it to Vertical during testing.
Image

There are also few more question for which I may bother you later. Once again thank you for your wonderful job.

Regards,
Sadik Bhatkar
India

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