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Class A Headphone Amplifier with IRF610 and LM317 CCS
http://diyaudioprojects.com/Forum/viewtopic.php?f=10&t=55
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Author:  Gio [ 01 May 2012, 23:51 ]
Post subject:  Re: Class A Headphone Amplifier with IRF610 and LM317 CCS

Hi Quartz, welcome to the forum.

This project is a mosfet follower which will be able to supply high current, but the voltage gain will be less than one. In theory the circuit should be able to drive an 8 ohm load but I don't know how well it will sound.

I found that the amp sounded better with a higher supply voltage, but I did not try more than 20VDC and that was with 32 ohm headphones. For an 8 ohm load, higher voltage and increased current should help.

I would go with 34vdc, but I suggest you also use a LM317 to regulate the power supply. Those tweeters are very sensitive and the last thing you want to hear is hum.

Cheers

Author:  quartz19208 [ 02 May 2012, 10:10 ]
Post subject:  Re: Class A Headphone Amplifier with IRF610 and LM317 CCS

Thank you very much Gio. I have built it going with the 34vdc with only 20000uf of filtering. Tried running one channel with one of the klipsch (both tweeter and woofer) and my phone as source. Really lovely sound ( no hum detected :) but really soft due to low gain ) surprisingly good bass. made my tda 2050 chip amp sound weak when its volume was attenuated to the same level. guess I need a bigger transformer as the 1 amp transformer got really warm. I noticed what seems to be resistors accross the input of the amp in picture 5 of the project page may I know what are they for? Will this amp oscillate as I fear for my tweeters ( sorry I am paranoid ) and would there be a simple preamp circuit you would reccommend me to go with this amp? Sorry for asking so many questions :)
Thank You and Cheers!

Author:  Gio [ 02 May 2012, 12:45 ]
Post subject:  Re: Class A Headphone Amplifier with IRF610 and LM317 CCS

First off, I'd reccomend you get an old driver to test out the amp before you use it on the tweeter. You don't want to blow that horn as it may be difficult and costly to do so. Car drivers work well for testing and you should be able to find them at 2nd hand stores.

For sizing the transformer, how much current are you pushing? 400 mA per side should be ok with that transformer.

Glad to hear it sounds good. You will need to put a preamp infront of the amp to get more volume out of the speakers.

Cheers

Author:  quartz19208 [ 03 May 2012, 03:32 ]
Post subject:  Re: Class A Headphone Amplifier with IRF610 and LM317 CCS

hello Gio thanks again! I should indeed follow your advice about using car speakers for testing.
I will be pushing about 0.6amps per channel. so I guess that warrants a larger transformer.
however can you please tell me the use of the resistor at the inputs in picture 5?
Cheers!

Author:  Gio [ 03 May 2012, 17:57 ]
Post subject:  Re: Class A Headphone Amplifier with IRF610 and LM317 CCS

In Photograph 3, the resistors you see at the RCA input is 100k to ground. On the schematic this is the first resistor after the input.

Cheers

Author:  quartz19208 [ 04 May 2012, 09:16 ]
Post subject:  Re: Class A Headphone Amplifier with IRF610 and LM317 CCS

Ahh I see. Will there be any benefit as to placing the resistor there rather than the board other than the convienience of it? thanks!
Cheers!

Author:  Gio [ 05 May 2012, 09:45 ]
Post subject:  Re: Class A Headphone Amplifier with IRF610 and LM317 CCS

I don't think so. Adjust this R to best load your source.
Cheers

Author:  quartz19208 [ 08 May 2012, 07:46 ]
Post subject:  Re: Class A Headphone Amplifier with IRF610 and LM317 CCS

Ahh I see. thank you !
Cheers!

Author:  redsky [ 28 Jun 2012, 13:15 ]
Post subject:  Re: Class A Headphone Amplifier with IRF610 and LM317 CCS

Hi Gio, Warm Regards from me. I'm a Novice.

I have a question, can I simple change IR610 transistor with BD139 ? I plan to build a preamp to drive my mini ZCA.

Thanks Before

Author:  Gio [ 07 Jul 2012, 11:32 ]
Post subject:  Re: Class A Headphone Amplifier with IRF610 and LM317 CCS

Hi Arie, sorry for the late reply, been very busy on my end. I have tried IRF510, IRF610 and IRF612 and all 3 work well in this circuit. I have not specifically tried the BD139 but from looking at the datasheet it looks like it would work. I would start by trying it out with about 50mA and see how that works.

Cheers

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