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PostPosted: 30 Jul 2015, 14:18 
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Joined: 18 Jul 2015, 14:27
Posts: 7
Location: Curepipe, Mauritius
Hi Gio, Thank you for replying my message.I finally found a way to eliminate the hiss by adding 2* 4700uf capacitor to the power supply, I used a 24v dc 4.5A laptop charger regulated at 22v using the lm317.
It is now free of hiss and hum.

One question, If I want to add more gain, what modification/addition must be done to the circuit ?
I saw in your previous post you talked about adding voltage gain before the mosfet follower, can you help me in what component to use , or do you have any schematic for that ?

Thank you in advance.

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PostPosted: 27 Nov 2015, 23:22 
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Joined: 16 May 2014, 04:23
Posts: 1
Location: Jogjakarta, Indonesia
Hi Gio, :smoking:

I am a newbie in this forum. I am from Indonesia, sorry if my English is bad.

Well I've built some dual opamp based headphone amplifier, based on chu moy design (cmoy). They work very well, but I need some more output current for driving low impedance/ hard to drive headphones/ iem. After some search, thank god I found your post here today :thumbsup:

I plan to combine my cmoy with your 'class A mosfet headphone amp' design as the output buffer.. I think it will be a nice combination as your design has 0,8 gain, and my cmoy gain is set at 5. Cant wait to build it.

so the signal setup will run more or less like this:
DAC ===> CMOY ===> Class A buffer ===> headphone

I hope it will work good :headphones:


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PostPosted: 05 Dec 2015, 16:10 
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Joined: 18 Jul 2015, 14:27
Posts: 7
Location: Curepipe, Mauritius
I did this using 2x dual opamps OPA2134 as a voltage gain stage (2 was used for more gain). Works great ! :D Enough to blow up my headphone :D

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PostPosted: 20 Dec 2015, 10:40 
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Joined: 28 May 2008, 21:53
Posts: 4565
Location: Winnipeg, CANADA
You don't need to use two op amps as you can get plenty of gain from just one. Try a gain of about 4 - 6 x.

Cheers

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[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


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PostPosted: 21 Dec 2015, 10:24 
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Joined: 04 Nov 2013, 21:18
Posts: 89
Location: Florida
Gio wrote:
You don't need to use two op amps as you can get plenty of gain from just one. Try a gain of about 4 - 6 x.

Gio, you know us... anything worth doing is worth overdoing!

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PostPosted: 08 Feb 2016, 12:15 
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Joined: 08 Feb 2016, 11:51
Posts: 3
Location: Iran
Hi . Gio . thank you for this project . excuse me i cant speak english very well .
i have some questions about this project .
we use high voltage ECC82 preamp for voltage amplification . it produce a gain about 20 db.
and output impedence about 10 kohms and its parallel with 1Mohms resistor with ground . we connect this preamp to your mosfet project .
but we remove first 100k resistor on your project. and lm317 resistor changed to 8 ohms . because our mosfets was very hot . and we use 50 ohms headphones or more . . .
power supply voltage is 24 volt .
the output Capacitors are two paralleled Solid Japanes Capacitors 470ohms 16v .
with these perfromance and changes is there any problem about sound quality or ????
thanks .


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PostPosted: 24 Feb 2016, 20:43 
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Location: Winnipeg, CANADA
16V is cutting it a little close with a 24V supply. Do you have a heat sink on the regulator? The output cap has a very large influence on the sound of this amp so you will want to try out a couple.

Cheers

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PostPosted: 17 Apr 2016, 11:43 
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Joined: 18 Mar 2016, 03:52
Posts: 1
Hello Gio, I've just finished the headphone amplifier project with the "transistor IRF 610", congratulations! It sounds in a magnificent way. It has a great sound both with the bass and with the high, very refined detail and soundstage. I buyed the box and the solid state components, with a voltage regulator "Im7812" while recovered the other components from old electronic stuff. The voltage is 12,76 volt regulated be the "IC LM7812" with a capacity of about "6600 mf" that never makes hums. The assorbed electricity is 0,46 ampere for both circuits, the two mosfets are hot but not as excessively as the "IC LM317". The exit cap has been calculated at 470 mf and not at 680 mf like the project. The used headphone is a Sennheiser HD518 of "50 ohm". I've also inserted a double channel and for the listening the stereo signal is took from the record out of the stereo amplifier control.

See you soon, Giovanni


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PostPosted: 29 May 2016, 17:22 
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Joined: 08 Feb 2016, 11:51
Posts: 3
Location: Iran
Gio wrote:
16V is cutting it a little close with a 24V supply. Do you have a heat sink on the regulator? The output cap has a very large influence on the sound of this amp so you will want to try out a couple.

Cheers

we use two capacitor 470uF (Series) .
Yes . we Use heat sink .
i have some questions again .
1.What is difference between LM317 and Constant Resistor (in other Class a Circuits)?
2.What is the input impedance of Your Mosfet Circuit?
3.Can we use separate Power Supply for Each channel ? is it necessary ?
thanks.
Image


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PostPosted: 30 May 2016, 18:05 
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Joined: 08 Feb 2016, 11:51
Posts: 3
Location: Iran
Ashkan_Heretic wrote:
Gio wrote:
16V is cutting it a little close with a 24V supply. Do you have a heat sink on the regulator? The output cap has a very large influence on the sound of this amp so you will want to try out a couple.

Cheers

we use two capacitor 470uF . its Parallel . And capacitance is about 940 uF .


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