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PostPosted: 08 Jul 2012, 21:46 
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Joined: 10 Jul 2011, 04:45
Posts: 68
Location: Banda Aceh, Indonesia
Gio wrote:
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.


Thanks Gio. So how about your test ?? What do you think about BD139 ???

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PostPosted: 24 Feb 2013, 23:09 
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Joined: 24 Feb 2013, 09:02
Posts: 6
Location: Taoyuan, Taiwan
I've made one, using IRF630 and the resistor between A and O in LM317 is 4.7 ohms, the capacitor in output is 220uF (originally 680uF).
The gain is obviously less than one though it's detected only by my ears.
When I plug the 32 ohms headphone the left channel become very hot and sounds weaker.
But it's ok using 56 ohms headphone.
What's the problem with that? Is any component wrong? How to modify it to increase the gain?


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PostPosted: 25 Feb 2013, 08:49 
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Joined: 14 Feb 2010, 13:13
Posts: 663
Location: Lisbon, Portugal
Hi moses1202!

Be sure to use some cheap headphones for testing, prior to you reference ones!

As for your issue, be sure the FET is properly biased. Check the current.

Also check the C3 470uF capacitor that will isolate any DC current to you headphones.


Cheers!


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PostPosted: 26 Feb 2013, 12:08 
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Joined: 24 Feb 2013, 09:02
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Location: Taoyuan, Taiwan
Thanks HT Performance.

I've found the problem which cause DC current directly go through the left channel of headphone due to a wrong connection.
The left of the 32ohms headphone was already burned, but the HD-668B still be good fortunately!

Another problem is that when I adjust the 100k resistor to let source leg voltage become half of supply voltage, the IRF630 got very hot and soon become unstable probably cause by over heat.
How big the heat sink should be? Should I change the resistor between A and O in LM317 from 4.7 ohms to 5.1 ohms?


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PostPosted: 28 Feb 2013, 20:55 
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Joined: 28 May 2008, 21:53
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Location: Winnipeg, CANADA
First off, check to make sure the metal tab of the mosfet and also the regulator are both isolated from ground (ie. no continuity between tab and ground).

I have only tested this amplifier with IRF510, IRF610, IRF611 and IRF612. so I can't comment outside of those mosfets. However, here are Rogers' comments from the NP-100v12: 12AU7 (ECC82) / IRF510 Headphone Amp project page.
Quote:
Q1 - The MOSFET (Q1) can be replaced by an IRF610, IRF611 or IRF612, all of which will work as well. Stay away from IRF530 or IRF540 types (commonly found in power supplies) as there will be terrible roll-off of the highs.

Otherwise, it could be the IRF630 (IRF530). Any chance you can try a IRF510, IRF610, IRF611 or IRF612 mosfet as they are known to work in this follower circuit.

Cheers

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PostPosted: 09 Mar 2013, 11:48 
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Joined: 09 Mar 2013, 10:53
Posts: 2
Hello,
I'm an *almost* beginner at diy audio projects, i've already successfully built a 15db preamp and the fuzz factory guitar pedal with success, so i've got the hang of it after a few years of tinkering with electronics.

I'm using the IRF620 as a beginning, i couldn't find the 610 in the local store. i've checked the connections like a hundred times but it just doesn't seem to work... i get no output at all, like it's dead or something...

i've used heatsinks from the very beginning so i doubt i've destroyed my 620 or the LM. these are some of the parts i use:

LM resistor: 4.7 Ohm
Output caps: 1000μF 35V electrolytic, 0.68μF 250V film cap (these were spare from salvaging)

Measurements:
Input voltage: 17.7V
Drain pin voltage: 17.7V
Source pin voltage: 0.0 - 8.4V
Gain pin voltage: 0.0 - 13.2V

No matter where i set the 100Kpot, nothing happens at all in the sound, but the higher i set it the warmer the mosfet gets.
Any ideas what could be wrong with it? I've tried using 8 16 and 32 Ohm headphone speakers but nothing... :(


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PostPosted: 14 Mar 2013, 03:15 
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Joined: 09 Mar 2013, 10:53
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It's alright, finally made it work :) i really couldn't find the bug so i let it aside and rebuilt it 4 days later, and now it works, really sounds great :)
so, add the IRF620 to the list :D


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PostPosted: 13 Jul 2013, 15:51 
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Joined: 09 Jul 2013, 21:11
Posts: 3
Location: Argentina
Hi, I tested the circuit in my protoboard and it works! I used the IRF510, but the only thing that I have found is that the circuito does not amplify the signal, instead it seems to attenuated the signal of my mp3, because I listen with less volume that directly on the mp3. Sorry for my english I'm from Argentina


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PostPosted: 16 Jul 2013, 22:50 
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Joined: 28 May 2008, 21:53
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Location: Winnipeg, CANADA
Hi, yes, gain is 0.8. This is a current amplifier for more demanding headphones.
Cheers

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PostPosted: 12 Aug 2013, 05:39 
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Joined: 15 Aug 2011, 08:01
Posts: 9
Hello!
I have built this amp before (as evidenced from my previous posts) the amp worked perfectly until I decided to increase the current draw of the lm317. Opting for a 1.5ohm resistor in place of the original value of 5ohms. On top of that I changed the bias pot to a conventional 'panel mount' linear pot aswell as dropping my B+ to 12V from a SLA battery.

Previously the amp would run hot all the time irregardless of the presence of input signal. However with the change, the amp would heat up accordingly to the input signal level, staying at room temperature while the input signal is absent. Another thing to note would be that half the B+ for biasing is impossible. As when the pot is fully open I get half the B+ (6V) but the output is null. Thus I halved the 6 volts into 3volts with the pot and I would get sweet music however with the above mentioned problem of the amp seeming to run at temperatures depending on the input signal.
Thank you in advance


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