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Old 27th January 2010, 12:44 AM   #1
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Default DIY headphone amp for beginner on a budget

Hi All,

I did not see a similar thread anywhere, so I figured it would be OK to start this. Sorrt for any redundancy.

I have a pair of Grado SR-325s, which are very nice. But I don't really have anything to drive them with. I was using my computer / ipod, but as soon as I turned up the volume even slightly, the bass became distorted. I have a Sansui AU-719 integrated with headphone outs, but its location is very inconvenient for me to use as a headphone amp.

I primarily listen to rock and jazz. Occasionally, I put on NPR's classical radio station.

What can I build that would put some life into the Grados? I would like to spend about $50. It must have easily obtainable parts, which are luckily the cheap ones in most situations. It also can't be incredibly difficult to build because I am a total noob. At the same time, I thought this would be an easier project than a DIY amplifier or crossover network.

Thanks, Jim
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Old 28th January 2010, 08:30 AM   #2
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Location: Aarhus, Denmark
Hi

I was wondering if any of the projects in this part of the forum could have your interest? In that case others also may work on the same project and you will have back-up in case something does not turn out the way it is supposed ..

Just a thought.

Greetings,

Jesper
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Old 28th January 2010, 09:40 AM   #3
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Under $50, you're not going to get much further than a decent CMOY variation.

I suggest the tutorial on Tangents website (How to Build the CMoy Pocket Amplifier) or, if you'd like something easily portable, the AMB labs Mini3 (The Minił Portable Stereo Headphone Amplifier). Read the documentation for both and you'll have a good start.

A good CMOY with a decent pot and a high quality opamp will get close to $50 by the time you've put it in a case.
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Old 28th January 2010, 11:02 AM   #4
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Hi,

I also have a pair of 325's. I have been pretty happy with my PIMETA amp, with AD825 opamps. The CMOY is probably not quite as good as the PIMETA for grados, as the PIMETA has a buffer circuit, and is therefore better at supplying current to the relatively current-hungry Grados.

For $50, you'll have to go with something like the CMOY. You'll probably want to do it 'Grado RA-1 style', meaning you'd use a JR4556 opamp, which is pretty good at delivering current.

You might be able to get away with using a simple no-gain buffer circuit, e.g. something that isn't an 'amp', only a current driver. The JISBOS buffer ought to be pretty good: JISBOS - overview
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Old 28th January 2010, 11:18 AM   #5
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I too use and recommend the pimeta, but you'd need to roughly double your budget to build it. Mine cost me nearly $100, and it's still not cased up.
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Old 28th January 2010, 11:57 AM   #6
tvrgeek is offline tvrgeek  United States
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Bought a Grado-clone/ripoff off the auction. 2 batteries and a box keeps you under your budget. Remember ,the Grado's are very low impedance. Their amp ( and the rip-off) have a very high current op-amp. A plain MCoy is really taxing a standard op-amp. The above solutions with higher current drivers would be a better match. National publishes an op-amp/driver tech note. If you can do it from batteries, (rechargeable, low Z of course) that keeps the cost way down. A really nice power supply is not cheap. I run my rip-off from 2 9volters at the risk of if one dies first, there is a possibility of DC offset. Not good. Better to use the artificial ground circuit.
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Old 28th January 2010, 12:04 PM   #7
ra7 is offline ra7  United States
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This will get you under $50. It will provide plenty of drive as well.
You can use two 9V batteries for power.

DIY IRF610 MOSFET Class-A Headphone Amplifier Project
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Old 28th January 2010, 04:32 PM   #8
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Not sure of your ability, but if your willing to stretch a bit, don't think you can beat this for the price.

ecp.cc

Tubes though, high voltages of course, B+, etc...so may be too difficult, but that will drive your grados with aplomb. I know Doug and some others might be doing some kind of board for it to be even easier.
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Old 29th January 2010, 05:27 PM   #9
jcx is offline jcx  United States
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you're going to blow through $50 quickly in batteries if you try to combine battery power and SE Class A output

cheap power is most readily had from sealed "wall wart" or brick modules - you should be able to find them for free - my last dead ink jet printer had a 12Vdc 800mA brick that could just be snapped out of the printer for easy recycling

depending on the amp circuit as little as 200mA rating could work, with SE Class A + active gnd requiring 800mA (assuming you'd like > 100 mWrms capability into the Grados)

another cost saving measure would be to go for fixed gain without a volume pot on the amp - just use the digital attenuation in the sources you have now - certaily will track better than a cheap audio taper pot
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Old 29th January 2010, 06:13 PM   #10
paulb is offline paulb  Canada
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Don't spend any money on the enclosure, or very little. Recycle something like an old SCSI hard drive box, serial port or printer selector box, something like that.
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