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Old 29th November 2013, 01:30 AM   #1
EmmEff is offline EmmEff  Canada
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Default Where do I start? (re: need a DIY amp project)

I'm looking to start on a DIY desktop headphone amp project ASAP. It will be used to power my humble Grado SR60i (for now, upgrading in the future) with their 32 ohm impedance.

I have solid soldering experience, but not with SMT. I do not want to build an O2 or CMOY. I would prefer something decent quality (Class A), but have a budget of $300, preferably less. I like tube sound, but solid state is good too. I want to build something that will last, while I upgrade to better headphones, even if it's overkill for my Grados now.

I'd love something that was upgradeable (ie. either tube rolling or op-amps). I like to tinker, especially if I can hear the effects of different upgrades. I am willing to spend more than necessary for a good volume pot, for example. This stuff matters to me.

I need something with PCB(s) readily available now. I am not opposed to collecting pieces either from local electronics stores or over the web.

Any recommendations?
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Old 29th November 2013, 01:47 AM   #2
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As you like to tinker, I recommend you start by winding a couple of ferrite transformers. That's because in my experience, typical headphone amps lack in dynamics due to inadequate power supplies for driving low impedances. If you wind a trafo with a 5:1 turns ratio (say) that will make your 32ohm headphones look like 800ohms to an amp - the dynamics will be noticeably better on practically any amp, assuming it still has enough voltage swing.

Mouser stocks some suitable cores now : 6695272521 Fair-Rite | Mouser

Since the sonic benefits of classA (IME) relate to having much lower load-induced noise on the supply, such a trafo will have an AB amp sounding much closer to classA.
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Last edited by abraxalito; 29th November 2013 at 01:52 AM.
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Old 29th November 2013, 02:36 AM   #3
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I would suggest you look at a kit. Jaycar, who sells in Australia and the UK, and altronics sell a silicon chip design that looks quite decent.

If you are ramping up the learning curve, thus is a great place to start
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Old 29th November 2013, 03:44 AM   #4
jcx is offline jcx  United States
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I start with headphone sensitivity and Z: 98 dB/mW and 32 Ohm for Grados

then calc I,Vpk for 120 dB SPL: 160 mWrms, +/- 100 mApk, 3.2 Vpk


DIY Projects | HeadWize is a good resource - if you look gilmore's amps are built point-point on perfboard
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Old 29th November 2013, 04:40 AM   #5
agdr is offline agdr  United States
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Quote:
Originally Posted by EmmEff View Post
I do not want to build an O2 or CMOY
You shouldn't lump the O2 headamp and a CMOY together, either. Not the same. A CMOY typically has just one chip that provides voltage gain AND output current drive. A single op amp chip likely cannot push even half the 100mA peak jcx calculated:

Quote:
Originally Posted by jcx View Post
then calc I,Vpk for 120 dB SPL: 160 mWrms, +/- 100 mApk, 3.2 Vpk
The O2 uses a separate chip for gain and two paralleled high current chips for output that can source/sink up to 120mA or so of current and hit jcx's number. A single battery CMOY with virtual ground may not even be able to hit jcx's 3.2Vpk swing number either because you are dividing the 9V battery in half, minus chip overhead. The O2 uses two batteries giving around 7V peak swing. A CMOY with two batteries (they exist) still likely can't push even half of 100mA if using just one chip.

I say "likely" because the Grado RA1 headamp is essentially a single chip CMOY that uses one of the two output chips paralleled in the O2, so it can hit 60-70mA. Most CMOYs use chips that are only good for 20-30mA or so of output current.

Last edited by agdr; 29th November 2013 at 04:49 AM.
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Old 29th November 2013, 04:46 AM   #6
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FYI: a link to the kit in question:
Altronics - K5503 Studio Series Pre Amp Headphone Amplifier Kit

A fully discrete design that looks quite sound.
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Old 29th November 2013, 09:54 AM   #7
00940 is offline 00940  Belgium
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Quote:
Originally Posted by jcx View Post
DIY Projects | HeadWize is a good resource - if you look gilmore's amps are built point-point on perfboard
There is also a single layer pcb layout for the Gilmore that isn't too bad. You'll have to adapt it anyway since the input dual jfet are gone

The CKIII looks quite perfect to me for you. It isn't very fashionable but it's a well proven design in class A, the pcb is available, the project is well documented and it easily fits your budget. Add a dc protection board and you're good to go.
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Old 29th November 2013, 12:32 PM   #8
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The Millet Minimax is perfect for you. The kit is 230$ well under your budget Beezar.com, it's a hybrid so you can rolling some tubes and tweakable. It's highly bias in class A and sound very good with grados and other headphones and you dont' need to do the case work which is the hardest part of Diy headphone amp.
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Old 29th November 2013, 02:59 PM   #9
EmmEff is offline EmmEff  Canada
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Thank you everybody for the replies so far... I do not want to pollute this thread with a bunch of targeted replies, so I will just let you know I am considering my options presented.

I will need to do my research as I am not familiar with any of the kits/projects (Altronics, CKIII, and Millet Minimax) that have been suggested.

Sorry if I gave the impression I was more "advanced" at electronics than I actually am, but I'm not quite ready to wind my own transformers and at this point, I'm leaving the math out Side story, I started but did not finish electrical engineering in university; this might've been useful at this point
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Old 29th November 2013, 08:38 PM   #10
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I strongly recommend the sapphire amp kit from RJM. The kit is easy to assemble, sounds really great and will come in well below your budget. Richard is great to deal with too and helpful with support should you need it.

Thread here:

RJM Audio Sapphire Desktop Headphone Amplifier

Apart from being able to solder through hole components, the thing you need to be most careful with is to use twisted pair for the inputs and outputs.


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