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Old 8th May 2007, 01:05 AM   #1
pk386 is offline pk386  United States
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Default I want your head phone amp Ideas

I think this is the best place for this thread...

Ok here's the goals for this project...

1) cheap (getting out of Debt and got a baby on the way. :-) )
2) will mainly be used for pc Listening at to in a cube farm.

I have two CenterTapped transformers that are small enough to make for a good head phone amp with. but they have +/- 35v and +/-45v windings.

I have built a chumoy and a sudo gainclone amplifier. I thought about using two of the LM3875 I had left over but, that seemed like a waste of an 8$ chip.

I was thinking about something that had IRF 610's (or around that) [CLass A or Class A/B doeen't matter to me] in the output stage.

bass boost and cross fade are the only two bells and whistles I'm thinking of incorporating in to the input stage....

I have an enclosure already and I don't ming buying a few parts (and I'm good at 'salvaging' parts)


so what do you guys think? what should I build?
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Old 8th May 2007, 04:27 AM   #2
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Years ago I built what I thought was a remarkably good sounding headphone amp using a couple IRF fets. It was class A, with a current sink consisting of a fet and a pot. An op-amp drove the other fet. You couldn't ask for cheaper. What's sneaky is the amplifier operates with an offset of the fets gate voltage, so the output doesn't cross zero until you get to a reasonably high level, where it shouldn't matter. With the bias cranked up high enough, it even did well on speakers. BW was over 100kHz and THD was under .002% most of the time. If it sounds interesting, I can find the schematic and scan it.
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Old 8th May 2007, 04:34 AM   #3
jaycee is offline jaycee  United Kingdom
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a simple class B follower is probably best. It is cheap, sounds good, and low parts count.

Rod Elliot's P113 is a good example of this. There's a few variations but they're generally the same.
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Old 8th May 2007, 04:45 AM   #4
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Ok, even if you don't want it, here it is. Try not to laugh. Or cry. This thing was built more than 20 years ago. It breaks every rule of sophisticated symmetrical amplifier design, but when you hear it, you won't care. Just use a really big heat sink so the bias stays stable. It says "stable into any load", but that probably doesn't include short circuits.
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Old 8th May 2007, 09:32 AM   #5
jaycee is offline jaycee  United Kingdom
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I've seen the same thing done with BJT outputs

The only thing I'd say here, is 20v rails with an NE5532 could be asking for trouble. Stick to 15v, regulated.
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Old 8th May 2007, 10:34 AM   #6
Nordic is offline Nordic  South Africa
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Conrad, like this?

Baby Zen Nursery - help needed
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Old 8th May 2007, 01:15 PM   #7
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Wow, and I thought mine was simple! More and more I'm thinking electrolytics are evil. I'm even coming around to some reasons not to use them as the actual output element of power supplies, though I can't say if those reasons are audible. Using the op-amp lets one use a very small input capacitor, increasing the number of types that can be selected. Even small value Teflon if desired. We seem to have some built in desire for symmetry, but I'm not sure it has any relevance to good audio, and may even be detrimental.

[I haven't looked at the 5534 data sheet in a while, but I think it has 22V rails- 20V is pushing it, but is still legal and works. Watch out for spikes. There's also nothing wrong with gluing a small tab heatsink on the top of op-amps to keep them cooler and thus reduce noise.]
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Old 8th May 2007, 02:21 PM   #8
Nordic is offline Nordic  South Africa
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Conrad, I always believed the same... about the elctrolytics...

But on advice from trusted sources, I just went with the circuit as is... and it sounds awesome... it is symply not optional in that circuit, or you will be makeing heater elements from your earphones with the DC output... I would say yuo could sayfely go to 17 to 18V on most chips I tried so far...

P.S. I built enough diffirent chip based headphone amps by now, to tell me this one is in another league... no comparison...
The only one I had hat came even close was ironicaly a hybrid with the same IRFs and an ecc88/6dj8 type tube... which also had huge signal path electrolytics... how counter intuitive...lol.

Rods P109 was one of the better sounding chip headphone amps I tired... and it was pretty good..., but heavy on batteries..
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Old 8th May 2007, 02:41 PM   #9
BillH is offline BillH  United States
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Hi, all.

pk386, have a look at the Szekeres VE Headphone Buffer. I'm using a variation of it with LM317 constant current sources instead of the power resistors. It does meet the 'cheap' requirement, but it doesn't offer any gain. I've qot OPA2134 opamps and a Meier/Linkwitz crossfeed circuit before the VE to get some gain and crossfeed. Let me know if you'd like to see the schematics.
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Old 8th May 2007, 05:59 PM   #10
pk386 is offline pk386  United States
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these are some great Ideas...

This is what I wanted. I think I'm going to have to dust off my analog brain (and note books) and see what I can come up with... (I'm a PCB desiger for an industrial PC company (CPCI and ATCA))

I just wanted something to jump start my brain a little.... after another night or two I should have an Idea what I want to build...

Tonight I want to dust off my oscope and do some measurements on my PS and do some more work to the enclosure.

(humm, maybe I'll build a lighted ZEN.... that would be a conversation piece on my desk in a dark cad room)
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