[DCameronMauch]

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Originally Posted by ezkcdude /img/forum/go_quote.gif Put up a schematic, and you may get more attention...I mean comments.

I provided the schematic, tons of comments, and even the complete Eagle pcb file ready to be sent for manufacture.

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Originally Posted by jbloudg20 /img/forum/go_quote.gif My comment isn't going to be helpful so I have held back. But: I think the idea of a cheap balanced amp is basically an oxymoron. For the money, a builder is better off building a better two channel amp. However, I like your inginuity, and I like the use of the single ended to balanced converter.

Not sure how you got the idea that this design was intended to be cheap. It isn't. It is physically small. Room for a few improvements, like biasing all the opamps into class A. But should compete nicely with most of the designs seen here. Especially since the headphones are driven differentially. Lots of advantages there.

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Originally Posted by motherone /img/forum/go_quote.gif I don't really have much to say. It's a straight-forward amp, basically a 4-channel PPA v1 with an OPA1632 and crossfeed.

Yeah, I guess so. But having a nice small balanced output amp is somewhat cool. Can you help with the J-Fet isolation transistor choice?

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Originally Posted by nikongod /img/forum/go_quote.gif there is a schematic posted. its one of the photo links. they can be cool for portable use. since pretty much NOTHING which is even close to portable has a balanced out.... umm, yea, balanced etymotics er4s's are the hotness. koss ksc-75's do good too.

The design is single-ended input. You can use it with any normal source. The headphone jack does need to be replaced with a 4 conductor. I have already done that with all mine. Even the regular single-ended output buffer ground ones, so they all use the same connector, and avoid the temporary output shorting that happens with phono plugs.

 

[jbloudg20]

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Originally Posted by DCameronMauch /img/forum/go_quote.gif Not sure how you got the idea that this design was intended to be cheap. It isn't.

I never said it was designed to be cheap, I said it was cheap. It is, when compared to any other high end headphone amp offering, when going balanced. There is a point where it must be considered the pros/cons of going balanced over building a better single ended amp.

 

[DCameronMauch]

Quote:

Originally Posted by jbloudg20 /img/forum/go_quote.gif I never said it was designed to be cheap, I said it was cheap. It is, when compared to any other high end headphone amp offering, when going balanced. There is a point where it must be considered the pros/cons of going balanced over building a better single ended amp.

Still a little confused. Which designs are you comparing it to? A PPA1/2? Or a monster Kevin Gilmore design? I think this design would compare quite well with something like the PPA2. I have heard the very noticable difference in power amplifiers for speakers that are single-ended versus balanced. The later always had obviously superior bass. They don't per say have actively buffered grounds on the SE models. But they are specifically designed to have a very low impedance to ground and handle that much current.

I had considered a follow-up design using pure discrete class-A buffers instead of chips such as HA-5002s. But I would definitely have to upgrade my Eagle license to get more pcb realestate. Ultimately I would like to do a fully discrete zero global feedback design. Possibly even current mode outputs instead of the almost universal voltage mode. The advantage is supposed to be great minimization of the effects of cables and length. Current mode is a problem with speakers because crossovers work differently driven this way. But that's not a problem with headphones.

 

[threepointone]

imo it seems a bit expensive for the design simplicity (though of course, simplicity doesn't always mean it sounds bad)
my biggest problem is with the opa1632--the entire design seems to be based around the chip, which you can't swap out like regular opamps.
wouldn't it be better to do a nice and simple, standard unbalanced-balanced converter and then use any other dual headphone amps to take care of the rest?

 

[DCameronMauch]

Quote:

Originally Posted by threepointone /img/forum/go_quote.gif imo it seems a bit expensive for the design simplicity (though of course, simplicity doesn't always mean it sounds bad) my biggest problem is with the opa1632--the entire design seems to be based around the chip, which you can't swap out like regular opamps. wouldn't it be better to do a nice and simple, standard unbalanced-balanced converter and then use any other dual headphone amps to take care of the rest?

Haven't actually figured out the total parts cost. But, yeah, not terribly cheap with 20 HA-5002s. The OPA1632 is definitely the main hub of the whole amplifier. A typical SE to balanced solution wouldn't be as "balanced" as these stupid tight tolerance chips designed specifically for this purpose. And check out the specs. The are amazing. Which doesn't necessarily equate to good sound. But it's not a bad start. There are a few replacement options, like the AD8138, but not many. I could have gone that route, but I wanted to do a whole end-to-end design. Mostly just for fun. True balanced all the way through would be cool. But I haven't been able to figure out how to do a balanced version of the Meier crossfeed circuit in a practical way. Getting the resistors matched between phases would not be too bad. But the caps would definitely be a problem. If the parts in the two phases of either channel are not nearly exactly matching, there will be some time delay smearing. Not good.