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Old 17th February 2007, 03:28 AM   #1
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Default 2 channel headphone amp

hi, im building a headphone amp based off the cmoy amp on tangentsoft. im using opa2132p op amps. my question is... i would like to make it a two channel amp (2 stereo channels), and was wondering if i needed to do something special when it comes to splitting the input signal to go to both opa2132's? can i do this or no? also i made my own psu (from scratch) which seems to be working correctly(im stoked on that) putting out 20vdc. can i also split that power source to go to both opa2132's?
i'd appreciate some help.
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Old 17th February 2007, 03:59 AM   #2
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Are you talking basically talking about 2 amps running off the same input signal and power supply?

If so then you could just duplicate the circuit - but you may want to add another opamp running at unity-gain in-front of the existing op amp to buffer the signal.

There should be a bunch of diagrams on www.headwize.com under Projects - look for something along the lines of 'distribution amplifier'.

As long as the power supply can provide enough current you can split it off to feed as many components as you like. The OPA2132 will feed 40ma into a short circuit, so as long as you can feed 2x that you'll probably never had an issue. You might want to add additional capacitors between v+/v- and gnd.
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Old 17th February 2007, 04:30 AM   #3
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ok thanks raro.
i did put a 63v 6800uf on my psu, and a 63v 1uf wima poly on it. and then on the op amp boards i have 50v 220uf on v+ and one on v-. that should be good no?
thanks for your reply i'll check out some dist.amps
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Old 17th February 2007, 04:37 AM   #4
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i actually have some DRV134PA in route from T.I. those should do the trick no?
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Old 17th February 2007, 05:28 AM   #5
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Woooo 6800uf!

I've build similar things with no more than 1000uf + .1uf per rail - you should be fine.

Ah, with the DRV134 - are you saying you want to create a headphone amp for balanced drivers? and not 2x headphone amps for two sets of phones?
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Old 17th February 2007, 05:53 AM   #6
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i dont know what im saying. ha ha.
i just ordered those the other day along with some other stuff.
but im using 2 opa2132p's. i just want to make a 2 channel head amp. not balanced, so maybe those arent the right item but i saw that it can be used as a diff.amp.
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Old 17th February 2007, 12:45 PM   #7
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I think I see your confusion, so I'll try and help.

The OPA2132/4 is a dual opamp. This means you only need ONE to make a stereo headphone amp. The original cmoy used two OPA134 opamps which are only single opamps, in which case you would need two.

If you use two single opamps like the OPA134, yes you can use the same supply on both of them.

The DRV134PA is a balanced line driver. I'm sure you were thinking of the OPA134PA when you ordered it.
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Old 18th February 2007, 12:45 AM   #8
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no actually i didnt order the drv134 for the headphone amp. i actually wanted to see about setting up my LM3886 amp to have balanced outs. but thats a different subject i'll probably be posting. im aware the difference between the opa134 and opa2132. But thanks for your post. My main worry was just splitting the input signal to go to both cmoys.
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Old 18th February 2007, 02:06 AM   #9
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OK, maybe I was the one confused.

So you want to send a left/right signal to two separate stereo headphone amps?

If this is the case, there isn't anything special you need to do as long as your source can handle the lower input impedance. The standard cmoy circuit has an input impedance of 100k, so two amps with parallel inputs will make it a single 50k load for your source. I don't think your source will have a problem with 50k.
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Old 18th February 2007, 03:21 AM   #10
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ok cool man. thanks
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