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SE in/out for balanced amp. Please help.

post #1 of 21
8/12/10 at 9:30pm
Thread Starter 

Is there a way to wire SE input and output for a balanced headphone amplifier?

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post #2 of 21
8/12/10 at 11:29pm

Not unless there are details as to which amp and hopefully some internal photos and even better - a schematic. ;)

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post #3 of 21
8/12/10 at 11:46pm
Thread Starter 

I am thinking about slapping two LBC clones together to make a balance amp.  I've tried it before with other cheap amps so I know it works.  I just don't know how to wire it for SE without maybe damaging the amps.

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post #4 of 21
8/13/10 at 6:22am

What is a LBC?

 

*inapropriate acronyms removed before posting* 

 

Anyways, if you want single ended inputs and balanced outputs you need a phase splitter somewhere along the line. the trend to towards 4 channels acting like 2 balanced channels does not allow this unless you do a LOT of work to the amps (certain global feedback configurations *may* work properly) so you have to put more stuff in the signal path :)

 

Pick:

Transformers or active phase splitters. 


Edited by nikongod - 8/13/10 at 6:23am
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post #5 of 21
8/13/10 at 9:22am

Balanced inputs should accept SE source, just tie amp -in to source gnd, with the more common dual single channel "balanced amp" you will be wasting 1/2 the Vswing, 3/4 of the power output potential

 

"Balanced" output usually requires rewiring the headphone to separate the R,L driver's 4 terminals - the standard "SE" TRS 3 wire jack-plug shorts R,L gnd return wires

 

a pair of quality output transformers could get around this - but they can cost >US$100 each

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post #6 of 21
8/13/10 at 10:17am
Thread Starter 

Thanks for the input guys.

 

LBC is Lehmann Black Cube.

 

Searching around, I've found comments about transformers and phase splitters also.  Don't know what they are but kind of figured they can be complex or expensive.  That's why I'm asking if there is a safe way just to wire it a certain way.  Since I will be using two SE amps, can I wire in a selector switch to run only one amp for SE or something along a selector so I won't short or fry any components.

 

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post #7 of 21
8/13/10 at 11:03am

See my post here

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post #8 of 21
8/13/10 at 12:18pm
Thread Starter 

Thanks nikongod, I have read that thread before starting this one.  The more serious problem for me is the SE output.  I have a balanced source so I can get by without the SE input.  I can use a RCA to XLR adapter if I must.  The issue is driving SE headphones out of the balanced amp.


Edited by sunneebear - 8/13/10 at 7:52pm
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post #9 of 21
8/13/10 at 3:15pm

a pair of 1:1 output transformers would let you drive each balanced and to connect the negative phase outputs of both channels to the TRS "gnd"

 

to spec them it would be good to know headphone and amp specs - but there may not be good "off the shelf" standard parts for some combinations


Edited by jcx - 8/13/10 at 3:19pm
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post #10 of 21
8/13/10 at 5:45pm

 

Which is it that you actually want? Balanced inputs and outputs or a pair of bridged amplifiers?

 

se

 

 

 

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post #11 of 21
8/13/10 at 8:08pm
Thread Starter 

jcx: thanks but transformers can be hard to find, expensive or add to the signal path.  Even if their color is a improvement, I want to experiment first with how this setup actually sounds like.

 

Steve Eddy: right now I'm kind of hooked on balanced.  All my headphones can run both balanced and SE so I have no problems with a balanced only DIY amp but if there was a way to easily put in a SE jack, why not.

 

Thank you both for you answers.

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post #12 of 21
8/13/10 at 8:39pm
Quote:

Originally Posted by sunneebear View Post

 

Steve Eddy: right now I'm kind of hooked on balanced.


Just to clarify, what I was getting at is that in the headphone world, "balanced" typically refers to a pair of bridged amplifier channels and in my opinion, is rather a misuse of the term "balanced." So I was wanting to know if you wanted "balanced" as in a pair of bridged amplifiers, or "balanced" in the traditional sense the word is used.

 

se

 

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post #13 of 21
8/13/10 at 8:59pm
Thread Starter 

I am bridging two stereo amps.

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post #14 of 21
8/13/10 at 10:05pm


 

Quote:
Originally Posted by sunneebear View Post

I am bridging two stereo amps.


Ok.

 

One thing you can do is feed the single-ended output from just one pair of amplifier channels (i.e. L+, R+ and ground). The output voltage will be half the bridged voltage, but as long as a single LBC is sufficient to drive your headphones to sufficient levels, you'll still be ok.

 

You can also use a pair of output transformers. CineMag's CMOQ-3's go for around $35 each. Wiring the primaries and secondaries in parallel would end up adding 20 ohms of output impedance to whatever the output impedance of the pair of LBC's is.

 

The first method would be the simplest and least expensive. Sound-wise it's hard to say as some people prefer the sound of their headphones when driven from a bit higher source impedance which is what you'd get from the output transformer option.

 

se

 

 

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post #15 of 21
8/13/10 at 10:36pm
Thread Starter 

Thank you Steve Eddy.  I will try your first method first.  I did try that before with a cheap little kit amp.  It works but the SE output picked up all kinds of RF while the balanced side was dead quiet.  Also I wasn't sure if a common ground between the two amps was safe.

 

If I don't like the results then I will try the transformers.  The CMOQ-3 comes in 3H and 3L.  CineMag does not list any data for either CMOQ-3's.


Edited by sunneebear - 8/13/10 at 10:37pm
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