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Beefy headphone amp with balanced inputs, new design?

post #1 of 11
Thread Starter 

To the extent that there can be anything "new" about patching together well-worn circuit elements in a different way, I believe this design is "new."

 

Like the cmoy, it uses a passive ground splitter.

Like the 02, it uses opamps in parallel to double output power.

And like nothing else (?) it has balanced inputs for the pro audio folks.

 

What do you think?

 

post #2 of 11

The design of your virtual ground is not going to cope at all. It needs to be able to source, and sink, the same current as both outputs put together.

post #3 of 11
Thread Starter 

Thanks for taking a look at it, Dingo. So I need to lower the value of the "rail splitters" correct?

post #4 of 11

I agree with Dingo, IMO the easiest way to handle the supply is to go dual rail (as if you use a rail splitter you pretty much have to have an active ground, which I am far from a fan of). Besides you've drawn this up with +5 and -5V rails, it's really easy to build a +/-5V power supply with just a few components, unless that is you're going to attempt to battery power this, in which case I think you'd have to resort to an active ground like AMB's mini^3...

 

However with a bit more information on your ideas I'm sure we could help you come up with something quite cool for your application :)

post #5 of 11
Thread Starter 

Thanks for your feedback. The application is not a typical one--the amp will be used to amplify monitor feeds for musicians in a recording studio. As such, power, headroom, affordability, and portability are the main design goals. The balanced input is necessary because the amps will often be fed by a long cable run from the control to live rooms. There will most likely be two or more amps per unit fed from the same audio source and power supply.

 

I agree with you Goobley, that dual rails are ideal, but a DC wallwart supply provides so much in the way of convenience and cost savings that it's hard to opt for a linear, dual-rail supply for this application. Unless there is a way to build a dual rail supply with out the need for an expensive transformer with dual secondaries?

 

Thanks for pointing me towards the MINI3, it looks like it uses a rail splitter followed by a buffer. In this case, is the source/sink capability of the PSU simply the rated output power of the buffering opamp?

post #6 of 11

Righty ho, it's good to have a bit more insight into the aim of this design.

 

Whilst I wouldn't necessarily agree that a dual rail (not necessarily linear) HAS to be cumbersome, it often is. If you're interested in portability, why not use batteries? A pair of 9V batteries NiMH followed by a beefy opamp buffer or a sijosae discrete buffer (detailed here http://tangentsoft.net/elec/vgrounds.html ) could be a valid choice as I'm sure you could find room in the studio to have spare sets of 9V batteries on charge (obviously investing in twice the necessary batteries to minimise downtime).

 

While it is possible to just use the mid point between two batteries as the VGND I am certainly not a fan of this as one battery will almost always discharge faster than the other, giving seriously uneven rails.

 

Your analysis of the Mini^3 is correct.

 

What sort of headphones are you expecting to power of this (something like DT-770m or easier I would expect), Are you sure you need the paralleled buffers on the output or is this just a 'nice to have'? Is there a set budget for this amp? How are you planning to build it (custom run of pcbs, or stripboard etc...)?

Have you considered using something like the O2 and just putting a Bal-SE converter in front of it?

 

Should be some food for thought there...

One more question: on which continent are you located?

 

Cheers!

post #7 of 11
Quote:
Thanks for taking a look at it, Dingo. So I need to lower the value of the "rail splitters" correct?

Lower value resistors and larger capacitors would help, but it's still far from ideal. For your situation, you can do better.

 

Quote:
Originally Posted by Meathands View Post

Thanks for your feedback. The application is not a typical one--the amp will be used to amplify monitor feeds for musicians in a recording studio. As such, power, headroom, affordability, and portability are the main design goals. The balanced input is necessary because the amps will often be fed by a long cable run from the control to live rooms. There will most likely be two or more amps per unit fed from the same audio source and power supply.

Just build a design like the O2 with a balanced input, or use the O2 as is, with active bal-se converters or input transformers.

The O2 gets a +/- supply from a single AC wallwart by using a dual-half-wave rectified setup. It should be easy enough to source AC-AC wallwarts/bricks capable of powering mulitple O2s.

post #8 of 11
Thread Starter 

The dual half-wave setup is exactly what I was looking for! Just built one up today to test and it's much cleaner than the DC wall wart supply. Thank you for pointing me in the right direction, guys!

post #9 of 11
Quote:
Originally Posted by Meathands View Post

The dual half-wave setup is exactly what I was looking for! Just built one up today to test and it's much cleaner than the DC wall wart supply. Thank you for pointing me in the right direction, guys!

Huzzah!

 

Glad to be of assistance atsmile.gif

post #10 of 11
Thread Starter 

So here's what I've got for the power supply. I decided to make it a separate board since it could be useful for a lot of projects. Thanks in advance for any thoughts or criticisms.

 

All of the diodes are 1N400x Schottky type

The regulators are 78xx, 79xx

I'm planning on using 1000uF caps for C1-C4 and .1uF for C5, C6

 

 

 

post #11 of 11

I'd recommend using a CRCRC filter if you can spare the board space, something similar to what is used in this design http://www.head-fi.org/t/599224/some-lme49600-implementations/240  check post 252. This should reduce pre-reg noise a fair amount without losing too much power (due to very low current draw)

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