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"Modifying" cMoy circuit for Dual/Split Supply

post #1 of 12
6/17/11 at 6:47pm
Thread Starter 

Hello,

 

I'm working on a non headphone amp. A fairly enormous LM3886 x 2 + LM4780 which will make a 200W+ 2.1 setup for my computer. One of the preamplifier boards is going to use a +/- 6V transformer (effective 12V)...More on that in a second.

 

 

My front panel headphone jack on my computer just recently went kaput, and I do not know why, nor do I feel like replacing something like that at the moment.

 

So I thought I I'd integrate a cMoy right into the amp itself, since it will be sitting right on my computer desk..I'll use a 4PDT switch to switch the RCA inputs to either the power amp or the headphone amp. Should work right?

 

Op amps are supposed to be run of split supplies, but for the portable versions, we cheat and split the rails of a single supply.

 

So I was just going to build Tagent's pocket cMoy schematic like everyone else in the world, but what do I remove from the schematic? The two electrolytic buffer caps? Anything else? 

 

Truth be told, I've never built anything with an op-amp, besides single supply cMoys, so I'm not sure which pins get what. (Where does 6V go? 0? 6V? 

 

I'm going to use a OPA2134 I believe.

 

Thanks!

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post #2 of 12
6/18/11 at 7:56am

Read through the data sheet for whatever op amp you are using. All the pinouts will be in there, and almost always example circuits as well.

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post #3 of 12
6/18/11 at 8:46am

Basically, just build a CMoy without the rail splitter.

I can whip you up a schematic if you need one, but

it really is that simple.

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post #4 of 12
6/18/11 at 5:21pm
Thread Starter 

Whould this work? Is it okay to have the LED on only one of the "rails". I don't know how else I could do it.

 

cMoy.png

 

I used to know how to use one diode bridge for a center tapped/dual winding. I'll need to figure that out again.

 

And then the rest of it is just a normal cMoy?

 

 


Edited by TheLaw - 6/18/11 at 5:23pm
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post #5 of 12
6/18/11 at 5:27pm

pretty much. 

 

Try for +/- 9-12V 

 

You can send the LED & its resistor from + to - skipping ground. It doesnt really matter though

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post #6 of 12
6/18/11 at 5:57pm
Thread Starter 

Ah...Thanks. 

 

Well I'm using the 6V/6V transformer already, and I don't have space in the amp/money to go about buying another transformer.

 

6V+ 6V is already more than the ~4.5V + 4.5V that the 9V battery cMoys use, so I think it'll be alright. I don't have any amazing headphones right now, anyway. Sennheiser HD201s and CX300s, so I don't need anything too crazy. The HD201s are nice amped, but they can't handle too much more power than just a little boost.

 

I am curious to see what a OPA2134 sounds like on +/- 15V though...

 


Edited by TheLaw - 6/18/11 at 6:00pm
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post #7 of 12
6/22/11 at 11:59am
Thread Starter 

Is a 0.025W (1/40W) potentiometer good enough for cMoy volume control?

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post #8 of 12
6/22/11 at 12:27pm

The volume control should not dissipate any significant amount of power in most designs (cmoy included) BUT it must be a stereo, and logarithmic or "audio" type.

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post #9 of 12
6/22/11 at 12:29pm
Thread Starter 

Yeah totally. I got that much. I don't really know the actual voltage levels of typical inputs so I couldn't really do any ohms law calculations....

 

http://www.mouser.com/ProductDetail/Bourns/PTD902-2020K-A103/?qs=sGAEpiMZZMsEGgLEzQVyduEXDMDNUkpt3KO6hu5bqD4%3d

 

That's what I plan on using. Bourns PTD902 signifies dual gange.


Edited by TheLaw - 6/22/11 at 12:31pm
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post #10 of 12
6/22/11 at 8:20pm
Thread Starter 

Alright. I made the big order....I bought an OPA2134PA.

 

I understand this is "harder to work with". I would have bought a 2132 but I it was like $3 more, and I didn't feel like dishing any more money. =P

 

Anyway, what are the design considerations to keep in mind when working with a 2134? Is the general rule of thumb to keep everything as close to the op-amp as possible? Shortest leads possible. Don't spread things out too much...right?

 

Are there any particular components that this applies to? Is this mainly regarding the resistors which set the gain amongst other things? How about the input film capacitors? Does there positioning matter too much?

 

I'm building this on the standard Radio Shack board, so I can't do anything crazy? Would tangents Radio Shack pcb layout work fine?

 

Thanks.

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post #11 of 12
6/23/11 at 4:59am

OPA2134 should not give you any trouble and Tangents layout will work fine.


 

Quote:
Originally Posted by TheLaw View Post

Alright. I made the big order....I bought an OPA2134PA.

 

I understand this is "harder to work with". I would have bought a 2132 but I it was like $3 more, and I didn't feel like dishing any more money. =P

 

Anyway, what are the design considerations to keep in mind when working with a 2134? Is the general rule of thumb to keep everything as close to the op-amp as possible? Shortest leads possible. Don't spread things out too much...right?

 

Are there any particular components that this applies to? Is this mainly regarding the resistors which set the gain amongst other things? How about the input film capacitors? Does there positioning matter too much?

 

I'm building this on the standard Radio Shack board, so I can't do anything crazy? Would tangents Radio Shack pcb layout work fine?

 

Thanks.



 

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post #12 of 12
6/23/11 at 1:35pm
Thread Starter 

Thanks Avro.

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