CMOY amp question 2
May 21, 2002 at 9:20 PM Post #2 of 27

mkyy

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Essentially, the opamp has two channel on the same chip.
Only one power supply needed. Take a look at tangent's tutorial.
The picture illustrated it pretty clear.
 
May 22, 2002 at 12:26 AM Post #7 of 27

tangent

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Oh my, so much confusion in such a short thread.... Let's see if we can't shed some light:

1. The OPA2132 and the OPA2134 have the same pinout. This is the standard dual op-amp pinout -- I don't know of a single dual op-amp with a different pinout.

2. Those two op-amps are also available in single-channel chips that are also DIP-8. Don't confuse them.

3. I don't recommend single-channel chips unless you're trying to do something advanced or the chip you want is only available in a single-channel version. Beginners should use duals. It makes life a lot simpler.

4. CMoy's original amp uses a pair of the single-channel OPA132s. The amp in my article uses a single dual-channel OPA2132.

5. When powering multiple chips, you just run the V+ line from chip to chip and same for the V- line. If you use a dual-channel chip in the CMoy design, there's only a single pair of voltage lines going from the power supply section to the amp section.
 
May 22, 2002 at 12:42 AM Post #8 of 27

eric343

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Heh, don't knock singles. I've built 3 out of 7 amps using singles
biggrin.gif


(of course, the last amp uses a BrownDog adapter, but STILL...
 
May 22, 2002 at 1:24 AM Post #9 of 27

tangent

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Quote:

don't knock singles


...but you're not a beginner. I phrased that advice very carefully.
smily_headphones1.gif
 
May 22, 2002 at 3:18 AM Post #10 of 27

eric343

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True, true, true. But I built my *first* amp with singles... And regret it to this day
eek.gif



Follow Tangent's advice. Duals make life *so* much easier it's almost funny. It's the difference between building a one medium-complexity amplifier versus two simple ones. You'll make fewer mistakes, TRUST ME. I had to do a total rebuild because I'd fux0r3d up the wiring on my first amp because I thought it'd be a walk in the park. (the schematic looked simple enough!) Little did I know that things are rarely a walk in the park when you're building on protoboard and have rather little experience...
 
May 22, 2002 at 3:27 AM Post #12 of 27

tangent

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No need to apologize, mkyy. I was clueless, too, recently. Some would say I still am.
smily_headphones1.gif
 
May 24, 2002 at 3:43 AM Post #14 of 27

millerdog

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Besides being more difficult to build, is there an advantage to using a single channel chip? Does it affect the sound in any way?

Since building Tangent's cmoy, would trying the original cmoy be a good next step before moving on to more difficult projects?
md
 
May 24, 2002 at 4:51 AM Post #15 of 27

tangent

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"Tangent's Cmoy" is just one layout of Chu Moy's circuit -- the only differences are just common ones like maybe I like to use bigger caps than in Chu's original schematic or something. It's not a significantly different design.

If you already have a layout (like my article gives you) duals are simpler -- only one chip to worry about, one set of voltage lines, etc. If you're starting from scratch, singles can sometimes be simpler to use depending on your protoboard's design -- their pins are less "dense", so you have more room to work with your wiring and external components. It's not so clear-cut an issue, really.

Personally, I only use singles when the chip in question comes in single-channel versions since in three different tests, I was unable to hear a difference between a pair of single-channel chips and the dual-channel version of the same design.

Duals are cheaper. Not only is one dual chip cheaper than two single chips, you have to buy twice as many sockets if you use singles, you may have to buy adapters, and you use more board space.

Some people will point out channel separation as an advantage of singles. Examine your op-amp's datasheets and decide for yourself. You'll probably find that any channel crossover ends up being inaudible at headphone amp signal levels.

One possible advantage of single-channel chips is that you can get them physically hotter than duals, which might matter if you're driving a chip right to its limits. That's not a situation you're going to encounter building a CMoy, though.
 

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