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The role of opamps in a DAC

post #1 of 12
2/23/08 at 8:29pm
Thread Starter 
I have a question mainly regarding the electronic aspect of the DAC: if I'm only using the line-out of a specific DAC, and using a separate amplifier to drive my headphones, do the opamps/amp circuit of a given DAC matter? Are they used in producing a line-out, or just for amplification after the line-out stage?

Thanks for your help - this is basically because I have an external amp and am trying to see whether or not better opamps in the DAC will impact positively/negatively considering my usage.
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post #2 of 12
2/23/08 at 8:34pm
The circuitry implementation is more important. I HATE it when people are so focused on what opamp an amp or equipment uses. FWIW, the LisaIII uses AD744's, which to many builders are a sub par opamp, yet the Lisa sounds great. So, that in itself should shut up all those spec sheet people for the most part.

Get the DAC which best fits your budget. DACs IMO are mostly a "point of diminishing returns" piece of equipment. Anything over what you can easily afford is likely far too much for you to use. Spend your extra money on a better amp or headphones and your money will do much more for you than a "better" DAC will.
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post #3 of 12
2/23/08 at 9:11pm
Thread Starter 
Sorry, allow me to clarify: It's not that like, I'm wondering if x opamp will make a difference. I'm just wondering if they're going to be in my signal path at all if I'm just using the line-outs of a given DAC. Basically, will I even utilize them if I'm not using the "phone out" of a given DAC?

EDIT: btw, regarding your comment about DACs fitting one's budget: I have Beyer DT880's and an original master headphone amp. I currently have a chaintech AV-710. Is that good enough? I know little about the specs honestly, I just know it uses some Wolfson DAC. I don't intend for this thread to become a "what should I do?" thread, but just offhand.

Thanks.
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post #4 of 12
2/23/08 at 9:18pm
Quote:
Originally Posted by royalcrown View Post
Basically, will I even utilize them if I'm not using the "phone out" of a given DAC?
Yes, inevitably.
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post #5 of 12
2/24/08 at 2:17am
Thread Starter 
So I guess my question then, is: what exactly is the function of an opamp in terms of DAC's?
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post #6 of 12
2/24/08 at 2:35am
a DAC usually consists of power supply, the digital to analogue converstion stage and the analogue output stage

opamps are usually in the analogue output stage - this basically boosts the signal from the DAC chip to line level voltages

the AV-710 is good value for money, but there are much better sounding pieces of equipment. i am a firm believer that after the transducer the source is the next most important thing
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post #7 of 12
2/24/08 at 2:53am
Quote:
Originally Posted by royalcrown View Post
So I guess my question then, is: what exactly is the function of an opamp in terms of DAC's?
It depends upon the DAC chip. Most of the better DACs are current out, and require a current to voltage conversion (I/V). Voltage out DACs only require some amplification or buffering to line level output. DACs also require filtering (to get rid of HF hash, shaping, etc.) so the opamps many times also perform this duty. Simplistic explanation, but maybe someone can fill it in more...
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post #8 of 12
2/24/08 at 4:09pm
Quote:
Originally Posted by royalcrown View Post
So I guess my question then, is: what exactly is the function of an opamp in terms of DAC's?
it *really* depends on the dac.

I like PAR's description of how op-amps are commonly used on less expensive DAC's. if you have experience with ACTIVE crossovers for loudspeakers, the opamp in the output stage of a V-out DAC is often setup as a VERY steep slope low-passs filter with the "knee" at some absurdly high frequency. most opamps can do "ok" driving medium lengths of cable, so it serves double duty in the output stage of a DAC.

regarding the comment of "they are inevitably in the signal path":
applied to less expensive gear, i pretty much agree. but applied to more expensive gear, I can think of QUITE a few ways to use opamps that keeps them out of the signal path and SIGNIFICANTLY improve the operation of other parts. DC servos for various parts, and opamp-based voltage regulators both come to mind. i'd take an opamp based DC servo over a DC blocking cap at 4 times the cost any day.
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post #9 of 12
2/24/08 at 4:15pm
Op-amps, discrete transistor stages or even tubes generally perform 4 main functions in a DAC:

1) I/V or current to voltage conversion since most D/A chips have a current output

2) voltage gain

3) filtering of digital artifacts - eliminates the stair-steps

4) drive for cables or headphones - this provides more current and is less sensitive ot capacitive loads.

Steve N.
Empirical Audio
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post #10 of 12
2/24/08 at 11:14pm
Some explaination.

>> IV conversion

More articles below.

>> alexhardware.com
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post #11 of 12
2/25/08 at 12:01am
Inside OMZ v4, I found an OPA2134 on the discrete module?
I thought discrete means no opamps at all?
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post #12 of 12
2/25/08 at 12:24am
Quote:
Originally Posted by Capunk View Post
Inside OMZ v4, I found an OPA2134 on the discrete module?
I thought discrete means no opamps at all?
it's a DC servo
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