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In Reply to: RE: JA's Moon Evolution P-7 Review posted by audiophilect on March 21, 2009 at 08:13:43
in a well executed circuit.
Music making the painting, recording it the photograph
I would ask for more than "good" sound from a $6900 preamp that provides but 6 db of gain. Speaking of good sound, I am quite pleased with the sound of a Bellari VPI 129 phono preamp used in the vintage system. While it incorporates a 12AX7 tube, most of the gain comes from a pair of op amps. As compared with an Audio Research SP-9MKIII used in the main system, it gives up a bit of resolution and noise, but its sins are mostly of omission. Quite listenable unlike the dreadful implementations used back in the 70s when I got started. And only $250.
Yes, op amps can sound good. And they can be inexpensive.
rw
opamps, although may have a lower THD, do not sound as good as the best discrete circuits. I wonder if the ones used in this preamp is an exception. If yes, I very much would like to know the make and model.
Oops there goes every CD player. None of them can sound any good; they alluse op amps, one or two use dicrete device op amps but they're op amps. Seriously in most cases it's knowing what you are doing and doing a good job knowing the rules of electrical engineering and having a good ear for final design rather than what circuitry is chosen in the first place. There are good ways to do things and not so good ways though I suppose op amps have had more than their share of bad ways. Just don't assume all op amp designs are inherently poor.
"Oops there goes every CD player. None of them can sound any good; they alluse op amps,"
No you are wrong... my Monarch Audio M24 DAC has no opamps or even transistors after the DAC chip at all. It uses passive IV conversion directly into an output tube that is configured SRPP to give gain and a low output impedance...no op amps for IV conversion, filtering or buffering. There are a few others on the market that do something similar.
"Oops there goes every CD player. None of them can sound any good; they alluse op amps, one or two use dicrete device op amps but they're op amps."
I should have made it clear that what I meant was opamps in the form of integrated circuits, not discrete opamps.
CD players that use opamps, especially for IV conversion, probably are not the best. An exception is the Ayre CX-7e, which uses the current-feedback (not the usual voltage-feedback) opamps for the purpose.
JA preferred the Moon over the Parasound JC-2. If the Moon's performance is indeed this impressive it is good news for audiophiles as components can be made at much lower costs with opamps.
Hahax is wrong about needing an op-amp in a CD player. Even a discrete one. There are many that are built with discrete, non-op-amp circuits. Two examples are the Ayre D-1xe DVD player and the Ayre C-5xe MP universal player.
The Ayre CX-7e uses *integrated circuits* to keep the costs down, but they are not op-amps. An op-amp uses feedback as its basic operating principle. The integrated circuits in the Ayre CX-7e (and AX-7e) use no feedback. They are essentially just a collection of transistors in one package.
Charles,
Thanks for the clarification.
Just want to make sure I understand correctly your comment about the CX-7e. The output of the IV circuit is NOT connected to its current input via a resistor, right?
> > The output of the IV circuit is NOT connected to its current input via a resistor, right? < <
None of our circuits in any of products have the output connected back to the input via any connection of any type. That would constitute a feedback loop, which we do not use.
Charles,
I just looked at the datasheet for the integrated circuit. Do you use a resistor connected to pin 5 to set the output voltage? If you do not feel comfortable answering the details I can understand. Thanks.
Yes, access to pin 5 is crucial. It is one of the few IC's that allow access to that node.
Thanks for the info.
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