I'll start by telling you, I'm an electronic design engineer
specializing in audio. I'm also a musician so I have at least some
idea of what I'm hearing from a musical standpoint.
I believe the stock amps in the Auzentech X-Meridian are called
S4580P. Some of the amps on your list may sound better than the 4580.
It's a derivative design of some earlier amps in the series. The
letters at the start are often specific to the manufacturer, but the
model is 4580. The same amp from is made by NJR (New Japan Radio),
aka JRC (Japan Radio Co.).
Here's the specs for the S4580P:
Neither manufacturer specs noise voltage correctly, although it can be
calculated from the spec they give. A well spec'd amp should give the
figure in nanovolts per root hertz (nv/√Hz). Their spec is 0.8 μV over
a 30 KHz bandwidth. Dividing that number by the square root of 30,000
gives you 4.62 nv/√Hz, which isn't bad.
The slew rate (the maximum rate at which the amp can go from positive
to negative or from negative to positive) only 5 volts/μs, which isn't
bad, as long as you're not running on +/- 15 volt supplies, but other
amps are much better.
Two inexpensive amps you could try would be National LF353 and Texas
Instruments (TI) or Phillips NE5532. Of the two, the LF353 is noiser
than the NE5532, but I like the overall sound of the LF353 better. The
noise of the amp, itself may or may not make a difference, depending
on how much gain it takes and how much noise is present in the signal,
Note that parts with the same numbers from different manufacturers are
NOT necessarily exactly the same circuits, and even they are, one
maker's part may not sound or work as good as another's with the same
number. Many manufacturer's re-label their own product designs having
closely similar specs as a second source for a popular product. For
example, TI is the originator of the TL070 series of amps (TL071, 72
and 74 single dual and quad amps). If you order TL072 from National,
they will send you a LF353 or LF412 (same as amp as the current LF353)
marked as LF353, and if you order LF353 from TI, they will send you a
TL072 marked as an LF353. They are close enough that it doesn't
matter in many applications, but different enough that they can sound
or work differently in some critical circuits. You have to test each
vendors' products individually for your applications.
Of the new amps on your list, I'm most interested in National
Semiconductor's new op-amp targeted for audio, LM4562 and
TI/Burr-Brown's OPA134 family, including the dual amp, OPA2134. The
LM4562 has great specs all around, including being quieter than the
4580 but I've never had a chance to listen to it or test it for
stability, etc. It could be a winner if it is used in the microphone
preamp section. The OPA2134 is a FET input stage, which could be to
its advantage. Although not as quiet as the LM4562, it likewise has
great specs and could be a winner for applications where the noise of
the circuit is not the dominant consideration.
What's more important is, since they[re pluggable, these amps should
just plug and play. If it were me, I'd be go for it and try for
better sounding amps than the 4580. Setting up a test for more than
just subjective impressions could be difficult unless you have a good,
neutral test circuit where you can switch the same signal source
between two identical circuits with the only the difference being the
OPA132, 2132, 4132
OPA134, 2134, 4134
Both amps have the same key specs:
Slew rate: 20 volts/μs
Noise voltage: 8 nv/√Hz at 1 KHz
Gain bandwidth product: 8 MHz.
They may or may not be the same amp. The 134 family specs appear to be
more oriented toward audio, while the 132 family gives more
conventional engineering specs, but so many of their graphs and scope
photos are exactly the same that I think they are the same part
possibly with different guaranteed specs related to the application.
I e-mailed TI to ask their tech support people for more info about the
differences. I want to know, as well.
I haven't had the opportunity to test or listen to the OPA2132 or the
National LM4562, and the specs for both are great, but some amps with
great specs still sound bad in actual use for reasons too technical to
get into at length. Both should work better than the LF353 if the
gain exceeds 12 dB, or if it's being used in some other critical
applications, such as a filter (equalizer) circuit, but I can't say
anything definite without more info.
After that, there are still more considerations in choosing the right
amp. For example, a great noise spec is meaningless if, in the actual
application, the noise from the signal source (the program material
and all the stages preceding the circuitry) exceeds the noise
contribution of the stage under evaluation.
Some of the other amps you mentioned:
Linear Tech's LT1024 is a SINGLE amp in an 8 pin package. It's an
excellent, if somewhat pricey, amp but it won't fit in the socket for
an DUAL amp without an adapter, and that's FAR more work than it's
worth considering all the good alternatives that will just plug in.
The same applies to any other single amp on your list.
The original NE5532 originates from Philips/Signetics, noted above, is
a dual of their part number NE5534 that is slowed down to maintain
stability without the optional external compensation needed in some
applications because there aren't enough pins (2 per channel)
available on an 8 pin package to connect to the external components
Other amps with the numbers 5532 and 5534 are second source copies or
near copies of these parts. Without evaluation, the only other
manufacturer I trust for them are Texas Instruments and possibly
They are OK, but not great sounding audio amps. The 5534 (single)
tends to sound brittle. The slower 5532 just sounds... well...
slower. However, for a jellybean component, they have good noise
performance, and they could be the best sounding part for an
inexpensive product design. I would not consider them for a high end
product where absolute cost was not the first consideration.
To summarize, I think you can do better than the 4560 that come stock
in the X-Meridian. I can't say whether the LF353 would sound as good
as I would hope without knowing the circuit and the component values
around it. Any op-amp good enough to give excellent performance can
also be disappointing due to poor circuit design and layout, so it
also depends on the skill of the designer, and it still gets down to
listening to it in a specific application.
I wish I could help you more, but you're still down to listening
tests. You can measure stuff all day, but it still gets down to
enjoying what you're hearing.
If your competition brings you to developing commercial products, I
would be glad to discuss providing professional design services for
your products. If you are doing this for the competition without
commercial goals, I hope the above info is helpful, and I wish you the
best of luck. I live in the San Fernando Valley area of L.A. Ca.
I'll be glad to give you more contact info if you're interested.