Opamp Upgrades for Mixing Board (holy war)

[Harry Bissell]

Religious debate... cool

Well, My sect has a little experience with the 4558. I worked on an early
guitar/CV converter which used the 4558, and I decided to get rid of those shitty
op amps (which I associated with the 1558). After consulting the data sheets (TI)
i found they were actually not bad at all, so I left them.

A classic "rule of thumb" is that the first stage of the circuit or device
contributes most of the noise... So I'd look  at that tranny pair and maybe start
with a premium pair there...If that's weak nothing else will help.

IMHO there is more to be gained by repalcing carbon comp resistors with quiet,
stable metal films... This is always a lesson we impart to the acolytes at our
temple...

Thoughts on your choices... (no opinion means no experience)
TL072... Good if you need very high impedance... but may do unpleasent things due
to very high slew rate (like oscillate...) You may need to add some pF caps to
tame this one...

NE5532... Good if you have (how zen-like this is, eh...) very low impedance, and
lots of power (it's hungry for mW). Resistor noise will dominate unless values
are kept much lower than is common for most audio circuits not specifically
designed for this part.

Flames welcome...  Only the blasphemers need fear the fires of Hell...

Archbishop Harry  <|;^)



WeAreAs1 at aol.com wrote:

> Hello listfolk,
>
> I have a Yamaha RM2408 recording mixing board that was made in the
> mid-1980's.  It was pretty nice for its time, but I'm thinking that it's
> probably possible to make some sonic improvements to it.  I'm considering
> replacing all the 4558 opamps in it with more modern, better sounding parts.
> I'm also going to try replacing the carbon composition resistors in the audio
> path with metal film types (I'll try it on one channel first, to see how much
> effect it has on the sound).
>
> Anyway, I'd like to get some suggestions as to what opamps to try.  The mixer
> has 24 channels, and each channel has four 4558's in it.  Each channel's
> audio passes through a total of seven opamp stages:  First, a unity gain
> differential follower (following the mic preamp's differential transistor
> pair), then four stages for the EQ section, one stage for an active low-cut
> filter section, and finally one last stage which buffers the output of the
> channel fader (and adds 10dB of gain) before the feeding the signal to the
> panpot and main busses.  The opamps run from a very clean +/- 16 volt supply.
>
> I'd like to know what you guys think of the following types, and what you
> like or don't like about them.  I'd also like to hear of any other types that
> you think are worth checking out, and why.  I would especially like to hear
> from people who have actually done some hands-on comparisons, as opposed to
> just reading about specs.
>
> I'm probably not willing to buy a bunch of ten dollar Burr-Brown
> instrumentation amps (remember, I have to buy 96 of them for the whole board,
> not counting the handful of buss summing amps and aux busses), so try to keep
> your suggestions on the practical side.  I'll buy a few of each of the most
> likely candidates, try them out on a channel or two, then report back with my
> findings.
>
> Here are some that I'm considering:
>
> OP275
> TLO72  (the old standby..)
> NE5532  (very popular in the 80's... now??)
> TLE2072  (ti's "Excalibur" series)
> NJM4560  (used in all Mackie products)
>
> These parts range in price from about $0.35 each to about $2.00 each, which
> works for my budget.  I would consider buying more expensive parts, if they
> can show considerable sonic improvement (for instance, if even my girlfriend
> can hear the difference...)  I'd also consider mixing types - for example,
> using one type for the mic pre section and another type for the EQ stages,
> etc.
>
> I know this subject is almost a religious debate for some, so play nice,
> folks.
>
> Michael Bacich