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Eric Bartlett
 
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Default What makes a mix buss sound good?

I have been thinking about about analog mixers. I understand
(somewhat)the electronics behind good pre's and eq's, but wonder what
makes a good mix buss. A design I saw on a cheaper board is a
resistor on the output of each channel connecting to the mixbuss
amplifier. What in the design (besides quality components) sets a
cheaper board apart from a good console? Is there a diference in the
way the channels are summed? Or is it just a better line amp?
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Scott Dorsey
 
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Default What makes a mix buss sound good?

Eric Bartlett wrote:
I have been thinking about about analog mixers. I understand
(somewhat)the electronics behind good pre's and eq's, but wonder what
makes a good mix buss. A design I saw on a cheaper board is a
resistor on the output of each channel connecting to the mixbuss
amplifier. What in the design (besides quality components) sets a
cheaper board apart from a good console? Is there a diference in the
way the channels are summed? Or is it just a better line amp?


1. Passive vs. active summing designs.

2. Component quality

3. Quality of the make-up gain amp at the end, as well as the quality of
whatever summing amps are used.

4. The buss drive amplifier stages. If you have big amps with a lot of
current drive, you can use smaller valued summing resistors on a passive
buss and therefore get lower noise.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Arny Krueger
 
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Default What makes a mix buss sound good?

"Eric Bartlett" wrote in message
om

I have been thinking about about analog mixers. I understand
(somewhat)the electronics behind good pre's and eq's, but wonder what
makes a good mix buss.


The major concerns are dynamic range and frequency response.

A design I saw on a cheaper board is a
resistor on the output of each channel connecting to the mixbuss
amplifier. What in the design (besides quality components) sets a
cheaper board apart from a good console?


Improved sound quality often comes from keeping internally-generated
distortion, noise and externally-generated interference pickup to a minimum.

Is there a difference in the way the channels are summed?


While passive mix buses seem to rule, it would be possible to do an active
mix bus driven by amplifiers that have a relatively high output impedances.

With passive mix buses each signals being mixed passes through a relatively
large resistor going into the bus, so the output sage of the amplifier for
each input has to swing a large voltage, even if very little signal from
that input is required. If the amplifier itself had a high output impedance,
the voltage swing at its output would be minimized.

Or is it just a better line amp?


It seems that the most attention is paid to the quality of the circuitry
driving each input to the mix bus, as well as the amplifiers that buffer it
out. One feature of better equipment is more headroom, usually obtained by
powering the amplifiers with higher voltages like +/- 24 volts, which of
course demands that the active and passive components be able to handle such
voltages.


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Jeremy Stephens
 
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Default What makes a mix buss sound good?

(Jim Williams) wrote in message . com...
(Eric Bartlett) wrote in message . com...
I have been thinking about about analog mixers. I understand
(somewhat)the electronics behind good pre's and eq's, but wonder what
makes a good mix buss. A design I saw on a cheaper board is a
resistor on the output of each channel connecting to the mixbuss
amplifier. What in the design (besides quality components) sets a
cheaper board apart from a good console? Is there a diference in the
way the channels are summed? Or is it just a better line amp?


Most of the cheaper stuff uses a plain opamp in an inverting config.
Problem is as you add more inputs you take more loop gain off the
opamp so it gets pretty dirty with over 24 inputs. Your bandwidth
shrinks a lot too.

The higher end consoles use some sort of transistor in the loop of
an opamp design mostly based on Paul Buff's "trans-Amp" (tm)(Hi
Paul!). This reduces loop gain on the opamp to unity, or like 1 input
summed as the transistors do most of the gain, just like your favorite
solid state transformerless mic pre. With this design many more inputs
can be summed cleanly. Some of these consoles use this topology in a
balanced mode, this decreases the crosstalk as capacitive leakage
currents in the buss resistors are common moded out. I've measured
over 90 db separation (stereo crosstalk)in some of these consoles
while most of the cheap stuff measures -60 db.

Jim Williams
Audio Upgrades


When mixing, would I better off turning off channels (on my soundcraft
600) that I am not using?


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