Re: 2 into 1 will it work.
- From: "Mike Rieves" <mriev@xxxxxxxxxxx>
- Date: Fri, 13 Jul 2007 22:01:53 -0500
"Todd H." <bmiawmb@xxxxxxxxx> wrote in message
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"Mike Rieves" <mriev@xxxxxxxxxxx> writes:
"Todd H." <bmiawmb@xxxxxxxxx> wrote in message
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"Mike Rieves" <mriev@xxxxxxxxxxx> writes:
Nope, not at all, when I was kid, we used to do it all the time. You
won't
get the best quality sound, but it won't hurt anything and it usually
sounds
okay if you don't turn it up too much.
It's worth noting that you kids probably didn't have active
instruments with low impedance outputs and up to 18V of supply voltage
to work with.
Supply voltage has nothing to do with it, the output is an Ac signal and
it's buffered.
Buffered by op amps that may have split rails with as much as 18V
available between them, which depending on the care taken in the
design may or may not have a lifespan affected by a relatively dead
short to ground possibly at their output.
Since the outputs are NOT tied to either supply rail, that ain't gonna
happen. Outputs also nearly always have resisters in series that prevent
them from actually being shorted, those that don't have built in short
circuit detection and current limiting to prevent them from being damaged.
Any piece of equipment that doesn't isn't worth owning. Most active circuits
use op amps that are designed to be pretty much bullet proof.
As a matter of fact, the organ player played a Farfisa
compact through my amp along with my guitar when we were practicing. That
would have been the eqlivalent of mixing active and passive
equipment.
Mixing active and passive isn't as much of a problem as active and
active, and the two active devices wanting to go in opposite
directions at the same time.
If we were talking power amp outputs, I'd tend to agree with you, but we
aren't and modern active preamp circuits have plenty of tolerance for this
sort of thing. Their manufacturers know that they're dealing with musicians,
most of whom know nothing about electronics and who will try any combination
of connections in a pinch, and design with that in mind. :-)
I totally agree that in most cases nothing will break, but to try to
say "in all cases, it's totally fine based on these things I've done"
is ill advised.
Again, the output is decoupled from the supply voltage
Decoupled how?
See my paragraphs above.
I've never seen a battery powered preamp circuit transformer-coupled
to an output, I'll tell that. And capacitively coupled outputs would
be rather ill advised for use in a bass guitar due to the high pass
filtering effect.
Resistive coupling is common and the resistors are small in relation to
the input impedance of the circuitry they'll be plugged into, but plenty
large enough to prevent a short at the output from drawing enough current to
damage the circuitry. Even capacitor coupling has been used in bass
circuits, they just use big non-polar electrolytics so the 3 dB down point
is well below 20 Hz..
In a lot of cases you're dealing with only a FET source-drain or a BJT
emitter-collector resistance between your output and the supply rail,
...maybe a small resistor...and it ain't much.
But it's enough to protect the circuitry, otherwise, manufacturers would be
spending huge amounts servicing their instruments because of folks plugging
them in wrong. Besides, FET's are like tubes in that they current limit when
overdriven.
Without knowing the power dissipation that the various (perhaps highly
integrated) components are capable of withstanding, it's impossible to
say "it's totally safe--I've tested your specific eqipment."
Preamps are buffered,
Buffered how? Show me a schematic. Buffered with an opamp? Inside
the op amp are transistors and resistors--they're not magical black
boxes with ideal properties.
Of course not, but they typically have built-in short circuit protection.
I'll concede that there may be some cheaply built active instruments out
there that might possibly be harmed, but the odds are greatly against
someone plugging two of them into the same "Y" cable. However, it's likely
that the cheapos are capacitor coupled at the output so the manufacturer
doesn't wind up with a lot of service issues.
Sorry, I can't recall your background and whether you're throwing
around some buzzwords, or actually know what these things look like at
the transistor level.
I had over thirty years in electronics, including several years as a
senior electrical/instrumentation designer, and many years as a tech
servicing industrial, commercial, and consumer electronics. I've designed
and built my own preamps, both transister and op amp, power amps, both
discrete transister and hybrid power amp modules. I've had a lot of
experience with tube circuits as well, and worked on all sorts of musical
electronics equipment.
It's really unlikely that anyone who can afford to buy instruments with
active electronics won't be able to afford separate amps for each of them,
so I stand by my original statement, plugging two instruments into one amp
with a "Y" cable isn't likely to hurt them, though it may not sound very
good.
.
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