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impedance of direct out


WagGag

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I use a high-impedance piezo pickup on my upright bass. I don't usually use a preamp, but I plan to use one on an upcoming job in order to send the mixing console a low impedance balanced output. But I guess I could also do that by sending the signal from the direct-out of my amplifier instead - sound people often seem to use that. But will the direct-out signal have a low impedance? Neither of my amps (GK, Walter Woods) seem to have any specs on the output impedance of the direct-out.
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Welcome to the Lowdown Waggy Gaggy dude.

 

I don't really know much about this, but I do know that the DI is a balanced out, so It should be plugged into the balanced input of the board.

 

A low impedance signalshould be plugged into the jack that gives some or no gain.

 

A high impedance signal shouldn't be plugged into the board at all. IE: the Speaker out on the amp.

 

I also don't understand how your Piezo pickup can be high Impedance...I probably jsut don't understand it. It may be a hotter pickup, meaning it give more output leading to a hotter signal from the bass.

 

isn't there a tech forum or something on this site?

 

sleepy time for me now. :wave::freak:

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Originally posted by phil6006:

I don't really know much about this, but I do know that the DI is a balanced out, so It should be plugged into the balanced input of the board.

Correct!

 

Originally posted by phil6006:

A low impedance signalshould be plugged into the jack that gives some or no gain.

Not necessarily - a line level signal is low impedance and doesn't need much or any gain, but a mic signal is also (even) low(er) impedance and needs loads of gain.

 

Originally posted by phil6006:

A high impedance signal shouldn't be plugged into the board at all.

Correct, because the impedance of the board's inputs will not be sufficiently high to prevent a the signal being loaded down (i.e. more current attempting to flow than the source is capable of providing, common with passive pickups)

 

Originally posted by phil6006:

IE: the Speaker out on the amp.

What?

 

Originally posted by phil6006:

I also don't understand how your Piezo pickup can be high Impedance...I probably jsut don't understand it. It may be a hotter pickup, meaning it give more output leading to a hotter signal from the bass.

All piezo pickups are ultra high impedance and really need to be matched up to a preamp with an input impedance of greater than 3 megohms. Just because they're high impedance doesn't mean they're high output, in fact the reverse is often the case.

 

WagGag, your WW will have a very high impedance input because they're designed for URB, so your pickup should sound good with that without an external preamp. I'm not sure about the GK. The DI outputs on both amps should be about 600 ohms and will match up well with any mixers' balanced mic inputs.

 

Alex

 

Alex

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All piezo pickups are ultra high impedance and really need to be matched up to a preamp with an input impedance of greater than 3 megohms. Just because they're high impedance doesn't mean they're high output, in fact the reverse is often the case.

 

WagGag, your WW will have a very high impedance input because they're designed for URB, so your pickup should sound good with that without an external preamp. I'm not sure about the GK. The DI outputs on both amps should be about 600 ohms and will match up well with any mixers' balanced mic inputs.

 

Alex

 

Alex[/QB]

 

Thanks Alex, that's very helpful. I noticed that my preamp's XLR output is also 600 ohms. So apparently balanced outputs in general are about 600 ohms, whether coming off a preamp's xlr output or coming off an amp's direct out?

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Originally posted by WagGag:

So apparently balanced outputs in general are about 600 ohms, whether coming off a preamp's xlr output or coming off an amp's direct out?

I'm not sure. My SWR GP has:

XLR Balanced Record Out Jack =1.5K ohms

XLR Balanced Line Out Jack = 10 ohms

 

The key difference is that the output level of the preamp out is that much higher than the DI out, so you can drive a PA power amp to full volume (ADA MB-1 notwithstanding).

 

Alex

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Originally posted by WagGag:

I use a high-impedance piezo pickup on my upright bass. I don't usually use a preamp, but I plan to use one on an upcoming job in order to send the mixing console a low impedance balanced output. But I guess I could also do that by sending the signal from the direct-out of my amplifier instead - sound people often seem to use that. But will the direct-out signal have a low impedance? Neither of my amps (GK, Walter Woods) seem to have any specs on the output impedance of the direct-out.

I use a similar setup: URB with a Fishman piezo pickup on the bridge direct into a GK. I've always found that the XLR out of the GK is a good clean signal and works well for going direct out to the board. The only thing is that the signal level tends to be really high - it practically pins the level on some boards. I usually just warn the sound guy that it's a hot signal and they'll probably need to put a pad on it.

I've always wondered why that is though - does it have to do with the impedance?

 

I've never used a separate pre-amp. I'd be curious to know how that goes for you.

 

By the way WagGag, how do you like your Walter Woods? If you ever consider selling, let me know.

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Using the preamp is working out well. Soundman is getting a good clean signal. Since I'm just bypassing the preamp settings, both for the output to the mixer and the output to my own local amp, I guess I could just as easily use the amp's direct out. But I like my volume pedal, and I need to have it in the chain after the send to the mixer. (If I used the direct out from the amp, then I'd have to put the vol pedal in the effects loop, which would entail using a 25k ohm vol pedal instead of my 250k ohm pedal??)
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