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Double Bass Input Impedance

BassDuex

BassDuex

Jul 15, 2006
187
122
Placerville, CA
#1
I am using a B-15N head for Upright with a dual piezo pickup (6-Rounds Sound)

The Ampeg has a 5.6M input impedance to my understanding. I'm not sure what the pickup is - could find out, I'm sure.

Anyhow my question is really if 'Matching input impedences' whould be expected to have any effect on feedback'

Clearly feedback is dependant on output volume and input sensitivity.
I am under the impression that impedance matching ultimately optimizes signal transmission.
If so, perhaps this may effect feedback, be it better/worse or insignificant.
 
#2
bodker,

if your amp has 5.6MOhm impedance, it should be fine for piezo pickups. So, if you are trying to solve feedback issue by matching impedances, there's nothing to do here IMO.

As far as impedance matching and its influence on feedback, the best I can do is guess, and I guess matching impedances makes the amplifier/pickup system less prone to feedback. But- that's a guess and gut feeling.

Best
Sidecar
 
#3
First, what we're really discussing here is not impedance matching. It is optimal loading. Click here for details. Optimal loading vs. non-optimal loading of a piezo pickup will alter the frequency response. Typically, optimal loading extends the low-end response. This is not likely to have any substantial overall effect with regard to susceptibility to feedback.
 
#5
And from me, thanks Drurb, for getting me straight on this. It felt "wrong" talking about matching there, but I couldn't put the finger on why. Might be in part a language/terms&definitions issue. As to the effects of sub-optimal loading, good to know as well, as I have never experienced it myself. Maybe I shoulda kept my mouth shut :-)

Best
Sidecar
 
#6
BassDuex said:
I am using a B-15N head for Upright with a dual piezo pickup (6-Rounds Sound)

The Ampeg has a 5.6M input impedance to my understanding. I'm not sure what the pickup is - could find out, I'm sure.

Anyhow my question is really if 'Matching input impedences' would be expected to have any effect on feedback'

Clearly feedback is dependant on output volume and input sensitivity.
I am under the impression that impedance matching ultimately optimizes signal transmission.
If so, perhaps this may effect feedback, be it better/worse or insignificant.
Click to expand...

This certainly sheds a whole new light on using a piezo with a B-15N. I posited the question to the Jess Oliver thread over on the bass guitar side of TB.

One of the regular technical contributors to that thread did some research (thanks, Beans on Toast) and revealed that the B-15N(C) had three different
possible input impedances 1 Meg Ohm, 2.2 Meg Ohms and 5.6 Meg Ohms, depending on which of the three inputs you plugged into. This was pretty
savvy thinking for 1964, when piezo pickups for Double Bass didn't exist.

Ric
 
#8
MrSidecar said:
And from me, thanks Drurb, for getting me straight on this. It felt "wrong" talking about matching there, but I couldn't put the finger on why. Might be in part a language/terms&definitions issue. As to the effects of sub-optimal loading, good to know as well, as I have never experienced it myself. Maybe I shoulda kept my mouth shut :)

Best
Sidecar
Click to expand...

Oh no, please do speak up! :) Your advice was right on target if one interprets "matching" to be "loading." The truth is that, with regard to these matters, the term "impedance matching" seems to be most-often used incorrectly. In these threads, people seem to generally understand "impedance matching" to be what is really "optimal loading." As you seem to appreciate, my goal is to help further understanding. If the difference between the terms is not really understood, then it can lead to confusion when true impedance matching is discussed vis a vis power amps and speaker cabs.
 

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