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A question about pad switches...

M

mesaplayer83

Jun 27, 2017
3,930
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#1
A discussion about pad switches on amps has me at odds with another TBer, and I'm wondering if I'm wrong about it... Now, he claims that an amp's pad switch's function is to deal with impedance differences between instruments... I have always thought that a pad switch is merely a way of dealing with variances in incoming signal strength... Am I wrong about this???
 
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#4
el murdoque said:
AFAIK you are right.
I use the pad only when absolutely necessary. All my active basses do fine without it.
Click to expand...

Yeah, my thinking is that I've had passive basses that put out hotter signals than many actives... I don't think impedance has ANYTHING to do with the function of a typical amp's pad switch - but will gladly admit that I'm wrong, if that's the case...
 
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#5
mesaplayer83 said:
A discussion about pad switches on amps has me at odds with another TBer, and I'm wondering if I'm wrong about it... Now, he claims that an amp's pad switch's function is to deal with impedance differences between instruments... I have always thought that a pad switch is merely a way of dealing with variances in incoming signal strength... Am I wrong about this???
Click to expand...

In electronics a Pad is slang for attenuator.
To attenuate a signal is to reduce its level.

There may be some changes in impedance between the input and output of a pad, if either poorly designed, or if intended to also act as an impedance matching device.

In actuality, a pad should not change impedance, but an impedance matching circuit will attenuate a signal, thus acting like a pad.

In an instrument amplifier, the intent of the pad is to reduce the incoming signal from an instrument with a hotter than normal output. It is NOT intended to be used as an impedance matching device. Impedances between instruments and amplifiers does not require matching as may be needed with a tube amplifier output. If there is any impedance change in the process of switching in the pad, it is unintentional, and insignificant relative to the other impedances involved.
 
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#6
Old Garage-Bander said:
In electronics a Pad is slang for attenuator.
To attenuate a signal is to reduce its level.

There may be some changes in impedance between the input and output of a pad, if either poorly designed, or if intended to also act as an impedance matching device.

In actuality, a pad should not change impedance, but an impedance matching circuit will attenuate a signal, thus acting like a pad.

In an instrument amplifier, the intent of the pad is to reduce the incoming signal from an instrument with a hotter than normal output. It is NOT intended to be used as an impedance matching device. Impedances between instruments and amplifiers does not require matching as may be needed with a tube amplifier output. If there is any impedance change in the process of switching in the pad, it is unintentional, and insignificant relative to the other impedances involved.
Click to expand...

Thank you - that's exactly how I see it as well...
 
#7
This is a bit murky sometimes because pad circuits are often better suited to an active bass than a passive one, impedance-wise. Depending on how the circuit is implemented, the padded input may have a much lower input impedance than it would with the pad disengaged, which may or may not be problematic for the high output impedances of passive basses. But the primary purpose for them is not impedance-related, it's signal attenuation.

It's never about impedance matching, though, as that's not usually a thing in audio. Almost all audio amps are voltage amplifiers so impedance bridging is what you want. This just means that you want low source impedances driving high input impedances so the voltage of the signal is preserved. The de facto standard is about a 10X ratio for optimum bridging. Passive basses can have output impedance above 10k Ohms so you want at least 100k for a proper bridging input and most bass amps have input impedances of 1M or more. If the pad is a simple voltage divider in front of the first gain stage then it will inherently lower the input impedance of the amp because it's in parallel with the un-attenuated input impedance. Sometimes you will see the pad implemented with 47k or less, which might be an issue if your bass' output impedance is 10k (it also might not).

tl;dr: Pads are not for impedance matching but there is sometimes an impedance factor involved with passive basses and pad circuits.
 
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#8
Mark and OGB have it right. A pad does not gave to affect impedance but depending on the design, it might as a byproduct of how the attenuation is accomplished. This generally isn't a problem with active pickups but can certainly be with passive pickups.

With some passive high output pickups becoming popular in the past 10-15 years, all the input pad networks I have designed do not lower the impedance in the padded mode for this reason.
 
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#9
OK, now the guy is backpedaling, and stated this:

"Yes, thats exactly what a pad switch does. it does not match or change or do anything to impedances. But impedances whether high or low are the science and the reason for the existence of a pad/attenuator switch."
 
#10
mesaplayer83 said:
OK, now the guy is backpedaling, and stated this:

"Yes, thats exactly what a pad switch does. it does not match or change or do anything to impedances. But impedances whether high or low are the science and the reason for the existence of a pad/attenuator switch."
Click to expand...

Nope, not in the slightest.
 
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#11
agedhorse said:
Nope, not in the slightest.
Click to expand...

Yeah, I didn't think so - so, instead of just admitting he was wrong, he's still trying to spin his way out of his ealier misinformation...

Ironically, here's a couple other quotes of his from the same thread:

"You should not be commenting on this subject whatsoever/"

"That's true.. I just hate when humans self righteously pass along false uneducated information. No excuse for that now what so ever with the internet."
The science of impedance is irrefutable."

Gotta love it when someone doubles down on the derp, lol...
 
#13
We all get one wrong occasionally or have been the victim of false information that seemed credible. When that happens you just need to say thanks for the education and move along in life a little smarter than you were yesterday.

Sometimes folks have a hard time letting go of inaccurate perceptions or misinformation they've been comfortable with for a long time...TB has certainly helped me clarify some things that I didn't have quite right.
 
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#15
Al Kraft said:
We all get one wrong occasionally or have been the victim of false information that seemed credible. When that happens you just need to say thanks for the education and move along in life a little smarter than you were yesterday.

Sometimes folks have a hard time letting go of inaccurate perceptions or misinformation they've been comfortable with for a long time...TB has certainly helped me clarify some things that I didn't have quite right.
Click to expand...


Yeah, I've learned some things here, to be sure - and am appreciative of the resources we have here...
 
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#16
mesaplayer83 said:
A discussion about pad switches on amps has me at odds with another TBer, and I'm wondering if I'm wrong about it... Now, he claims that an amp's pad switch's function is to deal with impedance differences between instruments... I have always thought that a pad switch is merely a way of dealing with variances in incoming signal strength... Am I wrong about this???
Click to expand...

Nope, the other fella is wrong: a -10dB pad has nothing to do with impedance.
 
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#17
mesaplayer83 said:
OK, now the guy is backpedaling, and stated this:

"Yes, thats exactly what a pad switch does. it does not match or change or do anything to impedances. But impedances whether high or low are the science and the reason for the existence of a pad/attenuator switch."
Click to expand...

Spoken like someone who understands neither science nor reason ;)
 
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#19
I creeped your profile :whistle: to find this other thread and I see what's happening there now. The other poster is right about the output impedances of active and passive basses. However, what he has wrong is that output impedance determines output signal strength. That isn't the case at all. Obviously all the parameters are interrelated but as an example, in a passive pickup, higher output impedance often indicates higher signal output (not always though, of course :D).
 
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