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A question about pad switches...

#41
agedhorse said:
No, this is not true. Depending on how the circuit is implemented, changing the pad may not change the input impedance even a little bit. There are 2 common ways to change the effective gain (lower the level) in a circuit. The first way is to insert 2 resistors into the signal path, a series and shunt resistor. Together these resistors form a voltage divider the reduces the voltage. Generally (though not always) when the pad is engaged on this type of circuit, the input impedance goes down.

The second way is simply to reduce the gain of the circuit itself, which has the same effect but generally does not affect the input impedance. This is usually how I do it.



The design rule of thumb of what is called a bridging connection or bridging circuit (which has nothing to do with bridged amps or BTL (bridge tied load) connections) is the the source impedance is at least 10x lower than the input impedance that you are connecting to. If your pickup's output impedance is 20k ohms then your input impedance should be a minimum of 200k ohms. See my above explanation on how the switch works.



It is there to prevent INPUT overload distortion of the preamp from hot pickups, and scale the input gain control better.



Audio outputs from wireless receivers are almost always (like 99.9%) low enough source impedance that anything 10k and higher on the amp is plenty fine. The transmitter is more of an issue, some transmitters input impedance are low enough to interfere with the bass and can cause loss of tone. This is getting more rare but was common 20 years ago.
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Alright. I think I get it now. General understanding at least. Thank you for that.
 
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#44
DavC said:
i change my Pad once a month ...
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#45
agedhorse said:
The second way is simply to reduce the gain of the circuit itself, which has the same effect but generally does not affect the input impedance. This is usually how I do it.
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...and it is safe to assume that this is principally why on the D-800/800+ using the pad (passive/active switch) doesn't result in the change in tone/voicing that occurs with some bass heads?

IME over the years it was best to find a way to avoid engaging the pad on most heads as it usually did a lot more than simply attenuate signal strength, at least to my ear. Oddly enough though, engaging a pad on a (higher quality) mixing board usually didn't often seem to affect the signal characteristics other than a gain reduction.
 
#46
Al Kraft said:
...and it is safe to assume that this is principally why on the D-800/800+ using the pad (passive/active switch) doesn't result in the change in tone/voicing that occurs with some bass heads?

IME over the years it was best to find a way to avoid engaging the pad on most heads as it usually did a lot more than simply attenuate signal strength, at least to my ear. Oddly enough though, engaging a pad on a (higher quality) mixing board usually didn't often seem to affect the signal characteristics other than a gain reduction.
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Correct Al the pad on the Subway does not affect the input impedance or tone. Since I designed pro audio equipment (consoles included) over the decades, I could never understand why pads used in bass amps were done in a way that dropped the input impedance so that modern high output, high impedance passive pickups sounded terrible. That's one important application for the pad function, it's not just for active pickups. (This is what I have seen and heard from in the field again and again).
 
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#47
I have never owned a bass, either active or passive, that sounded better with the pad/cut on. I do question if there would be a need to use a pad if you were using a Sansamp or other pedal that would increase the signal.
 
#48
OK, one last quote from the moron that inspired this thread:

"Well unless the science of impedance has changed, and he has misinterpreted the statement, the jokes on you buddy. The fact of the matter is that low imp active basses and high imp passive pickups are the reason for a pad. Oh..did you hear 'impedance' there...look it up//There is a lot more to it than you will ever understand."

Some people simply refuse to admit when they're wrong - I didn't bother replying to this last "bit of wisdom", as he's not worth catching a ban...

FWIW, the first sentence of the above quote was referring to agedhorse, lol...
 
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#49
bulldean said:
I have never owned a bass, either active or passive, that sounded better with the pad/cut on. I do question if there would be a need to use a pad if you were using a Sansamp or other pedal that would increase the signal.
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I have never needed to use a pad switch on an amp - there has always been a better workaround available... I've yet to engage any bass amp pad that produced a desirable result... In the above hypothetical, such a pedal will usually have a method of trimming it's sent signal to the amp...
 
#50
As Andy said, having a means of changing the gain of the first stage is a good and simple way to "pad" the input signal as it maintains a fairly consistent sonic signature.

Anything in the signal path affects tone and the typical pad found in many amps can do. If you want to maintain bandwidth and not be affected by Miller capacitance issues, a cascode configuration is a one option, it isn't affected by the tube's input capacitance as much as a triode.
 
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#52
beans-on-toast said:
As Andy said, having a means of changing the gain of the first stage is a good and simple way to "pad" the input signal as it maintains a fairly consistent sonic signature.

Anything in the signal path affects tone and the typical pad found in many amps can do. If you want to maintain bandwidth and not be affected by Miller capacitance issues, a cascode configuration is a one option, it isn't affected by the tube's input capacitance as much as a triode.
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There are ways to design circuits where none of this is a problem. It just requires an appropriate circuit for the task. Some circuits are naturally more forgiving of Miller capacitance (and other limitations).
 
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#53
mesaplayer83 said:
OK, one last quote from the moron that inspired this thread:

"Well unless the science of impedance has changed, and he has misinterpreted the statement, the jokes on you buddy. The fact of the matter is that low imp active basses and high imp passive pickups are the reason for a pad. Oh..did you hear 'impedance' there...look it up//There is a lot more to it than you will ever understand."

Some people simply refuse to admit when they're wrong - I didn't bother replying to this last "bit of wisdom", as he's not worth catching a ban...

FWIW, the first sentence of the above quote was referring to agedhorse, lol...
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Some funny stuff here! The guy should take an entry level electronics course, that way he could argue his point in front of the class for added "foolishness in public points".

When I refer to hobby-hack experts, this guy is a good example... somebody educated beyond their own intelligence, unable to see how wrong they are.
 
#55
agedhorse said:
Some funny stuff here! The guy should take an entry level electronics course, that way he could argue his point in front of the class for added "foolishness in public points".

When I refer to hobby-hack experts, this guy is a good example... somebody educated beyond their own intelligence, unable to see how wrong they are.
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Agreed - in the past, I would've told this guy what a dumbass he was being, and probably caught a time out, lol... However, I'd rather stick around - so I'm trying to adhere to the rules, but sometimes it isn't easy, lol...
 
#56
You guys wonder where the urban myths come from? This is a good example because there is some truth in how some manufacturer's products (especially legacy products) do this BUT it doesn't have to be this way, and in fact much of the industry has moved away from it.
 
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#57
mesaplayer83 said:
Agreed - in the past, I would've told this guy what a dumbass he was being, and probably caught a time out, lol... However, I'd rather stick around - so I'm trying to adhere to the rules, but sometimes it isn't easy, lol...
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It's a good thing you took the high road and stuck with more civil personal insults such as "moron."

Honestly, this thread is kind of ugly. It comes off as a big "see, I told you so" moreso than a discussion about impedance. I might be biased because I once had another member do this exact same thing to me. Had the thread gone in the direction that user imagined, I'm sure he would have loved to gloat about his intellectual superiority and call me a moron too. I don't think anybody wins in an internet pissing match.
 
#58
DiabolusInMusic said:
It's a good thing you took the high road and stuck with more civil personal insults such as "moron."

Honestly, this thread is kind of ugly. It comes off as a big "see, I told you so" moreso than a discussion about impedance. I might be biased because I once had another member do this exact same thing to me. Had the thread gone in the direction that user imagined, I'm sure he would have loved to gloat about his intellectual superiority and call me a moron too. I don't think anybody wins in an internet pissing match.
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Easy for you to say, you weren't the one here being told the things I was by him, all the while knowing I wasn't wrong... Go white knight somewhere else - I don't see where this is any of your business, to be honest...
 
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#59
mesaplayer83 said:
Easy for you to say, you weren't the one here being told the things I was by him, all the while knowing I wasn't wrong... Go white knight somewhere else - I don't see where this is any of your business, to be honest...
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Talkbass is a community, we're all involved in it. I will agree that the user was not polite to you but, honestly, I have been called far worse things on this forum and had no problem refraining from name calling. Denigrating others does not strengthen your position nor does it strengthen the community.
 
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