Mike McLane
Active member
What are the differences in the following approaches to attenuating a signal? What's the best way to preserve the "integrity" of the signal?
Calling all smart guys!!
- Thread starter Mike McLane
- Start date
Big Monk
Well-known member
Preserve the integrity?
1 and 3 are the same if the resistance to ground is larger than the series resistance. 2 is a Voltage divider.
If we use an input control on something like a Fuzz Face as an example, 1 would be like the "Clean" trimmer on a Sun Face. As a series resistance, it's more of a texture control rather than a signal limiting control. 2 would be like a "Pre-Gain" found in the form of the Sustain control on the Big Muff or Buzzaround/Dizzy Tone.
2 will actually knock down the signal in a significant way.
BuddytheReow
Breadboard Baker
This would depend on the resistor values, but potentially yes.
the effectiveness of 1 and 3 is highly dependent on the input impedance of the following circuit. (Basically, forming a voltage divider between the in line resistor and the input impedance (resistance to ground) of the following circuit.
2 is still somewhat dependent especially if the input impedance of the next circuit is low. But generally 2 is the most effective and predictable.
2 is still somewhat dependent especially if the input impedance of the next circuit is low. But generally 2 is the most effective and predictable.
Mike McLane
Active member
I read that resistance disproportionately blocks high frequencies so I can understand that #1 would knock off high end. #2 is what we typically use for a volume control on guitars so we've all had first-hand experience with loss of high end as you turn down volume (hence, treble bypass circuits). I was hoping that #3, particularly if both resistors were of equal value, could get a signal reduction with minimal loss of high end. Sounds like #2 (the "old reliable") is the best way if you're into simple. So do I want a buffer to attenuate the signal and still retain its "integrity"?
My understanding is the high end loss associated with guitar vol Pot has to do with impedance interaction with pickups inductance, and the capacitance in the long cable from guitar to pedals/amp.
Not sure what context you’re wanting to attenuate volume, since what’s before/after will affect it.
#2 shouldn’t have any high end loss if:
-it comes after buffer or at the end of a pedal circuit (as long as it’s not seeing the guitar pickups directly)
-it goes through a reasonably short cable (or low capacitance cable)
Not sure what context you’re wanting to attenuate volume, since what’s before/after will affect it.
#2 shouldn’t have any high end loss if:
-it comes after buffer or at the end of a pedal circuit (as long as it’s not seeing the guitar pickups directly)
-it goes through a reasonably short cable (or low capacitance cable)
Mike McLane
Active member
I built a blackface Fender tube preamp pedal using Sushi's HV PSU and I want to run it into a Class D amp (Ducan PowerStage) to play through a conventional speaker cab. I note that Sushi (as well as Kingsley, et. al.) report running their pedals directly into such animals without undue concern except that the signal must be attenuated so as not to spazz out (technical term) the power amp. The experience of others, such as the TPA3118 thread on this Forum, seem to pitch for the need to "condition" (buffer?) the signal coming out of the preamp stage in order to get optimal results.
Mike McLane
Active member
Hmm? . . could it be that the preamp's output impedance is low enough such that it is somewhat analogous to buffer? Guitars with active (lo z) pickups or passive guitars with on-board buffer ahead of the volume control don't experience this loss of highs or need for treble bleed circuits. They put out a low impedance signal. Does the preamp itself function somewhat in the same fashion?
Bricksnbeatles
Member known well
tangential and possibly useful:
Imagine both 2 and 3 as potentiometers— while 2 is the common arrangement for a guitar’s volume control, 3 is preferred by many for volume controls on multi-pickup guitars as it allows for one pickup to be rolled down without muting the other. Worth keeping in mind if you’re looking to attenuate multiple signals.
Imagine both 2 and 3 as potentiometers— while 2 is the common arrangement for a guitar’s volume control, 3 is preferred by many for volume controls on multi-pickup guitars as it allows for one pickup to be rolled down without muting the other. Worth keeping in mind if you’re looking to attenuate multiple signals.
Mike McLane
Active member
BnB. . . noted.
BTW, I like Steely Dan
BTW, I like Steely Dan
Mike McLane
Active member
According to the Amp Book Impedance Calculator a single stage 12AX7, 100K plate resistor, cathode bypass cap = 38.46K ohms.
This is certainly minuscule compared to the output impedance of the pickup (1M +/- ?). I don't know if a second identical gain stage would reduce that further or not. Oh, such a tangled techno-web we weave?!?!?!
This is certainly minuscule compared to the output impedance of the pickup (1M +/- ?). I don't know if a second identical gain stage would reduce that further or not. Oh, such a tangled techno-web we weave?!?!?!
With the pickup / vol knob interaction, I believe the pickup inductance is a key element. Simple resistance in theory affects all frequencies equally. (I’ve heard resistors start to act funny at really high frequencies, way beyond audio).
Impedance is an odd thing since it’s usually denoted by a single resistance number. But element with inductive or capacitive qualities will have a different ‘resistance’ at different frequencies.
I highly doubt there’s any issues with using the #2 (standard) with your situation, but definitely interesting to learn the technical details. (For instance, I’m not sure if that calculated tube stage impedance has significant inductive or capacitive qualities or not, but I doubt it’s anything like pickups).
Impedance is an odd thing since it’s usually denoted by a single resistance number. But element with inductive or capacitive qualities will have a different ‘resistance’ at different frequencies.
I highly doubt there’s any issues with using the #2 (standard) with your situation, but definitely interesting to learn the technical details. (For instance, I’m not sure if that calculated tube stage impedance has significant inductive or capacitive qualities or not, but I doubt it’s anything like pickups).
Mike McLane
Active member
I guess that puts us waist deep in the big muddy (obscurity test) . . . not sure where we are at this point . . . not sure where we're goin' . . . too far to turn back. But I'm guessing Phi1's right. Just plug the SOB in and see what happens. And it appears that it's been workin' for a lot of people.
