Amps and True By-Pass.

Zim

Member
Messages
1,973
I love the tone of my amp when I plug straight in. But when I have some stomp pedals in, I notice the tone suck. How can I over come this?

Are true By-Pass effects the way to go or some kind of buffer, loop pedal of some sort?

Advice please.
 

chervokas

Member
Messages
6,839
I love the tone of my amp when I plug straight in. But when I have some stomp pedals in, I notice the tone suck. How can I over come this?

Are true By-Pass effects the way to go or some kind of buffer, loop pedal of some sort?

Advice please.

Well, the answer to this is always "it depends."

A guitar with passive pickups, a volume pot, and a cable connected to a amplifier with a typical input inpedance of 1 megohm or higher will have certain sonic characteristics. Those sonic characteristics will be impacted by the capacitance of the cable--first of all the cable's capacitance will act like a low pass filter rolling off high frequencies perhaps audibly if the the cable run gets long enough or the cable itself is of high enough capacitance; second the inductance of the pickup, resistance of the pot and the capacitance of the cable together form a resonanting circuit with a resonant peak at a certain frequency..the higher the frequency the brighter the guitar/amp will sound; add more capacitance to the cable and you will tune the resonant frequency lower making your system sound darker. Those sonic characteristics will also be changed by changes to the relationship between the source impedance of the guitar and the input impedance of the amp. Electric guitar output impedances are complex and variable, changing with frequency played for example. But in general you want the input impedance to be at least 10X the source impedance or you'll start to get signal loss, perhaps a rolling of the high frequencies, in short "tone suck."

Ok, so what happens when you plug into stomp boxes. Well, first, you're adding length to the cable run (plus you're adding plugs and connection points) so you're adding a bunch of capacitance. This is going to effect your tone. Second, it can also be possible that you're plugging into a stomp box that has a low input inpedance--say a vintage wah or fuzz or Univibe clone--which will most likely have the effect of darkening your sound and/or reducing its overall power.

So, how do you overcome this? Well, first use low capacitance cables. (I use Gepco XBand which is 22 pF/ft, on par with super high end cables for $37/15 ft). Second, use the shortest possible runs of cable with the fewest possible plug/jack connections. Third, run your pedals true bypass if possible to avoid tone suck from impedance mismatches. Fourth, if you're running buffered bypass pedals (or if and when you have more than one pedal on at a time) make sure they're set in a signal chain order so that the input inpedance of device B is at least 10X the output impedance of device feeding it. Finally, if necessary, run buffered bypass pedals, a buffered looper or some kind of buffer at the front and possibly back of your signal chain--immediately after the guitar and immediately before the amp. A buffer is a circuit that changes impedance so it will take the guitar's complex variable impedance in, and send out to following devices a constant, low source impedance.

Buffering can create its own problems. First, some effects--like vintage style fuzzes, vintage style treble boosters or even vintage wahs--work best by interacting with the guitar's variable electrical characteristics. If you put them behind a buffer they won't do everything they're supposed to do. Second, some buffers are more sonically transparent than others. But buffering is a way to avoid the tone suck that results from impedance mismatches.

Personally I run all my vintage style effects--wah, treble booster, fuzz, vibe--ahead of any buffers on my pedal board, I make sure they're all true bypass (which sometimes requires modification) and when I'm using the wah into the fuzz I buffer the output of the wah to avoid impedance mismatches there. It still doesn't sound quite as good as jacking direct into the amp with a short cable, but it's pretty darn close.
 
Last edited:

Loop-Master

Member
Messages
3,516
Well, the answer to this is always "it depends."

A guitar with passive pickups, a volume pot, and a cable connected to a amplifier with a typical input inpedance of 1 megohm or higher will have certain sonic characteristics. Those sonic characteristics will be impacted by the capacitance of the cable--first of all the cable's capacitance will act like a low pass filter rolling off high frequencies perhaps audibly if the the cable run gets long enough or the cable itself is of high enough capacitance; second the inductance of the pickup, resistance of the pot and the capacitance of the cable together form a resonanting circuit with a resonant peak at a certain frequency..the higher the frequency the brighter the guitar/amp will sound; add more capacitance to the cable and you will tune the resonant frequency lower making your system sound darker. Those sonic characteristics will also be changed by changes to the relationship between the source impedance of the guitar and the input impedance of the amp. Electric guitar output impedances are complex and variable, changing with frequency played for example. But in general you want the input impedance to be at least 10X the source impedance or you'll start to get signal loss, perhaps a rolling of the high frequencies, in short "tone suck."

Ok, so what happens when you plug into stomp boxes. Well, first, you're adding length to the cable run (plus you're adding plugs and connection points) so you're adding a bunch of capacitance. This is going to effect your tone. It can also be possible that you're plugging into a stomp box that has a low input inpedance--say a vintage wah or fuzz or Univibe clone--which will most likely have the effect of darkening your sound and/or reducing its overall power.

So, how do you over come this? Well, first use low capacitance cables. (I use Gepco XBand which is 22 pF/ft, on par with super high end cables for $37/15 ft). Second, use the shortest possible runs of cable with the fewest possible plug/jack connections. Third, run your pedals true bypass if possible to avoid tone suck from impedance mismatches. Fourth, if you're running buffered bypass pedals (or if and when you have more than one pedal on at a time) make sure they're set in a signal chain order so that the input inpedance of device B is at least 10X the output impedance of device feeding it. Finally, if necessary, run buffered bypass pedals, a buffered looper or some kind of buffer at the front and possibly back of your signal chain--immediately after the guitar and immediately before the amp. A buffer is a circuit that changes impedance so it will take the guitar's complex variable impedance in, and send out to following devices a constant, low source impedance.

Buffering can create its own problems. First, some effects--like vintage style fuzzes, vintage style treble boosters or even vintage wahs--work best by interacting with the guitar's variable electrical characteristics. If you put them behind a buffer they won't do everything they're supposed to do. Second, some buffers are more sonically transparent than others. But buffering is a way to avoid the tone suck that results from impedance mismatches.

Personally I run all my vintage style effects--wah, treble booster, fuzz, vibe--ahead of any buffers on my pedal board, I make sure they're all true bypass (which sometimes requires modification) and when I'm using the wah into the fuzz I buffer the output of the wah to avoid impedance mismatches there. It still doesn't sound quite as good as jacking direct into the amp with a short cable, but it's pretty darn close.

Couldn't have said it better myself.
 

stinkfoot

Member
Messages
6,138
Yes - excellent description! Although it might be a little long for some (which is exactly the way I tend to write :D)

I love the tone of my amp when I plug straight in. But when I have some stomp pedals in, I notice the tone suck. How can I over come this?
It depends on the specific pedals you have and the cables etc. If you lose treble, it can be because you don't have any buffers in the chain, and then add a second long cable (from pedalboard to amp). It could also be that you have pedals that steal treble in bypass mode ("hardwire" bypass) or you may have a volume pedal with a tuner in the tuner out. And of course, it may be any combination :)

Are true By-Pass effects the way to go or some kind of buffer, loop pedal of some sort?
The solution depends on the problem (as above). If you list your pedals, we could probably point you in the right direction.
 

Zim

Member
Messages
1,973
The solution depends on the problem (as above). If you list your pedals, we could probably point you in the right direction.

Well, That is the thing, what I have I am planning on purging and getting new ones. Maybe I should start a thread on that. A list of great true by-pass and maybe helping me choose some new ones.
 

chervokas

Member
Messages
6,839
Well, That is the thing, what I have I am planning on purging and getting new ones. Maybe I should start a thread on that. A list of great true by-pass and maybe helping me choose some new ones.

Well, there are tons of true bypass pedals manufactured today. Like I said, how it all will work in your rig--and whether or not you'd benefit from buffering--depends on the capacitance of the cable you're using, the length of the cable runs, the number of pedals you're using, etc. And most, but not all, pedal manufactures make input/output impedance specs available. So with a little knowledge its pretty easy to put together a pedalboard that doesn't suck tone (especially if you use low capacitance cables). Chances are you're going to wind up with some pedals that are TB and some that are buffered bypass so you'll just have to take a little care in setting up your signal chain.

It mostly gets tricky if you have many many effects and/or a bunch of vintage effects which can require modification. I have an old Arbiter Wah Face that I love and which has sentimental value, but it was a huge tone sucker in bypass but I needed it in front of my chain for sonic reasons, not behind a buffer. So I switched in a new switch w/ TB wiring. I also added a switchable buffer circuit to the output so that when I use it in a chain with a vintage style germanium fuzz it has a sufficiently low output impedance. These were simple mods (I didn't build the buffer circuit, I bought it from Area 51) anyone with a little soldering experience could do.
 

chervokas

Member
Messages
6,839
Get a buffer and put it first in line.:D

This is often offered as conventional wisdom but it's not always the best choice. Like I said before, certain kinds of effects work part of their mojo by interacting with the guitar's output, they basically become part of the guitar circuit. If you put 'em behind a buffer they won't work the same way. And if you run just two or three TB pedals with short runs of low capacitance cable you may not really benefit much from a buffer at all. So, like I said, it always depends on the entirety of your set up.
 
Messages
1,596
This is often offered as conventional wisdom but it's not always the best choice. Like I said before, certain kinds of effects work part of their mojo by interacting with the guitar's output, they basically become part of the guitar circuit. If you put 'em behind a buffer they won't work the same way. And if you run just two or three TB pedals with short runs of low capacitance cable you may not really benefit much from a buffer at all. So, like I said, it always depends on the entirety of your set up.
I agree, I just happen to use none of those pedals. You are correct though, case by case for sure.:D
 




Trending Topics

Top Bottom