buffer useful after a long cable?

[sfprint]

Sorry this is not exactly specific to building. I'm trying to get around a live sound issue of muffled guitar tone vs a realistic solution. This guitarist I travel with plays with his amp about 20 feet away from him on stage with a series of several pedals. The big problem is that he requires two long cables, one from the pedals to the amp and the other from the guitar to the pedals. The reason he needs a long cable from the guitar to the pedals is that he has to walk back to the amp often to adjust the settings. He also uses 5 different guitars during the show, so buffering each guitar doesn't seem like a great idea. Does it make sense to have a buffer as the first pedal in the chain, after the first 20/25 foot cable just to keep the signal from degrading through the pedals and back to the amp? Is there any other solution while staying wired?

[alanlan]

First of all get him to buy decent cables, especially guitar to first pedal.
20 ft isn't that bad, if you said 60 ft then may be a problem
If you use a buffer it really needs to be at the guitar end which is a bit of a problem since he likes to be 20 ft away from his first pedal.
I can't imagine why anyone would have an amp 20 ft away when it needs adjusting between songs, practical measure might be do away with the 20 ft gap

[R.G.]

Most effects have a low impedance output, at least compared to a guitar, so most of the treble loss is coming from the first cable, I suspect. Most pedals have a high (ish in some cases) input impedance, so most of the damage is done in the first cable.

+1 for getting low capacitance cables, but putting a buffer at the guitar will give you the right answer to driving long cables.

A guy at the office sent me a really funny link. We make a buffer unit in a quite-small box for buffering signals, but one of the guys found the reverse thing. There is a company that is making a small, on-the-guitar-strap **load** for loading down the guitar and getting rid of all that sharp, biting, excess treble that buffered pedals can cause, and let you get back to the nice smooth/brown tone you know and love.   

Sure enough, if you read the advertising blurb, it's adjustable, completely passive (NOOOO BATTERIES!!  ) and fits a guitar strap. Yep - it's a metal box with a pot and two jacks in it. At least they had the integrity to NOT claim it was vintage, hand wired, point to point, tropical fish, carbon comp, solid silver, found in Atlantis, yada, yada, and charge $400 for it. 

I'm sure that there are some guitarists that like it. One man's fish is another man's poisson.

[CynicalMan]

Sure enough, if you read the advertising blurb, it's adjustable, completely passive (NOOOO BATTERIES!!  ) and fits a guitar strap. Yep - it's a metal box with a pot and two jacks in it. At least they had the integrity to NOT claim it was vintage, hand wired, point to point, tropical fish, carbon comp, solid silver, found in Atlantis, yada, yada, and charge $400 for it. 

With one more part, I can make one that works WITHOUT A CABLE! 

Of course the price would be 33% more...

[ashcat_lt]

A guy at the office sent me a really funny link. We make a buffer unit in a quite-small box for buffering signals, but one of the guys found the reverse thing. There is a company that is making a small, on-the-guitar-strap **load** for loading down the guitar and getting rid of all that sharp, biting, excess treble that buffered pedals can cause, and let you get back to the nice smooth/brown tone you know and love.   

Most guitars have at least one of these built in.  None of mine, but most...

There's always the JFET Buffer Cable.  I think a couple different people are selling these out there, but it's quite a simple build.

[boogietone]

Go wireless.

[sfprint]

Thanks everyone. I will certainly look into the buffer cable.

[Gus]

A buffer would be an simple thing to use.  A buffer can be placed in a a small shielded  box and you could use a clip to hold the box to the guitar strap and use a short cable from guitar to box.

Now an possible overlooked design issue with buffers is they can become unstable with a capacitive load(the guitar cable) so a simple fix could be to add a resistor in series with the output.  A resistor in series with the output will also help with some effects.

A buffer can be something like this add a series output resistor.
http://www.diystompboxes.com/smfforum/index.php?topic=90701.0

or a opamp based one or a JFET based one or a JFET BJT or a tube or a.............

If you use a buffer you might want to add a cap from buffer input to ground to simulate the cable length(cable capacitance) the guitar player likes.

[amptramp]

You can build the buffer into the cable and you only need a standard shielded single conductor cable to do it.  This topic has come up before:

http://www.diystompboxes.com/smfforum/index.php?topic=91237.0

with the best design here:

http://www.till.com/articles/PreampCable/index.html

and transistor comparison here:

http://www.hawestv.com/amp_projects/fet_preamp/fetpreamp1.htm

[Mark Hammer]

A built-into-the-cable buffer is handy in that it can be applied to any guitar one wishes, and involves no modification to the guitar itself.

The smallness of it, and ability to be packed into the plug housing, is dependent on the power source being located elsewhere.  So, the plug itself would be standard mono at the gutar end, but be a stereo (2 conductor + shield) cable with a stereo plug and jack at the pedalboard end.  The plug would go into a box that simply provides "phantom" power, whether by battery or use of a tap from your power supply.  Alternatively, the circuit gets built into a small strap-on box that the player wears.  The cable/plug from box to guitar is standard, as is the jack/plug/cable from box to pedalboard. 

The purpose of the buffer is to fight the challenges posed by a long cable.  The cable from the guitar to a worn box is short, so having the supply and buffer circuit in here is, electronically, not a hell of a lot differen than having it in the guitar or plug; a few inches of cable isn't changing anything...unless it is really bad cable.  The distance the power source has to travel, in the case of the Tillman active plug, matters not, since the buffering is done essentially at the guitar.

I've mentioned in past that the very first JFET buffer I ever built was in 1976, and it was built into the dental cement "headcap" of a rat in a research lab.  It was about the size of a jellybean or small wine gum, and sat perched atop his skull like a fez.  Just like the Tillman preamp, the purpose was to fight what the very long cable between animal and electrophysiological recorder normally did to the micro-volt level brain activity signals, and the power was provided remotely.  It loked pretty much like what you see here:  https://www.aalaslearninglibrary.org/demo/course2.asp?strKeyID=32969062-C27C-4635-9855-D12610836275-0&Library=10&Track=11&Series=1229&Course=245&Lesson=6283

[B Tremblay]

I've mentioned in past that the very first JFET buffer I ever built was in 1976, and it was built into the dental cement "headcap" of a rat in a research lab.  It was about the size of a jellybean or small wine gum, and sat perched atop his skull like a fez.

Did that buffer have enough headroom? 

[amptramp]

The smallness of it, and ability to be packed into the plug housing, is dependent on the power source being located elsewhere.  So, the plug itself would be standard mono at the gutar end, but be a stereo (2 conductor + shield) cable with a stereo plug and jack at the pedalboard end.  The plug would go into a box that simply provides "phantom" power, whether by battery or use of a tap from your power supply.  Alternatively, the circuit gets built into a small strap-on box that the player wears.  The cable/plug from box to guitar is standard, as is the jack/plug/cable from box to pedalboard. 

If you check the www.till.com drawing, the shielded two-conductor cable is not strictly necessary.  There is a ground and a drain connection.  It may be better with a separate shield, but it may not matter or may actually be worse - the voltage at the guitar end of the shield is different due to the current through the source.  Using the shield as the source return may be OK and this may enable standard cables to be retrofitted.  If not, there are always stereo cables.

[Gus]

If you use a buffer you can lose the interaction of the cable capacitace if you do not add a cap to sim the cable.  I simmed a buffer with 3 values of cable sim about 0pf(green) 470pf(blue) and about 980pf(red) at C6.
I used 47pf a foot as the cable cap and a simple one pickup volume at max guitar sim .3VAC drive.



If you use a JFET buffer you might want to add a cap from gate to ground to sim the cable length and type you like.

I just picked 1k for R6 and 1uf for C4 you can move them up and down in value.

That is a bootstrapped EF circuit in the sim.

note the sim is with the guitar volume control at max

[ninjadave7]

I agree with boogietone, go wireless.  I've been working professionally with live touring bands for a long time and there isn't any appreciable difference in tone with a pro wireless setup, especially by the time it gets through the whole guitar rig and out a PA, or into IEMs.  One pack on the belt, plug in and go with every guitar...