How about a built in guitar buffer?!

[sajy_ho]

Hi guys, hope you're fine. Anyone here who experienced long guitar cables and the how they affect the whole sound, probably is thinking about this idea.
I'm thinking about a buffer with low parts count that could fit in a strat's jack hole:
Also something with low power consuming. Becouse the source would be a guitar (in my case a strat with pickups that can deliver maximally about 500mV p-p), a simple jfet or bipolar buffer will be the best choice:http://www.beavisaudio.com/techpages/Buffers/
So what do you think? Please share your thoughts.
Thanks
Sajad

[Gus]

This has been done before it has been posted about at this forum and other places.
A search here and at GEOFEX and other places should find buffers or boosters

http://alembic.stores.yahoo.net/blaster.html

If you search you might even find buffers built in cable ends

[Mark Hammer]

Like Gus says, not a particularly revolutionary idea, but still a VERY good one.  The only thing I would suggest is, if this is your only, or primary guitar, include some means to fully bypass the buffer.  Some circuits benefit from the high impedance of the guitar's passive electronics and high output impedance, and you don't want to have to forfeit that.

[R.G.]

Here's one designed specifically for the issues brought up here.
http://www.diystompboxes.com/smfforum/index.php?topic=102719.0

The problem with onboard electronics is always how to power it.

[diydave]

If you search you might even find buffers built in cable ends

Check till.com where their is an idea about a pre-amp in a guitarcable.
But with some minor changes, you can make a buffer instead. I've build one and use it all the time.
The problem with building it in your guitar (which I did initially), is that it's a pita for the screwholes. Over time, they wear out by srewing and unscrewing for changing the battery.
And it's rather embarrasing to do a surgical procedure on your guitar whilst on stage because you've forgot to refresh your battery. 

[jubal81]

Here's a link to my shared project:
http://www.diystompboxes.com/smfforum/index.php?topic=106832.0

I just built a second one with my new favorite opamp (OPA1642) and running it at 18V. Works great.

[sajy_ho]

Thank you all guys for helpful answers, and also sorry for bringing back an old idea
I have only two remaining questions about this circuit:
1. what is the minimum violtage that I can run this circuit on it? (for example a j201 with Vp of 0.8V)
2. How can I calculate the current draw of the circuit, and how the value of R2 will affect it? I've seen different values for that resistor in other schematics (4k7, 10k, 33k...)
Thank again

[R.G.]

I have only two remaining questions about this circuit:
1. what is the minimum violtage that I can run this circuit on it? (for example a j201 with Vp of 0.8V)

That's not a good idea. There are problems with JFETs, in that they have quite wide variations in Vp. The MPF102, for instance says that Vgs will be between 0.5V and 7.5V at a drain current of 200uA. That's huge - a range of 15:1. Since the gate is held at 0V, the source could possibly be at any voltage up to the Vgs as long as the Idss current is not being exceeded. So for an MPF102, you probably can use that circuit, as most of them will be somewhere in the middle between 0.5 and 7.5V. For a J201, the Vp may be as small as 0.1V. So the source may bias at 0.1-0.2V, and it would be easy for even a strat single coil to overload it.

This gets to being even more of an issue when you start trying to use less than 9V to power it.

2. How can I calculate the current draw of the circuit, and how the value of R2 will affect it? I've seen different values for that resistor in other schematics (4k7, 10k, 33k...)

You can calculate the curerent draw as Vs/Rs. That brings up the problem from above in that you have to know what Vs is for your particular JFET, which varies not only between JFET types (i.e. J201 to MPF102) but also by about 5:1 or worse for a particular TYPE of JFET. So the correct answer to this is - you can't. You can *estimate* it as being less than Idss for the JFET type you use, but in practice you're going to pick a JFET, try it out, and replace it with another one if you don't like the voltage and current that results.

There is a reason that the industry doesn't like JFETs.

[sajy_ho]

I have only two remaining questions about this circuit:
1. what is the minimum violtage that I can run this circuit on it? (for example a j201 with Vp of 0.8V)

That's not a good idea. There are problems with JFETs, in that they have quite wide variations in Vp. The MPF102, for instance says that Vgs will be between 0.5V and 7.5V at a drain current of 200uA. That's huge - a range of 15:1. Since the gate is held at 0V, the source could possibly be at any voltage up to the Vgs as long as the Idss current is not being exceeded. So for an MPF102, you probably can use that circuit, as most of them will be somewhere in the middle between 0.5 and 7.5V. For a J201, the Vp may be as small as 0.1V. So the source may bias at 0.1-0.2V, and it would be easy for even a strat single coil to overload it.

This gets to being even more of an issue when you start trying to use less than 9V to power it.

2. How can I calculate the current draw of the circuit, and how the value of R2 will affect it? I've seen different values for that resistor in other schematics (4k7, 10k, 33k...)

You can calculate the curerent draw as Vs/Rs. That brings up the problem from above in that you have to know what Vs is for your particular JFET, which varies not only between JFET types (i.e. J201 to MPF102) but also by about 5:1 or worse for a particular TYPE of JFET. So the correct answer to this is - you can't. You can *estimate* it as being less than Idss for the JFET type you use, but in practice you're going to pick a JFET, try it out, and replace it with another one if you don't like the voltage and current that results.

There is a reason that the industry doesn't like JFETs.

WOW man! I wish I has your electronic knowledge, but unfortunately I'm a nurse and way much away from that 
I once measured Vp and Idss of all of my single jfets around and wrote it on them, so what type of fet is the best choice for that application? low Idss and Vp or high?
Thanks