matt239 wrote:RLC !
2 other points:
1 - I'm thinking that,
if necessary, diodes would be as cheap/simple for protecting an op-amp as a BJT transistor and it's associated components.
Google "protection diodes" and "diode clamps" check out "
differential protection diodes" (the diodes are connected anti-parallel from inverting to non-inverting inputs.)
2 - While guitar pickups are considered "high Z" compared to dynamic microphones, they are low Z relative to our discussion here. (6k to 12k vs. our many-mega-Ohm op-amp input)
A transistor buffer would not be necessary for "impedance conversion" to present a relatively low Z to our op-amp input. - Right?
These 2 items, plus the parallel resistance of the guitar controls with our pull-down resistor, affirms for me the utility and appropriateness of connecting directly to an op-amp as our input, with a 680k to 1M pull-down resistor, 150 Ohm to 1k series input resistor, and maybe the addition of protection diodes.
...
Unless I've got everything completely ass-backwards...
which is entirely possible..
So, have I got you guys talked into this topology now?
Matt Your the one asking ,,, Not me.
No it is all very much dependent on a lot of variables.
Note* kleuck's * last post where he is down to 100k depending on what is happening. ????
Matt,,,,Go build some circuits ,,, then get back with results.
FWIW, I USE LIVE my home built equipment that gives me no great noise issues>>>
Has more treble than any guitar player would ever need>>> Has incredible sustain>>>Delivers amazing tonal options,,,,
Yet no one here is interested?
I often compete against some big name Amps at our local musicians club; Fender twins, Fender cyber Deluxe, Carvin Legacy, Line 6 Crap ,,, to name a few.
Yet
They come and Ask ME? Go Firure
Meanwhile checkout the Mesa VTwin Schematic for more clues.
Note the opamp buffer has 1 meg input yet the triode (V1 clean mode) has 220k on the grid.
Shoved in between the buffer and Valve is a 10k pot WTF?????
Again I say ,,, Go figure???
Trust me I use a circuit based on the clean channel of the V Twin and it's just a stunning unit and leaves me in no doubt that many roads can lead to the same result.
You need to build a few circuits before you get the joke,, haha.
My circuit setup is fine tuned for my own needs and will not suit everyone,,, but again I stress they come ask me,,,, not the other way round,,,,
I've learned that It pays great rewards to read between the lines.
Phil.