why 1M input on most M style amps?

[daz]

Why is it the input on most marshall style amps with cascaded gain stages have a 1M input resistor? Why not smaller?

[R.G.]

Why is it the input on most marshall style amps with cascaded gain stages have a 1M input resistor? Why not smaller?

Input jack input?
One part not loading the guitar signal down to one part 1M is the traditional tube grid pulldown value, possibly an other part of "we're sure that with 100k plate resistors, 1M won't load it much".
I guess those all distill down to "doesn't load the source down much and doesn't need much thinking".

Can you point to a schemo and the resistors? If you can, I'll gladly opine more.

[daz]

Input jack input?
One part not loading the guitar signal down to one part 1M is the traditional tube grid pulldown value, possibly an other part of "we're sure that with 100k plate resistors, 1M won't load it much".
I guess those all distill down to "doesn't load the source down much and doesn't need much thinking".

Can you point to a schemo and the resistors? If you can, I'll gladly opine more.

yeah, the 1M input jack to ground resistor. I'm just wondering because i put a 220k on a switch to paralle the 1M and create 180k to compare and it seemed like there was only slightly less gain but a more dynamic tone. With a classic rock amount of gain and the guitar on 10 I couldn't really tell a difference worth noting. But with the 180k load engaged it was much more dynamic in that i could get a wider range of dirt to clean with the vol control. I will have to play with it for some time to really know if it's better, but i wanted to see if there was some reason why i never see this in other amps.

[R.G.]

If you like the tone, do it. It knocks off a little of the high end from the guitar, but then lots of people have liked that in the past, some quite famous and well thought of.

There is at least one commercial pedal that has advertising babble talking about how wonderfully mellow, less harsh, yada, yada that the magic box makes guitar sound. Inside are two jacks, a pot and a resistor so you can dial the pot down to load the guitar pickups more.

And people pay money for it, I guess.

[J M Fahey]

Your guitar volume pot is usually 250 or 500K and the volume regulation depends on its own taper, so if it's log ... it's plain log and it will work like that into an open load, or into a *large* impedance (such as 1M).

But if you load it with a lower impedance (220K to 47K) it loads it down, specially at intermediate volume settings, so you get an "enhanced log" response, with seemingly wider and smoother range.

If so, why isn't it used often?

Because too low an input impedance "kills" pickup "character/sparkle" and as you know, "tone" is more important than "convenience".

Yet some amps have low input impedance on purpose, "to make them more controllable from the guitar pot", such as a couple Mesa Boogie "Blues" amps.

[Steve Conner]

My current favourite amp has a switch to select 1M or 100k input impedance. I've been playing it on 100k a lot lately.

[daz]

loads it down, specially at intermediate volume settings, so you get an "enhanced log" response, with seemingly wider and smoother range.

If so, why isn't it used often?

Because too low an input impedance "kills" pickup "character/sparkle" and as you know, "tone" is more important than "convenience".

Yet some amps have low input impedance on purpose, "to make them more controllable from the guitar pot", such as a couple Mesa Boogie "Blues" amps.

Thats it. It does really enhance the feel and range of the pot, and i'm a constant pot manipulator and my single channel amp goes from clean to dirt that way. So like a lot of people that use that method, it seems like a great way to go. I now see it IS knocking off some gain, but not a lot, and the high end is rounder due to some attenuation. I will have to play it in a mix and see what i think. But so far like steve i don't seem to wanna play it with the 1M anymore. But we'll see......you know how kind of thing often this goes.

[Steve A.]

My current favourite amp has a switch to select 1M or 100k input impedance. I've been playing it on 100k a lot lately.

That makes a lot more sense to me than the Hi/Lo jacks that Leo came up with using only 3 resistors (that must have saved Fender a whole bunch! ) So what do you use for a grid stopper?

I replaced the 1M grid load on one of my amps with a linear pot but I think that a switch between 1M and 100k would have worked just as well.

Steve Ahola

[pdf64]

Turning the instrument tone control down a bit (eg 7/8) acts to load the pickup and so damp its resonance somet.
Pete

[Steve A.]

Turning the instrument tone control down a bit (eg 7/8) acts to load the pickup and so damp its resonance somet.
Pete

The amount depends on the value of the cap and the taper and resistance of the tone pot. Even setting the tone control to 10 loads down the signal, usually in a good way.

I played guitar for 35 years before I ever tried turning down the volume and tone controls- I always had them set to 10! No wonder I thought that most teles were way too harsh. Not too long ago I got a tip to start off with the tele knobs set to 5 and then play around with them until you get the sound you want. I think that is the reason that tele knobs don't have numbers on them.

Steve

[loudthud]

The classic Fuzz Face has a really low input impedance and the real ones don't have true bypass so it's always loading the guitar.

[Steve A.]

The classic Fuzz Face has a really low input impedance and the real ones don't have true bypass so it's always loading the guitar.

So did Jimi run his strat into the wah pedal and from there to the Fuzz Face, or the other way around? IMO it is more interesting to run the wah before a fuzz because it seems to change the resonant frequency of the fuzz. The other way around its as though the wah pedal just cuts the highs of the fuzz. Or so I remember- its been a long time since I used either.

Steve

[Steve Conner]

I believe it is Fuzz Face into wah. It simply doesn't work right the other way around, because the classic wah pedal had an unbuffered output.

My input impedance thing was actually inspired by Fender. If I read the schematics right, plugging into the "Lo" jack puts your signal through a potential divider made of two 68k resistors, for an input impedance of 136k and a 6dB attenuation. I found this was a tonal option I liked, so I put it on a switch instead of having a second jack. I used two 47k resistors.

I still use the regular 68k grid stopper at the other end of the wire leading from the front panel to V1.

[dai h.]

I think the Fuzz Face does have true bypass (maybe the wah was in mind?). Some Jimi fans apparently think the Univibe was used as a buffer between the wah and FF. Don't know if that is true, but a buffer does seem to help the two work together better.

[Steve A.]

Okay I looked it up and this was what he used at Woodstock (lots of people would have seen his rig that day so I think that it is correct.)

Guitar>Vox Wah>FF> Univibe>two Marshall stacks

Here is a link to the web page:

http://www.guitargeek.com/jimi-hendr...setup-diagram/




Steve