Bring down noiselevel in amz mosfet boost

[hilbi]

I recently built a 2nd amz foost for my bandmate, he wants to use the amz mosfet boost to bring up his strat to the same volume as his les paul.

The volume level is working fine only he complaints that his signal has become more noisy when using strat with amz mosfet boost turned on, escpeccially when he is also using his overdrive.

When he is using the boss eq to boost up the volume of his les paul his signal has much less noise.

Is there a way to bring down the noise in the amz mosfet boost?

[boogietube]

Get noise cancelling pickups for the Strat. If it's got stock single coil pickups,they're inherently more noisy than humbuckers. I had the same problem so I changed pickups-noise gone.

[hilbi]

but when he is using the boss eq to boost up the volume of his strat his signal has much less noise.

[boogietube]

MMM

[Dragonfly]

i havent checked the GE7's schemo, but theres a good chance that Boss added some noise filtering in there....the AMZ mosfet boost, in itself, is "dead quiet"...it only boosts signals that are *already* present in the chain, at least in my experience.

AC

[hilbi]

i think indeed that there is noise filtering in the ge-7 wich makes the difference.

The mosfet boost itself is quiet, but only in extreme circumstances (single coil and before overdrive pedal) teher is some noise wich isn't there with boss ge-7.

is there a schematic for noise filtering?

[zachary vex]

reduce R3 to 1M and change all resistors to metal film.

[petemoore]

  try it with nothing on the gate..unplug the input and see how much noise happens then..

[Plectrum]

Is the strat a stock fender guitar?
I know some copies can have low output unit's which are intrinsicaly noisier, and you'd have to boost 'em that much more to get the right level.

The noiseless strat unit's are getting better all the time and a good ones will sound 90% like a real single. Good enough for most.

Grant.

[JHS]

Check some BS170 and use the quitest, the noise/hiss level can vary a lot on MOSFETS.

JHS

[hilbi]

reduce R3 to 1M and change all resistors to metal film.

Thanks, i will try this option first and see what it does.

BTW are there any schematics for a noise filtering circuit? Something that is probably applied in the GE-7.

[amz-fx]

Change R3 to metal film but leave it as 10M.  Don't change any of the others to metal film as that wil not make much difference.  The pedal should be stone-quiet, but like any booster, it will amplify noise already existing in the signal path.

Make sure the guitar volume is turned up all the way.   Running the guitar volume less than max makes for a more noisy signal.

regards, Jack

[hilbi]

Thanks jack, oK i will try the R3 only first.

The mosfet boost is quit, but only in front of an od pedal (barber direct drive or boss od) with single coil guitar there is quite a lot of noise at least compared to a eq pedal boss ge-7.

[zachary vex]

you'll have to string up a bunch of high-value metal film resistors to make 10Mohms, because the highest value i've seen available is 2.2M.  my most recent mosfet booster design (in the box of rock) has an input impedance of about 1M and the "sparkle" isn't dramatically lowered... but it does sound more like an amplifier's input than an effect, and the hiss is quite a bit lower.

[R.G.]

You guys do know that you can bootstrap the input bias from the source and get an effective input impedance of way OVER 10M with resistors 1M and under, don't you?

[Jay Doyle]

You guys do know that you can bootstrap the input bias from the source and get an effective input impedance of way OVER 10M with resistors 1M and under, don't you?

I hope so. This is the way to go...

[R.G.]

It's also possible to bootstrap the input bias from *another* source if you are using a fully-bypassed source.

[zachary vex]

you can bootstrap from a the source/emitter of any unity-gain stage, but not from one with gain higher than 1.  the source/emitter will only be of use as a bootstrap if it can provide a signal that is "almost equal" to the input.  a famous bootstrap is used on the phase splitter circuit from the univibe.  in RG's own words, ...there is a capacitor from the emitter that connects to the biasing string of 100K/47K.  This capacitor from the emitter to the biasing voltage point is a "bootstrap" capacitor that, in conjunction with the 100K resistor to the base of the actual transistor, raises the input impedance to very high levels. It does this by applying the signal from the emitter, which is almost equal to the input signal, to the other end of the 100K biasing resistor.

[puretube]

.?.

[R.G.]

Let me add my confusion. Huh?

Of course you can bootstrap from any unity gain stage. You an also bootstrap from a more-than-unity-gain noninverting stage if you pad the output down to below unity to keep it Nyquist-stable. That goes without saying.

But what I meant was this:

The gain of every source follower is the same to a first approximation - unity minus a gnat's eyelash. If you have a situation where you'd otherwise like to bootstrap a MOSFET input but can't because you have the source at a very low resistance to ground or fully bypassed to ground, you can do the same thing by using a second MOSFET as a source follower, and AC coupling that source to the bias supply for both MOSFETs. This will bootstrap the input resistance of both devices to a quite high level.

A bootstrap doesn't have to be driven from any specific place, just from a low impedance source that approaches but does not pass unity or over loop gain.