Why are mu amp pedals (BSIAB) much more noisy then tube screamers?

[rgm]

Is the gain on the mu amp pedal so much more then a tube screamer pedal it is much more susceptible to noise?

[BAARON]

Comparing a stock BSIAB2 to a stock Tube Screamer: yes, the amount of gain available from the BSIAB2 is much higher.  When you aren't playing, it's still applying all that gain to the noise from your guitar (and from thermal and active components in the pedal itself) and amplifying it to a very loud level.

A stock TS doesn't have nearly as much gain as a stock BSIAB2 running full tilt.

[Ed G.]

I propose that the BSIAB is no more noisy than a TS.
Try this: Turn on the BSIAB to your normal settings. Plug in your guitar and turn the guitar volume all the way down.
What noise do you hear? If anything, you hear a little hiss. That's the noise the pedal circuit is responsible for.
When you turn up your guitar, if you hear hum, it's not the pedal generating it. It is only amplifying the noise in your guitar.
That's why I take issue with people saying the BSIAB is "noisy." For the amount of gain it generates, it is incredibly quiet.

[Paul Marossy]

When you turn up your guitar, if you hear hum, it's not the pedal generating it. It is only amplifying the noise in your guitar.

As is the case with a whole lot of high gain pedals out there.

[Processaurus]

I'd noticed the couple mosfet pedals (mosfet boost and red llama) I made seeming noisy for what they do...

[R.G.]

A lot of MOSFET input pedals have very high input impedances and do not roll off highs much either before or after the distortion/limiting. This leaves any amplified hiss in the signal. The tube screamer has a high frequency rolloff that cuts some of the amplified hiss.

[rgm]

Interesting response from RG, does that mean putting in a filter would remove hiss... or else remove desired signal frequency content?

If do able, what parts and where in a bisab?

[GibsonGM]

As a quick guess, try some very low value caps, 1 at a time, from input to ground - on the order of 10, 100, 470 pF and see how things sound....that will roll off very high freq's before they can be amplified...if you go too high in value, you will notice a loss of 'sparkle' and have to back off....

[R.G.]

Interesting response from RG, does that mean putting in a filter would remove hiss... or else remove desired signal frequency content?

Capacitors don't know if what they remove is signal or hiss. It's all frequency to them.

[realizewhoitis]

Interesting response from RG, does that mean putting in a filter would remove hiss... or else remove desired signal frequency content?

Capacitors don't know if what they remove is signal or hiss. It's all frequency to them.

I really want a reason to say this to someone. great quote

[WGTP]

Would trying different jfets and selecting for low noise help.  I guess the ideal combination would be high gain and low noise. 

[Paul Marossy]

A lot of MOSFET input pedals have very high input impedances and do not roll off highs much either before or after the distortion/limiting. This leaves any amplified hiss in the signal. The tube screamer has a high frequency rolloff that cuts some of the amplified hiss.

Interesting. That must have been the problem with Joe Davisson's original "Obsidian Overdrive" using 2N7000s. It sounded really good, but the hiss was almost too much to really be useable.

So, what can be done about that? Small value pF caps to ground on the input(s) or something like that?