Swell Fuzz

[R.G.]

Change the bias of a tube makes it swell?

Sorry - do the homework first. As you find out about tube self bias, you'll also run into the curve of transconductance versus bias, and that's the answer to your gain question.

Go do the homework, then we can talk some more.

[markphaser]

Thanks for the insight R.G about the  curve of transconductance versus bias

[R.G.]

Go read about it, then come back and tell us what's happening when a tube gets an external DC voltage impressed on its grid. What happens to the gain?

[markphaser]

What is the label or name for this?

[markphaser]

because to Bais power tubes they use negative DC offset so with preamp tubes the DC offset throws off the bias

[R.G.]

It's just grid bias. Grid bias can be positive or negative. Read and see what happens with both, and then what happens to the gain as you change the bias.

[markphaser]

But Grid bais is DC offset it makes the waveform symmetrical so positive and negative cycles are not clipping

Inputing DC offset changes the Grid voltages i would think this swell circuit would make the preamp tube/stage asymetrical or clipping one half of the cycle

Whats the difference between baising a Tube with DC offset VS inputing a DC offset voltage on the Grid?
because some amp have Grib baising it seems like the same thing but whats going on is two different results
they both have DC offset on the grid so whats the difference one way its baising the other way is Gain curve but still
its the samething because its DC voltage on the grid so i don't see how it can operate different 

[R.G.]

Tubes operate on hundreds of volts. What happens when the input signal is tiny compared to both the plate voltage and the grid bias voltage?

[markphaser]

it gets ampilified

[R.G.]

it gets ampilified

Yes. The signal is too small to clip, it gets amplified.

Now relatively ... how much... does it get amplified as the DC level on the gate changes from 0 to -10V? How about 0 to +10V?

Remember that the cathode resistor is holding the cathode at about +1.5V for a typical 12AX7 preamp tube, and the grid is held at ground by the grid leak resistor. This will cause it to have a gain of about 30 if you do nothing to it. What happens if you pull the grid slowly 10 below ground? How about as you raise it slowly 10 volts above ground?
How does the gain change?

[markphaser]

Thanks R.G

does it get amplified as the DC level on the gate changes from 0 to -10V? i guess it only amplifies a certain range and not the rest

How about 0 to +10V? i guess it only amplifies a certain range and not the rest

Remember that the cathode resistor is holding the cathode at about +1.5V for a typical 12AX7 preamp tube, and the grid is held at ground by the grid leak resistor.

Cathode resistor= +1.5v
Grid= ground zero volts

What happens if you pull the grid slowly 10 below ground? +1.5v-10volts= -8.5v

How about as you raise it slowly 10 volts above ground? +1.5v+10v= +11.5v

How does the gain change? it changes the "gains range or Q point"

[markphaser]

I think the DC offset input changes the "Compression" of the tube gain?

The compression is what gives that swell sound

[seanthomas46]

Can anyone suggest any other available schematics and or projects that give the violin type swell effect sound?

[markphaser]

Ebow with a volume pedal

[Quackzed]

A swell effect WOULD be cool...hi, kinda new here but love all the creativity and patience i see here.
i'm learning some electronics through guitar effects pedals!! and getting some cool sounds too ...
   im interested in an easy way to get an auto swell effect for "non guitar" type sounds...
    what if... you amplified the signal and clipped it sending the clipping diodes to another inverting opamp and mixed the first (clipped signal) in with the inverted peaks of the second signal... wouldn't any part of the signal that is above the clipping threshold be inverted and thus cancel out the "attack" of a guitar signal..if the two were "mixed" correctly? like if the clipped peaks were of equal but opposite strength?
would it be as easy as blending the inverted peaks with the original signal? i should just try it...but i'm sure i'm missing something as i haven't seen a simple circuit that gives this effect...maybee the signal cancellation comes with baggage?!!?? ... anyway... love the posts and interest and work your all doing...
and this place is a fantastic resource for electronics enthusiasts and musicians and im sure that many people are stumbling in here from the net (like me) and leaving with  theory and tools and advice and mostly inspiration...

[markphaser]

you amplified the signal and clipped it sending the clipping diodes to another inverting opamp and mixed the first (clipped signal) in with the inverted peaks of the second signal?

wouldn't any part of the signal that is above the clipping threshold be inverted and thus cancel out the "attack" of a guitar signal..if the two were "mixed" correctly?

like if the clipped peaks were of equal but opposite strength?

would it be as easy as blending the inverted peaks with the original signal?

[nightingale]

The swell section of the Experience Pedal is the entire circuit of an early distortion pedal, one that appeared in Popular Electronics in about 1969, author of Anthony Leo.

To me,
This is some impressive knowledge.
very cool,
ry

[Jack]

....

They already did this. See gretch controfuzz
No swell effect though it does get intereting with feedback

[Quackzed]

i checked out the contro fuzz and it seems to turn up the fuzz as the clean signal fades out . i'll have to find a soundclip.. what i had in mind though was to split the signal into 2 identical signals and invert one side then use diodes to clip off the peaks of the inverted side, amplify them(just the peaks) THEN mix the amplified peaks to the other signal...
    i believe if you mix 2 identical signals and one is inverted(out of phase) they will totally cancel out .
   so if you could somehow mix just the parts of the inverted signal that are above a certain threshold back into the original signal then you could cancel out the "attack" or strongest part of the signal.you would have to amplify the inverted peaks to be the same size as the original signal peaks to "cancel them out" but it seems possible... any part of the inverted signal that didn't get clipped would not be mixed back in and would have no effect on the original signal but anything above the threshold would be of opposite phase and should, if amplified and mixed appropriately, "cancel" out the "attack"
    am i making sense?!! i'm still learning and wouldn't be surprised if my thinking here is a bit off)
still i like the idea of messing with the attack, most of an individual instruments identity is in the attack so changing the attack charicteristic of a guitar might make it sound like something else... which to me is great as i don't have the energy to learn to play everything... or do i?)
   come on... design an attack canceller... you can do it!!!   ---vvvvVVVV\/\/\/\/\/\/

[R.G.]

i checked out the contro fuzz and it seems to turn up the fuzz as the clean signal fades out

Actually, the fuzz is a constant level, and when the mixed clean signal fades away, it leaves the impression that the fuzz gets louder.

i believe if you mix 2 identical signals and one is inverted(out of phase) they will totally cancel out .

That is true, as long as the two signals are **identical** except for being inverted in phase.

if you could somehow mix just the parts of the inverted signal that are above a certain threshold back into the original signal then you could cancel out the "attack" or strongest part of the signal.you would have to amplify the inverted peaks to be the same size as the original signal peaks to "cancel them out" but it seems possible... any part of the inverted signal that didn't get clipped would not be mixed back in and would have no effect on the original signal but anything above the threshold would be of opposite phase and should, if amplified and mixed appropriately, "cancel" out the "attack"

That's good thinking, and you get an A for creativity.

There is one problem. It's impractical to separate the parts of the signal above some threshold as being the attack. "Attack" referrs to the overall envelope of the signal loudness, not to a certain part of the signal waveform. If you clip off the extra height to use in cancelling part of an inverted wave, it works all right - but it only cancels the clipped off part, leaving you with the original signal heavily distorted.

It is possible to invert and cancel the whole waveform, backing off on the "cancellation" part of the mixing to let the original signal come through, but that is exactly the same process of smooth gain change that you'd have to do with the original signal, only inverted in time. So if you can smoothly change the gain on the inverted signal, you might as well do that smooth gain change on the original and not have to do the invert/mix operations.

The "Slow Gear" attack decay works well for removing attack transients.