I call it Twang Banger but I need some help

[jneely]

http://img78.photobucket.com/albums/v255/JNEELY/twangbangerrev1.jpg

This was based off of the 360 degree phase circuit from the same national app notes that the mini booster app note was taken.

It sounds like a vari-tone in a box but.... when driven after another pedal like say over drive it sounds as if it gets loaded down.

If I put a resistor in series with the input it loses ALOT of the intended effect.

Any ideas?
:roll:

[Jay Doyle]

Man I don't know. It shouldn't load anything down, the input imped. is high.

The only thing that I can think of is because you are taking the output from both the source and the drain, each "side" has only 1/2 V+ worth of headroom.

Could it be parasitic capacitances?

Wish I could help more, sorry mr. neely.

Jay

[smoguzbenjamin]

Have you tried adding a FET buffer or something similar in front of it? That might sort some things out.

[puretube]

dunno the intended effect, nor vari-tone, but that Cs (1µF) hurts my feelings...  :cry:

[puretube]

Have you tried adding a FET buffer or something similar in front of it? That might sort some things out.

or tried a cap at the input?
any pedal with resistor-to-ground (or pot...) will ruin the 1st. Q`s bias...

[smoguzbenjamin]

Good point!  

[gez]

Jay may be onto something, perhaps it's being pushed into saturation with a larger input signal (probably wouldn't notice this if the signal is a distortion).  

Could you post voltages for sources and drains?  It's easy to fix if this is the problem.

Doesn't need a buffer Ben as the input impedance is pretty decent.

[gez]

Ignore me, PT strikes again!  

[smoguzbenjamin]

Sorry gez, my first solution is 'add a buffer to see if it helps' since I have one or two lying around with nothing to do so it's easy to stick in front :mrgreen:

[gez]

No problem Ben, didn't mean to be impolite or anything!  

Output cap is missing too...

[jneely]

It sort of cuts and adds bass so to speak. It gets trebley on one side and fuller on the other. It doesn't get the noise(hiss) of your std treble boost. But it's not really boosting I guess.

I'll have to try a cap in front it slipped my mind to try it.

Think of the old gibson varitone guitar circuit but picture it without the loss of vol in some settings.

It could also be like setting a wah in posistion and using that. However it's not as colored as a wah.

Imagine if the wah put your signal out of phase .

I'll try the cap thing and I'll post some voltages shortly.

Jeff

[R.G.]

It's a fixed position single notch phaser minus any LFO or dry blend.

Suggestions:
(1) as mentioned, use an input cap of 0.1uF or so and another 3.3M to ground outside the input cap.
(2) arrange for a switchable blend of the dry signal at the output of that source follower to make it into a real notch when you want.

[puretube]

that big cap at the source of Q2 shorts all signal* to ground, so Q2 doesn`t "shift" too much, it just inverts...

*except deep bass

[jneely]

Well after reading the replies since I went to experiment I think I may be off base.

I added the .1 caps on the in and out but this caused a great loss of volume.

So I changed the source resistors to pots adjusted measured and inserted fix resistors in place.

http://img78.photobucket.com/albums/v255/JNEELY/twangbanger2.jpg

These values allowed the 1M to be almost equal from "bass" to "treble" end.

It distorts a little. I'm wondering if I should reduce the overall gain of the circuit and add a booster after to bring it back up.

RG , should I still place another 3.3m in front of the in cap?

Thanks Guys
Jeff

[gez]

Source and drain resistors need to be equal, this is a phase-splitter.  Personally, I'd replace the 3.3M and 1M bias reistors with a 10k pot across the rails and attach the wiper to the gate via a 1M resistor (signal couples via cap directly to gate).  This will allow you to get bias right.

As PT mentioned, the 1u cap in the second stage prevents it from acting as it should.  Again, make source and drain resistors equal and use a dual-gang pot to replace the 10k resistor (second half of pot to do the honors for the 1M pot in first stage).

As RG metioned, you need to blend in the dry signal to get a notch and for it to act as a 'varitone' type circuit.

[puretube]

gez: this time I wanted you to be first  

[gez]

PT, no please, after you!  

[gez]

Jeff, might be an idea to take a look at RG's article on phasers and flangers over at GEO.  That should give you a better understanding of what's going on.

edit.  click on the 'Technology of' link at his site (top left, I think).

[jneely]

If I remove the 1uf it loses gain.

I realize the circuit should have equal source and drain but it doesn't do anything much when they are.


The 10k resistor was intentional also. I wanted that fixed to where i liked it.

Jeff

[gez]

If I remove the 1uf it loses gain.

Try doing the gain with the third stage instead (add drain resistor and bypass source - source resistor is a tad large by the way).

I realize the circuit should have equal source and drain but it doesn't do anything much when they are.

It won't unless you blend in the dry signal at the output to get cancellation (read the Geo article I mentioned).

The 10k resistor was intentional also. I wanted that fixed to where i liked it.

Better to use a dual-gang pot.  Once you mix in the dry signal, you'll hear the benefit.