HackWah2

[Kipper4]

I've been messing with the breadboard again.

Here's what I came up with

https://imageshack.com/i/nll7nxj

Please note that the series 1M from pin 5 of the TL072 goes to Vb of the power supply and NOT Gnd.

I decided to add a gain recovery stage using the second half of the TL072 because I felt it was below unity without.
Although you can leave this out and just tap the output straight from pin 1 of the TL072.

My brief was to create a starting point for a simple low parts envelope filter using common values and stock items.
Credit to RG and BYOC
Let me know what you think suggested, improvements are always welcome.

Rich

[PRR]

> Let me know what you think

I think it can't work as shown. Biased to slam the opamps to rails. Since you say it does, I assume these are transcription errors.

Also- you feed the filter from the jack. The filter input impedance can be as low as 30K (or worse). If I understand the intent of IC1-B, it is unity-gain buffer and could feed the filter without heavy load on guitar.

The 1Meg in the Inverting input of inverting stages just adds hiss. Replace with zero (or 10-100 Ohms if you need a jump). (Yes, *DC accurate* opamps may use a compensating resistor, especially if they are bipolar. But yours are FET and also there's no DC accuracy needed here.)

The output needs a blocking cap.

The sidechain gain-stage IC1-A probably wants to know where pin 3 should sit (true, for high levels it may work just floating/slapping around).



EDIT: input to IC1-A can just come straight from IC1-B, no C no R.

[Kipper4]

Thank you Paul
you are indeed correct there where some transcription errors.
Although now i must try it with the guitar signal going to the filter through the buffer as you have suggested.
I realised after I posted late last night that i had forgotten the output cap at the output but it was late. Too late to correct and repost.
Back to the breadboard me thinks when I finish work. Besides your changes I have a few more things to test.
I appreciate your time and effort and patience and the fact you drew me a diagram.
Thanks again.
Rich

[Blitz Krieg]

have you considered the state variable filter?

[duck_arse]

it looks, kipper, as though your "auto set junction" option is not set in eagle. if you ever do a board layout from that circuit, nothing will be connected.

[Kipper4]

Haha DA
I keep meaning to reinstate it.

I have since redrawn the schemo but am still in the process of development so it maybe a while until i get it done.
I'm in the middle of setting up a new to me pc and lots of other work commitments but stay posted.
I'll be back with more qauck than you can throw a ducks arse at.
Time to go

[mac]

I don't like how IC2_A works. A plot is LTSpice shows "reverse" or "mirrored" cry baby curves, peaky in the highs, flat in the lows.
I'd try something different, a single transistor a la Colorsound Inductorless Wah, a SVF as noted above or gyrating C10 and C11, but you want simplicity...



mac

[Kipper4]

i have a number of filter models to trial and funnily enough the transistor type twin T is one of them thanks for the recommendation
also included is the MFB op amp filter and the SVF.
as soon as I can I'll be back to the breadboard and thanks for the sim mac.

[mac]

The twinT, ie Colorsound, is a bit tricky too. Curves has the shape of a cry baby's, but they are not of the same height. A minor cap change fix this issue.
See my post about the Colorsound Wah in the Spice forum.

Talking about the SVF, I made a very cool wah with it. I'll post it soon.

mac

[Kipper4]

Cheers Mac I think I already read that one
20 or 22nf IIRC C4
this is going to be the first one on the BB

I can't wait to see what youve come up with too

[Kipper4]

The bjt  twin T sounds good i tried it on the breadboard I had to adjust the wah input resistor from 33k down to 100ohm
I think i'll try the SVF next and try to tap the bandpass out put first.
I'll try to get time to do an eagle schematic with the Twin T and post it up
cheers guys

[Kipper4]

Here's what I did with the twin T
I hope I haven't made any transcription errors this time
With hindsight I might have reduced R10 to a lesser value


https://imageshack.com/i/n1tb9uj

Here's the corrected schematic for my earlier experiment too
Thanks PPR

https://imageshack.com/i/mvfve0j

[mac]

Use the SFV wah I posted and your EF 

mac

[Kipper4]

Here's two versions with the SVF

Although I may have to adjust the voltage divider to drive two nsl32s


https://imageshack.com/i/n1hr0ej

[duck_arse]

your R18 appears to be shorting itself on that diagram. I have an envelope you might be interested in, kipper, single supply, up and down, NO diodes, drives leds. let me know.

I'm currently driving myself nuts by using both eagle and diylc on the same day. and on a half completed-setup linux box.

[Kipper4]

Thanks eagle eye. I'll sort R18
I'm always.up.for more envelopes pm me please DA.

[Kipper4]

I managed to make the SVF on the breadboard tonight despite how tired I am.
I'll test it in the morning if I get time.
Thanks DA nd RRing.

[duck_arse]

(every time I see "SVF", I think "SRV". how annoying.)

[Kipper4]

Haha I know what you mean

[Kipper4]

Update
I'm still struggling to make the SRV (SVF) work somehow.
when it did make some noise eventually, it was distorted and started to feed back. Grrrr not the outcome i expected.
So I've tidied up the breadboard rebuilt and am ready for another round of trials tommorow night if i get time.
Oh and I swapped the TL074 SRV (SVF)for LM324
Using Macs SVF and this trial will also invole 2 vactrols If I can manage to drive them both to light up.

Edit
I have one question though.
I'm guessing that r4/r5 voltage divider is there to help stabilise supply voltage to the led side of the vactrols.
Will adjusting the values of this voltage divider help me get the right voltages needed to drive two vactrols.
I ask because since the diode comes before it. The voltage won't affect the bias or output voltage of the ic before the diode.