Mad Professor - Snow White Auto Wah  [traced]

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Re: Mad Professor - Snow White Auto Wah

Postby Nocentelli » 20 Mar 2011, 20:59

Yep, I've got 2n5457s in mine and it works fine.
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Re: Mad Professor - Snow White Auto Wah

Postby Nocentelli » 20 Mar 2011, 21:04

Nocentelli wrote:Yep, I've got 2n5457s in mine and it works fine.


Sorry, meant to say I've got a 2n5457 nfet: I also subbed BC109cs for the BC550s and it works great.
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Re: Mad Professor - Snow White Auto Wah

Postby crguti » 28 Mar 2011, 11:55

great thread. nice work guys.

Is there any available mod to this pedal?
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Re: Mad Professor - Snow White Auto Wah

Postby roseblood11 » 28 Mar 2011, 19:19

A reverse sweep would be really useful. I used that very often in my tonepad- version of the MXR envelope filter
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Re: Mad Professor Snow White Auto Wah [gut shots]

Postby sevinisthenumber » 29 Mar 2011, 06:57

DimebuGG wrote:PCB layout...

Hey... I just cant get this to work. I have checked all that is possible. Is there any known issue here?
"The man who says he knows everything will never know the truth"
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Re: Mad Professor Snow White Auto Wah [gut shots]

Postby ckyvick » 29 Mar 2011, 08:10

sevinisthenumber wrote:
DimebuGG wrote:PCB layout...

Hey... I just cant get this to work. I have checked all that is possible. Is there any known issue here?

Dimebugg's pcb(whatever the latest version was) has been verified working by a few people, I freaking love mine :thumbsup
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Re: Mad Professor - Snow White Auto Wah

Postby mysticwhiskey » 29 Mar 2011, 08:55

Ditto, I made mine using Dimebugg's layout and have no problems at all.
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Re: Mad Professor - Snow White Auto Wah

Postby bigmufffuzzwizz » 30 Mar 2011, 06:31

Thanks hbo's for your awesome vero layouts!
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Re: Mad Professor - Snow White Auto Wah

Postby seedseed » 26 May 2011, 12:47

Have any bass players out there tried this on bass to know how it responds i have heard some say its not good and others say its great on bass so iam confused as to wheather it is worth my time to build it or not :hmmm: I know they have released a bass snow white auto wah but as usual there is never any information on the bass one only the guitar one but i would appreciate any information anyone has on it. I don't think its just resistor changes as filters in most things if you know your filter theory need the value of capacitor changed as the reactance changes for different frequency ranges 1/2 pie resistor capacitor. But how to apply that to this circuit has me puzzled. Anyone Who has a bass one and would share some guts shots that would be fantastic. :thumbsup
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Re: Mad Professor - Snow White Auto Wah

Postby roseblood11 » 18 Jun 2011, 12:50

Can I run this pedal with a 12V DC supply? Would it work properly?
Maybe the 58L05 could get to hot?
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Re: Mad Professor - Snow White Auto Wah

Postby marshmellow » 21 Jun 2011, 00:40

The 5V section of the circuit draws next to nothing, so no problem at all. :wink:
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Re: Mad Professor - Snow White Auto Wah

Postby John3 » 21 Jun 2011, 14:23

I have a question about the 5 volt section. I had a mislabeled NTE 977 , turns out it was a 950 12 volt. So I sent more than 5 volts to the 13700 and everything else. Replaced the bad regulator with the correct one and the pedal works but does not get he same quack as some people's demos. So I am asking if there is anything in this circuit that would be fried buy this. The 13700 says that the supply voltage is 18 volts but the input voltage is 5 volt and my knowledge here is not that deep so any help would be great.

Thanks,

John
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Re: Mad Professor - Snow White Auto Wah

Postby handlefras » 22 Jun 2011, 10:54

Just built this using DimebuGG's pcb. Thanks, great layout and a good sounding circuit. One question, what is the function of the cap labelled 100n on the pcb layout diagram (goes between the output of the 5V reg and ground)? Maybe this was mentioned somewhere in the thread, but I can't find it for the life of me.
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Re: Mad Professor - Snow White Auto Wah

Postby Ice-9 » 22 Jun 2011, 17:52

John3 wrote:I have a question about the 5 volt section. I had a mislabeled NTE 977 , turns out it was a 950 12 volt. So I sent more than 5 volts to the 13700 and everything else. Replaced the bad regulator with the correct one and the pedal works but does not get he same quack as some people's demos. So I am asking if there is anything in this circuit that would be fried buy this. The 13700 says that the supply voltage is 18 volts but the input voltage is 5 volt and my knowledge here is not that deep so any help would be great.

Thanks,

John


The 5v regulator in this circuit is to set a voltage around the bias control and rectifier stage that is a steady voltage when the battery voltage varies. With the associated circuitry around the this part or the circuit the control voltage send to the LM13700 is about 1.65v which varies slightly with the attack of the guitar being strummed. a 12v regulator would not work as your battery only has 9v anyway but it should not cause any damage at all.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?
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Re: Mad Professor - Snow White Auto Wah

Postby tuck » 29 Aug 2011, 15:30

Thank you Dimebug for the layout! I finished it a few weeks ago and it's just awesome.
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Re: Mad Professor - Snow White Auto Wah[gut shots,schematic,

Postby devastator » 31 Aug 2011, 12:51

ckyvick wrote:
devastator wrote:The signal goes into the filter whitout being changed (like a fixed wah ) .

Are you sure its not how you have it set? because it does a fixed wah too. if not it sounds like your wiring


Just a little back on that , actually I found the layout and see that a diode was wrongly placed. Works good now.

But seems a bit hard to set properly the circuit like mad proffessor says on his website. You have to be soft on pots . Really different than the Doctor Q I built .
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Re: Mad Professor - Snow White Auto Wah[gut shots,schematic,

Postby Nocentelli » 31 Aug 2011, 20:15

devastator wrote:But seems a bit hard to set properly the circuit like mad proffessor says on his website. You have to be soft on pots . Really different than the Doctor Q I built .


I've found this - There's a simple mod to improve the sensitivity posted at guitarpcb.com - I'll have a look for it - You just reduce a resistor value...
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Re: Mad Professor - Snow White Auto Wah[gut shots,schematic,

Postby my7of9 » 01 Sep 2011, 13:06

Nocentelli wrote:
devastator wrote:But seems a bit hard to set properly the circuit like mad proffessor says on his website. You have to be soft on pots . Really different than the Doctor Q I built .


I've found this - There's a simple mod to improve the sensitivity posted at guitarpcb.com - I'll have a look for it - You just reduce a resistor value...



Here are a couple Mods with an explanation from our site (GuitarPCB.com) which some really seem to favor.


Install a 1N34 germanium diode in D6 and a 1uf electrolytic cap for C8 and the thing really came alive.Sounds much funkier clean and before a light overdrive it cops a great Garcia-Like tone.

In Regards to adjusting R18 as well as much more here is the explanation.

R18 mod - short answer - increasing R18 will allow you to set the Sensitivity more towards the 12 o'clock position. I'd go with a 47kΩ resistor here. The only advantage is being able to turn the signal down a bit further (50% to 0% is better than 20% to 0%) at the expense of turning the signal up (20% to 100% is better than 50% to 100%)

I hope the following will give people a general idea of what is happening in the circuit:


Image


The circuit can be broken down into five main blocks:

Input buffer stage (blue) a high impedance input to get as much guitar signal as possible going into the circuit and a low impedance output to drive the next two stages.


State variable filter (yellow). Without getting too techie, this is the part that goes "Wah". If you are interested, look at the application notes (Google NE5517 or LM13700 data sheet) - warning !! this can be rather boring for normal sane people.


While we need to keep the signal going into the State Variable Filter (yellow) quite low, a slightly higher level signal might be needed for the envelope follower stages (green, pink and lilac).


The "green" stage boosts the signal, the "pink" stage converts the signal into a DC voltage, the DC voltage is proportional to the signal coming from the "green" stage - higher signal level, higher DC voltage level.

The DC voltage output of the "pink" stage drives the transistors in the "lilac" stage into producing a control current (more DC voltage at the base of Q2 means more current), the control current, which is connected to pins 1 and 16, tells the State Variable Filter (yellow) how much it should "Wah".


Since the question is about R18, a quick look at the "green" stage might be in order.


Nothing more than a gain stage. The gain is determined by whatever the Sensitivity pot is set at divided by the value of R18.

If the pot is set to 50% rotation, the resistance value of the pot (for a 100kΩ linear pot) is 50kΩ. Divide 50kΩ by 20kΩ - the value of R18 - and you have a gain of 2.5. If the input signal is 100mV, the output signal is 250mV.


So how did I arrive at a value of 47kΩ in the short answer ?


It would appear from many posts that setting the Sensitivity pot at the 9 o'clock position gives good results.

Since "9 oclock" is about 20% rotation, the value of the Sensitivity pot will be about 20kΩ.

The gain is therefore pot value divided by R18 which is 20kΩ / 20kΩ giving a gain of 1.

If I set the pot to 50% rotation, the pot value is now 50kΩ and if I change R18 to 50kΩ (47kΩ nearest standard value), the gain is 50kΩ / 50kΩ which is also a gain of 1.


It is possible to leave the value of R18 as it is (20kΩ;) and change the pot to a 47kΩ pot and still achieve the same results.


There is one other mod possible - called "side chain" which allows you to place effects such as fuzz and distortion before the auto wah and achieve good results. The only disadvantages are that you will require a simple buffer / splitter circuit (if you have got a Tonmann ParaMix available from GuitarPCB.com you won't need the extra circuit) plus you will need enough space on the enclosure to install another jack socket.

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Re: Mad Professor - Snow White Auto Wah

Postby Nocentelli » 03 Sep 2011, 10:38

Many thanks for that breakdown, i love my swaw and built the guitarpcb board as a paint-by-numbers exercise - Worked first time, which was brilliant considering this was my first go with anything more complex than a bigmuff. i've gazed uncomprehendingly at the schematic many times, so your explanation is much appreciated.

i'm planning another build, with a switchable fx loop pre-filter: if i want to use the pedals in the loop independently of the filter, do i have to wire it so the input buffer/splitter stage is permanently engaged? I don't mind doing this, btw, i wouldn't mind a decent buffer near the start of my pedal chain anyway.
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Re: Mad Professor - Snow White Auto Wah

Postby John3 » 06 Sep 2011, 00:48

I just did the R18 and Cap mods, didn't do the diode, and it is a amazing change. I always liked the pedal, but this makes it breath so much more. It gets a better quack and the knobs seem to be much more responsive overall. Thanks for the tip. :applause:
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