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Hello,
Maybe this is a stupid question, i don't know, but i've just breadboarded an Axis Fuzz face and with the 1K fuzz pot wired to the 15uf cap it creates a kind of tone roll off as i turn the fuzz down. I'd quite like to have the option to wind the fuzz back but it just sounds all crap and wolly when reduced. I've noticed this is a pretty standard set up on all the fuzz schems i've looked at but no fuzz i've ever played through has rolled the tone off as you reduce the fuzz. Is it normal for it to do this?
axisfacesi3schematic.gif (7.25 KiB) Viewed 5531 times
Also, i got a bag of BC139 transistors but they don't seem to be working in my circuit. I'm using a BC108c at Q1 and a 2N3936 at Q2 which sounds pretty good to me but curious why the 139's won't work...are they too low gain?
Thanks a lot
Patrick
That "Attack" control would be configured as a sort of tone control with certain values, though 15uf should be an all pass. What are the numbers printed on that capacitor?
Quick check with google indicates the BC139 is PNP while the BC108 is NPN, that would be my first guess as to why they do not work in this circuit.
Hey thanks for getting back so quickly! I'm using a 10uf cap as don't have any 15's
Also i got the transistors off ebay, they're listed as '10 x BD139 NPN Transistor TO-126 - 1st Class' though i don't have any way to check
Ah, the D does make a difference it seems. I have some higher power transistors that don't seem to work well in low level circuits. I've loosely concluded that they are there to pump current rather than voltage, so in a given implementation they wind up doing the opposite of what you would want.
Cool well thanks very much for you're help, i think i'm just going to have to learn how to measure the hfe...been avoiding maths for so long now maybe it's time i get the calculator out. There is one other thing i'm fiddling around with in this circuit but i just can't figure out how to do it (though i think it's actually quite straight forward). If i place a cap (1nf for arguments sake) from base of Q1 to collector of Q2 i get a pretty cool squealing noise. I've been trying to hook up some kind of switch or pot so that i can have the circuit running normally and then either flick a switch or turn a pot to blend in the squealing. The guitar just about cuts through so thought it would be cool to have as something to bring in and out. Hopefully that makes some sense and also sorry for bringing something completely different up!
In a common emitter section, the signal relationship between input at base and output at collector is inverted 180 degrees. So when you take signal from Q2 and inject at input of Q1 you're in polarity and feedback ensues. A series resistance can temper it (and to a small degree alter the resonant frequency), and changing cap size will raise or lower the "knee" (tune) of the path. I would recommend a switch to bring it out of circuit, because even a large pot will affect the response of the circuit.
Ok great, would it just be a simple as wiring one side of the switch to collector of Q2 and the other to the base of Q1?
Thanks so much for your help, i'm really looking forward to getting this one built now!
Sorry to keep banging on in this thread but the more i play around with this circuit the more i find that i want to do (but inevitably don't have the knowlege) So i'm pretty happy with how this is all sounding now. I've got switch wired up between the base of Q1 and collector of Q2 which selects a 68pf cap and 500k pot wired in series. It's a cool sound, a hint of ring mod and envelope filter (though i know technically it's neither). My question is whether it is possible to use some kind of noise gate to cut out the whine in between playing. It sounds great in the background whilst playing notes but once they ring out the feedback takes over and it would be nice if i could set a gate to eliminate it. 1) Is this possible? 2)...How the frig? I can upload a crappy video if it'll help you know what the hell i'm banging on about
Thanks again!
depends how functional or simple you want the gate to be. you can do it with a resistor but it would change the sound and you might not want that. you can do it with diodes but you might not like it. you can put a gate circuit on the front. ultimately though, a high gain pedal and a high gain amp will never stop ringing out as it has a total loop gain > 1. in that case, the noise gate will do nothing until you actually mute the strings to activate the gate. an intelligent feedback eliminator like the ISP decimator or the waves soundgrid intelligent feedback eliminator plugins will do this. they basically look at the waveshape, harmonic content, envelope (or lack of envelope) to determine if you are a guitar player or a noise musician who should be muted.
Well i'd like to give it a shot with the diodes or resistor, just see what happens/what it sounds like. It's not the end of the world if i can't do it, just thought it would be a cool thing to try
Thanks for your reply!
I'll give this a go tomorrow and get back to you! It's like 2 in the morning here and as much as i'm dying to do it right now my flatmates would hook me up to the mains
crochambeau wrote:What happens when you stick a small value capacitor across the 100K resistor?
maybe better to put it at the base and emitter of Q1 47pf instead. this will determine the bandwidth. I don't think it will gate the noise. for that I would put a 500K trimmer from Q1 base to ground. there is a sweet spot on the trimmer that fixes noise without changing the sound much.
another option is the diode gate, put germanium diodes side by side then put that entire thing in series with the input capacitor. this will mute all guitar signals and also radio signals smaller than +/- 0.2v
