[sdiy] quadrafuzz ICs

[Derek Holzer]

Hi Tom,

nope, don't do this often, just started in the last year. Doing it more 
often now ;-)

Reason for single-supply is the difference between making a module for 
my Doepfer or a single-unit box that runs from a normal wallwart or 
batteries. It's mostly about packaging, and what bits I want to put 
where (and whether it all fits into my gig flightcase or I have to carry 
the Dopefer on the plane with me!). Besides that, I just don't have a 
good dual-supply wallwart. But I understand the technical limitations of 
single-supply, mostly very low dynamic range, etc. I'll think it over.

Thanks for the detailed explanation!
d.

Tom Wiltshire wrote:
> 
> On 10 Nov 2007, at 14:34, Derek Holzer wrote:
> 
>> And what about if it were single-supply?
> 
> The same. You'd need a virtual ground point in the usual 9V fuzzbox 
> style (do you do this often?!). It amounts to a voltage divider to give 
> you a +V/2 point, and a largeish capacitor from the virtual ground to 
> the true ground. All the double supply 0Vs then connect to this halfway 
> bias point instead. Essentially, you're treating the supply voltage (say 
> 9V) as +4.5V 0V -4.5V rather than 0 to 9V. What's your motivation for 
> using a single-supply? If you want a battery-powered unit, choose a 
> low-power chip that can run down to low voltages - ideally something 
> that can cope with 10V or more, but still runs down to 4 or 5V. If 
> you're not using batteries, I really would advise a +/-15V dual-supply - 
> it really does make life a lot easier with op-amps.
> 
>> I'm actually more interested in the filter section here, and the 
>> possibility of converting it to a 3 or 4 band EQ with possibility for 
>> high self-resonance via feedback through the distortion sections (i.e. 
>> reversing signal order with distortion before filter, and filter 
>> resonance sent back through distortion). TL074? LM358? Bonus points 
>> for single-supply power, of course. Need not be hifi, the sound I'm 
>> going for with it is pretty gritty.
> 
> The LM358 looks like an excellent choice for starters. Fits all my 
> parameters above: supply range from 32V down to 3V, so it won't pack up 
> when the battery is less than brand new, and the current consumption is 
> ok at 0.25mA per amp, although they've got an ultra low power version as 
> well (See the 'also recommended' on this page: 
> http://www.national.com/mpf/LM/LM358.html)
> 
> The other thing to remember is that it is easy to socket the chips and 
> then experiment. I used to do this as a matter of course for fuzzes, 
> partly so that I could experiment to see if different chips really did 
> give different sounds (and some do, especially when the batteries are 
> flagging) and also so that I could upgrade things if I found a better 
> chip. I sometimes went back and replaced chips with lower-power versions 
> to improve battery life in pedals.
> 
> Regards,
> Tom
> 
> 

-- 
derek holzer ::: http://www.umatic.nl ::: http://blog.myspace.com/macumbista
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