4093 quad oscillator project - question

[spectreman]

hello all,

i'm building a quad-oscillator pedal/synth as shown here:

http://getlofi.com/shop/4093-quad-oscillator-kit/

my question is, what value capacitors can i swap into the design to get the lowest possible frequencies?

i'm new to this stuff, so i'm unsure which capacitors in the initial design to keep, and which ones to swap out and play around with for low tones...

here is what comes with the kit:

2 x 1uF Capacitor
1 x 47uF Capacitor
2 x 10uF Capacitor

if you have any suggestions, let me know!

thanks!

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[PHOBoS]

spectreman

without a schematic I can't really tell but judging from the components my guess is that it probably has 2 modulated oscillators.
The ones responsable for the tone use the 1uF capacitors which you could lower a bit but too much will just result in
a clicking sound. And they are probably modulated by oscillators build with the 10uF capacitors.
It might be nice to actually use 4 different capacitors, with one set having a low frequency with slow modulation and the other
set having a higher frequency with a faster modulation. You could even make it patchable for more options and add a switch
to choose between different capacitors.

IMHO the GETLOFI kits are overpriced and you're better of with a breadboard and some components to play with.
This will teach you more about why it's doing what it does and how to adjust it to your liking. Of course a kit is the
easiest way to get something working in a short time. But I would advice you to take a look at the lunetta section.


(note: I moved this thread to the general DIY section of the forum)

[spectreman]

hey thanks! that helps a lot.

i also got a suggestion to use 1M pots instead of the 1ooK pots (the 1M pots will make it 10 times slower).

so, the kit comes with (4) Reverse logarithmic Pots.

can i use 1M single linear taper rotary pots for the swap? i'm guessing they will work backwards from the reverse logarithmic pots...correct?

OR do i have to use logarithmic taper pots as opposed to linear taper...

thanks again!

[PHOBoS]

You can replace the pots with 1M which will indeed give you a wider range but it will also make it harder to 'tune'.
I'm somewhat surprised they supply it with reverse log pots, not that it's bad, on the contrary it works the best
and it's what I use most of the time for these kind of oscillators. If you use a standard linear pot what happens
is that most of the rotation will control the lower frequencies while all the higher frequencies are at the end.
A reverse log pot will spread it out more evenly. If you would use a standard log pot it would be even worse,
but the direction is not affected.

You could use standard log pots and use them backwards by soldering them on the other side of the PCB
but than the direction will be reversed.


edit: here is a bit more info with a nice graph of the different pot. kinds. (lin/log/rev log)

[spectreman]

OK - so i decided to go with a rotary switch and add a series of different value capacitors for different tones. a few questions since i'm new to this:

1. do i just use a single pole 12 position switch?
2. what capacitor position on the board do i connect the switch to? (there are 5 unique cap positions on the board)
3. any suggestions on a range of capacitor values?
4. do i need to mess with resistor values when i do this?

thanks for any help. i'm sure this is all common knowledge to most of you, but any help from you helps me understand how this all works.

thanks!

[PHOBoS]

[spectreman]

Thanks for the reply!

so, i attached the front and back of the board (please excuse the beginner solder job).

i'm going to go with a 2 pole 6 position switch for now, i also attached a drawing of how my brain is understanding the circuit...am i thinking about this correctly?

please let me know what suggestions you have as far as range of capacitors go. i'll keep switch position (1) as the initial 1uf and 10uf that is noted on the board, and raise cap values for switch position 2 through 6.

really, thanks for your help. it's a bit intimidating, but a lot of fun.

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[spectreman]

wait...i'm making this too complicated i think.

on the board, the 10uf caps modulate the 1uf, right? so i just need the switch i'm adding to go to the (2) spots labeled 10uf.

i think this new drawing is correct...

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[PHOBoS]

[spectreman]

ok! i think i got it this time...

really, thanks for the help! i think i will go with 2 switches & if you have suggestions on caps to use, i'm all ears!

thanks a ton.

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[PHOBoS]

yes that's it
It's not that your previous version wouldn't have worked, but it's more common to connect all the - sides together
and because all the capacitors on the board have them connected too you will only need 1 wire for all of them if you do
it this way. (so that's 5 wires in total). I hope to do a test later today or else this weekend and I'll let you know my findings.

[PHOBoS]

ok I just did some tests with it. Good thing I looked at the BOM pdf on the GetLoFi site or I wouldn't have known
that those diodes are actually zenerdiodes, which makes some difference in sound. It actually wouldn't even produce
any sound if those where standard diodes without adding an extra resistor.

so here's how I would connect up the switches, which gives you the following settings.

MODULATION SWITCH:
1) 47uF + 47uF
2) 47uF + 10uF
3) 10uF + 10uF
4) 10uF + 1uF
5) 1uF + 1uF
6) 1uF + 100nF

AUDIO SWITCH:
1) 10uF + 1uF
2) 1uF + 1uF
3) 1uF + 100nF
4) 100nF + 100nF
5) 100nF + 10nF
6) 10nF + 10nF

there are still some duplicate setting:
M.switch 4 + A.switch 2 = M.switch 5 + A.switch 1
M.switch 4 + A.switch 3 = M.switch 6 + A.switch 1
M.switch 5 + A.switch 1 = M.switch 4 + A.switch 2
M.switch 5 + A.switch 3 = M.switch 6 + A.switch 2

but this will give you a very wide range.

note: the 100nF + 10nF capacitors aren't actually polarized so it doesn't matter which way you connect them

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[spectreman]

oh man...you rule!

perfect.

i have to order some parts, but i'll post a photo when it's done. thanks a million for all the help...i appreciate your instruction and help more than you can imagine.

[PHOBoS]

you're welcome
and it made me design a little NAND noise maker myself. (No I didn't copy the GetLoFi design )

Looking forward to see and hear the result.

[spectreman]

[PHOBoS]

Honestly I can't tell without testing it. I only once used a zenerdiode in a circuit like this and that was actually by accident. A happy accident though
In this circuit I think they might produce somewhat of a stepped voltage.

If I just look at 2 oscillators then when both are high the output will be roughly 9V (a bit less because of the voltage drop across the diodes).
when 1 is high and 1 is low the voltage should be around 4.7V and when both are low the diodes are blocking it, but because the ouput is
connected to GND through a resistor it's probably 0V. So instead of having an output that is either 0 or 9V you'll get an extra voltage halfway
in between. So if you use zenerdiodes with a different voltage for each oscillator you might get more variation.
This only what I think is happening, I could be wrong.

1Watt zeners will probably work but a zenerdiode needs a certain current flowing throw it to properly work so I can't really tell how much
that would affect it.

[spectreman]

hey there again...

on you schematic, where you say "to + side of 10uf capacitor", you mean to the + side of where it is labeled on the getlofi board, correct?

i'm not actually going from the switch to a capacitor on the board, just to where a capacitor used to be on the board, right?

[PHOBoS]

yes, you got that correct.