MXR flanger subbing oscillator caps with a bipolar. Which changes?

[pietro_moog]

Hi guys.
I am designing my own veroboard for a MXR flanger.
I have a problem of space and i wanna substitute the two 15uF caps in the oscillator with a single bipolar cap (4,7uF).
I like the speed of the original design, what changes do i need to do?
Where can i learn about oscillators?

Thanks guys

[PRR]

It will work but will not go so slow. You can then try a 1Meg pot to make it go slow.

[pietro_moog]

I understand.
I don't know how the oscillators work, i would like to learn (but i don't know where).
I see interesting similarities between the MXR Flanger oscillator and the Small Clone Chorus oscillator, while the MXR uses 2 caps in series, the Small Clone has only one cap, and it doesn't care about the polarity.
Could i use a 6,8uf polarized cap in the same way (to achieve almost the same speed without taking a big space on the board) ?

[garcho]

These oscillators work by charging and discharging capacitors. The rate at which they charge and discharge determines the frequency of the oscillator. Change the value of the capacitor, and you change the charge and discharge rate, thereby changing the frequency of the oscillator. You cannot simply swap out caps of different values and expect a similar response (resistor values also change the rate of charge/discharge).

Basically, when you see two equal-value capacitors in series, you halve the value. e.g. 15 + 15 in series = 7.5.

The two schematics you posted are not similar enough to swap values between them, they are different circuitry.

I don't know how the oscillators work, i would like to learn (but i don't know where).

These kinds of oscillators are made out of the basic building blocks of circuitry. Start off with just basic electronics knowledge. Here are a few books and sites I recommend:

Teach Yourself Electricity and Electronics - Stan Gibilisco

Practical Electronics for Inventors - Paul Scherz

https://www.allaboutcircuits.com/textbook/

https://www.electronics-tutorials.ws

Make sure and check this out too:

https://www.falstad.com/circuit/

[PRR]

....the Small Clone has only one cap, and it doesn't care about the polarity.

The Small Clone uses a Tantalum Electrolytic. This can tolerate several volts of reverse bias (Aluminum Electrolytic gets leaky at 1V-2V). Tantalum is small, expensive, prone to explode in higher power uses, and is a "Conflict Mineral". Over the last 30 years the Aluminum Electrolytic industry has worked to improve their product and steal most of Tantalum's market.

[antonis]

https://nvhrbiblio.nl/biblio/boek/Marston%20-%20110%20Operational%20amplifier%20projects.pdf
or
https://archive.org/details/110OpAmpProjects

Chapter 4, pages 63 - 81

[pietro_moog]

Thanks guys.
I have a lot to study

[Rob Strand]

I like the speed of the original design, what changes do i need to do?

The speed or frequency of many RC oscillators depends on the product of R and C. If you make C smaller (say from 15uF to 4.7uF) then you need to make R larger by the same factor.

For the MXR oscillator that means making the pot value  larger by a factor of 15/4.7 = 3.2.  So you might have got rid of the inconvenient 15uF cap but now you have stuck with an inconvenient pot value!    Moreover increasing the pot value has some follow-on effects.   The rest of the circuit loads down the  oscillator a bit.   By making the pot bigger the loading problem is made worse.

All said and done the reason the inconvenient 15uF is there is because it's not easy to get around without affecting the circuit and having to compensate by redesigning other parts of the circuit.  (The inconvenient pot value is not resolved.   That's going to need a parallel resistor to massage the value.)

A much simpler path is to use a 10uF cap in parallel with a 4.7uF cap.  That will give you 14.7uF, more than close enough.

[Fender3D]

those caps in series have a total value of ~7.5uF....
Considering the usual 20% tolerance, you can use a standard 10uF bipolar cap and be happy enjoing the missing 0.0xx Hz, resulting in a sliiiiiiiiiiiiiightly slower LFO speed

[ElectricDruid]

+1 what Fender3D said, the original caps are 7.5uF in total.

Otherwise Rob is right - you need to think about the RC product. If C goes down, R needs to go up by the equivalent factor, and vice versa.

[Rob Strand]

the original caps are 7.5uF in total.

Thanks for catching that, I only read the text but looking at the schematic obviously the target value is 7.5uF not 15uF (and that doesn't change the funky pot value and other stuff.)

[garcho]

I also mention that at the top, whatami, chopt liver?! 

Remember, you're not tuning communications equipment!

[ElectricDruid]

I also mention that at the top, whatami, chopt liver?! 

Sorry Garcho!

In the end, we get there. You might have arrived sooner than the rest of us.

[garcho]

You might have arrived sooner than the rest of us.

For the first (and probably last) time that's ever happened!