Is this possible

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Is this possible

Postby McHuge » 02 Feb 2013, 09:18

I recently built a treble booster with a dpdt switch that gave me the option of 2 different sounds. What I was thinking of doing was to fit 6 on-off switches that are wired in series and have a different cap on each one. In theory (or in my mind) it should give me 6 individual sounds or a combination. Would this work??
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Re: Is this possible

Postby McHuge » 02 Feb 2013, 09:25

Also, I've been looking online but I can't find the answer. Whats the rule with tone caps? What I mean is what code would give me a bright sound and what would give me a bassier sound??
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Re: Is this possible

Postby Nocentelli » 02 Feb 2013, 10:52

A single 1x6 rotary SP6T switch would allow you to selct six different caps: you wire the input to the common and the six caps to the the six "throws", with the other side of each cap connected to the circuit input (e.g Q1 base). I believe you can even get 1x12, i.e.SP12T. Input caps are a form of high pass filter, frequencies below a certain point are "rolled off":The smaller the cap value, the higher the frequency of the roll-off point. This means a 1 nanofarad cap will let only quite high frequencies through and will roll-off lower mids and bass. A 10n will allow more low end, and 100n even more. Basically, smaller caps sound brighter and thinner.

I personally tend to use a small cap (e.g. 10nF) in parallel with a larger value cap (e.g. 10uF) and a pot in series (variable resistor): this adds like a simple bass or fat control, and is a lot simpler that switching caps.
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Re: Is this possible

Postby McHuge » 02 Feb 2013, 16:43

Thanks for that.

With a rotary switch, you can't blend the caps though (or can you?) My idea was to give me a choice of individual "tones" by selecting a single switch or if I selected 2 or more, their sounds would blend. I can picture the idea in my head but I'm just wondering if it would work.
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Re: Is this possible

Postby FiveseveN » 02 Feb 2013, 16:55

It wouldn't really work like that, it wouldn't "blend" the roloff frequency but you can add various values in parallel. Or select a number of "presets", but that requires a more complex control circuit.
Concepts you have to grasp:
capacitors in parallel: http://en.wikipedia.org/wiki/Series_and ... pacitors_2
RC filters: http://en.wikipedia.org/wiki/RC_filter
Bonus, useful RC frequency calculator: http://www.muzique.com/schem/filter.htm (mind the units!)
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Re: Is this possible

Postby McHuge » 03 Feb 2013, 15:56

But on the original layout, it suggests a cap loaded on off switch to add an option of mid range boost. I just though I could add on that idea to give me multiple options. The switch that I have installed is an on-off-on with different caps and I now have 2 different options.
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Re: Is this possible

Postby Nocentelli » 03 Feb 2013, 18:12

McHuge wrote:But on the original layout....


What original layout? Show us a schematic/diagram of the actual circuit, and we can comment.

An input cap on it's own will only vary the low-end roll-off: Adding two of them in series (as per your original idea) reduces the total cap value, since total capacitance of caps in series is 1/Ctotal = 1/C1 + 1/C2 etc: Two 10n caps in series = 5n. Adding them in parallel sums the total, so two 10n in parallel = 20n. To get mid boost, I suppose the simplest way would be to roll-off some low end with a series (input) cap, and roll-off the high end with a small cap to ground before or after the input cap, leaving you with the mid frequencies more prominent.
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Re: Is this possible

Postby FiveseveN » 03 Feb 2013, 18:21

An on-off-on switch gives you three options. A schematic would have been useful but let's take the following example:

caps.png


SW1 is an on-off-on type though not properly represented here because GM's library doesn't have that symbol. Anyway, in the "off" (middle) position, pin 2 would be left open. That means the signal only passes through C1. C1 and R1 form a high-pass filter with a roll-off frequency of 1600 Hz, so pretty much only the treble is passed.
When you flip the switch to connect pins 2 and 3, you put C2 in parallel with C1, giving you a total capacitance of 4 nF. That makes the roll-off frequency about 400 Hz, so now mids also pass through.
In the other position, pins 2 and 1 are shorted so C3 is now in parallel with C1, yielding a total capacitance of 11 nF and a frequency of 144 Hz. If you make C3 100 nF the frequency would be 16 Hz and so on.
Use Jack Orman's calculator to check.

If you had individual switches to add C2 and/or C3 in parallel you'd have four options:
C1 alone (both switches open) = 1 nF, 1600 Hz
C1 and C2 (one switch closed) = 4 nF, 400 Hz
C1 and C3 (the other switch closed) = 11 nF, 144 Hz
C1, C2 and C3 in parallel (both switches closed) = 14 nF, 114 Hz
And that's how my suggestion would work. Notice how the options don't offer a "blend", just more capacitance in parallel, which means a lower roll-off frequency.
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