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Technical Topics => Equipment => Topic started by: Strange Beacons on January 07, 2018, 0137 UTC

Title: Question re placing an audio capacitor on a small speaker
Post by: Strange Beacons on January 07, 2018, 0137 UTC
I have built a DTMF tone generator following this guide (http://www.emdrc.com.au/vk3er_-/wp-content/uploads/2017/08/DTMF.pdf) that I found online.

In the construction section of the guide, the author recommends soldering a 4.7mF capacitor to both of the speaker's negative and positive terminals.

Can anyone explain to me what the purpose is of having that capacitor in place? Does it improve the sound quality? Or does it do something else? (I've got the tone generator built and it works great, but the sound quality is slightly tinny).

And my apologies if this post is placed in the wrong section of the board. I looked and didn't see an area that was less about radios in general and specifically for electronics.

Thanks,

Curt / W9SPY
Title: Re: Question re placing an audio capacitor on a small speaker
Post by: Azimuth Coordinator on January 07, 2018, 0152 UTC
Looks like it's used for wave shaping
Title: Re: Question re placing an audio capacitor on a small speaker
Post by: Strange Beacons on January 07, 2018, 0231 UTC
Quote from: Azimuth Coordinator on January 07, 2018, 0152 UTC
Looks like it's used for wave shaping

Wave shaping, as in sawtooth, sine, and square?
Title: Re: Question re placing an audio capacitor on a small speaker
Post by: ThaDood on January 07, 2018, 0300 UTC
             Another thought (It didn't hurt that bad.), is the 4.7uF CAP across that speaker maybe a crude LPF (Low Pass Filter.) There maybe some oscillator clock hash that maybe audible at the speaker, and this is a quick way to suppress that. I'm just speculating here, but I've seen it done in circuits where that's happened, and this is a quick way to remedy that.
Title: Re: Question re placing an audio capacitor on a small speaker
Post by: Strange Beacons on January 07, 2018, 0310 UTC
Quote from: ThaDood on January 07, 2018, 0300 UTC
             Another thought (It didn't hurt that bad.), is the 4.7uF CAP across that speaker maybe a crude LPF (Low Pass Filter.) There maybe some oscillator clock hash that maybe audible at the speaker, and this is a quick way to suppress that. I'm just speculating here, but I've seen it done in circuits where that's happened, and this is a quick way to remedy that.

Thanks. The guide says that the capacitor is "used to round off the generated square waves." So that sounds like the capacitor will help to generate more of a smoother, sine wave-type sound.