C3 is supposed to be .1 uF not 10 uF on the schematic sorry for the mistake. I am trying to create a synthesizer with a single 555 timer chip using the schematic I uploaded (it's a modified version of this). I want it to be modular (I think that's the right term for it) so I can add resistors and buttons at C3 to make different noises. For some reason the timer itself keeps getting hot and stops working properly and has to be replaced with another one, which ends up doing the same thing. I am fairly new to circuits and was wondering if there is something I should change with the circuit to prevent this from happening. I'd also like to know what the resistors and capacitors in this are actually there for. Thanks!

 

8 ohms is too low a resistance for a load on a 555 output. Besides being poorly drawn, this is a serious flaw in the schematic you started with. Change to a 32 or 60 ohm speaker like what is used in some headphones, or use a small audio output transformer.

Separate from that, a 555 output cannot swing very close to its Vcc, so the peak-to-peak output voltage will be only around 3 V. A CMOS 555 is better, but its output stage can handle even less current that a bipolar 555.

ak

 

8 ohms is too low a resistance for a load on a 555 output. Besides being poorly drawn, this is a serious flaw in the schematic you started with. Change to a 32 or 60 ohm speaker like what is used in some headphones, or use a small audio output transformer.

Separate from that, a 555 output cannot swing very close to its Vcc, so the peak-to-peak output voltage will be only around 3 V. A CMOS 555 is better, but its output stage can handle even less current that a bipolar 555.

ak

I don't mean to challenge what you're telling me but all the schematics I've seen online use an 8 ohm speaker. Is there something that I'm doing different that would require using a higher resistance speaker? Also sorry for the poor schematic drawing.

 

My comment about the schematic was directed at "the schematic you started with", not yours.

Many hobby sites copy stuff from other hobby sites, so one bad idea can be widespread. The 555 has output current and power dissipation specs on the datasheet. You can use them to calculate the minimum load resistance that is safe for the device. Note that if you run a solid state device at or near its ratings, it will greatly decrease its life. The standard rule of thumb is to halve / double everything. A 12 V circuit needs 25 V capacitors. A 1 amp load needs a 2 amp transistor. An output rated for 200 mA should not have to deliver more than 100 mA. Etc.

ak

 

My comment about the schematic was directed at "the schematic you started with", not yours.

Many hobby sites copy stuff from other hobby sites, so one bad idea can be widespread. The 555 has output current and power dissipation specs on the datasheet. You can use them to calculate the minimum load resistance that is safe for the device. Note that if you run a solid state device at or near its ratings, it will greatly decrease its life. The standard rule of thumb is to halve / double everything. A 12 V circuit needs 25 V capacitors. A 1 amp load needs a 2 amp transistor. An output rated for 200 mA should not have to deliver more than 100 mA. Etc.

ak

So the problem my circuit is having is that it's drawing too much current, correct? Would adding resistors in between output and the speaker reduce how much it's drawing?

 

I'm saying that it appears that you are over-currenting the output stage, but I have not probed the circuit or even seen its construction. Yes series resistors will decrease the output current, but also reduce the speaker volume. If that is not an issue, then ok. It is a simple thing to try and will help to diagnose the problem.

ak

 

I'm saying that it appears that you are over-currenting the output stage, but I have not probed the circuit or even seen its construction. Yes series resistors will decrease the output current, but also reduce the speaker volume. If that is not an issue, then ok. It is a simple thing to try and will help to diagnose the problem.

ak

Would checking how much current is coming out of output with a multimeter be a good idea to check if that's the problem?

 

I just realized that I've been using 2 8 ohm speakers in parallel. I had them set up like that for a different project and forgot. I'll try just running one with some resistors once the 555s I ordered arrive. Thanks for your help.

 

I just realized that I've been using 2 8 ohm speakers in parallel. I had them set up like that for a different project and forgot. I'll try just running one with some resistors once the 555s I ordered arrive. Thanks for your help.

Or try running both in series and you'll be able to use smaller resistor values, converting more energy into sound, and burning less of it in the resistors. I don't know how significant the difference will be, but as long as you've got two speakers there already, why not?