Envelope Generator 555 Timer overheating

Thread Starter

kerigrevemberg

Joined Feb 25, 2021
4
Hi,
I'm working on a project designing a modular synthesizer. My envelope generator includes a 555 timer to control the timing of 4 parameters. Attack, decay, sustain and release. I'm using a +/-12V power supply to power the circuit and a 5v pulse to trigger the timer. Can someone offer advice as to why my lm555n timer is overheating almost as soon as I turn the power supply on?:) any advice is appreciated. this is not my schematic, I found it online with little explanation. I'm still an engineering student!ADSRschematic.JPG
 

dl324

Joined Mar 30, 2015
12,786
Welcome to AAC!
Can someone offer advice as to why my lm555n timer is overheating almost as soon as I turn the power supply on?
Does the circuit work? There's an error around C1 that will prevent Q2 from working correctly.

Is the 555 known to be good?
this is not my schematic, I found it online with little explanation. I'm still an engineering student!
If you're studying electronics, this is an example of how NOT to draw a schematic.

Circuit intent is obscurred by using a brain dead timer symbol. Good ones will have the inputs primarily on the left and the output on the right to facilitate the preferred left to right flow in the schematic.

We don't draw wires over components.

The ground symbol always points down.
 

Thread Starter

kerigrevemberg

Joined Feb 25, 2021
4
Hi,
Thank you for the advice! This is my first project without much supervision so I really appreciate your input. I tested my 555 timer using a simpler testing circuit and have verified that it does work. Can you further explain the error of C1?
 

dl324

Joined Mar 30, 2015
12,786
Can you further explain the error of C1?
The low side of C1 is connected to ground. The reset pin is also connected to ground which means the timer will always be in reset mode. Reset is also connected to the collector of Q1. The base of Q2 will have a high impedance pull down to ground. That pull down is so weak that Q2 might switch randomly from electrical noise (i.e. line frequency).

clipimage.jpg
 

Thread Starter

kerigrevemberg

Joined Feb 25, 2021
4
My goodness, I just realized C1 is incorrectly connected to pin 4. This is the schematic I sent to the PCB manufacturers so this very well might be the issue. I can't believe I overlooked that for months! I will research ways to alter PCB traces at home. Thank you for your help.
 

AlbertHall

Joined Jun 4, 2014
11,217
Connecting the reset pin to ground will certainly stop the '555 from working but it won't make it overheat. There must be some other problem.
 

Thread Starter

kerigrevemberg

Joined Feb 25, 2021
4
Connecting the reset pin to ground will certainly stop the '555 from working but it won't make it overheat. There must be some other problem.
I have yet to find the issue. I've fixed the overheating issue but my output waveform isnt what i want it to look like and my potentiometers seem to have no effect when adjusted
 
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