Author Topic: Reduce the thump sound from a analog drum circuit  (Read 1999 times)

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Offline nathanpc

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Reduce the thump sound from a analog drum circuit
« on: June 05, 2016, 07:17:29 pm »
I've been thinking about building a drum machine for quite some time. To start things out I decided to look for some of the basic circuits that are required for it, so I stumbled across this circuit and decided to try it out. It does produce a very convincing sound. This is the circuit I've prototyped on a breadboard:



The only difference is that I'm using a LM358 opamp and the input is a push button with a 10k resistor to ground and a 10k resistor to the 9V rail, but I'm having a bit of a problem (or maybe the circuit is supposed to be like this and I'm just being dumb), as you can see are are two very loud thump sounds when I press the button and when I release it, what can I do to remove, reduce or improve the circuit to have a better drum sound?

 

Offline sync

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Re: Reduce the thump sound from a analog drum circuit
« Reply #1 on: June 05, 2016, 07:57:57 pm »
You need a short pulse on the input. Maybe 1ms. When using a single supply the input should be about V+/2 with the short pulse to V+ or ground.
 

Offline nathanpc

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Re: Reduce the thump sound from a analog drum circuit
« Reply #2 on: June 05, 2016, 08:46:36 pm »
Oh! Thanks very much sync! That solved the problem it's now working great!
 

Offline Zero999

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Re: Reduce the thump sound from a analog drum circuit
« Reply #3 on: June 05, 2016, 09:00:24 pm »
Yes, you were saturating the op-amp too.

How are you generating the short pulse? You could try a piezo transducer or a monotstable+ switch.

The LM358 isn't the best opamp for this because it suffers from crossover distortion.
« Last Edit: June 05, 2016, 09:04:56 pm by Hero999 »
 

Offline nathanpc

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Re: Reduce the thump sound from a analog drum circuit
« Reply #4 on: June 05, 2016, 09:08:20 pm »
Hero999, for now I'm using a PIC with a super simple program to turn on a MOSFET for about 1ms when I hit a switch, but the finished project will be controlled all from 7400/4000-series logic and a huge amount of switches.

I'm using the LM358 just because it was the first thing I saw on my bench haha, in the final design I'll probably use the LM833 since I have a massive amount of them.
 

Offline sync

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Re: Reduce the thump sound from a analog drum circuit
« Reply #5 on: June 05, 2016, 10:29:05 pm »
Btw: the real 808 drum voices using more complex circuits. For example the base drum. TRIG is the trigger shared with all voices. It's a positive pulse. When an accent is played the amplitude of TRIG is higher. BD selects the base drum. See the TR-808 service manual for more information.
 

Offline amyk

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Re: Reduce the thump sound from a analog drum circuit
« Reply #6 on: June 06, 2016, 04:26:08 am »
I thought drums were supposed to make a "thump" sound. :D
 


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