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Electronics => Beginners => Topic started by: nathanpc on June 06, 2016, 05:17:29 am

Title: Reduce the thump sound from a analog drum circuit
Post by: nathanpc on June 06, 2016, 05:17:29 am
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 (http://mickeydelp.com/images/stories/projects/BridgedT.png) and decided to try it out. It does produce a very convincing sound. This is the circuit I've prototyped on a breadboard:

(http://i.imgur.com/DmchMFz.png)

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?

(http://i.imgur.com/7xAB0Hg.png)
Title: Re: Reduce the thump sound from a analog drum circuit
Post by: sync on June 06, 2016, 05:57:57 am
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.
Title: Re: Reduce the thump sound from a analog drum circuit
Post by: nathanpc on June 06, 2016, 06:46:36 am
Oh! Thanks very much sync! That solved the problem it's now working great!
Title: Re: Reduce the thump sound from a analog drum circuit
Post by: Zero999 on June 06, 2016, 07:00:24 am
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.
Title: Re: Reduce the thump sound from a analog drum circuit
Post by: nathanpc on June 06, 2016, 07:08:20 am
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.
Title: Re: Reduce the thump sound from a analog drum circuit
Post by: sync on June 06, 2016, 08:29:05 am
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.
Title: Re: Reduce the thump sound from a analog drum circuit
Post by: amyk on June 06, 2016, 02:26:08 pm
I thought drums were supposed to make a "thump" sound. :D