DS8 Drum Synth - problem with constant sound

Thread Starter

lonesoulsurfer1

Joined Sep 25, 2020
4
Hi All,
I have used the attached schematic to build my own DS8 Drum Synth. Everything works but I'm having an issue with constant sound being created. If I hit the trigger which in this case is a Peizo disc, I get a sound effect but then as it fades, the circuit still continues to make a sound. It should cut off after each hit of the peizo but doesn't.

I have built 2 of them and get the same thing happened. I'm not too sure if I have done something wrong or not and can't for the life of me work out how to have the sound cut off after each effect has played.

Do I need to add a component to have it cut off?
would it be something to do with the peizo? I have tried it unplugged from the circuit but the constant sound still persists.

I know that I am missing something simple but van't work it out - any help or hints would be much appreciated.

Thanks Lonesoulsurfer
 

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Alec_t

Joined Sep 17, 2013
11,641
I'm just guessing, but if the sensitivity pot is cranked down perhaps the input offset voltage of U2A is enough to keep the output of U2A high? Try a 1meg pull-up from the inverting input (pin 2) to 5V.

Edit: Piezos can generate quite high voltages when hit. I'd be concerned that with the sensitivity pot cranked up the non-inverting input of U2A could be driven to a damaging high or low level.
 
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Thread Starter

lonesoulsurfer1

Joined Sep 25, 2020
4
I'm just guessing, but if the sensitivity pot is cranked down perhaps the input offset voltage of U2A is enough to keep the output of U2A high? Try a 1meg pull-up from the inverting input (pin 2) to 5V.

Edit: Piezos can generate quite high voltages when hit. I'd be concerned that with the sensitivity pot cranked up the non-inverting input of U2A could be driven to a damaging high or low level.
Thanks for the response. I gave it a shot but no go. However, I think you might be onto something. I wonder if I changed out the 50K timmer to say 100K that would help at all?
 

Thread Starter

lonesoulsurfer1

Joined Sep 25, 2020
4
Probing around I managed to get rid of the continuous sound by connecting pins 11 & 12 together on IC U3 together!

I checked my board and schematic and they are exactly as per the attached schematic - no unconnected pins etc.

Go figure.
 

Audioguru again

Joined Oct 21, 2019
1,912
Probing around I managed to get rid of the continuous sound by connecting pins 11 & 12 together on IC U3 together!

I checked my board and schematic and they are exactly as per the attached schematic - no unconnected pins etc.

Go figure.
U3 pins 12, 13 and 14 are a follower with pin 12 as the input biased at half the supply voltage. pin 11 is grounded. Your connection disables it and the other opamps it feeds.
 

Thread Starter

lonesoulsurfer1

Joined Sep 25, 2020
4
Update. Thanks to everyone that supplied suggestions. In the end it was a faulty IC (3080) which was the culprit. I swapped it out and it all works perfectly.
 

sparky 1

Joined Nov 3, 2018
334
Digging up an antiquated Bass sound machine a modifying it for maker's fair.
Just looking at the schematic trying to relate design methods with as much going on, and video having short demo of sound output.
I tryed to think of a current percussion equipment analogy...to the retro " VIC 20 is to sound machine as C64 is to robust sound machine. "
I looked for the latest drummer stand alones to try to get an analogy but I was'nt able relate the old great stompers to simplify the design when the technology has advanced so quickly. The C64 percussion programmers were few there seems to be a disconnect. The old drum machines hard to find the instructional and hardware part. The old drum machines, what is that?
https://consordini.com/best-drum-machines/

 
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Audioguru again

Joined Oct 21, 2019
1,912
I noticed that the circuit in the video of the drum machine used low-fi LM324 opamps that produce fuzzy crossover distortion and lots of hiss. The circuit has a lowpass filter to make that distortion and noise sound muffled.
 
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