Well six out of eight is batting 750 so that's pretty good. Without a scope it's hard to tell. The voltage may be pulsing or have a lot of noise causing the issue.
The 555 circuit is called a monostable multivibrator or a "one shot". When triggered by the piezo in the drum kick via the LM386, it sends out a square wave pulse on pin3. The duration or width of the pulse depends on the setting of the 100K pot. That's how it suppose to work.
I would just try and compare the wiring from a good circuit.
SG

 

Well six out of eight is batting 750 so that's pretty good. Without a scope it's hard to tell. The voltage may be pulsing or have a lot of noise causing the issue.
The 555 circuit is called a monostable multivibrator or a "one shot". When triggered by the piezo in the drum kick via the LM386, it sends out a square wave pulse on pin3. The duration or width of the pulse depends on the setting of the 100K pot. That's how it suppose to work.
I would just try and compare the wiring from a good circuit.
SG

I've been doing that extensively, haha. I'm wondering if I happen to have a bad part, but the only thing I can see that would be bad is the 555 but I've disproven that. Could noise be bleeding through some of the wires? Of course none of them are shielded. But I suppose 3.8v is a lot to bleed through, haha. Ah well, I'll just build another one and see what's going on .

 

I breadboarded the 555 circuit and the only way I could duplicate somewhat what you are seeing is removing the ground connection from pin1.
In my test circuit I was getting a steady 2.75 volts on pin3. BTW I'm using a TLC555 the cmos version of the original 555.
SG

 

I breadboarded the 555 circuit and the only way I could duplicate somewhat what you are seeing is removing the ground connection from pin1.
In my test circuit I was getting a steady 2.75 volts on pin3. BTW I'm using a TLC555 the cmos version of the original 555.
SG

I've been using pin 1 on my solderable breadboard as one of my ground buses . It's directly connected to the ground of the USB cable. Other things connected to that pin is the ground leg of the transistor. I can't imagine that being an issue. The ground is chained around the circuit.

I've tried two different brand 555 chips and both of them work fine in a functioning circuit. I'm currently building a 3rd one. I really should have a breadboard for troubleshooting.

 

You can check the connection with the ohmmeter. Remove the 555 and measure from the socket to ground on pin1. Possible the leg of the socket is not soldered good.
SG

 

You can check the connection with the ohmmeter. Remove the 555 and measure from the socket to ground on pin1. Possible the leg of the socket is not soldered good.
SG

Should I just test continuity I assume?

 

Yes.

 

Yes.

I get solid continuity even with the chip installed from the ground of the USB to the leg of pin 1. And 0.3 ohms of resistance across them as well. I've tested continuity all over the circuit looking for things to be connected correctly or incorrectly and have found no issues .

I assume all ICs are keyed the same way meaning the cutout goes left when counting pins?

I'll let ya know how #3 turns out.

 

Could the 10uF cap be causing the issue? That's the one thing I just realised has changed between old and new circuits

 

Changed in what way?
SG

 

Changed in what way?
SG

Different brand / size. The new one is a 10uF 25v cap, the old one was a 50v.

 

No, that won't make any difference. But speaking of caps try adding another 47uf filter cap from pin8 to pin1 of the 555. Plus side of cap to pin8.
SG

 

Added that filter cap to one of the bad circuits with no change, thanks for all the troubleshooting you've been doing

 

Your welcome. Any chance you could borrow a scope?
SG

 

Not sure who would have one but I could certainly ask around! I assume they're a substantial investment?

 

Hah, looks like i could build one for reasonable

Kuman DSO 138 DIY KIT Open Source 2.4" TFT 1Msps Digital Oscilloscope Kit with DIY parts + Probe 13803K (SMD pre-soldered) https://www.amazon.com/dp/B0195ZIURK/ref=cm_sw_r_cp_apa_lcXRAbPYB6FWE

 

I assume they're a substantial investment?

Just depends on the specifications. That kit is probably all you need if you are up to the challenge. From reading several of the reviews it seems like figuring out the correct components is the hardest part. If it doesn't work when you get it finished I can't help! I'm thinking this USB unit
SG

https://www.sainsmart.com/products/dds140-pc-based-usb-oscilloscope-40mhz-bandwidth-200ms-s-black

 

Yeah, I had a feeling you'd say that . Yeah, that's reasonable for sure . I asked a few folks of they have access to one but if I get no luck I may have to go that route.

 

Finally figured it out. Something was wrong with the pulse width pot. Once I replaced it everything was good.

I transfered the new circuit into the existing project box with the jacks and pots still installed which is why circuit 2, and then 3 all behaved the same way.

Thank God that's over, ha!

 

I assume it would be fine but could I used a polarized .1uF cap in place of the non polarized ones as long as i connect the negative legs to ground?

I'm only asking as I have lots of polarized caps and only a few non polarized ones left.