Comments on: A simple light to sound converter – with video !

By: admin

admin — Mon, 01 Mar 2010 11:05:01 +0000

@Derek and Andrew,
try removing C3 (the capacitor between pin 1 and 8 of the LM386). This lowers the gain of the amplifier to 20 against 200 as with the cap mounted.
For now I can’t add anything else…
Please let me know.
Best regards, for now.
Alex

By: Derek Holzer/TONEWHEELS

Derek Holzer/TONEWHEELS — Sun, 28 Feb 2010 09:36:35 +0000

PS… I have made a PCB for this circuit here:

http://www.umatic.nl/tonewheels_technical.html

If there are improvements please let me know and I will update it.

Best from Berlin,
Derek

By: Derek Holzer/TONEWHEELS

Derek Holzer/TONEWHEELS — Sun, 28 Feb 2010 08:21:52 +0000

@Andrew,

I’ve used this circuit for a workshop now, and I can definitely say that there are some problems with the LM386 self-oscillating! One thing to look at is whether there are any ground loops in your circuit. If the ground of the LM386 has more than one path to the – of the battery, that is a ground loop and will cause the amp to oscillate by itself.

HTH,
Derek

By: admin

admin — Mon, 14 Dec 2009 13:56:10 +0000

@Andrew,
As a first test, try moving C2 to the upper pin of the volume potentiometer (R2) (the one closer to U1A).
I’ll try this at home as soon as possible and in case replace the schematic.
Also, try raising C1 to 100 or 200 microFarads.
The sound you hear might be the so called “motor boating” which happens when there’s positive feedback (through power supply) between high gain input circuit (U1A and the photodiode) and output power (the amplifier + loudspeaker). The R3+C1 RC filter is used to the purpose. It is customary to say “to de-couple power supply of the two stages”.
Please let me know.
Ciao, Best regards
A.

By: Andrew Back

Andrew Back — Sun, 13 Dec 2009 00:22:06 +0000

Hi Alex,

Thanks for putting this circuit online!

So I built one myself and it works, however, it is extremely fiddly and seems to go into feedback all the time. I need to leave gain set to as low as possible or near to it, and then when I switch on it almost always feeds back, until I turn the volume up and down a few times. By turning the volume up around full I can usually get it to stop feeding back. Even then the sound is quiet and if I turn the gain up it becomes even more temperamental.

Any ideas where I’m going wrong?

Cheers,

Andrew

By: admin

admin — Thu, 10 Dec 2009 12:58:31 +0000

Ciao Ulysse, U1B is the unused half portion of U1 that actually includes two op amps. Grounding the unused inputs lowers dissipation and prevents noise.

R1 is a potentiometer used as a simple variable resistor, hence the unused pin.
Best
A.

By: Ulysse

Ulysse — Tue, 08 Dec 2009 00:15:02 +0000

Hi!

I’m trying to make this circuit and it is not working yet. I think I blowed my LM386 amp.

I have two questions :

- What is exacly the perpose of the U1B part on the schematic? It is simply a closer view of the U1A part?

- The third connector of R1 is not connected to anything, Is that right?

Thanks a lot for your aswer!

By: Derek Holzer/Tonewheels

Derek Holzer/Tonewheels — Wed, 02 Sep 2009 17:11:56 +0000

Thanks for sharing this Alex. I’ve been using phototransistors for a performance called TONEWHEELS for a couple years now

http://www.umatic.nl/tonewheels.html

but this is a great circuit for workshops and I’ll be having people build them in Belfast next week!

For those who are afraid of soldering irons, Eric Archer has a LITE2SOUND kit you can buy

ericarcher.net/devices/lite2sound/

although personally I don’t see what “all that stuff” one would have to buy is, besides the parts themselves and one soldering iron. I guess there will always be people with more money than time or interest to learn something new

Curious to see what the major project this came out of will be.

best!
Derek

By: Paul

Paul — Mon, 09 Mar 2009 17:21:54 +0000

I would be very interested in buying a couple as well

By: Rose

Rose — Tue, 20 Jan 2009 20:36:33 +0000

Can i buy one from you as well?
I would not be able to do all that, and to buy all of that stuff for one thing seems pointless. I would love to have one.
Rose