Hi all,

i'm quite new to elektronics and after building a small mp3 speaker i am now planning to build a stylophone . i think its a great project to learn PCB etching.

this is what i'm talking about:
http://www.otherlandtoys.co.uk/stylophone-p-2405.html
its a tone generator build as a musical intrument

this is where i got the idea from:
http://www.instructables.com/id/A-Stylophone/

but then i found this:
http://www.waitingforfriday.com/index.php/Reverse_Engineering_the_Stylophone

it's a reversed engineered circuit of one of the first stylophones of the late 60's with a UJT transistor instead of a 555 timer. where the newer versions with 555 chips create a square wave this device has an different (nicer) sound.
i build a prototype on breadboard with a potmeter to adjust the tone and it works great!

because the original circuit uses a 75 Ohm speaker, which is hard to find and expensive. I used a lm386 and a 8 Ohm speaker instead of the BC337 and 75 Ohm speaker just like the instructables project.

the part on which I need some advice is this:
how could I make a line out connection on my circuit?

should I use the amplified signal from the lm386 and lower the voltage to accomodate a line out connention?

or should I use the unamplified signal, which I think is to weak?

also I would like the speaker to be silent if the line out is in use.
I can't tell if this is already the case in the reversed engineered circuit.

here is the reversed engineered circuit (without the lm386 of course):

EDIT: don't know why it does'nt work but you can right click and open in a new tab

 

to make things a bit more clear
here is the reversed engineered circuit with line out:

and this is the circuit with the lm386 with no line out yet:

 

Line out should be a 1V p-p max signal. It would probably be best to get this by using an op amp, such as a TL082 (NOT a 741) tapping off the input to the LM386, and providing the gain needed for the 1V peak to peak on the output.

Some amplifiers support up to 10V p-p inputs, but line level is usually around 1V, you'll need to experiment, but don't blow up your home amp.

Lastly, the sound may be a bit worse when put through a good amplifier and speakers due to the many harmonics.

 

If you used a 3.5mm headphone socket as your line out, many of them have a built in switch which you can use to somehow mute the speaker output.

 

maybe it would be a good idea to use a BC337 as amplifier as in the original circuit for creating the line out signal?
then i could use a switch to lead the output through either the lm386 for it's own speaker or R6 and the BC337 for an external amplifier. the only minor issue would then be an extra switch. or is it possible the two sound significantly different?

 

Line out should be a 1V p-p max signal.

i measured the signal going in the amplifier and it ranges from 0,08 - 0,56V RMS depending on the frequency. if it would be a continues sine (which it's not) then it would already be far above 1V p-p right? apparently it does need amplification otherwise it would not have been part of the design

 

Without knowing the waveform, that may be on the low side. I'd still recommend a buffer amp/unity gain or maybe a gain of 1.5 op amp circuit just as a buffer. Not a 741, a more modern op-amp that can deal with the full audio range.

The LM386 is connected physically and electrically close. When you add an RCA Cable, you get a few unwanted parasitics. An external inductive or capacitive load from a cable connection may cause the oscillating circuit to misbehave. The buffer amp would prevent this possibility and give a better impedance view from the "amplifier side" of looking at things.

 

so the point is to use a amplifier to shield of the oscillator from any external device whether it needs amplification or not, right?
but wouldn't the BC337 transistor from the original circuit be suitable for this?

ps: there is a neat picture of the waveform the oscillator produces in the third link in my first post if your interested

 

What in the heck is this thing supposed to do?

 

http://www.youtube.com/watch?v=Plt0IoqXrMc

 

The one in the video is an accurately tuned variable pitch buzzer.

If you make the one with a 555 oscillator then its pitches will be wrong and will change so it will sound like hell.

I think about 25 years ago, stylophones with a very accurate divider IC and a real keyboard sold for only $2.00 in toy stores.