Yet another bulb lamp amplifier: the bulbamp

[tca]

Hi,
I just want to share with you this little amplifier.



I use it, with a smaller output cap (470u), as a guitar amp (it needs a buffer in this case).

Cheers.

[Nico Ras]

Using a bulb amp leads to compressor as the bulb resistance changes with current. Using a current source in stead of the bulb it improves it by orders of magnitude. A simple regulator chip and single resistor configured as current source. It does not add much to the complexity and t is probably even cheaper than a bulb.

[tca]

Originally Posted by Nico Ras

Using a bulb amp leads to compressor as the bulb resistance changes with current.

That is a nice thing to have if you want to use this amp as a guitar amplifier

Originally Posted by Nico Ras

... cheaper than a bulb.

Two lamps costs 1.5 Eur (auto/car lamps).

[Frank Berry]

I'm questioning the gate bias resistor. Might it not be a better idea to replace the 10 meg resistor with a voltage divider pot which is connected between +9 and Common Ground? This would permit you to accurately adjust the optimum operating point of the MOSFET and reduce the very high input impedance.

[tca]

Originally Posted by Frank Berry

I'm questioning the gate bias resistor. Might it not be a better idea to replace the 10 meg resistor with a voltage divider pot which is connected between +9 and Common Ground? This would permit you to accurately adjust the optimum operating point of the MOSFET and reduce the very high input impedance.

I've done a version just like you said, a few days ago and it works great...



For a guitar amp it is a good thing to have an high input impedance.


Thanks.

[Frank Berry]

I was afraid that the very high input impedance might lead to unstable operation.
It could also increase the possibility of RF and other interference on the input of the amplifier.
Good job!