Hi All: Here are several modifications you can make to your Chiara amplifier.
1. Increase power output; (this will make it capable of driving some of the phones that are harder to drive, ie AKG K340).
remove R6 (this is the emitter resistor for the output transistor). Replace it with a 5 ohm 2 watt resistor. If the 5 ohm value is
not available then a 5.5 ohm value will work.
2. Increase the gain, if desired: remove R4 (this is the feedback resistor) the 27k ohm resistor & replace it with a 48k ohm 1/4 watt
resistor.
3. Replace the rotary volume control with a 23 step switched attenuator, (I got mine from Valab).
4. Change the dual opamp to either an AD823; (no circuit changes are necessary).
These modifications will raise the amp to a new level & add value.
Bill Wilson
I forgot to mention that mods 1 & 2 must be performed on both channels.