ACA as 5W guitar power amp

[kacernator]

Hi,

I know that this topic should be propably in "Instrument amps" forum, but this forum is more relevant because of the design and designer.

I would like to tweak the ACA amplifier for mixed-mode feedback to better mimic tube amplifiers.

I don´t know if I have connected correctly the feedback paths and how to calculate the resistors with question marks to obtain same voltage gain to the 8R load as original - 14dB of gain.

I have found some document how to calculate resistors values for mixed-mode feebdack, but don´t know how to appy it to ACA topology

Thanks.

 

[kacernator]

I think I have it done. I have simulated schematics in Multism and both types of feedback are set to reduce total gain evenly, they are mixed in 50 to 50 ratio. Closed loop gain of the amplifier is unchanged - 5x. Don´t know how much output impedance is raised.

 

[kacernator]

After a little bit of tweaking, this schematics sounds the best to me as guitar power amplifier. Gain and the input impedance of the circuit is unchanged - 15db and 10k.

 

[kacernator]

Latest schematics

Hi,

here is the latest schematics of Amp Camp Amp modified as guitar power amp.
Apart from little tweaks I have added presence filter control as many guitar preamps do not include it. For more bass increase 1uF after opamp. It sounds great!

Enjoy.

 

[Loudthud]

So you gave up on the mixed mode feedback and just added a resistor in series with the speaker? Have you tried disconnecting the feedback? Just remove the 68K. Have you tried changing the 0.22 and 0.33 resistor ratio?

 

[kacernator]

It is easier in this design to add output resistance then to mess with mixed-mode feedback.
I have tried disconnecting the feedback and I didn´t like the sound - it was harsher.
I dnd´t mess with resistor ratio. I think it sounds pretty damn good as it is right now.