ACA as guitar power amp?
Hi,
is ACA suitable as guitar power amp for home practice? Mosfets in class A, simple circuit, low damping factor seems it could work well. Does it have the liveness and warmth of tubes?
Thanks.
Hi,
is ACA suitable as guitar power amp for home practice? Mosfets in class A, simple circuit, low damping factor seems it could work well. Does it have the liveness and warmth of tubes?
Thanks.
From my experience hi-fi amps are not good as a guitar amps 🙂. Make you one using ax84 2w SE or PAp designs. They are quite good 🙂
Me too - I have one 2K2 and a pair of 2.7K resistors in the stash. How critical is that value?
I have a whole strip of 2K2 SMD but no idea if they will work.
Last edited:
I'll get some matching Dales later, but this worked. Noticed something interesting though. With the new part the initial bias read 9.38. I got it to 9.98 and decided to turn on the other one for warm up. The bias jumped to 10.17 then settled back to 9.78. Probably no big deal but a bit surprising as each amp has it's own 18.5 Vdc power supply. Didn't think these were that sensitive to line fluctuation. I'll adjust to 10V with both amps on over time.
Attachments
Last edited:
They are sensitive to temperature - blow on the PCB with the meter attached and watch it change and recover.
This may sound silly, but is there a test spot to read the actual power being fed to the speakers with a meter - or is that primarily a calculated value?
With a simple sine wave as input, Attach a load resistor to the output and hook up your scope - when it starts to clip, back off a little, look at the voltage swing and do a little math.
Vrms^2/load = power in watts.
Vrms^2/load = power in watts.
Last edited:
Thanks - had to pull off scope purchase due to an unforeseen expense, but I'll have it sometime in January.
The ACA makes a great little power amp for guitar. The low amount of feedback and generous amounts of 2nd harmonic distortion make it ideal.
Experiment with the output voltage adjustment (P1) and connect/disconnect the 68K feedback resistor (R12). Just be aware that you could damage some FETs if you drive the input with too much voltage like from a tube preamp. Keep the input under something like 10V peak to peak or be prepared to replace some parts. It might be a good idea to replace C3 with a film cap. Experiment with the value but something like .22uF or .47uF might work just fine.
See my posts in this thread: http://www.diyaudio.com/forums/instruments-amps/230639-low-wattage-power-amp-preamp.html
Last edited:
Thanks to PASS concerns
Because of low supply voltage, IRF240gs>4V, so I switched to K1058.
In order to reduce power consumption and heat, I used 11V power supply voltage.
My speaker is 94DB/1W FE126EN.
In order to attempt an inductive load, I use a switch.
Because of low supply voltage, IRF240gs>4V, so I switched to K1058.
In order to reduce power consumption and heat, I used 11V power supply voltage.
My speaker is 94DB/1W FE126EN.
In order to attempt an inductive load, I use a switch.
Grappling with the Mu in ACA and J2 clone
I'm still trying to get a feel for the Mu Follower. In the ACA, is the value of R7 a major factor in the bias? If one wanted higher bias, what are the best options?
Can you lower the value of R7?
Would a Darlington at Q3 work well (to get a Vbe of 1.3 instead of .65)?
I used the addition of R15 in my build of the ACA, but would that type of solution work for any bias desired?
I'm also trying to understand how the J2 CS works, and I'm having a hard time drawing analogies to the ACA when it comes to the opto-isolator. Is the opto-isolator forcing a Vbe of 1.4V to get the 1.7A bias?
I'm still trying to get a feel for the Mu Follower. In the ACA, is the value of R7 a major factor in the bias? If one wanted higher bias, what are the best options?
Can you lower the value of R7?
Would a Darlington at Q3 work well (to get a Vbe of 1.3 instead of .65)?
I used the addition of R15 in my build of the ACA, but would that type of solution work for any bias desired?
I'm also trying to understand how the J2 CS works, and I'm having a hard time drawing analogies to the ACA when it comes to the opto-isolator. Is the opto-isolator forcing a Vbe of 1.4V to get the 1.7A bias?