A friend recently sent me his pair of ACAs to try out. So far I've only messed with tubes, so it proves to be an interesting comparison. I just recently also got my first scope and signal generator, so as part of my learning to use those I went ahead and hooked up the ACAs and tried taking some basic power output and square wave readings.
Things look seriously amiss, but it's likely I'm making a mistake in my test setup so I wanted to get a reality check.
The ACA is running in stereo mode into 8Ω dummy loads, fed with a 1kHz signal from a Tag-101 type signal generator and the compensated 1x probe connected across the dummy load. Scope is a Tektronics 2445. These readings are in DC coupled mode:
Slightly up in amplitude from that I start getting distortion of the wave form:
So the first image indicates .42Vpp, or .148v RMS. Square that and divide by 8Ω load to get the power output...we're at a tiny fraction of a watt.
I must be missing something, as the amps sound quite good.
Turning the amplitude down even further the square wave looks like this:
Any thoughts about how to explain what I'm seeing?
Things look seriously amiss, but it's likely I'm making a mistake in my test setup so I wanted to get a reality check.
The ACA is running in stereo mode into 8Ω dummy loads, fed with a 1kHz signal from a Tag-101 type signal generator and the compensated 1x probe connected across the dummy load. Scope is a Tektronics 2445. These readings are in DC coupled mode:
Slightly up in amplitude from that I start getting distortion of the wave form:
So the first image indicates .42Vpp, or .148v RMS. Square that and divide by 8Ω load to get the power output...we're at a tiny fraction of a watt.
I must be missing something, as the amps sound quite good.
Turning the amplitude down even further the square wave looks like this:
Any thoughts about how to explain what I'm seeing?
Have you remembered that the ACA speaker outputs are 'reversed' to allow for phase reversal.
In other words speaker + is actually ground.
Are you shorting the output via your test leads and scope???????
(and don't worry, the ACA won't mind one bit 🙂)
In other words speaker + is actually ground.
Are you shorting the output via your test leads and scope???????
(and don't worry, the ACA won't mind one bit 🙂)
Ah yes, I did have the probe on the wrong side, thank you! Things are more normal now, but both amps look like they're putting out just under 5wpc in stereo rather than the rated 7.5wpc, and the clipping kicks in unevenly, with the troughs flattening off before the peaks.
That's good 🙂
As you have a scope you can adjust the midpoint voltage setting of the ACA to give symmetrical clipping.
Are these ACA's built from the kit or are they totally diy'ed from scratch. Also are they using the recommended Meanwell 24 volt power supply?
My simulation of the ACA shows about 7 watts rms into 8 ohms as a maximum achievable. If yours looks like this then you will probably find the midpoint volts is to low.
As you have a scope you can adjust the midpoint voltage setting of the ACA to give symmetrical clipping.
Are these ACA's built from the kit or are they totally diy'ed from scratch. Also are they using the recommended Meanwell 24 volt power supply?
My simulation of the ACA shows about 7 watts rms into 8 ohms as a maximum achievable. If yours looks like this then you will probably find the midpoint volts is to low.
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