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@ericrosenfield , check these posts, THD should be magnitudes lower. There must be something odd with your build. Did you check the voltages?
I was playing with QA403 (an audio analyzer) and tried a few things with my ACP+. I noticed there is something happening ~18kHz. It does not seem to be related to the power supply and the input. I tried both a battery and wall mount switching power supply, and I do not see this when the analyzer is in loop back so it is not related I guess to the source. Is this normal, why would be the reason for this ?
ACP+ powered with battery, no input signal:
ACP+ powered with battery, and with input signal from the analyzer:
ACP+ powered with wall mount switching...
ACP+ powered with battery, no input signal:
ACP+ powered with battery, and with input signal from the analyzer:
ACP+ powered with wall mount switching...
I get 0.1V across both R12 on both sides. R13 rises up to 0.6V before falling down to 0. For current, I get 0.2uA on R12 while R13 jumps up to 40uA before dropped down rapidly to 0. This is also consistent on both sides. I have no idea if that's good or bad.
It's entirely possible I did something wrong, though I don't know what it might be. Also I didn't measure the distortion until after I'd changed the caps, so I don't have a measurement before the mods to compare to. (In case I did something wrong when modding.)
EDIT: When I turn the volume knob all the way up the voltage on R12 goes up to 0.15V.
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@ericrosenfield , just to be sure: In your build, R12 is 2.2 ohms and R13 is 6.8 ohms?
What kind of voltage meter are you using? Is it capable of measuring in the mV range?
If the resistors are what is in the original schematic, the values you measured are too low. But there might be an error in the measurement as well if your voltage meter is not appropriate.
Also, what do you mean with "for current, I get 2.2uA..." Measuring the voltage across the resistors is supposed to tell the current, when applying Ohm's law (I=U/R). Do not try to measure the current directly.
The current through the resistors R12 and R13 needs to be around 150mA for proper setup. So for the 6.8 ohm resistor the voltage across it should be around 1V and across the 2.2 ohm it should be 0.33V.
Jumping to 0V also is weird.
Also, for clarification: You built the 24V version, not the one that was posted in this thread that uses a +/-12V supply?
What kind of voltage meter are you using? Is it capable of measuring in the mV range?
If the resistors are what is in the original schematic, the values you measured are too low. But there might be an error in the measurement as well if your voltage meter is not appropriate.
Also, what do you mean with "for current, I get 2.2uA..." Measuring the voltage across the resistors is supposed to tell the current, when applying Ohm's law (I=U/R). Do not try to measure the current directly.
The current through the resistors R12 and R13 needs to be around 150mA for proper setup. So for the 6.8 ohm resistor the voltage across it should be around 1V and across the 2.2 ohm it should be 0.33V.
Jumping to 0V also is weird.
Also, for clarification: You built the 24V version, not the one that was posted in this thread that uses a +/-12V supply?
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That's what the bands on them say
It's a Klein multimeter. It's pretty good.
You can see how if you ask me what the current is, the most logical thing to do would be to set the multimeter to current mode and measure it? Anyway, okay, I'll calculate it next time.
I mean, it's possible I don't have the probes firmly on it or something, but that's the behavior I'm seeing. I should try again with alligator clips, but I'm leaving town and won't have a chance again until I get back week after next.
24V. That's what my power supply is putting out, that's what the ACP+ is getting.
Assuming that the voltage is too low--what should I do about it?
@ericrosenfield , no offense, but I wrote this
I think what needs to be done is a basic health check of voltages in a couple places (which also tell current through the diff stages).
Just ping here when you have time. I will post a schematic with voltages how they should be and you can post how they are and we should be able to sort out what needs to be adjusted.
The 2nd line is telling how to calculate current from he measured voltages.
I think what needs to be done is a basic health check of voltages in a couple places (which also tell current through the diff stages).
Just ping here when you have time. I will post a schematic with voltages how they should be and you can post how they are and we should be able to sort out what needs to be adjusted.
Just in case...
That may seem intuitive, but you did not tell us exactly how you measured the current. If you set your DMM to current mode and place the leads across a resistor, that's not how to measure the current through that resistor. If you did that, you'd have effectively placed a very low impedance / resistance "wire" in parallel with the resistor. Don't do that. In a lot of situations, you can cause too much current to flow through the circuit and damage parts.
If you wanted to measure the current through the resistor using your DMM set to current mode, you'd need to lift one leg of the resistor and place the DMM in series with the part. It does not seem as if you've done that. It's MUCH easier to measure the voltage across the part and calculate the current from the known voltage / resistance as described.
You may know that... but your results seem suspect, and others may interpret your statement to mean that they could measure the current directly.