I see. So you dont need the scope since you have a measure on it?
Since you have a lot of measuring instruments can you advise whether the Keithley 2015 is something worth purchasing? Pcx is offering them for around USD350.
Thanks. nash
Correct, you don't need the scope, just set it up to measure the 2nd Harmonic and measure in dB and you're good to go.
For the price it's worth it purely for it's high precision bench meter functions and 4 wire resistance measurment. So if you don't have a good bench meter it's definitely worth getting.
From memory it measures harmonics down to -87dB which isn't spectacular but it's good enough for me, I like a generous amount of 2nd harmonic distortion.
If you want to measure harmonics lower than that say for a low distortion preamp stage maybe it's not the best tool.
If I lived in the US I'd probably get a HP339a but once you add shipping to the price they are not cheap and they're old so it's hard to know whether they will need servicing until you've already paid for it.
I like the idea of being able to see the residual waveform which you can't output to an oscilloscope using the Keithley.
If you're still undecided the biggest thing to bear in mind is the distortion meter needs an ultra low distortion sine wave generator and that is often the limiting factor to get low distortion measuremenrs.
For the price it's worth it purely for it's high precision bench meter functions and 4 wire resistance measurment. So if you don't have a good bench meter it's definitely worth getting.
From memory it measures harmonics down to -87dB which isn't spectacular but it's good enough for me, I like a generous amount of 2nd harmonic distortion.
If you want to measure harmonics lower than that say for a low distortion preamp stage maybe it's not the best tool.
If I lived in the US I'd probably get a HP339a but once you add shipping to the price they are not cheap and they're old so it's hard to know whether they will need servicing until you've already paid for it.
I like the idea of being able to see the residual waveform which you can't output to an oscilloscope using the Keithley.
If you're still undecided the biggest thing to bear in mind is the distortion meter needs an ultra low distortion sine wave generator and that is often the limiting factor to get low distortion measuremenrs.
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Having built a couple of amps with help from you all, I want to get some more equipment to further my understanding. Need to go beyond simple multimeters and thats why the Keithley 2015 caught my eye. If I understand you correctly even though the 2015 has a sine wave generator it is not with ultra low distortion.
Since we are on the subject of equipment what used scope in the USD350 range would you suggest?
Thanks for your advice.
Kevin thanks for your generous offer but I am afraid I wouldnt know how to play with it!
I am in Southern NJ about an hour and three quarters drive from Roselle. Perhaps by that time you will figure out how to use this. Lets keep in touch.
nash
That's silly talk. You just start pushing buttons till it does something, then you go to the manual and try to figure out what you just did.
It's good enough for most firstwatt amps but not good enough if you want to measure accurately around the 0.001% thd region or lower. Most Firstwatt amps are greater than 0.01% thd so no problem. If you want to measure lower distortion, you could measure the amp at 4W and 16W then plot the results on a graph to roughly determine distortion at 1W. It can do a few more things if you connect it to a pc but I haven't had a chance to do that as yet I need to get a gpib/usb cable.
If you don't have a good bench meter it's definitely worth getting, the distortion meter is icing on the cake.
So to measure 2nd harmonic in isolation I'm just setting upper harmonics to 2 "UPPR HARM: 02"?
Yes, I've found a position that sounds better, but still getting a handle on testing and taking notes.
I started with P3 in the middle position and then actually increased the second harmonic distortion. The sound seems to have more texture is the best I can do at explaining it.
As I've played with P3 I've found there's a point where 2nd harmonic goes very low and then increases again while turning P3 in the same direction. But I'm not sure which direction I'm at from the nulled out point, or if it matters.
Here's my problem...I've been fiddling with my turntable at the same time, taking a little weight off the cartridge and adjusting anti-skate, so I can't say with certainty what's contributing to the good sound I'm hearing.
I started with P3 in the middle position and then actually increased the second harmonic distortion. The sound seems to have more texture is the best I can do at explaining it.
As I've played with P3 I've found there's a point where 2nd harmonic goes very low and then increases again while turning P3 in the same direction. But I'm not sure which direction I'm at from the nulled out point, or if it matters.
Here's my problem...I've been fiddling with my turntable at the same time, taking a little weight off the cartridge and adjusting anti-skate, so I can't say with certainty what's contributing to the good sound I'm hearing.
Turning the pot one direction will give you an in phase 2nd harmonic and turning the pot the other direction will give you a 2nd harmonic which is 90 degrees out of phase.
And somewhere near the middle you'll have cancellation of the 2nd harmonic as you have observed already.
There is no right or wrong setting, only the setting which appeals most to you.
Yeah, it took my brain a little while before the light bulb turned on.
Because the 2nd harmonics period is half that of the fundamental, it is 90 degrees out of phase.
In both cases ie both +ve and -ve phase 2nd harmonic, the 2nd harmonic is 90 degrees out of phase, except in one case it is negative 90 degrees out of phase and in the other case it is positive 90 degrees out of phase.
The in phase 2nd harmonic will produce a maxima turning point at both the maxima and minima turning points of the fundamental and vice versa for the negative phase 2nd harmonic.
Probably clear as mud but if you draw it, it will start to make sense.
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Subjectively speaking, NP says in his F6 article, " The two phases of second harmonic do sound different, in fact the most consistent observation people have reported is that positive-phase has a little more projection to it, that it's a little more in-your-face and immediate. Negative phase tends to add more depth"
Based on my fiddling with my F5TV3 I found the above quite representative and this effect is easily discerned if you are listening to music that has a violin in it. I found it is also dependent on the volume level.
nash
I have said before that it's a little confusing, but what I mean is that when
the 2nd harmonic peaks positive with the fundamental peaking positive, I
call that "in phase". When it peaks negative when the fundamental is
peaking positive, that is "out of phase".
The alternative description is that when the 2nd is "in phase" the fundamental
is showing slight expansion in the positive half and slight compression in the
negative half.
