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I would like to buy a used Distortion Analyzer. Refurbished, scratched, not a problem. What's a good unit to consider ? My purpose.., to be able to adjust Phase Splitter balance, to tweak some old Harman Kardon Award series integrated amps that have adjustments specifying a distortion analyser to and adjust for a null 'minimum reading.' Thanks, Rich
Since you likely have a computer, just use it's sound card and a free FFT program such as wavetools or Visual Analyser. Far more information, no cost.
If you've already acquired a distortion analyzer you can still use it in conjunction with your computer to enhance the dynamic range of the residues.
Sorry to be so late, I don't normally look at this forum.
Rick
OK. I haven't spent a dime yet... the PC aproach sounds awesome. I have an old desktop PC that uses Windows 95 and has a Pentium 150. Maybe my buddy can scrounge an old sound card ans I can leave this permanently on my bench. Will look around... great suggestions. This is out of the box thinking completely!
Using a computer sound card and FFT software is not a great way to go for measuring audio equipment. The bandwidth is limited to 20kHz, including harmonics. This means that harmonic distortion measurements of higher frequencies will be limited and perhaps misleading. Also, the input voltage capability is limited to only a few volts and is not tolerant to overloads. To use it with a power amp will require building some type of input attenuator.
Well, your point about the power amp is a good one, but it's just takes a pot, nothing fancy.
The upper end isn't much of an issue, most sound cards will sample to at least 96KHz so you can see out to ~40KHz which is well beyond what your ears will respond to on a continuous basis.
As far as misleading, nothing on the face of the earth is more misleading than a distortion analyzer. The rub is that it gives you a pat answer to two decimal places which on it's own hook means absolutely nothing if you are doing design or repair. It is of some value for production. You end up always having to have a scope on the output so you can get a clue if it's measuring hum, residual noise, 2nd, 3rd, what?
The sound card/FFT scheme is outstanding by comparison, one glance and you see what's going on. And the cost/benefit is beyond belief. About 20 years ago I was doing a project where I needed to see the signal more clearly than I could with a distortion analyzer. So I bought an HP dynamic signal analyzer. It was a 50KHz, ~14 bit FFT machine. $12,000 used. The price of a good new car. Now you get better performance for essentially nothing. Some things in life really are better than the "good old days".
Rick
100% agreement. With free software like sinegen coupled with WaveSpectra and a pair of ten turn pots fine harmonic analysis down to <-120 dB is a pip with little more than a $150 M-Audio Audiophile Firewire.
The distortion analyzer needed depends on the capability of the unit you will be testing. I am most familiar with the older Hewlett-Packard units. The HP333A and HP334A are nice but are not fully automatic and require an external signal generator, which will also contribute to the capability of the system. The HP339A is a nice, automatic analyzer with a built-in generator but is more valuable. The Sound Technology 1701A is nice and similar to in capability to the HP339A. It has about the same value as the HP339A. Look on E-Bay for these units to get an idea of their value.
Great now I will check the refurbished test equipment stores for a 339A or 1701A. Thanks for the recommendation. Probably best to get one with a built-in signal generator.
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