Dynamic Signal Analyzer tutorials? Audio in particular.

[almstsobur]

     I recently picked up a HP 3562a that needed some power supply work, I was able to fix it, but now I need to figure out how to use it. I've always been a bit of an audiophile and I own quite a few amplifiers; most that I have purchased broken and managed to repair. I have been using a Keithley 2015 for THD up until this point, but I got the 3562a to dig a little deeper into audio signal analysis. I am just not finding any good write up's or videos related to DSA testing of audio gear, I was hoping someone might have some links or documents on how to do a bode plot, THD, and any other useful tests for audio gear or audio amplifiers in particular. It's time that I thin the herd a little bit, I just have way more gear than I can use. My objective is to "scientifically" determine which of the amps I have are the most accurate and therefore I will keep and use, but I would also like to test the ones I plan to sell to ensure that they at least meet the factory specifications for peace of mind before passing them on. Any help is much appreciated.

Thank You,

-RP

[_Wim_]

This one might be interesting (The Fundamentals of Signal Analysis): http://cp.literature.agilent.com/litweb/pdf/5952-8898E.pdf

Have not read it myself, but browsed though it and give a good start...

This book is also quite a good read: http://www.cordellaudio.com/

[simmconn]

I found the 3562A operating manual (03562-90001) quite well written and easy to follow. You may want to get a paper copy that's easier to navigate.

The unit takes some practice to get used to. Depending on what kind of amplifiers you work with, the 3562A may not have the dynamic range you need. However, it has many features that a typical audio analyzer does not have, and would be more useful in an R&D environment than in a production line verifying whether an amplifier is up to its spec.

[almstsobur]

I found the 3562A operating manual (03562-90001) quite well written and easy to follow. You may want to get a paper copy that's easier to navigate.

The unit takes some practice to get used to. Depending on what kind of amplifiers you work with, the 3562A may not have the dynamic range you need. However, it has many features that a typical audio analyzer does not have, and would be more useful in an R&D environment than in a production line verifying whether an amplifier is up to its spec.

I agree on the manual, it is well written and has good general operating principles. It just kind of lacks the "how-to" section for someone not at all versed in this type of equipment. At a cost of $20,000+ when new, I guess they would assume you more or less know what you are doing when you buy one of these. Nothing in the manual seems to direct anything towards "audio" testing either. Some of what I end up doing does involve some R&D on these repairs. I mostly work on semi-vintage solid state equipment, 70's, 80's, 90's. NAD, Parasound, Carver, Mcintosh Etc. You can't always find direct part replacements, sometimes you need to experiment with a modern version of similar components. For instance, below is the factory spec's for one of the amps I have a Parasound HCA-1500a. I would lkiek to think most/all of these specs should be measurable. Obviously output before clipping can be done with a scope fairly easily, THD I have figured out, but frequency response from 5Hz to 100Khz, headroom, SNR ratio .. those I do not know how to test.

SPECIFICATIONS

Continuous Power Output - Stereo:
    205 Watts RMS x 2, 20 Hz-20 kHz, 8 ?, both channels driven
    315 watts RMS x 2, 20 Hz - 20 kHz, 4 ?, both channels driven
Continuous Power Output - Mono:
    630 watts RMS, 20 Hz - 20 kHz, 8 ?
Current Capacity:
    60 amperes peak per channel
Slew Rate:
    > 130 V/µsecond
Frequency Response:
    5 Hz - 100 kHz, +0/-3 dB at 1 watt
Total Harmonic Distortion:
    < 0.03% at full power; < 0.01 % typical levels
IM Distortion:
    < 0.03 %
TIM:
    unmeasurable
Dynamic Headroom:
    > 1.5 dB
Interchannel Crosstalk:
    > 80 dB at 1 kHz; > 60 dB at 20 kHz
Input Impedance:
    33 k ?
Input Sensitivity:
    1 V for 28.28 V, THX Reference Level; 1.2 V for full output
S/N Ratio:
    > 110 dB, input shorted, IHF A-weighted
Damping Factor:
    > 800 at 20 Hz
Power Consumption:
    500 watts
Dimensions:
    w 19" x h 5 1/4" x d 16", h 5 7/8" with feet
Net Weight:
    40 lb

[uncle_bob]

Hi

There are some very interesting things you can do with one of these that get pretty deep into theory before they make sense. A few useful things that are fairly simple to start out with:

1) Noise plots. Simply being able to *see* where this or that device is noisy can be very useful. This analyzer has very good capability in that regard.

2) Swept frequency response. As long as you are careful about levels, you can find out far more about a set of speakers with a frequency sweep than you ever really wanted to know. (Hint: they all look really messy like that .... the published data has been smoothed).

3) Impulse response. Once you see the "real" frequency response it raises all sorts of questions. An impulse response test will help answer some of them.

Can you do all this other ways? Sure you can. Does this gizmo give you a *calibrated* way to do it? Yes indeed.

Lots of Fun !!

Bob