AES 2006 - Bob Pease, Sunday

The last day of the AES conference had a great talk by National Semiconductor’s Bob Pease. Bob had heard that the golden-ears audio crowd insisted that there was an audible difference between electrolytic and film capacitors when they were used in the audio signal path. Bob thought this was highly doubtful so he set out to measure the difference between several high-end audio capacitors. Turns out the golden ears guys were right and Bob is the first to admit that he can see a clear difference on the cross-plots put out by his favorite analog scope.And furthermore polypropylene capacitors are better and far more consistent than the oil-paper capacitors that some people tout as being the best for audio. Click on the little thumbnail and you can see the 193kB gif file of Bob’s handout.

The circuits on the left side of the page are some great test circuits that Bob uses for measuring gain and distortion. These are set up to drive a scope in cross plot mode. This is where the scope is not sweeping on a time base but rather, one output from the circuit drives the vertical like normal but a second output drives the horizontal deflection. Bob loves the cross plot setup and uses it for a ton of things.If you do not understand it, well tough, I don’t have the time to explain it but maybe I can convince Bob to send me a little blurb we can publish right here in the anablog, your place to find out the real dope on analog circuit design and lynchpin for the analog community here at EDN. Bob is using this to evaluate the distortion of the new LM4562 amplifier, which has a distortion of something like 0.00003%. Bob is as amazed by this part as he is the other Audio Group offering—the LM4702 power transistor driver chip

OK, back to Bob’s handout.I hope you have downloaded the free image reader irfanview. That way you can see Bob’s handout in a decent viewer done by a great Serbian engineer. The only trick is to do a View/Display options/Fit images to window; this way the image is sized to fit whatever window size you have irfanview running in.I change my file associations to make gif, jpeg, tiff and the new version will play those evil QuickTime* movies from my Konica Minolta Dimage X50 camera.

OK OK, now really back to Bob’s presentation that you are admiring in the great free irfanview image software that does not clog up your registry or anything else. Well sorry, Bob did not show the capacitor test circuit.But you can see it and read about it from the horse’s mouth here**. Bob did surprise himself that there is a difference between polypropylene and Electrolytic capacitors in the signal path. One cool thing that Bob has done is to not try and measure the capacitor differentially in the signal chain. He has referred one side of the capacitor to ground. A little thought on the principles of superposition should convince you of the validity of this approach. As Bob said: “It's a matter of viewpoint— what point you define as ground.”

What Bob did draw up on the right side of his handout is a nice RIAA filter circuit that was used back in the vinyl record days to take out the pre-emphasis that was used on records to make the signal to noise better and keep the needle from jumping out of the groove. Well I better go before I hit that 7000-character limit (in HTML no less!) that the IT department puts on our blogs.

*No, I am not going to link to a company that is so despicable that their cross-platform movie player nags you to upgrade EVERY SINGLE TIME YOU PLAY IT. Pigs.Try MPlayer (along with Real Alternative for THOSE pigs) and VLC all of which I highly recommend. “If Internet advertising has proven one thing, it’s that you simply cannot annoy people into liking you.” G.M.O’Connell (pdf)

**I see the competition has instituted those great layover or interstitial ads that puts up a whole page and expects you to wait for 20 seconds to see what you really came to see, just like EDN does. I am sure you love this and be sure to tell our publisher how much you value having this important information thrust on you at no additional cost. Don’t complain to me or the other editors. You are preaching to the choir.