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GEEK PEAKS:
THE RMS TITANIC

Figure 2: RMS formulae (click image for larger view).

During the Stone Age, Peak Power ratings drew a consumer’s attention to a power amp’s performance. (Eventually, RMS power specs were also published, revealing the truth.) RMS stands for Root-Mean-Square, not Royal Mail Steamer, but the end result is about the same. Consider that the Titanic had 2,200 “peak” passengers. Sadly, the 705 survivors number only 72 passengers short of the RMS formulae detailed in Fig. 2.

The peak-to-peak value of a sine wave is converted to RMS so that it is “effectively” equivalent to that of the same DC voltage. (For a square wave, the “peak-to-peak” voltage would simply be halved.) The bottom formula works in reverse to determine the peak-to-peak value from the RMS. Plug into your local wall outlet—the juice is 120- volts RMS or 339.46-volts peak-to-peak.

Note: Visit www.whatis.com to get a detailed explanation on RMS and many other geek subjects.

FEEDBACK
Anyone who’s ever built an amplifier knows the importance of feedback for reducing distortion and improving frequency response. I rely on reader feedback to better hit the target and to fill in the gaps in my own knowledge. For example, the LA-4 upgrade project detailed in the November 2000 Mix replaced a RC4136 quad op amp with two dual op amps. Two readers responded—Mark De Martini (formerly of Sigma Sound in Philly and now of Larrabee in L.A.) and John Roberts (of Peavey)—reminding me that a TL075 is pin-compatible, if you can find them (I couldn’t). I still like my dualing-duals version, but anything is an improvement over the RC4136.

Figure 3: In case your brain is dense like mine, these pictures show the blow-by-blow. Also note the quote “not recommended for new design” applies to both capacitor styles, but only radial suggests that you “use the FC Series,” which is not available in axial format. (Illustration courtesy of Panasonic and www.digikey.com.) (click image for larger view).

Regarding capacitor upgrades, a few readers told me that Panasonic’s HFS/ HFQ Series were no longer available. This is not entirely true. The line is being discontinued with some inventory re maining. (The FC Series is the replacement.) My most recent experience at www.digikey.com allowed the option to check availability for each part and the FC Series, which is smaller by design and only available in the radial format. See Fig. 3 for a closer look.

Finally, I get asked for vintage schematics all the time. One source for a variety of documentation is www.tri odeel.com, specializing in vacuum tubes, amplifier schematics and related parts (not to mention links galore—related and not, some quite humorous).

That’s enough random wanderings for now. Next month, I’ll be back with a bit more on digital recorders.

Send unused cross-country ski equipment to Eddie Ciletti at www.tangible-technology.com for a maintenance credit.

Reprinted with permission from

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