Audio Investigations: Air has noise, and other measurements

Tuesday, October 19, 2010

Air has noise, and other measurements

Unplugging my Parasound HCA-1500A amplifier from the Meguro noise meter, the meter immediately jumps up (not down) to a higher reading: 10.5 mV. That is apparently the EMI/RF voltage in the air across a pair of banana jacks, in my room at this time. (I've noticed a little variation over time, the range seems to be 9-11mV so far.) The Meguro has a bandwidth of something like 1 Mhz, and an impedance of 1 Megohm.

It's particularly funny to remove an amplifier and see the voltage reading go up IN THIN AIR. It's like the amplifier cables are shorting out the air around the banana jack. Fortunately the air has a rather high impedance so the cables win. But one can wonder what affect this has on amplifier circuitry.

BTW, with 6dB's of attenuation dialed in on its level control, but otherwise being fed by the noisy Behringer DCX 2496, I get 1.8mV wideband and 0.3mV "A" weighted noise from the Parasound amplifier. The majority of that may still be from the Behringer itself.

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Living Room System

2-way with Acoustat 2+2 from 125Hz to 17k, and a pair of SVS Ultra PB 13 below 125Hz (linear phase LR8 crossover). Now using the best from 2 pairs of 2+2's, one white and one black, EQ'd to be the same. Acoustats powered by Aragon 8008 BB. All amps including Subs and Tweeters driven by Emotiva Stealth DC-1 DACs. DACs for each way driven by AES from Behringer 2496 DEQs (EQ and limiting), driven by AES from MiniDSP OpenDRC (linear phase FIR crossovers or corrections generated by RePhase). Driven by AES from a Henry Engineering AES 4-way splitter. Driven by AES from a Tact RCS 2.0 Digital Preamp with Room Correction and PEQ bypassed. The Tact receives most sources as digital. Analog sources are converted to digital at 24/96 by Lavry AD10 analog to digital converter on the side wall and sent via a 12 foot AES cable to the Tact. Emotiva XSP-1 serves as phono preamp and analog selector and level adjuster feeding the Lavry. Oppo UDP 205 plays most discs, and does streaming from my library and Qobuz using Roon, through digital coax output to the Tact, but in other cases through HDMI and a Kanex Pro De-Embedder, and in the rare remaining cases (used to be more) where neither digital transfer method retains full resolution, analog through balanced cables to the Emotiva and Lavry. Denon DVD-9000 plays HDCDs better than anything I know of and connects to Emotiva and thence Lavry for conversion to 24/96. A Sonos Connect is an alternate Tact source, and destination for the Pioneer F-26 FM tuner, which also plays in other rooms through Sonos. A Dynavector 17DIII is mounted to the hockey-tape dampened Ittok tonearm on a Linn Sondek LP12 with Lingo external power supply, using a Michell plastic low spindle clamp is with a trimmed felt washer. There are seperate AC circuits for Subwoofers, Acoustat Poweramps, and Rest of System. The Rest of System circuit is conditioned and regulated by a Panamax MB 1500 and served via a variety of audiophile grade power strips. Single ended digital cabling by Blue Jeans Cable using Belden coax, and Blue Jeans LC-1 audio cabling. AES by Canare, Mogami, Gotham City, and Geistnote/Canare. PTFE balanced audio cable by Surf Cables. Speaker wire mostly hand twisted milspec PTFE coated 12g silver plated copper. Playlists generated by mplay version 0.69 soon to be released.