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I examined the electrical impedance of the Etymotic hf2 & hf5 headphones with my Audio Precision System One and with both pairs of headphones inserted in my ear canals. Fig.1 reveals that other than a small difference in the presence region, the two have identical impedances. The rise in positive phase angle with increasing frequency for both headphones is due to the armature's inductance; with earlier iPods and other players that have a high source impedance, this will boost the Etymotics' top-octave response a little.

Fig.1 Etymotic hf2 (…

When I first wrote about Pure Vinyl in the March 2009 "Analog Corner," Robinson recommended…

Description: Solid-state phono preamplifier with flat and RIAA-equalized inputs. Inputs: XLR (balanced); RCA (balanced; functions as single-ended/balanced adapter). Outputs: XLR (balanced), RCA (single-ended). RIAA compensation curve (with Hardware RIAA Correction Module) accuracy: ±0.1dB.Voltage gain (add 12dB for Hardware RIAA Option): 43, 46, 48, 52dB. Frequency response: DC–5MHz, –3dB at all gain settings. Maximum input resistance: 2k ohms; rear-panel rotary switches for selecting 25, 50, 100, 150, 200, 500, 1k ohms; custom-value plug-in resistors can also be…

Analog Sources: Continuum Audio Labs Caliburn, Cobra, Castellon turntable, tonearm, stand; Graham Phantom II tonearm; Ortofon A90, ZYX R1000 Sigma 2 cartridges.
Digital Sources: Playback Designs MPS-5 SACD/CD player, Camelot Roundtable Anagram Technologies DAC, BPT-modified Alesis Masterlink hard-disk recorder, Sooloos music server, Macintosh G5 computer with Lynx L22 soundcard.
Preamplification: Abbingdon Music Research PH-77, Boulder Amplifiers 1008 & 2008, Vitus Audio MP-P201 phono preamplifiers; darTZeel NHB-18ns preamplifier.
Power…

I measured the Seta Model L with Stereophile's loan sample of the Audio Precision SYS2722 system (see the January 2008 "As We See It" and www.ap.com). I experimented with the grounding between the preamp and the analyzers to get the lowest level of noise. To fully charge the Model L's batteries, I left it plugged into the wall overnight. It ran off battery power for the measurements.

All the Model L preamplifier's inputs and outputs preserved absolute polarity; ie, were non-inverting. However, there was a problem with the right channel's Flat output. While…

When I first wrote about Pure Vinyl in the March 2009 "Analog Corner," Robinson recommended…

Description: Solid-state phono preamplifier with flat and RIAA-equalized inputs. Inputs: XLR (balanced); RCA (functions as single-ended/balanced adapter). Outputs: Flat signal, XLR (balanced); RIAA Corrected (switchable to Flat) on single-ended RCAs. RIAA compensation curve accuracy: ±0.1dB, 20Hz–20kHz. RIAA compensation curve channel match: ±0.02dB, 20Hz–20kHz. Switchable RIAA high-pass filter: 10Hz, 12dB/octave, –0.3dB at 20Hz. Voltage Gain: 47dB (flat output): 60dB (RIAA). Frequency Response: DC–8MHz, –3dB (Flat Outputs, Balanced Input, with MC Cartridge…

Analog Sources: Continuum Audio Labs Caliburn, Cobra, Castellon turntable, tonearm, stand; Graham Phantom II tonearm; Ortofon A90, ZYX R1000 Sigma 2 cartridges.
Digital Sources: Playback Designs MPS-5 SACD/CD player, Camelot Roundtable Anagram Technologies DAC, BPT-modified Alesis Masterlink hard-disk recorder, Sooloos music server, Macintosh G5 computer with Lynx L22 soundcard.
Preamplification: Abbingdon Music Research PH-77, Boulder Amplifiers 1008 & 2008, Vitus Audio MP-P201 phono preamplifiers; darTZeel NHB-18ns preamplifier.
Power…

I measured the Seta Nano phono preamplifier with Stereophile's loan sample of the Audio Precision SYS2722 system (see the January 2008 "As We See It" and www.ap.com). I experimented with the grounding between the preamp and the analyzers to get the lowest level of noise.

Housed in an enclosure the size and proportions of an Apple Mac mini computer, the Nano crowds together pairs of balanced and unbalanced inputs and outputs on its rear panel, as well as rotary switches for adjusting the resistive loading of each channel, a ground terminal, and a trimmer to…