For your kind consideration is this Dynaco PAS stereophonic preamplifer. It's in great condition with just a few very light scratches as shown in photos. It has been upgraded with a modern black faceplate showing input options for CD/DVD. The tube on far right is a vintage RCA 12X4 made in USA and the four 12AX7s are modern JJ replacements. Unit came from a working environment and is fully functional and sounds great. Enjoy!
The venerable Dynaco PAS is perhaps the most famous stereo preamplifier of all time, Much like the Dynaco ST-70, it introduced the magical sound of tubes to thousands of audiophiles throughout the past decades. The PAS is still a popular model, both in stock form or as a platform to be tweaked and modified.
All PAS preamplifiers share the same circuit: For the phono stage, one 12AX7 per channel, each section in series, using loop negative feedback connected to a capactior and resistor network to provide the RIAA equalization. For the linestage, a 12AX7 per channel, each section in series, utilizing loop feedback to lower distortion and provide a low enough output impedance to drive cables into a high impedance input of an amplifier. Power supply rectification is handled by a 12X4 tube. Filaments for the 12AX7s come from a voltage-doubler circuit, which - as the namesake suggests - doubles the supplied AC voltage from the transformer and smooths it out to DC. Having DC on the filaments also helps to reduce hum.
Specifications
Frequency response: 10Hz to 40kHz
Total harmonic distortion: 0.05%
Gain: 60dB (MM), 20dB (line)
Signal to noise ratio: 74dB (MM)
Valve complement: 4 x 12AX7 (ECC83), 1 x 12X4
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