Dynaco PAS-2 Preamplifier

Name: Dynaco PAS-2
Brand: Dynaco

Fifty dollars and ninety-five cents bought you a kit, a pair of factory-wired circuit boards, and roughly eight hours of soldering between you and a tube preamp.

Overview

The PAS-2 is a two-channel tube preamplifier control unit. Dynaco sold it as a factory-wired instrument and as a kit. The kit price was $50.95. The wired version ran $99.95. That gap tells you who the kit was for: the hobbyist with a soldering iron and a Saturday, not the customer who wanted a box to plug in.

For that money the buyer got a self-powered preamp with all the amplification, equalization, and control facilities needed for phonograph records, tape, radio, or microphone sources, in stereo or mono. Dynaco's own literature calls it a deluxe stereo control unit with unusual versatility and flexibility. As many as seven stereo or fourteen monophonic inputs can be used, and the front panel stays simple and uncluttered anyway.

Dynaco's assembly documentation is candid about the build. The kit uses two factory-assembled printed circuit boards that carry roughly three-quarters of the components. Average construction time is quoted at approximately eight hours. That number comes from the people who wrote the manual, not from a marketing estimate. It also explains why so many surviving PAS-2s are somebody's build project rather than a factory product.

Dynaco states that all stages are enclosed in feedback loops and adjusted for minimum distortion and noise, and that the topology was the subject of patent applications. The manual's claim is that signals passing through the preamplifier are not audibly changed. The stated goal is amplification and reproduction of the original signal without alteration. Whether any tube circuit fully delivers on that is a separate argument, but it is the design intent on record.

Dynaco's published figures give frequency response of 10 cps to 30,000 cps, plus or minus 0.5 db, and intermodulation distortion below 0.05 per cent at sufficient output to drive an amplifier. The equalization network used components of one-per-cent tolerance in the critical RIAA stage, which is tighter than a lot of contemporary gear bothered with. High Fidelity (June 1964, p.29) reported on the PAS-2 in its individual Dynakit test coverage, and Dyna advertising of the era leaned on that kind of third-party validation. The ad copy is Dynaco's, not the reviewers'. The magazine's test reports are the part that carries weight.

The preamp breaks into five functional blocks. One is the shared power supply, with a full-wave rectifier and a power transformer. The other four are audio stages. There is an equalizer-amplifier stage for left and another for right, handling high-gain duties for magnetic phono cartridges and imposing the proper playback characteristic. There are also two amplifying-tone-control stages, one per channel, where high-level signals from a tuner pass through and where volume, tone, and similar controls live.

The power supply uses a separate rectifying system to provide direct current for heating the tube filaments. Many tube preamps of the period did not do this. Dynaco attributes the preamp's near-total absence of hum to it. That costs money and complexity in a budget product, and it is a large part of why these units are still usable today when plenty of cheaper contemporaries hum themselves out of the room.

Living With One

Owners report that the PAS-2 is a quiet preamp when it's healthy, and the DC filament supply is doing real work there. Dynaco's own troubleshooting notes are a useful field guide to what goes wrong. Hiss, per the manual, is almost invariably a tube or a noisy resistor. The diagnostic procedure is low-tech: swap tubes between channels and see whether the noise follows. If hiss is present with the volume all the way down, the trouble is more likely on the PC-5 board, with the 470,000-ohm and 4,700-ohm resistors in the first stage as the prime suspects. On the PC-6 board, check the 150,000-ohm and 1,000-ohm resistors in the first stage plate or cathode.

One piece of advice in the service documentation catches out first-time owners. With the cover off, hum level is many times higher than with the cover on and properly secured with the sheet metal screws. Testing for hum or noise has to be done with the cover in place, or you'll chase a problem that doesn't exist.

Voltage checks are the other diagnostic route, and they need a decent meter, either a vacuum tube voltmeter or a 20,000-ohms-per-volt unit. Deviations greater than 20 per cent from the published voltage chart may indicate malfunction. The manual notes that deviations as high as 50 per cent won't cause complete loss of sound, so the unit can be measurably off-spec and still play.

The preamp is designed for the conventional 117-volt line input found in most homes. Dynaco states operation up to 125 volts causes no problem. Above that, a voltage regulating or adjusting device is recommended, and the guarantee is void if the unit is run above the 125-volt rating.

The PAS-2 deliberately has no phase reversal and no channel reversal. Dynaco's reasoning, spelled out in the manual, is that both are standardized in all program material. Pre-recorded tapes and discs have standardized left and right channels, and phase must be maintained for compatibility with monophonic equipment. For the experimentally inclined, the manual notes that small double-pole-double-throw switches can be added in the speaker leads between amplifier and loudspeaker, and that Dynaco would supply the information on request.

Factory Support and the Guarantee

All parts in the PAS-2 carried a one-year guarantee from purchase, with tubes on the standard EIA 90-day terms. Defective parts were replaced at no charge if returned prepaid to the factory, directly or through the dealer. After the guarantee period, Dynaco would supply any non-standard parts at net prices, and standard dealer items could be sourced from most electronic supply stores.

Factory service for a kit that didn't work or broke down ran $7.50 plus the cost of parts damaged by the user or past the guarantee period. The documentation is blunt about the conditions. No parts were replaced and no service was available for kits where the guarantee post card hadn't been returned, and the factory reserved the right to limit the service facility to one year from date of purchase. Kits with incomplete wiring, non-rosin-core solder, or unauthorized modifications were excluded. The serial number had to be mentioned in all correspondence, and the instruction book carried its own serial number for that purpose.

One specific warning: if the PA-211 transformer is returned for factory repair or exchange, it should be removed without cutting the leads short. Leads cut rather than unsoldered void the transformer guarantee.

Shipping instructions were just as specific. A preamp sent for service needed a note giving symptoms, sender name and address, and serial number. It also needed stuffing inside the cover to keep tubes from falling out of their sockets, and a rugged carton with several inches of soft packing. The original carton is explicitly called out as not suitable for shipping a wired preamplifier. Dynaco also disclaimed responsibility for damages or injuries sustained in assembly or operation. These were kits, and the builder owned the outcome.

Who It Was For

The PAS-2's pitch was versatility at a price, and the contemporary advertising makes the target plain. Dynaco's magazine campaigns of 1964 posed two customer questions side by side. One came from the buyer who wanted the finest possible system with price no object, the other from the buyer with a limited budget. Both got the same answer: Dyna. The supporting argument was third-party validation, citing editors, reviewers, test laboratories, and independent consumer testing organizations, with High Fidelity (August 1964, p.8) among the magazines running individual Dynakit test reports. Audio (October 1964, p.71) carried the same Dyna advertising that October.

That's marketing, but the proposition behind it was real. The preamp could handle seven stereo inputs, run from any power amplifier thanks to its built-in supply, and be assembled by a competent hobbyist in an evening for half the wired price. The PAS-2 was designed to pair with Dynaco's own power amplifiers, but the self-powered design means it doesn't require one. It works with any amplifier, which is part of why so many survived in systems that long ago shed their original Dynaco power stages.

A period owner writing in 1961 documented one point of friction: the master volume control had to be changed several times, at Dynaco's expense, before one was found that tracked reasonably accurately. The same owner argued the volume control should have been a stepped design, even with 20 per cent tolerance resistors. A PAS-2 whose channels don't track evenly at low volume may simply be showing a known weakness rather than a fault.

That same 1961 account notes the PAS-2 addressed a limitation of the earlier PAM-1 and DSC-1 combination by providing for both a tape head and a second RIAA input. In that owner's assessment, the PAS-2 offered several advantages over the earlier pairing, particularly in cost, but did not have quite the same versatility.

Market Value

┌──────────────────────────────────────────────────────────────────────────┐
│ DYNACO PAS-2                                                    Nov 2026 │
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│ High      $959                                    Latest            $445 │
│ Median    $374                                    Trend                — │
│ Low       $60                                     Volume           ~3/mo │
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│ $1,000 ┤                                                                 │
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│   $593 ┤                                                                 │
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│        │      .     .  . .  .                    .           ..          │
│    $50 ┤         .  .           .                                        │
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│    vol │▂     ▂  ▂ ▂█ ▂▂ ▂  ▄▄  ▄   ▂   ▂▂   ▂  ▂▂        ▂  ▂▂         ▂│
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│         2026-02                      2026-06                      2026-09│
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