Hafler P500
Six MOSFETs per channel, a 255-watt conservative rating, and enough reserve to open a supply fuse into a dead short — the pro-rack Hafler that studios bought by the pair.
Overview
The P500 is a two-channel professional power amplifier from the David Hafler Company, and the spec that tells you what it is comes from the manufacturer's own literature: 255 watts per channel continuous into 8 ohms, conservatively rated, with more than 300 watts available across the audio band before clipping ever sets in. That gap between the printed number and the real one is the whole personality of the thing. Hafler underrated it on purpose, and the design team backed the rating with six high-power MOSFETs per channel — devices with enough current capability to shrug off reactive loads that would send a lesser amp into protection.
The short-form ratings are impressive enough on paper. Short-term continuous output runs in excess of 500 watts per channel into 2 ohms, and bridged to mono the amplifier is rated at 800 watts into 8 ohms — enough, per the manufacturer's own documentation, to drive a 70-volt line distribution system directly. In practice, the literature claims well over 900 watts of mono power is available. The caution that accompanies those figures is worth repeating: each channel can deliver more than 20 amperes into a short circuit before the supply fuses open, and Hafler's own manual warns plainly that such reserves will disable most loudspeakers if improperly applied. This is not a polite audiophile amp. It is a workhorse with a temper.
The design choices reflect the professional installation market rather than the living room. Load connections are notably rugged binding posts on ¾-inch centers, spaced so dual banana plugs drop straight in. The mono-stereo bridging switch lives on the back panel instead of hiding inside the chassis. A choice of input connectors is provided for, and both balanced and unbalanced inputs can be accommodated — Modern Recording (January 1984, p.49) noted that the P500's internal circuitry is not too unlike the company's DH-500A, with the differences between the two lying mainly in the professional version's provision for a variety of input connections and options. Air filters and loudspeaker fuses can be swapped without dismounting or opening the amplifier, which matters when the amp is bolted into a rack and the session is running.
That rack heritage is not marketing talk. Mix (March 1984, p.14) described the David Hafler Company as having earned a reputation for producing state-of-the-art power amplifiers at rock-bottom prices, with the DH-220 and DH-500 well known for sound quality, reliability, and value — the family the P500 grew out of. The pro-audio press took the P500 seriously on its own terms. Recording Engineer ran the same assessment of the company's standing, and the amplifier turns up in the period's studio equipment lists: one facility in Burbank acquired a P500 specifically to drive a pair of Yamaha NS-10M close-fields, and a Los Angeles studio's gear inventory lists the P500 alongside a GML mic preamp and a Mastering Lab tube preamp. When the small monitors that define an era's mixing sound need an amp that will not flinch, this is what got bolted in.
The price story is part of the appeal. Allied Broadcast Equipment's catalog listed a manufacturer's suggested list price of $950.00 for the P500 — serious money in early-1980s dollars, but modest against what 255 conservative watts per channel normally cost. Hafler's whole reputation rested on that ratio, and the P500 carried it into the professional market without apology. The MOSFET output stage, the overrated components, the rugged construction — all of it was aimed at installers who needed an amp to survive a decade of abuse and still measure clean.
What the P500 is not is a collector's showpiece. It is a black-box professional amplifier, and the market treats it accordingly: buyers want working units with intact binding posts and unblown output stages, not museum pieces. The design's thermal limits are the practical ceiling — operation into loads below 2 ohms is safe but restricted by heat, so rack ventilation is not optional. The supply fuses are the sacrificial part, and the fact that the amp can open them into a dead short is a feature, not a fault. For anyone running inefficient speakers or a small studio's monitor chain, the P500 remains one of the honest bargains of the MOSFET era: underrated, overbuilt, and entirely unbothered by the load you attach to it.
eBay Listings
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.