Introduced in 1978, the Hitachi SR-2004 receiver fits snugly into the monster category at 200 watts per channel. Hitachi’s top-of-the-line receiver was on par with, or better than, other leading brand receivers. At $949.95 the retail price of the SR-2004 was steep but reasonable given its features and performance. The amplifier, phono and FM sections are all excellent.
Styling
The styling of the SR-2004 is a bit industrial but still looks nice. The cabinet is similar to the Pioneer SX-1250 in that the front half of the cabinet is wood (actually rosewood vinyl I believe) and the back half, metal and heat sinks. The back half is where the massive toroidal transformer sits along with four large power supply capacitors.
Controls
The front panel is well laid out and symmetrical. The light-colored dial scale for FM station frequencies is flanked on the left by a pair of power output meters. On the right are signal strength and tuning meters. FM frequencies are linearly marked, with indicator lights above the dial for selected program source, stereo reception, and auto-lock tuning. The auto-lock activates when releasing the tuning knob after selecting a station, providing a refined version of automatic frequency control.
Below the dial is a protection circuit indicator light. Four groupings of oval push buttons follow. The first three select speakers, with additional buttons for low and high cut filters, MPX noise filtering, FM mute defeat/auto-lock cancel, IF bandwidth selection, and multipath switching for the signal strength meter. Other buttons allow switching between mono and stereo, loudness compensation, and an adapter mode to insert external processors.
The lower section of the front panel has controls for power on/off, headphone jack, bass/treble turnover frequencies, bass/midrange/treble tone adjustments, balance, muting lever, master volume, tape recording/monitoring, program source selection, microphone mixing level, mic input, and a large tuning knob with flywheel mechanism.
Tuning Section
The FM tuner section of the Hitachi SR-2004 uses three dual-gate MOSFET transistors and a five-section variable tuning capacitor for station selection. The intermediate frequency (IF) amplifier system has both wide and narrow bandwidth settings. The IF section also has six differential amplifier stages using three integrated circuits (ICs).
FM stereo decoding starts with quadrature detection to recover the composite stereo multiplex (MPX) signal. A phase-locked loop circuit in a dedicated MPX IC then decodes the left and right stereo audio channels.
The AM tuner uses a ceramic filter and three-gang variable capacitor for station tuning.
The Hitachi SR-2004 looks fabulous when it’s lit up in a darkened room.
Here’s what owner’s of the Hitachi SR-2004 have to say about it:
I am just going to say it. The Hitachi SR-2004 is (all things considered) the best home vintage audio receiver ever made.
The SR-2004 is one fine sounding receiver. It is better than any Pioneer or Yamaha receiver I’ve heard and I have heard plenty.
One of the most awesome looking receivers I’ve ever owned.
In this picture from the cover of the May 1978 Stereo Review magazine, you can see the Hitachi SR-2004, second down from the top. It’s in good company along with a Pioneer SX-1980, Rotel RX-1602, Marantz 2500, Kenwood KR-9600, and the hard to find Nikko NR-1415 on top. By the way, is that guy in the ad levitating above the chair?
Specifications
- Tuning range: FM, MW
- Power output: 200 watts per channel into 8Ω (stereo)
- Frequency response: 10Hz to 40kHz
- Total harmonic distortion: 0.08%
- Damping factor: 75
- Input sensitivity: 3mV (mic), 2.5mV (MM), 450mV (DIN), 150mV (line)
- Signal to noise ratio: 75dB (MM), 90dB (line)
- Output: 150mV (line), 40mV (DIN)
- Dimensions: 22 3/4″ W x 7 1/2″ H x 17 1/2″ D (580 x 186 x 447mm)
- Weight: 56.2 lbs (25.5kg)
Here’s an ad touting the Hitachi SR-2004’s Class G amplifier and 200 watts per channel.
Amplifier
The amplifier in the SR-2004 is what Hitachi called ‘Series E’ but is also known as a Class G amplifier. Here’s an explanation of the idea behind the Class G amplifier circuit for those that are unfamiliar with it.
The “Class G” amplifier design uses four transistors per channel instead of the usual two transistors. The transistors are connected in series in pairs. One pair of transistors is powered by a lower voltage supply, while the other pair is powered by a higher voltage supply.
When the output signal amplitude is small, only the lower powered transistor pair amplifies the signal. When the signal amplitude increases past a certain level, the higher powered transistor pair turns on and takes over the amplification, while the lower powered pair turns off.
This design allows each set of transistors to operate in their most efficient and linear range, improving the overall efficiency compared to a Class B amplifier. The tradeoff is increased complexity with four transistors per channel instead of two, and more transition points as each pair turns on and off. Extra circuitry is used to minimize switching distortion at these transition points.
The Class G design can deliver higher “dynamic” or “music” power than a Class B amplifier, since the high voltage transistors can handle greater power demands. In summary, the Class G design improves efficiency and power delivery through the use of multiple power supplies and transistor pairs operating in their optimal ranges.
Hitachi called the extra power utilized for brief intervals as ‘Music Power’ and rated it at 400 watts. It’s really what is called ‘Dynamic Headroom’ and was measured a 4 dB by a leading magazine at the time. That’s a substantial amount of headroom.
Audio magazine had this to say about the SR-2004’s amplifier section after bench testing it:
Continuous power output per channel, with an input test signal of 1 kHz, was 252 watts per channel for the rated THD figure of 0.08 per cent. At 200 watts per channel output, using 8 ohm loads, THD measured only 0.01 per cent while IM distortion measured 0.04 per cent. With power bandwidth (at the 200 watt level) extending from a low 9 Hz to 44 kHz, actual FTC rated power within the stated power band from 20 Hz to 20 kHz was 222.6 watts as opposed to the 200 watts claimed. Dynamic headroom was higher than that of any receiver we have measured since we began testing for this new specification. It measured just under 4.0 dB, substantiating Hitachi’s claim that the receiver can deliver far more power under short-term musical signal conditions than might be suggested by its continuous power rating. Harmonic distortion plus noise is plotted as a function of continuous power output per channel for this receiver in Fig. 7, while in Fig. 8 we have shown the THD plus noise at all frequencies within the audio band for rated (200 watts per channel) output.
That toroidal transformer and the power supply caps are HUGE!
Rear Panel
The rear panel of the SR-2004 provides connections for multiple speakers and external components. There are three sets of spring-loaded speaker terminals as well as three AC powered outlets, with two un-switched and one switched. Preamp output and main amp input jacks allow connection of external processors in the signal chain.
Horizontal and vertical oscilloscope output jacks are provided for visually monitoring multipath distortion. Connections are included for tape recording and monitoring, an auxiliary input, and two phono inputs. An extra set of adaptor jacks are controlled by the front panel adaptor on/off switch which is handy.
Antenna connections are provided for AM, 300 ohm FM, and 75 ohm FM. A chassis ground terminal is located near the phono inputs. An AM ferrite bar antenna can swing out from the rear panel for better AM reception.
Hitachi’s SR-2004 is quite a receiver. The audio magazines of the day had great things to say about it:
The Hitachi SR-2004 offers a classic example of a receiver that delivers “louder” sound without distortion than other similarly rated units. – Stereo Review 1978
Needless to say, the Hitachi SR-2004 leaves little to be desired in the way of power capacity. It is a receiver that will take even a low-efficiency speaker system in stride, and we’d have to stretch our imagination to conceive of a home situation in which higher sound levels would be desired. By coupling this brawny amp with a tuner that is above average, Hitachi has created a strong contender in its SR-2004. – High Fidelity 1978
Monster receivers with similar features and performance can go for ridiculous money these days. Especially if they are named Marantz, Pioneer, or Sansui. But a Hitachi? Fortunately, if you’re looking for one, the SR-2004 is far more reasonably priced than say a Marantz 2500. So, if you have a chance to check one out, do so.
