DENON PMA-235
¥ 66,500 (around 1975)
Commentary
A pre-main amplifier developed with an emphasis on the wide range response.
The PMA 235 is designed not only with good frequency-to-amplification characteristics, but also with careful consideration of all physical characteristics including output bandwidth, input / output impedance, phase, transient characteristics, crosstalk, etc., even in the inaudible range.
A pure complimentary service circuit using a Darlington power transistor of Motorola U.S.A. is adopted for the output stage of the power amplifier section. By combining a direct-coupled OCL circuit for all stages of differential amplification, a large radiator with good heat radiation effect, and a powerful power supply circuit, the sine wave continuous rated output has a margin and a stable design.
The power supply section is equipped with a triple magnetic shield power transformer and a large-capacity power supply capacitor.
The equalizer amplifier section uses a 3-stage direct-coupled emitter-emitter negative feedback circuit using a low-noise, high-voltage NPN transistor. It is operated at a high voltage of 53 v using a stabilized power supply without ripple voltage or voltage fluctuation. This increases the bare gain of the equalizer amplifier, increases the maximum output level, and ensures a maximum allowable input of 200 mVrms or more at 1 kHz.
The large naked gain can apply deep negative feedback to suppress the high-frequency bounce phenomenon caused by the lack of RIAA negative feedback. In addition, the negative feedback circuit uses a film capacitor with an error of ± 1% and a non-inductive resistor with an error of ± 2% to achieve good RIAA deviation. At the same time, DC negative feedback is also adopted to ensure high accuracy up to the inaudible region, as well as improvements in ultra-low transient characteristics, SN ratio and harmonic distortion rate.
A 3-stage direct connection circuit composed of NPN-FET-NPN transistor is adopted for the control amplifier section.
In addition, a newly devised tone control negative feedback circuit is incorporated, and both Bass and Treble are automatically at the center. This eliminates an independent defeat switch and dramatically improves the frequency response at the time of defeat by flattening from 5 Hz to 300 kHz.
The low filter has a cut-off frequency of 20 Hz as low as possible so as not to affect the low-frequency audio characteristics, and the attenuation characteristic is 12 dB due to the active type using transistors.
When this filter circuit is OFF, the transistor circuit is degraded.
The high filter has a characteristic of a simple octave of 6 dB.
As for the internal structure, the power transformer is placed in the center of the rear part and the large radiator of the output stage is arranged on the left and right sides. This improves heat radiation and convection effect, eliminates structural waste, and improves the balance and separation of the left and right channels electrically.
In order to make the power stage more stable and bring out the true value of the speaker, we carefully select the materials including wire and contact to lower the output impedance.
The speaker terminal uses a screw structure with low contact resistance and reliable connection.
In order to respond to erroneous operations such as short-circuiting of the speaker terminals, a unique protection circuit with an extremely fast response speed is incorporated to prevent damage to the power transistor.
All printed circuit boards are made of copper-clad laminate with self-quenching properties. The power cord is coated with synthetic rubber, which is resistant to heat and aging, and is designed with safety in mind.
Tantalum capacitors with high selection rank are used throughout the circuit to reduce switching noise.
There was a wood cabinet as an option sold separately.
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Model Rating
| Type | Pre-main amplifier | ||
| Power Amplifier Unit | |||
| Circuit system | Pure complimentary service all-stage direct connection 2 power supply OCL circuit | ||
| Dynamic Power (IHF) | 160W (80W + 80W, 4 Ω) 108W (54W + 54W, 8 Ω) |
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| Rated Output (Both Channels Driven, Sine Wave Continuous Output) | 50W + 50W (4 ω, 1 kHz) 40W + 40W (8 ohm, 1 khz) 43W + 43W (4 ohm, 20 hz to 20 khz) 35W + 35W (8 ohm, 20 hz to 20 khz) |
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| Total harmonic distortion factor | 0.08% or Less (at Rated Output) | ||
| Intermodulation distortion factor (60 hz : 7 khz = 4 : 1) | Not more than 0.1% | ||
| Power Band Wiz (IHF, both channel drive) | 5 Hz to 45 kHz | ||
| Frequency characteristic | 5 Hz ~ 200 kHz + 0 -1dB | ||
| Input sensitivity | 1Vrms | ||
| Input impedance | 80k Ω | ||
| Output impedance | 0.16 Ω or less | ||
| Residual noise | 0.3 mVrms or less | ||
| Output terminal | Speaker terminals A and B : 4 Ω ~ 16 Ω Headphone terminal : 4 Ω ~ 16 Ω compatible |
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| Preamplifier Section | |||
| Input Sensitivity / Impedance | Phono1 : 2.3mVrms/60k Ω Phono2 : 2.3mVrms/30k Ω Tuner, Tape : 150mVrms/70k Ω Aux : 150mVrms/40k Ω |
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| Equalizer amplifier section (Phono to Rec out) | |||
| Circuit system | NPN transistor 3-stage direct connection E-E feedback type | ||
| Maximum allowable input | 200 mVrms or More (1 kHz) | ||
| Maximum power output | 20Vpeak | ||
| Rated output | 150mVrms | ||
| Total harmonic distortion factor | 0.02% or Less (1 kHz at Rated Output) | ||
| Rec Out Compatible Load Impedance | 100k Ω or more | ||
| RIAA deviation | 20 Hz ~ 20 kHz + 0.15 -0.3 dB or less | ||
| Tone amplifier (Aux to Pre out) | |||
| Circuit system | NPN, PNP, NPN transistor 3-stage direct connection NFB type | ||
| Total harmonic distortion factor | 0.02% or Less (1 kHz at Rated Output) | ||
| Pre-out applicable load impedance | 100k Ω or less | ||
| Frequency Response (at Tone Defeat) | 5 Hz ~ 300 kHz + 0 -1dB | ||
| Tone Control Variable Range | Bass : 80 Hz ± 10 dB, Turnover frequency 400 Hz Treble : 12 kHz ± 10 dB, turnover frequency : 2.5 kHz |
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| Filter characteristic | Low : 20 Hz, 12dB/oct. High : 8 kHz, 6dB/oct. |
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| Loudness control characteristics (for a level of 1 kHz) | Low:100Hz +8.5dB High:10kHz +4.0dB |
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| Muting (vs. level at 0 dB) | -20dB | ||
| Overall characteristic | |||
| Transmission frequency characteristic | Phono in ~ Speaker out : 20 Hz ~ 20 kHz + 0.15 -0.4 dB Aux in ~ Speaker out : 20 Hz ~ 20 kHz + 0 -0.3 dB |
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| Total harmonic distortion factor | Phono in ~ Speaker out : 20 Hz ~ 20 kHz 0.1% or less | ||
| S/N ratio (IHF, input short circuit, A-network used) | Phono1, 2 : 75 dB or more Tuner, Aux, Tape : 80 dB or more |
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| Channel separation |
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| Power outlet | Switched : 2 systems, 250W Unswitched : 1 line, 150W |
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| Pwer | 100 VAC, 50Hz/60Hz | ||
| Power consumption | 100W (Electrical Appliance and Material Control Law) | ||
| External dimensions | Width 396x Height 147x Depth 281 mm | ||
| Weight | 11kg | ||
| Sold Separately | Wood Cabinet ACA-5 (¥ 5,000) | ||
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