DENON TU-355

Commentary

FM stereo tuner using drum type tuning system.

A drum type tuning system is used for the dial part.
In this system, a 12 cm diameter drum is used for the dial part, and the scale is lengthened while the panel area is reduced. The total travel length of the scale (75 ~ 91 MHz) is 28.3 cm, and it is easy to see that one scale is equal spacing of 200 kHz together with the frequency proportional type varicon.
Since high-precision stainless steel shaft and alloy bearing are used for the dial rotation mechanism, even the frequently used tuning knob maintains the initial smoothness for a long time.

The tuning instruction is a 2-meter type consisting of a signal meter and a center type tuning meter.
The large meter at the left end is also used as a signal meter and can read the input voltage of the antenna terminal.

The left and right level meters can also be used as independent measuring instruments.
With a high input impedance of 200k Ω, it is possible to measure the steady state audio signal voltage from approximately -30dB (24.5 mV) to + 33 dB (34.6 V) by switching the front external Att.
It can also be used as an amplifier output meter by combining it with an amplifier that does not have a level meter.

In the front-end section, the input signal is first passed through a single tuning circuit of a series of varicon, and then the high-frequency amplification of the dual-gate MOS-FET is performed immediately to maintain high S/N against weak radio waves.
After that, it is mixed and amplified with local oscillation frequency by a dual-gate MOS-FET through a triple tune circuit of three varicon series, and the configuration is designed so that it does not distort even strong radio wave and does not cause blocking phenomenon with appropriate gain setting.
A modified clap-type oscillation circuit is used for the local oscillation circuit. This circuit has many advantages such as that the transistor is less affected by voltage fluctuation and temperature change due to the grounded collector type, and the output has less harmonics.
In addition, a temperature compensation capacitor and an oscillation coil with resistance to temperature and humidity are adopted. Moreover, the oscillation output is injected into the second gate of the dual gate FET for mixing through one stage of buffer amplifier, so the oscillation frequency is extremely stable. This eliminates the problematic AFC circuit.

The IF section consists of two circuits. It consists of an original amplifier circuit and a sub amplifier circuit for the control system such as signal meter, multi-pass vertical output terminal and muting circuit. This configuration reduces the occurrence of new harmonics, phase modulation and cross modulation interference in the main IF section.
The main through differential amplification by transistors with a wide dynamic range, the main amplifier circuit forms multistage amplification with good linearity mainly by IC-2 pairs directly connected to three stages of differential amplification. Four pairs of ceramic 2-element type filters with high selectivity and flat phase characteristics with an emphasis on sound quality are used as coupling and selection elements between them. Finally, a ratio detection circuit for wide band with low output impedance is adopted for FM detection.
A PLL circuit is used in the MPX section.

Both the left and right channels of the low-frequency amplifier are designed as two stage direct-coupled amplifier circuits.
In addition, unnecessary leakage such as pilot signal and subcarrier is cut off with a low-pass filter of LC3-stage configuration.

Equipped with muting switch and high blend switch.

The Function Selector has a Stereo only position in addition to Mono and Auto positions.
This is a convenient function to select only stereo programs from the broadcast.
There was a wood cabinet as an optional item sold separately.

Model Rating

Type	FM tuner
Tuner Section
Circuit system	Frontgate MOS FET, RF1 stage, front end of 5 series varicon IF stage using 4 2-element phase flat filter
Receiving frequency range	76 MHz to 90 MHz
Intermediate frequency	10.7MHz
Practical sensitivity (IHF)	1.7 μ V
S/N 50 dB sensitivity	33 μ V
Effective selectivity (2-signal method))	85dB(IHF)
Image interference ratio	120dB(83MHz)
IF interference ratio	110dB(83MHz)
Capture Ratio (IHF)	1.0dB
Spurious response	110dB(83MHz)
AM suppression ratio	60dB(IHF)
<Audio section>
Circuit system	Adoption of phase-locked loop type stereo demodulation circuit
19 kHz & 38 kHz suppression ratio	75 dB or more
Frequency characteristic	20 Hz ~ 15 kHz + 0.2 -0.5 dB (with 19 kHz Filter)
Signal-to-noise ratio	mono:80dB stereo:75dB
Total harmonic distortion factor	Stereo : 0.15% at 1 kHz, 90% modulation Mono : 0.1% at 1 kHz, 100% modulation
Stereo separation	45dB(1kHz) 40 dB (100 Hz to 10 kHz)
Output voltage (at 100% modulation)	Fixed : 1 Vrms Variable : 0 V ~ 1.5 Vrms
Output impedance	Fixed : 4.7k Ω Variable : 1k Ω
Level Meter Section
External signal measuring range	-20, -10, 0, + 10, + 20, + 30 dB (0 dB, 0.775 Vrms)
Input impedance	150k Ω or more 200k Ω or more (listed in separate catalog)
Indication error	Within ± 0.2 dB (each range, 1 kHz, near VU scale 0)
Frequency characteristic	20 Hz to 15 kHz ± 0.5 dB
<General>
Connection terminal	Antenna terminal : 75 Ω F-type connector, 300 Ω, 75 Ω, screw type Multipath detection terminal, detection output terminal (output for 4 ch & SCA), audio output terminal (fixed / variable) Level meter external terminal and same path terminal
Pwer	100 VAC, 50Hz/60Hz
AC Socket	Unswitched 250 Wmax, single line
Power consumption	16W
External dimensions	Width 396x Height 147x Depth 281 mm
Weight	6.8kg
Sold Separately	Wood Cabinet ACA-5 (¥ 5,000)