What is stereo?

There are now two system of high fidelity, monophonic (monaural) and stereophonic. Monophonic is a system that starts from one microphone and is fed through a single high fidelity set. Stereophonic is a double system. Two separate microphones are placed at different sides of the orchestra and two different systems are used to keep the two signals or channels separated. Two separate speakers are used, placed on different sides of you room. Stereo is much like 3-D photography, two slightly different sound reach your ears giving you a new dimension in sound.

H.H. Scott '59

Marantz 2325

Tuner Section
Steep Quieting Slope
The quieting slope specification measures a tuner's ability to provide good signal-to-noise performance under actual operating conditions. it's a far more reliable indication of performance quality than the IHF (Institute of High Fidelity) sensitivity figure often quoted as the prime specification to consider when evaluating an FM tuner.
The IHF figure gives only the number of microvolts necessary for minimum quality reception. A signal with 3% distortion and noise (30 dB quieting) hardly qualities as high fidelity. A signal-to-noise ratio in excess of 50 dB (the revised 1975 IHF specification) is generally recognized  to be necessary for high quality listening. It is most important then, to examine a receiver's ability to quiet quickly beyond the 30 dB quieting point.
Quieting slope sensitivity figures measure the signal-to-noise ratio in the crucial five to 500 microvolt range, where the majority of usable broadcast signals fall. The steeper the slope, the quieter, and therefore the more listenable the station.
 Highly Sensitive and Selective RF Front End
Superior selectivity is assured by a five-gang tuning capacitor in the Marantz 2325 and 2275 and four-gang in the 2250B. A triple-tuned RF interstage on Models 2325 and 2275 and a dual-tuned RF interstage on Model 2250B provide excellent image and spurious response rejection.
Marantz FET RF amplifiers and mixer stages provide excellent spurious signal rejection and extremely low noise operation that results in excellent quieting sensitivity.
 Phase Loced Loop FM Stereo Demodulator
The Phase Locked Loop (PLL) design was developed originally to provide  a state-of-the-art communication system for the space industry. Today  the same technology is used in all Marantz tuners and receivers to assure you of low distortion,excellent stereo separation and superior noise rejection.
PLL circuitry positively locks to the stereo pilot signal broadcast by a FM station. This precise "phase lock" is absolutely necessary for high performance in the stereo demodulation process. It enables the multiplex demodulator to separate the stereo channel information from the FM multiplex signal with more accuracy and less distortion than multiplex demodulators using other designs.
In addition, PLL is dependent on pilot phase and not on pilot amplitude, making it less susceptible to false triggering from various types of noise interference.

Ceramic IF Filters
The performance of an FM tuner is determined to a great extent by the performance of its Intermediate Frequency (IF) amplifier. The ideal IF amplifier should accept the desired band of frequencies with minimum phase distortion, while rejecting all adjacent frequency signals.
Marantz stereo receivers feature IF amplifiers consisting of ceramic filters, whose characteristics produce a 200 kHz passband that's linear in phase. This eliminates a major source of high frequency distortion and of loss of stereo separation. Sharp cut-off slopes improve the tuner's rejection and selectivity characteristics, permitting clear reception even when stations are closely spaced.
 Positive FM Muting
FM tuning is made completely noise-free by a special parametric-type muting circuit. The circuit responds to three characteristics of the FM signal: RF noise level, RF signal strength and DC offset at the ratio detector, thus assuring positive muting of the audio signal even under the most adverse conditions.
 FM Dolby De-Emphasis Network
Today there are more than 100 FM stations throughout the U.S. broadcasting with a Dolby Noise Reduction System, and others are sure to follow. To help you recieve the clean, quiet FM reception promised by these Dolbyized broadcasts, Marantz Models 2325, 2275, and 2250B incorporate a built-in 25 microsecond Dolby FM equalization circuit that provides complete de-emphasis compatibility when used with a Dolby Noise Reduction system. 
(NOTE: Model 2325 also has a complete Dolby Noise Reduction system built-in)
Noise from a Dolbyized FM broadcast can be reduced approximately 12 dB by changing the de-emphasis curve from 75 to 25 microseconds and utilizing the Dolby system. This is the equivalent of reducing the noise power of a received FM broadcast sixteen times below normal.
Dolby encoding allows an FM station the choice of operating with significantly reduces distortion, while still improving signal-to-noise ny approximately 9 dB - or of broadcasting a signal that's effectively double in strength with a signal-to-noise improvement of approximately 12 dB.

Flexible Tone Controls
The more flexible the tone controls, the more accurately you can adjust for non-linearities in frequency response caused by speakers, speaker placement, room acoustics of the program source itself. The tone control system in Marantz Models 2325, 2275 and 2250B features a sophisticated five-position tone turner/mode switch for versatile bass, midrange and treble control. This eliminates a major shortcoming of conventional tone controls - their tendency to affect too wide a band of frequencies. Optional frequency turnover points limit the effect of the bass and treble controls to just the desired range.
The advantages can be illustrated by a practical example: Boosting the low bass (under 100 Hz) to compensate for a deficiency in room acoustics. Most conventional tone control, even if capable of supplying the boost,  will also increase the output in the 300 Hz to 1000 Hz region. With the turnover point set at 250 Hz on a Marantz receiver, the bass control can provide the desired bass boost (or cut) up to the frequency point of 250 Hz, and leave the frequency range above the point essentially flat and unaffected.
This flexible, easy-to-set system permits over seven million combinations of repeatable tone control settings, enabling you to adjust for the desired tonal balance in any listening environment.
 High performance Phono Preamp
Low noise and a wide dynamic range are of paramount importance in the circuit design of a phono section.
The three-stage, 40 dB gain amplifier built into Marantz receivers utilizes feedback-equalized circuitry to maintain extremely low distortion.
the use of close tolerance, stable components, such as tantalum input coupling capacitors, low noise carbon film resistors, Mylar output coupling and polystyrene-type equalization capacitors assures superior performance.
RIAA equalization is precise - within +/-0,5 dB, from 20 Hz to 20 kHz -  and under test in the 2325, the equivalent noise input to the phono section measures a low 0,8 microvolts. The phono overload point occurs at over 100 millivolts in the 2250B, and at over 125 millivolts in the 2325 and 2275. These figures result in a dynamic range capability of greater than 96 dB.
 A full Complement of Inputs and Outputs
In addition to the standard phono and auxiliary inputs, two sets of tape inputs and outputs are provided to facilitate copying from one tape deck to another. Front panel dubbing jacks allow you to add a third tape deck without disrupting any rear panel connections.
The preamp-out/main-in jacks on the rear panel enable you to use the preamplifier and amplifier sections independently. You get simplified connection of external components such as noise reduction systems, equalizers and electronic crossovers - and the ability to use the receiver's preamp section to drive a separate power amplifier.
here's another benefit: Connecting the preamp section directly to a tape deck enables you to make specially equalized recordings by using the preamp's flexible tone controls.

Power Amplifier Section
 Full Complementary Symmetry Output
Assures higher stability, better linearity and lower distortion than the quasi-complementary outputs used in the amplifier sections of most receivers.
Quasi-complementary circuitry tends to generage high order harmonic distortion and is particularly susceptible to crossover distortion. To reduce theses types of distortion, manufactures increase the amount of feedback within the amplifier. Under actual dynamic conditions, however, the amplifier with exessive feedback is prone to higher transient distortion and also lower stability.
In contrast, full complementary symmetry output circuitry requires less feedback by incorporating positive and negative amplifiers which are balanced to mirror-image each other's characteristics. This design produces exceptional linearity, lower total harmonic distortion and lower intermodulation distortion.
For these excellent reasons, Marantz receivers feature full complementary symmetry design, as used extensively in Marantz professional products.
 Direct Coupled Power Output
Provides wide power bandwidth, excellent low frequency transient response and improved damping fators.
Early transistorized power amplifiers featured one of two types of output design. A transformer or a capacitor was incorporated between the power output stage and the speaker system. However necessary this was for proper output-to-speaker coupling, it tended to limit low frequency power response or to cause degrading phase shift, and thus impair sound accuracy.
Today's more advanced technology has eliminated the need for coupling transformers and capacitors and the sound inaccuracies they can cause.
The sophisticated direct coupled output stages used in Marantz amplifiers assure you of extremely high damping factors at low frequencies and the best possible low frequency response.
 Heavy-Duty Power Supply
High reserve power supply sections and power output circuitry ensure that Marantz receivers will continue to meet specifications through years of steady performance.
A massive power transformer forms the heart of a dual-balanced positive and negative power supply that symmetrically powers the amplifier stages. large capacity electrolitic capacitors assure high energy power reserves, while massive heat sink promote highly reliable, long-term operation even under full power output conditions.

Rated Power Output:  125 Watts (Minimum Continuous Watts per Channel, Both Channels Driven)
Power Band:  20 Hz to 20 kHz
Total Harmonic Distortion:  0,1%
Load Impedance:  8 ohms
I M Distortion (IHF Method, 60 Hz and 7 kHz mixed 4:1 at Rated Power Output):  0,1%
Damping Factor (at 1 kHz):  70
Main Inputs Sensitivity/Impedance:  1,0 V/55 kΩ
Frequency Response (at 1W Output, 20 Hz to 20 kHz): ±20 dB
Pre-Amplifier Section
Dynamic Range (Ratio of Input Overload to Equivalent Input Noise):  96 dB
Equivalent Input Noise (RMS, 20 Hz to 20 kHz):  1,5 μV
Input Sensitivity and Impedance:  1,8 mV/47 kΩ
Frequency Response (re. RIAA, 20 Hz to 20 kHz):  ±0.5 dB
High Level Inputs (Aux and Tape)
Input Sensitivity and Impedance:  180 mV/100 kΩ
Output Impedance
Tape record:  200
Pre-Out:  900
Tone Controls
Bass:  ±12 dB (50 Hz)
Mid:  ±6 dB (700 Hz)
Treble:  ±12 dB (15 kHz)
Quieting Slope (Mono) 30 dB Quieting:  1,8 μV (10,3 dBf)
5 μV (19,2 dBf) : 55 dB
10 μV (25,2 dBf) : 60 dB
50 μV (39,2 dBf) : 70 dB
1000 μV (65,2 dBf) : 75 dB
Distortion at 1000 μV (65 ,2 dBf, Mono)
100 Hz : 0,25%
1000 Hz : 0,15%
6000 Hz : 0,3%
Distortion at 1000 μV 965,2 dBF, Stereo)
100 Hz : 0,35%
1000 Hz : 0,3%
6000 Hz : 0,5%
Distortion at 50 dB Quieting (Mono and Stereo)
1000 hz : 0,6%
Hum and Ni=oise at 1000 μV (65,2 dBf)
Mono : 70 dB
Stereo : 60 dB
Frequency Response 30 Hz to 15 kHz
Mono : ±1,0 dB
Stereo : ±1,5 dB
Capture Ratio
at 100 μV (45,2 dBf) : 1,8 dB
at 1000 μV (65,2 dBf) :  1,25 dB
Alternate Channel  Selectivity:  80 dB
Spurious Response Rejection:  100 dB
Image Response Rejection:  100 dB
IF Rejection (Balanced):  100 dB
AM Suppression at 100 μV (45,2 dBf):  62 dB
Stereo Separation
100 Hz : 38 dB
1000 hz : 42 dB
10 kHz : 30 dB
Pilot (19 kHz) Rejection:  65 dB
AM usable Sensitivity:  20 μV

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