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Pioneer C-21 Stereo Preamp

Brand: Pioneer
Model: C21
More Information:
Description: The C-21 is a stereo preamplifier composed of an equaliser amplifier and a flat amplifier and designed to display the ultimate in sound quality. It is a streamlined model and so does not feature a tone control circuit or accessory circuitry.
Specifications: (see more detailed specs below)

Frequency response: 10Hz to 100kHz
Total harmonic distortion: 0.005%
Input sensitivity: 2.5mV (MM), 150mV (line)
Signal to noise ratio: 80dB (MM), 100dB (line)
Output: 150mV (line), 1V (Pre out)
Semiconductors: 36 x transistors, 47 x diodes
Dimensions: 420 x 81 x 357mm
Weight: 6.3kg

Accessories: connecting cord and hex wrench
schematics  schematic 2 Quickview Schematic PDF
instruction/owners manual   Manual PDF 2

Meticulously upgraded by Monarchy Audio with WIMA and other high value audiophile grade film caps
(see images below)


Condition: used, but very clean and neat.


Images below are of the actual Pioneer C-21 Preamp that is for sale


Pioneer C 21  
Pioneer C 21
Pioneer C 21
Pioneer C 21
Pioneer C 21

Pioneer Series 20

Center of the Series 20 and a Japanese favorite of many a budding audiophile who either couldn't afford an Exclusive C3 or fancied the no-frills design.

Inside is however plenty of frills: Class A SEPP two-stage current mirror differential circuits for both phono and flat amp sections, ultra parts with ±1% tolerance polyproylene caps and±100ppm /C° metal film resistors, ±37V phono stage power supply and two constant voltage main power supplies.

Even more important is the volume attenuator which 2 gangs of 32 steps made of silver printed contacts - same as that of a Sony TA-F7B. Both were sourced from ALPS.Neither are ZP-1 ALPS as those of the Sony TA-E88B, but the latter cost three times as much as aC-21...

The gain/balance controls are also stepped attenuators with 22 contacts made of silver palladium quite probably sourced from ALPS as well.

Reviewers of the Audio Accessory Japanese magazine very often used the C-21 as center of their test rigs well into the 1980s.

Courtesy of:

Pioneer C-21

The preamplifier of a simple stream composition of having been devoted to the single functionality, in order to pursue a tone quality on the contrary at the origin of a preamplifier and to realize a tone quality with a high purity.

Two steps of differentials and current mirror circuitry Class-A SEPP are used for the circuit system of an equalizer amplifier. Many properties are improved by this circuitry that made importance the improvement in a distorted reduction and an SN ratio. Furthermore, ±0.5% of a resistance-value error and the precision small metals skin membrane resistance of ±100 ppm/degree C of temperature characteristics are used for an equalizer element. Moreover, elements selected carefully, such as a polypropylene capacitor of ±1% of a capacity error, are used. Moreover, the high voltage of ±37V was impressed to this circuitry, and the generous dynamic margin of 300mV of maximum permissible inputs is secured in it to the sensitivity of 2.5mV.

Since the performance of various cartridges is demonstrated, it can be independent respectively, six sorts of load resistance and six sorts of load capacity can be chosen, and a total of 36 sorts of cartridge loadings can be set up. Moreover, the position of 100 ohms of load resistance is suitable for connecting MC cartridge with a large Output voltage direct.

The flat amplifier part as well as an equalizer part has adopted the 2 steps of differentials amplification. The using and interval of an element which had adopted the current mirror circuitry as the middle amplification stage, and were selected carefully while using the low-noise transistor for the first rank are +0 the frequency characteristic of 10Hz - 100kHz. -0.2 dB, 0.005% of the distortion, and the property of an SN ratio of 100dB are secured.

The power-source part constituted the constant-voltage regulated power supply from a L/R independent coil transformer large-sized as a preamplifier, and has eliminated the cross interferencee between channels. Moreover, the quality of stereophonic reproduction, such as also using the reed relay of a muting circuit by two L/R independencies, and also considering it as the special design incorporating the spacer which suppresses the interference between channels also to a function switch, is thought as important.

The volume has adopted the attenuator type of 32 steps by which the silver print of the contact was carried out.

The gain control by 22 contact attenuator which achieved the L-R independency is carried in the flat amplifier output stage. The silver palladium treatment of the contact is carried out.


Pioneer C-21 Specifications

Form Stereo preamplifier
Circuit system Equalizer-amplifier part: 2 steps of differentials current mirror amplification Class-A SEPP
Control amplifier part: 2 steps of differentials current mirror amplification Class-A SEPP
Input terminal Phono: 2.5mV/100 ohm, 10kohm, 25kohm, 50kohm, 75kohm, 100kohm
Cartridge load capacity: 100pF, 150pF, 200pF, 300pF, 400pF, 500pF
AUX1, 2, Tape Play:150mV /, 50kohm
Phono maximum permissible input 300mV (1kHz, THD 0.01%)
Output-terminal Tape Rec: 150mV / 1kohm
Output(RL:50kohm): 1V/450 ohm (rate), 20V/150 ohm (MAX)
THD (20Hz - 20kHz) Phono: 0.006% (at the time of 1V output Volume-20 dB, gain-control 0dB)
AUX: 0.005% (at the time of 1V output gain-control 0dB)
Frequency characteristic
Phono: 20Hz-20kHz±0.2dB
AUX: 10Hz-100kHz+0 -0.2 dB
3Hz-300kHz+0 -1.0 dB
SN ratio (IHF, A network)
Short circuit
Phono: 80dB (output 1 V:00)
AUX: 100dB (output 1 V:00)
Phono Subsonic Filter 15Hz, 6dB / oct
The semiconductor used Transistor: 36 pieces
Diode, other: 47 piece
Supply voltage 100V, 50Hz/60Hz
Power consumption
(Electrical Appliance and Material Control Law)
AC outlet Power-switch interlock: Three lines
Power-switch un-interlocking.: Two lines
Dimensions Width 420x height 81x depth of 357mm
Weight 6.3kg

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