Our most esoteric product is the 300B Preamplifier . This is the first and only preamp to feature these classic tubes. We had been designing the 300B into small power amps for many years and have always had great respect for the smooth natural sound of this tube. However, a single 300B provides truly appropriate power and voltage swing for headphones and makes a remarkable line driver. Here is where the impedances are not too low and the power requirements are not too high: ideal for this kind of tube in a single-ended configuration. This was the genesis of a new preamp.

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We combine the historic 300B with another classic, the large octal based 6SL7GT, for the input stage- all triodes running in pure Class A operation. To complement this 'retro' feel, we implemented vacuum tube rectification and regulation in the power supply along with plenty of capacity. We also developed an additional(and innovative) ripple rejection circuit to filter out power supply noise making this an incredibly low-noise preamplifier- especially critical for headphone users.

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Complementing this lovely and rich sounding line-driver is the ALPS audiophile volume control, gold plated RCA connectors, high purity silver wire, mil-spec printed circuit boards with extra thick copper and plating, and custom designed output transformers which we wind right here in our own magnetics department. It all adds up...

For 2002, we returned to our classic and elegant "Manley-Blue" pewter grey color and the chassis was reworked to accommodate a few updates we had in mind. 

Whether you use headphones or loudspeakers this preamp will deliver the goods and spoil you for any other preamplifier.

Notes for current version not covered in the manual:

The transformer switch puts the output transformer in or out of circuit. You HAVE TO have it switched to "IN" to use the headphone jacks. It is recommended, in the spirit of "less is more", to switch to "OUT" when using the main line outputs.

The SUB out is a post-volume control output which can be used to drive a powered subwoofer unit so that the level of the subwoofer follows the volume level of the preamplifier. 

This was another version of the 300B Preamplifier, produced from 1996 to 1999:

 
 
 

SPECIFICATIONS

  • Inputs: 5 stereo pair unbalanced RCA jacks
  • Outputs: 2 stereo pairs MAIN out same as SUB out unbalanced RCA jacks
  • RECORD output: 1 stereo pair pre-volume control unbalanced RCA jacks
  • HEADPHONE Outs: 2 front panel 1/4" headphone jacks
  • Optimized headphone impedance switching: 30-400 Ohms to 300-4000 Ohms
  • MUTE: Selecting HEADPHONE operation mutes LlNE outputs
  • Output Vacuum Tubes: 2 x 300B Electro-Harmonix
  • Input Tubes: 2 x 6SL7GT Electro-Harmonix
  • Rectifier Tubes: 2 x 5U4GBEH Electro-Harmonix or 5AR4 China (Do NOT use the Sovtek 5AR4!)
  • Regulator Tubes: 2 x OD3 NOS JAN USA
  • Gain: factory set at 12 dB at max Volume
  • Internal Variable Feedback: 8.5 dB of global NFB is used @ 12 dB of gain, adjustable trim -1.7dB to +1dB
  • Noise Floor: typically -70 dB (1 Hz - 100 KHz)
  • S/N Ratio: typically 105 dB (A WGT, 20 Hz - 20 KHz)
  • Frequency Response: 5 Hz to 50 KHz 1dB
  • Channel-to-Channel Separation (L to R): @1KHz 48 dB; @10KHz 35 dB; @20KHz 34 dB
  • Channel-to-Channel Separation (R to L): @1KHz 50 dB; @10KHz 40 dB; @20KHz 37 dB
  • THD: 0.08 % @ 1KHz at 1V rms out
  • Distortion THD+N: -80 dB (.01 %) zero "crossover" distortion, mostly 2nd harmonic
  • Input Sensitivity: 250mV (-9.8dBu) yields 1V out
  • Input Impedance: 100 kOhm Noble volume control
  • Maximum Input Level: 5.5dBu or 1.459 Vrms @ 1KHz, volume control at maximum
  • Output Impedance (LINE STAGE): 100 Ohms
  • Maximum Output Level: 17.2dBu or 5.636 Vrms @ 1KHz, volume control at maximum
  • Output Power (100 Ohm Headphones): 1W (10 V RMS) (28 V P-P)
  • Output Power (600 Ohm Headphones): 1W( 25 V RMS) (70 V P-P)
  • Power Consumption: 170 Watts (1.4 A @ 120VAC)
  • Operating Mains Voltage: Factory set for 100V, 120V or 220-240VAC operation for original destination country's mains voltage.
  • Operating Mains Voltage: changeable with power transformer re-wiring and fuse value change.
  • Mains Voltage Frequency: 
  • Dimensions: W=19". L=13". H=11"
  • Shipping Weight: 28 Ibs.

Specifications subject to change because they just might.

 
 

NOTES

NOTES about the Rectifiers: We switched away from the Russian 5AR4 as these proved unreliable, and sometimes if they shorted would cause an internal part to fail. The 5U4 has a little higher ratings and is generally more rugged construction. Originally, years ago, we used a Chinese 5AR4 which rarely gave problems; how reliable these tubes are now and how they would work in the latest power supply configuration has not been tested. The difference in plate voltage on the tubes with a 5U4 vs 5AR4 is considerably less than 10%; whether you can hear this difference or not we will not comment on, but in actual measurements of the unit, there isn't any difference. 

UPGRADE: No remote control? I need a remote! You can UPGRADE your original Neo-Classic 300B Preamp version to the current RC Version by contacting your dealer to book the upgrade for you.

UPGRADE: MANLEY Neo-Classic 300B PREAMPLIFIER 5/1/2003  PURPOSE: To lower noise level. Serial numbers for units that will benefit from this update are: 3BMP000 – ALL; NEO3B036 –038, 040 - 047. Contact us for an upgrade.