Transcendent Sound

Making Music Better


Introducing the 300B OTL Tube Amp System

The Finest Sounding Amp We Have Ever Produced

Pure Class A Single-Ended Triode

Combines the sonic magic of the legendary 300B with

the incredible accuracy and realism of OTL technology.

Loaded with new features!

Includes breakthrough noise killing 25 Hz filament supply.

Completely automatic bias. No bias adjustment ever.

Virtually Dead Quiet

Outstanding Peak Power

Works with any 8 ohm speaker with a sensitivity of 95dB/watt or greater.

Full kit of 3 box system only $1699 without tubes.

With tubes $2549

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For nearly 20 years, Transcendent Sound has pushed the envelope in high-end sound reproduction.  This time the envelope has been ripped apart.  The 300B is world renown for the weight and body that it provides.  OTL is famous for extreme realism, accuracy and naturalness.  By marrying the two, the best characteristics of each are retained.  The result is a musical experience unmatched anywhere.  Once the music starts, you wont want to turn it off.

Using a 300B in an OTL circuit is very difficult.  In an OTL, the cathode is connected to the speaker.  A 300B triode has a directly heated cathode.  That means the cathode is the filament.  This places the filament in direct electrical contact with the speaker.  This will feed the AC filament signal right into the speaker causing a huge 60 cycle hum.  Through an innovative design, as shown in Tubes and Circuits, we were able to make a connection that cancels out almost all of the hum.  (DC filaments will not work with this design).  Since this is a low powered amp, it will be used with very high efficiency speakers and any residual hum is not acceptable for these applications.  The problem was solved by developing an outboard 25 Hz filament power supply.  Driving the filaments at the low frequency of 25 Hz, pushes the noise components to the lower reaches of hearing and out of the range of most speakers.  There is no buzz. The amp is virtually silent.

Another feature of the 25 Hz supply is that it is current limited.  When a filament is energized by transformer, a huge current inrush occurs which then tapers as the filament heats up.  The 25 Hz supply will limit the current to just over steady-state levels.  This produces a very gentle warm-up.  The tubes will require at least 45 seconds to glow, protecting them and extending life.  The user also has the option of preheating the filaments before applying plate voltage to the tubes.   

The 300B has amazing peak power.  Although the amp has a steady-state rating of 1.5 watts per channel, it plays every bit as loud as a 4-watt Mini Beast.  Listening to it, you would never believe the power rating measures that low.  It mates perfectly to the DIY speaker project shown on this web site which is only 95dB efficient.

This amp truly is a breakthrough in tube audio technology.  But then again, it’s a Transcendent Sound product.  That’s

what we do.

Tube compliment:

4-300B and 1-12AU7 per amp


Max. power: 1.5 watts

Bandwidth: Flat from 10 Hz to 100 kHz

S/N: 80 dBA ref. to 1 watt. See diagram above.  No buzzing.  No hissing.

THD: At 1/2 watt or less- 0.5%, rising to 1.5% at 1 watt.

Output Impedance: 2 ohms

Input Impedance:  100K

Input Sensitivity: 0.8 volt

Gain: 12.9 dB

Feedback:  21.5 dB

Size: 17 by 10 inch footprint.  With tubes, 9 inches tall.

Power consumption:  110 Watts each amp.  220 Watts for a pair. 

Voltage: 120V or 220 to 240 volts, 50-60 Hz.

Weight: 14 pounds each, 28 pounds for both amps.

Filament Supply:

Voltage output: 12.5 volts, plus or minus 0.75 volts.

Output current: 2 outputs at 2.6 amps each.

Frequency: 25 Hz, plus or minus 2 Hz.

Power consumption: 95 watts.

Voltage: 100-240VAC +/- 10%, 47-63 Hz single phase.

Size: 15 by 10 inch footprint.

Weight: 8 pounds.

Total power consumption for system: 315 watts.

300B OTL Amp System - Rack Not Included

Two mono block amps and filament supply

Noise spectra shows how quiet the amp is.  There is a 3 mV noise spike at 50 Hz and a 1 mV spike at 25 Hz with virtually nothing else.  Even though the filament circuit is 25 Hz, a rectification effect takes place through the constant current source which causes the 50 Hz noise.  The noise is so low in frequency and amplitude that that it is essentially inaudible.

Harmonic distortion at 1/2 watt at 500 Hz measuring 0.5%.  Spectra shows gradually descending harmonics that dissipate by the sixth harmonic. The bump at 50 Hz is the noise from the filament.  Distortion past the third harmonic is lower than the amps noise.