"SAPPHIRE" 300B.1 Monoblock Amplifier

Sapphire 300B front viewSaphire 300B side view

Our goal with the Sapphire was to design an amplifier around what is probably the most known and popular tube for audio use, namely the 300B. We have replaced the Full Music TJ mesh plate premium Gold 300B previously used with the upgraded Shuguang "A" Treasure 300B-Z. This amplifier also uses another rugged 5687 NOS triode for the voltage & driver gain stages that complements and allows the 300B to perform at its best.

Using a wide bandwidth custom Hammond output transformer has allowed this design to overcome the short comings that a lot of other 300B amplifiers are noted for. You will be surprised to know that the bass is quick, fast and deep, while the highs are smoothly extended to 40 kHz.

Separate high voltage DC power supplies isolate the voltage/driver stages from the output stage, which in a single ended amplifier is a critical attribute.

Our self-biasing stages, while completely eliminating all adjustments, insure long term stability and reliable operation. As in our previous Onyx design, we have implemented what we call a quasi-parallel circuit design where each of the two output triodes have their own independent automatic biasing circuit. Only the plates are tied together to drive the output transformer. Although this doubles the amount of parts in the biasing circuitry that normally would be employed, it results in a purity of sound that one would normally associate when using only a single triode, such as is implemented in our Topaz design.

We also use filtered DC on the filament of the input / driver tube to keep hum and noise at a minimum. The 300B output filaments each have their own regulated DC 5 volt supply that negates the use of hum minimizing adjustments that inferior amplifiers use.

We use large Teflon signal capacitors which are among the best in the world with an unlimited life expectancy due to their indestructibility that results from their self healing attribute which is a feature of their metalized construction.

Further refinement comes with a gold plated brass holder with 3M rubber feet inserts to accentuates the styling and to allow proper air flow for the vents under the chassis

We use a delayed DC power sequencing that maximizes tube life by preventing cathode emission deterioration. Low frequency response has been greatly enhanced by using very large signal capacitors and wide bandwidth custom output transformers. These combined attributes reduce overall distortion at higher power levels and give an overall impression of a much more powerful amplifier than what the specifications would suggest.

Unlike solid state amplifiers, that when clipped sound extremely harsh, this amplifier can be pushed beyond it's rating with little noticeable effect due to the tendency to compress when overdriven, which is much more benign than what normally occurs with solid state equipment.

OUTPUT LOAD IMPEDANCE SELECTOR SWITCHES

These switches allow selection between 2 and 16 ohm speakers. Using a lower setting than the rating of the speakers increases the damping factor which may increase the performance depending on the speaker being used. In general the best overall setting is usually what the speaker is rated for. The 12 Ohm position can be used to drive speakers rated at 12 Ohms and above. To set the proper impedance you need to insure both switches are in their proper position. Each switch setting shows two possible impedance's. The numbers that match from both switch positions tell you what impedance is selected. Thus four selections are possible, which are 2,4,8 and 12 Ohms.

Input Gain Selection: Low = 20dB, Normal = 25dB, High = 30dB


ABSOLUTE PHASE: None Inverting

If you have other equipment that inverts the phase, then the easiest way to adjust for absolute phase is to reverse the + and - speaker connector leads.

BURN-IN PROCEDURE FOR NEW OUTPUT TUBES

If you receive these tubes from Wyetech Labs, they will have already been tested and burned in. Otherwise, plug them in and play immediately. You may notice a subtle improvement over time, but nothing very dramatic, since these tubes do not need an extended burn-in period. If you have received these from an outside source then you should check the bias voltage using a voltmeter. The reading should be within 10% of 78 Volts DC.

DESIGN GOALS OF THE AUDIO CIRCUITS

We opted to keep the same circuit topology as that found in our more expensive Topaz amplifier, which is plate loaded single ended in all stages. For the signal and driver we use readily available NOS [New Old Stock] triodes that were made in the USA and have met JAN (Joint Army Navy) military specifications. We chose the Shuguang "A" Treasure 300B-Z output tubes for their superior sound and reliability.

We use a custom Hammond output transformer designed to our specifications which resulted in a wide bandwidth with exceptionally deep low frequency response.

DESIGN GOALS OF THE POWER SUPPLY

Single ended amps are more susceptible to power supply aberrations than push-pull amps. For this reason we have split the front end from the output by using completely separate power supplies. This eliminates power supply feedback non-linearity. To keep cost moderate and still uphold sound quality we opted for R-C filtering as opposed to the more expensive L-C used in the Topaz. (R = resistor, C = capacitor, L = inductor) We also use electrolytic capacitors with much larger storage capacity to make up for the loss in filtering when using resistors in lieu of inductors. The radiated heat is distributed inside the chassis, such that, it insures that the chassis runs only warm to the touch. The total power intake and heat dissipation is only 185 watts per channel, for an amplifier operating in pure class A1.

PARTS QUALITY

We use precision quality parts throughout. Our Printed Circuit Boards have a manually designed layout using computers to meet the needs of analog design which are radically different than digital or computer circuit design. We needed large signal and power traces and special footprints for parts like the tube sockets. This has resulted in short signal paths and more precise positioning of components on the board. We use wire wound silicone and ceramic high power resistors and computer grade electrolytic capacitors in our power supplies.

All wiring to the printed circuit boards is done with the use of screw down connectors. This is done for ease of repair should ever the need arise. We use a single OFC co-ax cable for the signal input wiring and Teflon coated silver plated OFC wire for the speaker connection and selector impedance switch wiring.

WARRANTY

Wyetech Labs warrants to repair or replace any part which proves to be defective through normal use, except external finishes and vacuum tubes ( 1 year ), for a period of 5 years from the date of purchase.

TECHNICAL SPECIFICATIONS

TUBE COMPLEMENT: (3)

1. Dual Triode 9-pin base 5687WB [JAN Military NOS] INPUT / DRIVER STAGE
2. Triode 4 PIN-base 300B SHUGUANG TREASURE premium grade / OUTPUT STAGE

CIRCUIT DESCRIPTION

All stages operate in pure class "A1" single ended and contain automatic self-biasing circuitry. We have maintained our Topaz tradition in the use of exceptionally large value Solen polypropylene coupling capacitors. This together with our custom built HAMMOND output transformer has endowed this amplifier with very extended low and high frequency response. Each of the two output triodes are individually self-biased, with only the plates tied together in a quasi parallel configuration, which is nearly equivalent to having one high powered triode. Our 12 pound output transformer provides 18 Watts RMS per mono-block with solid bass and absolute stability into all low impedance loads. The output windings can be toggled via two high current switches to allow selection of impedance for 2, 4, 8 or 12 Ohms. WE EMPLOY NO FEEDBACK of any kind due to the low distortion ultra-linear amplification stages employed in this design.

POWER SUPPLIES

MECHANICAL CONSTRUCTION

CIRCUIT BOARDS

The components are mounted on a Printed Circuit board [PCB] which is made from FR4 glass epoxy with double sided copper traces and plated through holes. Both sides have a protective green solder mask. A silkscreen is printed in white showing the component layout and parts value. This PCB was designed manually in house. It has enlarged power and signal line traces to attain the best analog integrity that automatic routing circuit programs cannot attain. Our Printed Circuit Board program allows for an infinite varieties of traces and component layouts that can be developed into our own custom library parts. We have created a library of custom component layouts that are specifically suited to develop our Analog circuits. Wiring to the PCB is attached via screw down crimp terminals to allow for ease of repair should the need ever occur where the board would need to be removed. We have reduced the signal path length to less than 6" on the PCB board. The final assembly of parts to the PCB is done by hand soldering of all components, which is superior to automated flow-soldering techniques, by allowing more solder on each and every joint.

AUTO-SEQUENCING

A time-delay relay provides extended tube life and proper power sequencing for stabilized circuitry on power up. The filament voltage is turned on for 45 seconds before applying the DC voltage power, after which the ready (green) LED comes on.

POWER SWITCH

Applies power to the automatic power up sequencing circuit.

OUTPUT IMPEDANCE MATCHING

FREQUENCY RESPONSE

1. + 0 / - 1 dB > 11 Hz to 28 kHz
2. + 0 / - 3 dB > 6 Hz to 43 kHz

INPUT IMPEDANCE

LOW 55 Kohms GAIN 20db > 1.28 VRMS for full output
NORMAL 50 Kohms GAIN 25db > 0.6 VRMS for full output
HIGH 200 Kohms GAIN 30db > 0.38 VRMS for full output
ABSOLUTE PHASE non-inverting (can be set to Invert at Factory)
POWER OUTPUT 18 Watts RMS per Channel
DYNAMIC HEADROOM music peaks up to 40 Watts
ENERGY STORAGE 300 JOULES
Universal Voltage Select 115/230 Volts 50/60 Hz
POWER CONSUMPTION 185 Watts per mono-block
WEIGHT (NET) 2 x 33 lbs. (30 kg)
WEIGHT (SHIPPING) 2 x 38 lbs. (35 kg)
DIMENSIONS 9.5" W x 16" L x 8.5" H
LIMITED WARRANTY Tubes: 1 year
Components: 5 years parts & labour

* Each unit comes with a brass nameplate and individually engraved serial number.