|The Original Design|
original schematics for the amplifier stage. This design was originally
published in Glass Audio 1991 by Bruce Rozenblitz.
The original drawing also showed a power supply and the input selector. These parts have been removed as I have made my own versions. Also, the design above have been slightly altered - the high impedance output have been taken away. I wasn't really in need of it. Then the anode voltage was increased - the amp is running at 350V instead.
|The amplifier ready for testing. Still, there are some parts that still have to be added and the cabling aren't finished.|
|The part everyone want to see - the tubes. The two ECC82's from Ruby Tubes are shown here - one for each channel. The copper plates are acting as a shield but also as a part of the design. The surfaces behind the tubes have been polished to shine...|
|Rectifier with the large capacitors and the filter choke. First, it was planned for a tube rectifier using the EZ81 full-wave rectifier, but it was scrapped and replaced with a silicon diode bridge rectifier built with discrete diodes filtered off with high-voltage 100n capacitors. The avantage with silicone in this part is that the capactitors can be very big. Tube rectifiers have a limited capacity of filter capacitors (50uF for a single EZ81) - they can't handle the current rush when the capacitors are charged. Also, silicon diodes runs much colder than tubes, making the interior of the amplifier colder.|
|Top view of the amplifier board. The IC's visible at left, under the cables aren't for the sound. These are plain 555's controlling the delayed turn-on of the amplifier.|
|This is the regulator for the heaters and the logic. They both runs at same 12.6V. Using stabilized DC for the tube heaters really takes off the need of hum reduction or other strange solutions to reduce induced hum in the catodes from the heaters. The bonus is that the 12V relays and the timer circuits runs fine from it too - no additional supply was needed.|
|The final interior of the pre-amp. All cabling are done and a extra copper wall have been placed to screen off the parts containing AC voltage.|
|Another view of the final mounting - only the top cover is missing.|
|The final result - all boxed up and ready to be used.|
amplifier running - note the two glowing tubes in the window. It would be
a mistake to hide these inside the box...
The red, fat cable shown behind the amp is that one that connects the transformer unit to the amplifier.
|The external transformer unit. Not the best color of the box, but it was rather cheap and it will be placed out of sight anyway. Note the two AXL-connectors - the leftmost is for the pre-amp and holds also the remote start wires. The right connector contains same power connections as the left one but without the remote start. This can be used for some future tube equipment (like a RIAA-stage) that could be switched on at the same time as the amplifier.|
look of the transformer unit - it contains two toroidal transformes. The
one closest to the viewer is the low voltage ring - it gives 2 x 15V for
low-voltage circuits and (via regulator in amplifier) tube heaters. The
other toroid is the high-voltage - a standard 2 x 115V transformer. The
box also contains fuses for both primary and secondary sides. The circuit
in the middle is the remote start.
This unit is connected to the amp via a 1m long lead containing screened cables - each voltage inside it's own screened cable. All three is hosted in a flexible tube and terminated in each end with angeled AXL-connectors.
scope pictures was taken under same condition:
* Voltage per square: 5V
* Input signal level: 1Vpp
* Output volume at full (volume potentiometer at max).
* Only the time base have been adjusted to show the same amount of periods for the different frequencies.
|1kHz square wave|
|10kHz square wave.|
|100kHz square wave.|
|20kHz square wave.|
|1kHz sine wave.|
|100kHz sine wave - can't hardly see any difference from the picture above.|
|Amplifier Stage||Show one channel, only the tube stage.|
|Power Supply||Enough for both channels and all logic needed.|