Hi all,
I recently built a very simple little amplifier which I though would be worth sharing. People might know that I have been a violent critique of the whole RH amp concept because of its inherent design flaws. I decided to see if I could design a simple cheap Schaded amplifier based upon a sound understanding of the principles of Schaded feedback. This is what I came up with.
Things to note are:
-it uses a Switch mode Power supply to generate a 12V regulated supply for the heaters and to feed the +B power supply. One of these can be had for €10.00 from:
AC 85 265V TO DC 12V 8A AC DC 50 60Hz Switching Power Supply SMPS Moudle Board | eBay
-the B+ is generated by using a boost supply which generates 230V DC. This can be had for €10.00 from:
150W Inverter Battery DC 12V TO DC 220V Voltage Step UP Boost Converter Module | eBay
At the power levels this unit is operated at there is no need for the fan which has an slight hum to it.
-the valves themselves are Russian dual tetrodes which I got from an eastern european suppler €12.00 (inc. P+P) for a quad.
-the toroidals used for the output need only be small 40-50VA units and can be had for about €15.00 a throw.
-the only really expensive item is the 12L8GT which is an obscure twin pentode valve which I used because I wanted a three valve design. Its quite expensive and generally only available from America. I will be working up a design which uses either the 6AU6 or the even cheaper EF91 which can be had for peanuts.
It should be possible to build this unit for less than a €100.00
The bias adjustment is used to ensure that the voltages at the top of the tetrode plates are exactly equal, which ensures that the DC standing current in the transformer are equal on both sides.
The pot on the IRF710 is used to set the voltage drop across the driver 10K plate load to about 80V.
I built the bias adjuster on a little perf board and used a salvaged 8+8V transformer. Any small dual secondary transformer of low voltage will do.
I also used tag strips to mount most of the components on.
The unit will produce about 5W of power per channel. This has an overwhelmingly second harmonic distortion profile and it measures very like a Triode SE design. It is not an ultra low distortion design and was not designed to be such. I am listening to it on my secondary system and it matches up extremely well to any of my other designs.
Shoog
I recently built a very simple little amplifier which I though would be worth sharing. People might know that I have been a violent critique of the whole RH amp concept because of its inherent design flaws. I decided to see if I could design a simple cheap Schaded amplifier based upon a sound understanding of the principles of Schaded feedback. This is what I came up with.
Things to note are:
-it uses a Switch mode Power supply to generate a 12V regulated supply for the heaters and to feed the +B power supply. One of these can be had for €10.00 from:
AC 85 265V TO DC 12V 8A AC DC 50 60Hz Switching Power Supply SMPS Moudle Board | eBay
-the B+ is generated by using a boost supply which generates 230V DC. This can be had for €10.00 from:
150W Inverter Battery DC 12V TO DC 220V Voltage Step UP Boost Converter Module | eBay
At the power levels this unit is operated at there is no need for the fan which has an slight hum to it.
-the valves themselves are Russian dual tetrodes which I got from an eastern european suppler €12.00 (inc. P+P) for a quad.
-the toroidals used for the output need only be small 40-50VA units and can be had for about €15.00 a throw.
-the only really expensive item is the 12L8GT which is an obscure twin pentode valve which I used because I wanted a three valve design. Its quite expensive and generally only available from America. I will be working up a design which uses either the 6AU6 or the even cheaper EF91 which can be had for peanuts.
It should be possible to build this unit for less than a €100.00
The bias adjustment is used to ensure that the voltages at the top of the tetrode plates are exactly equal, which ensures that the DC standing current in the transformer are equal on both sides.
The pot on the IRF710 is used to set the voltage drop across the driver 10K plate load to about 80V.
I built the bias adjuster on a little perf board and used a salvaged 8+8V transformer. Any small dual secondary transformer of low voltage will do.
I also used tag strips to mount most of the components on.
The unit will produce about 5W of power per channel. This has an overwhelmingly second harmonic distortion profile and it measures very like a Triode SE design. It is not an ultra low distortion design and was not designed to be such. I am listening to it on my secondary system and it matches up extremely well to any of my other designs.
Shoog
