Up for sale is a preamp based on the design of troels gravesen, see link TRAM w.
Reason for sale is I have moved to a fully active system now using a DSP so this preamp is redundant and has been sitting in the cupboard. It had a very typical with output transformers sound, used with some 6B4G amps feeding very efficient horns - low background noise, even when feeding 114db efficient speakers.
My version is based arround Bartolucci output transformers. I used a solid state HT power supply with regulation via a Salas Shunt board. The volume control is via a 30 increment stepped attenuators, around a shallco style switch, to with the resistors are directly soldered to it.
I used kiwame resistors, a obligato film capacitor and silver mica resistors in the circuit along with the 2 watch batteries per channel.
It is built on two chassis's keeping the PSU separated connected via a multi pin military connector, the psu is in a metal chassis. The preamp was built to show, with a stainless steel chassis to which all is bolted, in an oak plinth. As well as the transformers and teflon valve sockets, there is a copper plate, verdigris finish (attached to as focused heat sink for shunt regulator) On the front are two knobs ( industrial looking - can be easily changed to match you style) for volume control and input selection - currently wired for two inputs, holes for a third pair of rca's is provided on the back. All the rca's used are silver plated CMC ones. Two additional redundant holes in front panel, (easily covered by a plaque etc).
It is in full working order and its sound will make you forget about it's looks industrial looks. Comes with a number of 6n6p valves, you and mix and match the best pair from them. One picture shows the circuit I used, not including the valve power supply, a total of 2 resistors and 2 capacitors in the signal path.
My price is based around the cost of the transformers and the volume control. £425
This is a heavy amp, due to having 4 transformers. The preamp weights 10kg and the psu weights 5 kg. Postage will be at cost.
Reason for sale is I have moved to a fully active system now using a DSP so this preamp is redundant and has been sitting in the cupboard. It had a very typical with output transformers sound, used with some 6B4G amps feeding very efficient horns - low background noise, even when feeding 114db efficient speakers.
My version is based arround Bartolucci output transformers. I used a solid state HT power supply with regulation via a Salas Shunt board. The volume control is via a 30 increment stepped attenuators, around a shallco style switch, to with the resistors are directly soldered to it.
I used kiwame resistors, a obligato film capacitor and silver mica resistors in the circuit along with the 2 watch batteries per channel.
It is built on two chassis's keeping the PSU separated connected via a multi pin military connector, the psu is in a metal chassis. The preamp was built to show, with a stainless steel chassis to which all is bolted, in an oak plinth. As well as the transformers and teflon valve sockets, there is a copper plate, verdigris finish (attached to as focused heat sink for shunt regulator) On the front are two knobs ( industrial looking - can be easily changed to match you style) for volume control and input selection - currently wired for two inputs, holes for a third pair of rca's is provided on the back. All the rca's used are silver plated CMC ones. Two additional redundant holes in front panel, (easily covered by a plaque etc).
It is in full working order and its sound will make you forget about it's looks industrial looks. Comes with a number of 6n6p valves, you and mix and match the best pair from them. One picture shows the circuit I used, not including the valve power supply, a total of 2 resistors and 2 capacitors in the signal path.
My price is based around the cost of the transformers and the volume control. £425
This is a heavy amp, due to having 4 transformers. The preamp weights 10kg and the psu weights 5 kg. Postage will be at cost.
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