If I put my notes here, I might be able to find them again later!
47 Labs 0347 "Treasure" stereo amplifier
(regarding the Treasure 0347 stereo amplifier)
Well, think of it as a bulked-up headphone amplifier. The design is one of those "ah, I should have thought of that" moments, but the details are quite tricky, as usual.
If the extend the basic "voltage stage + current buffer" topology of the 0147 headphone amplifier out to 40 wpc territory, you end up with the 0347.
The high power means that unlike the headphone amp design you have to run it out of class A, and that means closed loop operation.
While most people might be tempted to wrap the voltage feedback around the whole shebang, this basically ends you up with a big op amp. Op amps, with their massive negative feedback design, are not so happy driving high inductance/capacitance loads like speakers.
The trick 47 labs uses is to have two feedback pathways, with heavy "local" feedback around the op amp and a small secondary global loop from the buffer output.
The op amp is a simple discrete circuit, so using higher voltage transistors its quite simple to run it at higher voltages needed to obtain sufficient voltage swing to give 30 W into 8 ohms (rail-to- rail is probably about 50 V)
Damn, more grey hammertone. Must ... resist...
Update: So I'm the happy owner of the 0347 - though I later sold my 0247. The product line has been discontinued, however.
Well, think of it as a bulked-up headphone amplifier. The design is one of those "ah, I should have thought of that" moments, but the details are quite tricky, as usual.
If the extend the basic "voltage stage + current buffer" topology of the 0147 headphone amplifier out to 40 wpc territory, you end up with the 0347.
The high power means that unlike the headphone amp design you have to run it out of class A, and that means closed loop operation.
While most people might be tempted to wrap the voltage feedback around the whole shebang, this basically ends you up with a big op amp. Op amps, with their massive negative feedback design, are not so happy driving high inductance/capacitance loads like speakers.
The trick 47 labs uses is to have two feedback pathways, with heavy "local" feedback around the op amp and a small secondary global loop from the buffer output.
The op amp is a simple discrete circuit, so using higher voltage transistors its quite simple to run it at higher voltages needed to obtain sufficient voltage swing to give 30 W into 8 ohms (rail-to- rail is probably about 50 V)
Damn, more grey hammertone. Must ... resist...
Update: So I'm the happy owner of the 0347 - though I later sold my 0247. The product line has been discontinued, however.
Total Comments 2
Comments
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Links to 47 Labs site no longer point to anything.Posted 16th April 2015 at 04:56 AM by abraxalito
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The 47 Treasure series has moved from the 47 Laboratory web site to Sparkler Audio, but the product line has been discontinued. Just a few items remain.
(I've updated the main post to remove the dead links.)Posted 19th April 2015 at 11:24 PM by rjm
Updated 19th April 2015 at 11:28 PM by rjm
