I've been thinking about the Pass DIY amp designs a lot lately and reading old threads about peoples efforts to taylor one of Nelson's designs to suit their personal tastes/needs. I was very curious to try the SOZ but didn't for 2 reasons
1)like so many others I could not justify the gross inefficiencies of the design.
2)No matter how hard I tried I could not get my head around how the circuit works (ie. how it can be scallable without changing resistor values) - Ohms law certainly doesn't explain things. As I believe everything I do should be a learning experience, building someone elses design without understanding how it worked did not appeal.
This is what I did:
I basically used 2 ZEN amplifiers per channel in a differential pair arrangement (as in the SOZ design). The amp uses a single positive supply rail (24V in this case). The gates are biased at 4 volts via voltage dividers directly from the supply (ie. no feedback). Because the inputs are above ground potential coupling capacitors are required as in the ZEN design. The mosfets are biased at 1.5A each through an 8 Ohm resistor per side giving 12V at the drain of each mosfet. This equates to 4W RMS per channel with an idling current of more than 4 times the maximum required by the load (8 Ohm).
I've only just finished this amp so I'll reserve my judgement on how it sounds (compared to the ZEN which I built) for a few weeks.
I would appreciate input from anyone who has an opinion on any of this especially the following.
1) Resistors Vs. Current sources
2) Benefits of operating at higher idling currents/employing deeper suppliy rails (I posted this question a little while ago but nobody was interested, figure I'll try it again)
3) There was mention in a therad some time ago (I think it was grey) of the possibility of doing away with the input coupling cap. Something about the preamp of a tube amp. Cananyone eleaborate on the possibilities of removing this capacitior while keeping a positive bias at the gate.
Cheers
Dan
1)like so many others I could not justify the gross inefficiencies of the design.
2)No matter how hard I tried I could not get my head around how the circuit works (ie. how it can be scallable without changing resistor values) - Ohms law certainly doesn't explain things. As I believe everything I do should be a learning experience, building someone elses design without understanding how it worked did not appeal.
This is what I did:
I basically used 2 ZEN amplifiers per channel in a differential pair arrangement (as in the SOZ design). The amp uses a single positive supply rail (24V in this case). The gates are biased at 4 volts via voltage dividers directly from the supply (ie. no feedback). Because the inputs are above ground potential coupling capacitors are required as in the ZEN design. The mosfets are biased at 1.5A each through an 8 Ohm resistor per side giving 12V at the drain of each mosfet. This equates to 4W RMS per channel with an idling current of more than 4 times the maximum required by the load (8 Ohm).
I've only just finished this amp so I'll reserve my judgement on how it sounds (compared to the ZEN which I built) for a few weeks.
I would appreciate input from anyone who has an opinion on any of this especially the following.
1) Resistors Vs. Current sources
2) Benefits of operating at higher idling currents/employing deeper suppliy rails (I posted this question a little while ago but nobody was interested, figure I'll try it again)
3) There was mention in a therad some time ago (I think it was grey) of the possibility of doing away with the input coupling cap. Something about the preamp of a tube amp. Cananyone eleaborate on the possibilities of removing this capacitior while keeping a positive bias at the gate.
Cheers
Dan