Do I have to change my plans for the 220C boards?
I did purchase the PCBs and FETs, but did not get to finish them at this stage.
My original plan was to use lower voltage transformers and larger heatsinks compared to the original Hafler amps with the intention of running 2-3x idle current. Will the amplifier design work with +/- 28 volt DC and 4-600 mA idle current per transistor or am I better of running voltage and currents closer to the original design.
I am not sure why you think that you should need to "change the recipe" i.e run at a lower V and 400-600mA of bias current?
The DH-220C is spec'd for 200mA per device.
Okay you have a bit more Class "A" region but is it necessary? I doubt so.
Using such a low supply +/-28V means it clips much earlier, do you really want to do that?
I think early clipping goes against more OPS bias current.
If you want more o/p juice, use 3 pairs and appropriate OPS pcb, as was done in the P230 and DH-500 designs.
IMO stick with what is known to work and be happy with that.
I can't recall if I measured the AFE operating at such a low supply of +/-24V, you will need to change R1, R2 that's for sure since the 15V zeners will be starved.
The DH-220C is spec'd for 200mA per device.
Okay you have a bit more Class "A" region but is it necessary? I doubt so.
Using such a low supply +/-28V means it clips much earlier, do you really want to do that?
I think early clipping goes against more OPS bias current.
If you want more o/p juice, use 3 pairs and appropriate OPS pcb, as was done in the P230 and DH-500 designs.
IMO stick with what is known to work and be happy with that.
I can't recall if I measured the AFE operating at such a low supply of +/-24V, you will need to change R1, R2 that's for sure since the 15V zeners will be starved.
Just so there are no misunderstanding, I have full confidence in the design.
So why then do I consider "changing the recipe"? While most people would use the 220c PCBs for updating an existing Hafler amp, my situation is different.
I do not own any Hafler product rather, I intend to use the published design as basis for a full DIY job.
I do have a cabinet with substantial cooling designed for 2 pairs of TO3 transistors per channel, I have 4 pairs of Exicon transistors, I already have a number of 400VA, 22V-AC transformers and I have 40 volt rated PSU capacitors.
Basically I am looking for a design suited for implementation with this setup. In theory, running at half the supply voltage should allow double bias current for the same heat dissipation. Hence I am considering the 220c design at lower than designed voltage and (provided the bias will be sufficiently stable) running the idle current as high as the cooling allow.
Now if bias current stability will be an issue I can stay at 200mA pr. device. As an alternative I can consider other designs like e.g the Lang Class-A amplifier, but my preference is for a modern design with J-FET and servo.
So why then do I consider "changing the recipe"? While most people would use the 220c PCBs for updating an existing Hafler amp, my situation is different.
I do not own any Hafler product rather, I intend to use the published design as basis for a full DIY job.
I do have a cabinet with substantial cooling designed for 2 pairs of TO3 transistors per channel, I have 4 pairs of Exicon transistors, I already have a number of 400VA, 22V-AC transformers and I have 40 volt rated PSU capacitors.
Basically I am looking for a design suited for implementation with this setup. In theory, running at half the supply voltage should allow double bias current for the same heat dissipation. Hence I am considering the 220c design at lower than designed voltage and (provided the bias will be sufficiently stable) running the idle current as high as the cooling allow.
Now if bias current stability will be an issue I can stay at 200mA pr. device. As an alternative I can consider other designs like e.g the Lang Class-A amplifier, but my preference is for a modern design with J-FET and servo.
I can not see why DH-220C will not work with your intended supply. Scale down R1,2, the supply for the OPA2134, so that the 15V zener diodes regulate properly. OPA2314 dual draws around 8mA? and use 10mA for the zeners. 28-15/.018= 722 ohm std value 750 ohm 1W is fine.
You can run the DH-220C pcb by itself as a test to measure and adjust the IPS and VAS currents for that supply V.
H1 jumper from pin 2-3 so driver (TP1) gets feedback to IPS
Once you run your design, with an OPS, H1 to 1-2, adjust your OPS bias current for what you deem necessary, monitor the bias current stability and see how it performs.
Good luck
You can run the DH-220C pcb by itself as a test to measure and adjust the IPS and VAS currents for that supply V.
H1 jumper from pin 2-3 so driver (TP1) gets feedback to IPS
Once you run your design, with an OPS, H1 to 1-2, adjust your OPS bias current for what you deem necessary, monitor the bias current stability and see how it performs.
Good luck
... has the DH-220C been tested with a rails like +/- 70V ? Rick, I can remeber from one of your earlier posts that you tested the AFE at higher rails, but wat about the OPS? Thank for any info.
zs.
I have run +95 Vdc / -95 Vdc rails successfully with the appropriate capacitor ratings using Rick's DH500C boards. The outputs I used were the Exicon dual die Lateral mosfets though.
- Dan