fubar3
100+ Head-Fier
- Joined
- Jul 16, 2011
- Posts
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- 12
The Edifier is an economy amp with nice aluminum case. There are photos and comments on this thread http://www.head-fi.org/t/412257/edifier-hall-ha11.
It is a shame that nice case hides a poor quality circuit which is prone to oscillation and latch-up. Consider the following schematic:-
I think there is positive feedback through the 33 ohm resistors which increases as the load impedance rises. This seems to cause an overshoot for percusive sounds such as cymbals. Once you hear it, you can't ignore the effect. Then there is the RF oscillation which the design failed to remedy with the miscellaneous HF bypass caps found in the circuit.
Fortunately, the HA11 can be repaired with an infusion of O2 technology. I could use an arbitrary circuit but the O2 local feedback design (from NwAvGuy) should be most stable with the hacking I need to do. I used parts from the Objective 2 BOM but got power from the existing HA11 9v regulators. I would love to use an O2 circuit board but it would not fit in the HA11 so a big effort was needed to hack the fix.
The parts are soldered point-to-point on a generic hobby board with interconnects for the front panel volume control and headphone jack. It looks ugly but sounds great with no visible oscillation on the scope and no output offsets. There probably is some cross-talk and ground looping but that is only a guess.
Here is the top view, the board is installed upside-down for routing wires and parts clearance
It is a shame that nice case hides a poor quality circuit which is prone to oscillation and latch-up. Consider the following schematic:-
I think there is positive feedback through the 33 ohm resistors which increases as the load impedance rises. This seems to cause an overshoot for percusive sounds such as cymbals. Once you hear it, you can't ignore the effect. Then there is the RF oscillation which the design failed to remedy with the miscellaneous HF bypass caps found in the circuit.
Fortunately, the HA11 can be repaired with an infusion of O2 technology. I could use an arbitrary circuit but the O2 local feedback design (from NwAvGuy) should be most stable with the hacking I need to do. I used parts from the Objective 2 BOM but got power from the existing HA11 9v regulators. I would love to use an O2 circuit board but it would not fit in the HA11 so a big effort was needed to hack the fix.
The parts are soldered point-to-point on a generic hobby board with interconnects for the front panel volume control and headphone jack. It looks ugly but sounds great with no visible oscillation on the scope and no output offsets. There probably is some cross-talk and ground looping but that is only a guess.
Here is the top view, the board is installed upside-down for routing wires and parts clearance
Excluding these serious flaws, this is essentially a A47 amp.