So I was doing some stability testing and found that even without pure capacitance on the output the positive side of the amp breaks out into oscillation. What was interesting was when I tacked on a 1uF cap on the output it appeared to start off as a ring then break out into oscillation (video attached). Meanwhile the negative side was perfect. The oscillation is not there when the fault relay is open. I can attach a schematic if needed.
Zero information to offer any kind of reasoned answer. Videos of oscillation == oscillation.....proof of the crime. Even Sherlock would be stumped.
Schematic?
Operating conditions?
Anything?
Schematic?
Operating conditions?
Anything?
I greatly apologise for not providing any context.
Testing Conditions
Load: 4 ohm resistor bank + 1uF film capacitor accross output and ground.
Signal: 8-12khz Square Wave via Function Generator 0-1V pkpk
Power Supply: Resonance LLC 1.5kW converter. 45-0-45
Testing Conditions
Load: 4 ohm resistor bank + 1uF film capacitor accross output and ground.
Signal: 8-12khz Square Wave via Function Generator 0-1V pkpk
Power Supply: Resonance LLC 1.5kW converter. 45-0-45
The NFB should be taken before the output inductor (as it is shown by connection).
But the schematic is marked wrong, NFB instead of SPKR. Same on relay.
Also, there should be 10R in parallel with the output inductor, marked but not shown.
But the schematic is marked wrong, NFB instead of SPKR. Same on relay.
Also, there should be 10R in parallel with the output inductor, marked but not shown.
It could be a layout/wiring related issue. Clearly your amp is designed for substantial output capability. I have found that series inductance in the +/- supply connections to the output transistors can result in some hard-to-diagnose problems. In one case I had a really nasty overshoot problem when the amp was operating into a resistive load and it turned out to be due to the inductance of the supply wires connected to the output transistor's collectors. Some local bypass capacitors fixed the problem.
Yes a Vbe multiplier needs to be decoupled as it has high/complex impedance at HF, and will go non-linear too given sharp transients - tying the two driver bases to each other at AC is important to prevent all this complexity entering the signal chain, it makes the Vbe multiplier look like a pure bias voltage source at HF as well as LF which is what its supposed to be.