I have designed couple current dumping amps. They have a common problem, too complicated. I never had the courage to actually build one.
I hope this my last attempt. I minimize all the unimportant parts and meanwhile retain the performance.
It has couple features that the original Quad 405 does not have.
1. Include the transistor Q2 in the opamp negative feedback. It creates a "super transistor" that has almost 0 impedance at the emitter.
2. I move all the gain to the output stage, The opamp works at unity gain. It simplifies the circuitry around the opamp. Also you can get most of performance out of the opamp. As you can see, I got 0.002% THD with LM358. It could be lower if switching to better one.
I leave the final stage 0 biased. I feel it isn't worth the effort to bias the final stage just to get the thd down to 0.001%.
Edit: 01/02/2025, overhaul the design.
I hope this my last attempt. I minimize all the unimportant parts and meanwhile retain the performance.
It has couple features that the original Quad 405 does not have.
1. Include the transistor Q2 in the opamp negative feedback. It creates a "super transistor" that has almost 0 impedance at the emitter.
2. I move all the gain to the output stage, The opamp works at unity gain. It simplifies the circuitry around the opamp. Also you can get most of performance out of the opamp. As you can see, I got 0.002% THD with LM358. It could be lower if switching to better one.
I leave the final stage 0 biased. I feel it isn't worth the effort to bias the final stage just to get the thd down to 0.001%.
Edit: 01/02/2025, overhaul the design.
Last edited:
My last stage has 0 biased current. My title is fine.
I can’t find better words to describe this topology when the last stage works in class ab.
Some readings.
https://connerlabs.org/current-dumping-for-dummies/
Optimized the circuitry around the SRPP stage (Shunt Regulated Push-Pull). More current capability than the original post.
Clipping behavior
Clipping behavior
Another overhaul, because CFP is the best dumper for current dumping.
Scaled up version.
20KHz into 8 Ohm, -94dB THD at 100W; -87dB THD at 1W.
20KHz into 8 Ohm, -94dB THD at 100W; -87dB THD at 1W.
Hello,
I Think C2 is strange. Take the same feedbackratio of R4/R6 with R1 and put this resistor of Pin2 to ground
I Think C2 is strange. Take the same feedbackratio of R4/R6 with R1 and put this resistor of Pin2 to ground
Hi,
C2 provides AC feedback, while R1 provides DC feedback. To understand it, you could start from the circuit in #7 first. The difference between #7 and #8 is that the #8 allow the opamp to provide some gain by tapping from different feedback point. It is beneficial for overall distortion.