I don't think that is need to improve this.
IMO this is very very good sounding simple-cheap amplifier.
Lets wait Terry's opinion.
I have it populated. I used 1k for the 1k2 because in Spice that got me closer to front end bias. I'm using 4k7/4k7 for the VAS bias for the same reason. I need to drill and tap a heatsink and then I can test it. I'm thinking of using the FX100PSU so I will have speaker protection. I'll try to test tonight but no guarantees.
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If your mod is for single supply, Please open a new thread and give details.
Non ltp input CFA no need to be single supply like AX5.
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I don't think that is need to improve this.
IMO this is very very good sounding simple-cheap amplifier.
Lets wait Terry's opinion.
OK, so I have it working. First off, the 100k pot in place of the 47k does nothing for the offset. My signal generator is on the blink so I was unable to use it. Instead, I hooked up the 1k test signal from my scope to it so I could at least see a square wave on the scope. The square wave looks fine however, When I hook it up, the offset shoots up to 150mV. The other thing I noticed is that turning the Bias pot affects the output voltage as well as the offset. When setting the bias I have to get the bias to about 200mA to get the offset to zero. Also, watching the scope, the higher the bias, the greater the output of the amp. I don't know if thimios found this to be true on his amp. Looking forward to hearing if he did.
Blessings, Terry
No Terry, i can't see something like this in my test amplifier.
Are you sure that you didn't mix the input trimmer setting with the bias one?
Testing mine i see:
Bias setting 22mA :6v RMS output when input is 155mV.
Bias setting 110mA:6v RMS output when input is 155mV.
You need 0,7v(700mV)input signal to drive the amplifier in the soft clip area that is 27,1v RMS.
122w RMS.
Test frequency =1kHZ.
Dummy load=6 ohm.
Offset=<10mV.
Power supply=+/-50v
16K LTP load resistor
5k6+5k6 VAS load resistor.
Are you sure that you didn't mix the input trimmer setting with the bias one?
Testing mine i see:
Bias setting 22mA :6v RMS output when input is 155mV.
Bias setting 110mA:6v RMS output when input is 155mV.
You need 0,7v(700mV)input signal to drive the amplifier in the soft clip area that is 27,1v RMS.
122w RMS.
Test frequency =1kHZ.
Dummy load=6 ohm.
Offset=<10mV.
Power supply=+/-50v
16K LTP load resistor
5k6+5k6 VAS load resistor.
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I can't see something wrong...
I will try again.
Now i have the second channel playing.
I think it's time for Cleaning.....
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I got it working but the offset is hard to manage. Very voltage specific. I think I need to nail down the rail voltage and then find the best value for the 6k8/6k8. I may just try the values you used and go from there. I got my signal generator working and it does have a very clean square wave. I will try to get it playing music today.
What are you using for VAS transistor?
I'm using bf869 in one channel and ksc3503E in the other.
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