Hi prasi, great you are quick 🙂 On a first look I don`t see any problems, but may be few minor changes in the schematic it`s stil a prototype and I`m open to suggestions..
Hi, ok thank you
Did you measure with higher bias current and/or with higher output levels?
What would you suggest in order to achieve higher output power, doubling BJT´s and MOSFETS?
This isnt too easy, as i see it, as you want to see current in both of them and you want to use emitter/source resistors for both of them in order to spread the load evenly
Did you measure with higher bias current and/or with higher output levels?
What would you suggest in order to achieve higher output power, doubling BJT´s and MOSFETS?
This isnt too easy, as i see it, as you want to see current in both of them and you want to use emitter/source resistors for both of them in order to spread the load evenly
I did detailed simulations few months ago, so I don`t remember quite well, but the solution is "simulation driven". I could try the difference, C61 to output bjt emitter?
Hi, I understand
I just think it could be of interest for those with not-so-efficient speakers
You suggest 1.5A bias current, right? Did you measure with this?
I just think it could be of interest for those with not-so-efficient speakers
You suggest 1.5A bias current, right? Did you measure with this?
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Prasi, great this version looks much better.
There are 2 controls I`m gonna put on my version that could be useful and you could place 2 pin connectors on a pcb as a option.
First is to adjust the bias current with 3-4 position, rotary switch and second is toggle switch for bypassing degeneration resistor and changing damping factor. See the attached schematic for example.
Cheers.
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Btw C13, output cap if it`s on pcb, it will consume lot of space, plus bypass caps..10mF for 8 Ohm speakers it`s an minimum imo. I`ve made separate pcb for ouput caps bank. As you wish this is just my opinion.
On the proto, I'm changing bias with a pot it's on wire, not shielded and there is no problem, cable it's not sensitive to any kind of noise. I think it's a good idea to have these controls on front panel to play with different sound characters and performance points to suit wider range of speakers..
Btw, any ideas for lowering 3rd harmonic?
Tonight I will send data for differences in distortion between BD140, BF872 and KSA1220 and 4 ohm load measurements on higher bias at full power.
Btw, any ideas for lowering 3rd harmonic?
Tonight I will send data for differences in distortion between BD140, BF872 and KSA1220 and 4 ohm load measurements on higher bias at full power.
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I've tried, it's stable both ways. Depending of the value of degeneration resistor, it alters operating point of the input jfet, with degeneration resistor, idle current of jfet is higher..
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Perhaps there’s nothing wrong with the simple 1+1 output cap but it means having this big can on there and I agree, aesthetically it’s ugly on the small pcb. One option is a chassis mounted cap. Another option is a collection of medium sized caps in parallel. Vladimirk made a separate pcb with a circle of caps; he had some interesting comments on this:
Rails Decoupled SE Amplifier
1.4A idle current, load 3R8 with output bjt, degeneration resistor bypassed :
18Vpp, 12Vpp, 8Vpp, 4Vpp, 2Vpp, 1Vpp
spike around 17KHz is a measurement / soundcard artifact..
18Vpp, 12Vpp, 8Vpp, 4Vpp, 2Vpp, 1Vpp
spike around 17KHz is a measurement / soundcard artifact..
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So, no 2nd harmonic cancellation like in simulation, that`s good, 5th appears out of noise floor just at levels near "current clipping".
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