hello
i only matched the input transistors but can't tell how much it affects the dc offet - in my case it's approx. 10mV in both channels.
I use other output transistors (MJ11015/16) and they are from the factory at quite the same range judging by the bias voltage drop on individual emitter resistors.
but i don't know what is the parameter distribution of TIP series transistors in this regard.
i only matched the input transistors but can't tell how much it affects the dc offet - in my case it's approx. 10mV in both channels.
I use other output transistors (MJ11015/16) and they are from the factory at quite the same range judging by the bias voltage drop on individual emitter resistors.
but i don't know what is the parameter distribution of TIP series transistors in this regard.
Amp ha been completed and it sings like crazy
Everything worked even without test boards. No hum, dc offset 2mV and 10mV per channel.
Bias 40mA per transistor - runs cool.
no turn on/off thumps.
PSU - +- 45V 30 000Uf in each rail.
indicator diode foe each rail.
Transistors - ztx450,550,MJ340/350, mj11016/15.
0,5 ohm emitter resistors and base stopper divided-100R on PCB and 100 on transistor base pin.
I will measure later with scope and sound-card - now I am a little tired after amp hobby work
nice front panel, " angry villagers armed with pitchforks and torches" as mentioned by NP in first post. just had a look at your work. congrats!
Got a chance to finish the boards. I have installed just 1 pair of OP transistors for testing. Running on +-40VDC. Bias is set to 20mA, DC offset on boards is 9-12mV and 15-18mV. I have just HFE matched the input transistors. Square wave looks good, 1kHz and 20kHz. I have used all die original resistor values except R3 is 1K.Sound is good, high frequencies are more subtle, sounds like more H2. I think I need a little more gain, maybe change R3 to 470R. I will first test with a decent preamp and not using a phone as source. What will the advantage be in changing the emittor resistors from 1R to 0.47R ? Thank you Mr Pass and Osscar for the help and thanks Prasi for the great pcb layout !
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HI,
Looks very good, no ringing etc. Yes , you can adjust gain. According to D.SELF's book - the smaller Re - the better, but you need a greater bias current and a greater risk of burning something
usually i see that all amplifiers use 0.22R or 0.33R or 0.47R.
Regarding FFT - according to LT spice - with TIPs you have more 3H, but with MJ - more 2H..i cant explain this - i don't know how accurate are the different transistor models..best way would be to measure but my EMU usb card doesn't work with win 10...so i need to buy a newer one - Focusrite for example.
Looks very good, no ringing etc. Yes , you can adjust gain. According to D.SELF's book - the smaller Re - the better, but you need a greater bias current and a greater risk of burning something
usually i see that all amplifiers use 0.22R or 0.33R or 0.47R.Regarding FFT - according to LT spice - with TIPs you have more 3H, but with MJ - more 2H..i cant explain this - i don't know how accurate are the different transistor models..best way would be to measure but my EMU usb card doesn't work with win 10...so i need to buy a newer one - Focusrite for example.
Well I have tested both boards today for an hour or two on idling with input shorted. 9-11mV dc offset, bias very stable at 20mV. It might be that the caps have reformed a bit but the sound is great, I'm sticking with 1R emittor resistors for now, can always change if needed. I might use another transformer with +-50V rails, but I dont think it is necessary. A very happy chappy I am.
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