If you build Figure 11, with a 16 Ohm speaker, 1W THD goes to around .5%.
With the adjustable version (Figure 10) with a 50V volt supply, I found a nice sweet spot at around Id=2.42A and Vds=19.9V. There, the 1W THD was .069%, which is pretty nice. You'll get more gain, but less power, so your 16 Ohm speaker needs to be pretty efficient.
Now, the point of minimum distortion won't necessarily be your favorite spot. You may want to play with the setting a bit and see what you like best.
As for impedances much lower than 8 Ohms, I wouldn't use this little amp with 4 Ohm speakers.
With the adjustable version (Figure 10) with a 50V volt supply, I found a nice sweet spot at around Id=2.42A and Vds=19.9V. There, the 1W THD was .069%, which is pretty nice. You'll get more gain, but less power, so your 16 Ohm speaker needs to be pretty efficient.
Now, the point of minimum distortion won't necessarily be your favorite spot. You may want to play with the setting a bit and see what you like best.
As for impedances much lower than 8 Ohms, I wouldn't use this little amp with 4 Ohm speakers.
😀 sorry for my dumb question , but i have never build a transistor amp just single ended tube amp , so for me i figure the Fig9 will be more appropriate . so what is the best Drain ( anode?) voltage for fig9 ?
is the 10uf input cap is obligatory?
cheers
rohan
is the 10uf input cap is obligatory?
cheers
rohan
You must mean Figure 10?
There's a table of possible supply values and operating points a little further down the page. Somewhere between 45-55V is good.
The cap? I'd just leave it in, but If you're absolutely certain your preamp output is cap-coupled, you could eliminate the cap.
There's a table of possible supply values and operating points a little further down the page. Somewhere between 45-55V is good.
The cap? I'd just leave it in, but If you're absolutely certain your preamp output is cap-coupled, you could eliminate the cap.
juanitox,
Fig9 is just a test setup. Fig11 is probably the easiest to build because it does not require a separate bias supply or the input cap.
I am interested in how Fig11 would behave with R3 bypassed with a cap. I suspect that you get much of the advantage of Fig10, but without the added complexity of the external bias supply.
Fig9 is just a test setup. Fig11 is probably the easiest to build because it does not require a separate bias supply or the input cap.
I am interested in how Fig11 would behave with R3 bypassed with a cap. I suspect that you get much of the advantage of Fig10, but without the added complexity of the external bias supply.
I agree, Figure 11 is an easier first time build. Grade KD-33 is needed for that one. Other grades have a different Vgs.
About that input cap: Given enough leakage current, the input will be offset from zero, so eliminating the input cap isn't a slam dunk. Having tested only four parts and and not knowing what to expect from the universe of 2SK82s, I put one in the drawing.
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Not necessarily. You could just build Figure 10 instead.
Have a look at the complete schematic I posted at the very beginning of this thread for more info.
http://www.diyaudio.com/forums/pass-labs/201655-lamp-simple-sit-amp.html#post2803913
Have a look at the complete schematic I posted at the very beginning of this thread for more info.
http://www.diyaudio.com/forums/pass-labs/201655-lamp-simple-sit-amp.html#post2803913
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Hi Michael,
I am curious to know more about the effect of leakage current in this circuit. Specifically, what sort of non-zero voltage would be expected at higher leakage numbers?
Also, any thoughts on cap bypass for the source resistor?
I would like to try the circuit as drawn below.
I am curious to know more about the effect of leakage current in this circuit. Specifically, what sort of non-zero voltage would be expected at higher leakage numbers?
Also, any thoughts on cap bypass for the source resistor?
I would like to try the circuit as drawn below.
Attachments
@PSz
The higher the leakage current, the higher the voltage drop (I X R)
I didn't try a source bypass cap. I didn't want to suffer the wrath of the purists, and I knew the source resistor alone would be pushing it. 🙂
I'll be interested in your opinion once you've tried it.
The higher the leakage current, the higher the voltage drop (I X R)
I didn't try a source bypass cap. I didn't want to suffer the wrath of the purists, and I knew the source resistor alone would be pushing it. 🙂
I'll be interested in your opinion once you've tried it.
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🙂 so in case of fig10 with 15/16V on the Vd can i use a 3V batterry on the gate for the bias like in tube amp grid bias? 
Look at the schematic I pointed you towards previously. http://www.diyaudio.com/forums/pass-labs/201655-lamp-simple-sit-amp.html#post2803913
A power supply (B+) of 45-50V will work nicely. Adjust the bias for 2.5-2.75A.
Bias batteries are not a good idea here.
A power supply (B+) of 45-50V will work nicely. Adjust the bias for 2.5-2.75A.
Bias batteries are not a good idea here.
🙂 ok michael and thanks for your time! a last dumb question , for the bias supply i suppose that P1 is a 10k pot but what is CW and CCW on the shcematic? and is 10000uF output cap the minimum value to get fullrange?
120V lightbulb is very difficult to find in europe, is it not as good using a 300W OHMITE - C300K10R -
An externally hosted image should be here but it was not working when we last tested it.
🙄
The cutoff frequency (-3dB) for the filter formed by the 10,000 uF output cap and an 8 Ohm speaker is:
Fc = 1/(2*PI*R*C(Farads)) = Hz
Fc = 1/(2*PI*8*.01) = 2Hz
Then the frequency response at 20Hz will be:
20*LOG10(1/(SQRT(1+(Fc/F)^2)) = dB
20*LOG(1/(SQRT(1+(2/20)^2)) = -0.04dB
You can do the math for a smaller cap and decide if it's suitable.
Also, the big resistor will work fine. You want 11-13 Ohms total. It will get very hot.
You could potentially string several 2 Ohm resitors in series and tap off to try different load values. But that might best be left for later.
or use this variable expensive one .. 🙄
An externally hosted image should be here but it was not working when we last tested it.
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