Ghee butter, 588 JFETs per channel looks UFOddball enough.
588 at 6mA each is about 50W peak in 4.
588 at 6mA each is about 50W peak in 4.
20W is voltage limited at 8 ohm.
50W peak is 25W RMS. That would be something like 3.5A, 14V for 4 ohm. I max will be 12mA per JFET, which means V grade or some forward bias.
50W RMS at 4R requires 17mA per FET. You need to use V grade AND forward bias. And dissipation at the required 20V rail will be a bit high, so that the case temperature will be a touch higher than the reported 45°C.
30W rms at 6 R is 3A 18V. 180mW dissipation per FET.
Patrick
50W peak is 25W RMS. That would be something like 3.5A, 14V for 4 ohm. I max will be 12mA per JFET, which means V grade or some forward bias.
50W RMS at 4R requires 17mA per FET. You need to use V grade AND forward bias. And dissipation at the required 20V rail will be a bit high, so that the case temperature will be a touch higher than the reported 45°C.
30W rms at 6 R is 3A 18V. 180mW dissipation per FET.
Patrick
Patrick, shouldn't that be: 50W peak is 25W average ?
My professors taught me that you get RMS value by dividing peak value with square root of 2 i.e 1.41. So 50W peak should be 35.46W RMS
You divide peak VOLTAGE by root 2 to get Vrms. But it is also the same for current in resistive load. So power is divided by 2.
Or am I still wrong ?
Patrick
Or am I still wrong ?
Patrick
Sorry Patrick, I don't know why I asked at all - absolutely unimportant because this calculation assumes pure resistive load and sinusoidal signal - pretty much useless in real life.
Peak voltage/current value might be informative - it determines the clipping limit, the rest is of no use, unless we want to go into really complex modeling...
> Peak voltage/current value might be informative ....
That we agree.
And in post #189 I was working back from what Nelson quoted in post #186 back into, exactly as you said, voltage, current, and thermal dissipation.
Patrick
That we agree.
And in post #189 I was working back from what Nelson quoted in post #186 back into, exactly as you said, voltage, current, and thermal dissipation.
Patrick
Last edited:
This is correct. The square of the square root of 2 is equal to 2...
Prms=(Vrms)^2/R
since Vrms=Vpk/sqrt 2 then:
Prms=(Vpk/sqrt 2)^2/R; this then equates to:
Prms=(Vpk^2/2)/R)=Vpk^2/(2*R) or the customary =(Vpk^2/R)/2
As an example with the known values Vpk=20V and R=8
Prms=(20^2/8)/2=25 watts
Hi Nelson,
I was wondering how this project was coming along. Have you had a chance to do any preliminary or even serious listening and if so can you share your thoughts on the sound?
Thank you.
Graeme
I was wondering how this project was coming along. Have you had a chance to do any preliminary or even serious listening and if so can you share your thoughts on the sound?
Thank you.
Graeme
At this time I have 5 pc boards completely stuffed, ready
for action. Four of them perform as previously described,
and one of them has a little extra distortion.
I began searching for the bad device by measuring the THD
at the Source pin of each of the 588 devices on the board,
and I got half way through before I had to go work on other
things for a while.
In actual testing the best performance looks to be with
supplies in the +/-15V area - battery operation is very
feasible. To get the power up I can run two pc boards
in balanced mode, and this looks like what I may do,
creating one stereo pair at about 40 watts and a single
board suitable for two channels at 10 watts or less.
I may have it a BAF, then again I might have something
else.
😎
for action. Four of them perform as previously described,
and one of them has a little extra distortion.
I began searching for the bad device by measuring the THD
at the Source pin of each of the 588 devices on the board,
and I got half way through before I had to go work on other
things for a while.
In actual testing the best performance looks to be with
supplies in the +/-15V area - battery operation is very
feasible. To get the power up I can run two pc boards
in balanced mode, and this looks like what I may do,
creating one stereo pair at about 40 watts and a single
board suitable for two channels at 10 watts or less.
I may have it a BAF, then again I might have something
else.
😎
- Status
- Not open for further replies.