illuminateddan, The relationship is not linear, so all you can do is keep on reducing the resistance until the current reaches 10mA.
When I mentioned calculating using Ohm's Law, I was referring to calculating the current through the resistor. Unfortunately it seems that many diyers do not know or understand Ohm's Law. 🙂
When I mentioned calculating using Ohm's Law, I was referring to calculating the current through the resistor. Unfortunately it seems that many diyers do not know or understand Ohm's Law. 🙂
That's a great tip... So it's a dark art in amplifiers component selection 🙂
You most often cannot anticipate the current by dividing resistor values. Q Vp plays a part, and other things. But what you can anticipate, is more current with lower R. Just don’t expect to be able to tell in advance.
I made a mini version of that part of the circuit on a breadboard to simulate and find the corrext value for R4 in advance, so no pot or sockets for me on board.
With only 5mA the circuit will not work or sound as intended, and you risk instability over time. So, reduce R4 to for example 15R and check then. Some 113’s have low IDSS, I needed to go for approx 11R.
I suggest continuing lowering the R4 resistor. It looks like you have a relatively low Idss j113.
One thing to keep in mind is that R4 = 125R shown on the schematics is based on the selected J113s Mr. Pass supplied for the ACP+ camp build. Use of a random J113 most likely requires an adjustment. The key is the 10mA shown on the schematics and that's what you should target for. (We'll ignore the possibility that your Idss is actually less than 10mA)
With only 5mA, almost all of it has gone to Q1 and Q2 isn't getting adequate current and distortion is likely higher than it needs to be.
One thing to keep in mind is that R4 = 125R shown on the schematics is based on the selected J113s Mr. Pass supplied for the ACP+ camp build. Use of a random J113 most likely requires an adjustment. The key is the 10mA shown on the schematics and that's what you should target for. (We'll ignore the possibility that your Idss is actually less than 10mA)
With only 5mA, almost all of it has gone to Q1 and Q2 isn't getting adequate current and distortion is likely higher than it needs to be.
Hi, thank you, that's great. However... I am now at 2R2 with a Vdrop of 0.016 giving 7.27mA.... Should I drop even lower? At this rate, and given the observed relationship, I'll be down to 0R1 before hitting 8-9mA!
Is this a J113 issue? and should I swap it them out? If so, what for?
Is this a J113 issue? and should I swap it them out? If so, what for?
It looks like a switch of J113 is needed. You can test the J113 to make sure that the Idss is greater than 10mA before installing it.
Yes, swap the J113’s. They seem to have an IDSS lower than 10mA. You will also get better performance out of the CCS with a higher resistance, so my advice is to swap them out in this particular case.
Edit: good morning, Ben!
Edit: good morning, Ben!
So, I went through and tested all (8) my JFETs using this guide as the circuit above cause lots of heating and the occasional popping JFET..
and the closest I found gives me ~9mA in with 9v in series with a 100R, and ~9mA on the ACP+ with a 2R2. I'm using this J113 from Element14. Is there a better JFET to use with a high IDSS?
Thanks again!
and the closest I found gives me ~9mA in with 9v in series with a 100R, and ~9mA on the ACP+ with a 2R2. I'm using this J113 from Element14. Is there a better JFET to use with a high IDSS?
Thanks again!
There is no need to use anything but a J113. Most of them have high idss. Just order from a different producer or two, and order a few when at it. Then match/measure IDSS and build a proto circuit to find correct value, or use a pot+resistor in circuit. Alternatively order the stores parts kit. It is there for this exact reason.
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Idss for the J113 is all over the place. But most people report numbers in the 15mA to 25mA range, I believe. Maybe you have some old stock that are lower or something, I don't know. Really, higher Idss is better because more degeneration (big resistor to hit your target) is a good thing with a CCS like this. But ya, there's a million ways and parts to make a CCS. J113 is just super cheap and plentiful, and works great (when you get the right ones that is.. 😛).
I can second both last two posts. I am a degenerate myself, and work even better faced with a little resistance.
Yes, I picked my own components as a learning exercise... and it really is... 😀
Thanks all... hunting a different supplier for the same parts from the same (onsemi) manufacturer! Who'd have thunk it?
I have semis, but it will be a looooong journey in the mail to Aussie land 🙂
That said, it is a pitty you ended up with low IDSS parts. I did too, and so degen is lower than I would have liked.
That said, it is a pitty you ended up with low IDSS parts. I did too, and so degen is lower than I would have liked.
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