FarisElek said:Okay, scrubbed it and it changed and the slowly went back to working perfectly in figure 8 and poorly in the other two positions. I think I can safely assume this is a switch problem? If i toggle the switch back and forth and turn it on, it will be weird in all three positions and then slowly go back to the way it's been. Where can I buy just a single 3 way switch?
DT_Music said:Has anyone used the LA-8 Capsule from Luke Audio? I had been planning on using the Heiserman Capsule but prices seem to have gone up recently so I'm checking alternatives. Luke Audio mics have gotten good reviews and I just saw that he sells capsules for DIY builds. Here's what he had told me about the LA-8 (K87 Style)
"Yes, we make a K87. 34mm , electrically isolated, 1 micron Mylar, platinum sputtered, and are $250. All around a fantastic capsule, slightly brighter than what you may consider a vintage 87 but that depends on the circuit and how true it is as well"
I'm intrigued but I'm also going for as legit of a vintage 87 clone build that I can. Has anyone used these or compared them with the Heiserman capsules?
poctop said:If you are working on the Blue Version of the pcb you should adress your question in the other thread for this one ,
I have posted in the opther thread for this one.
Matador said:Thanks for all the kind words!
I created a simple PHP script to do all the calculations for everyone. It's located here:
You plug in the two values that you measure for your JFET, and it will do all of the math and tell you the values of all the resistors, the gain, and calculate the maximum input signal before clipping. If you have a handful of JFET's (even different types), you can plug in the data and see what it gives.
For example, if I use my nominal JFET that I have (IDSS = 10.79mA, VGS at 1% IDSS = -3.4V), this is what is spit out:
VP = -3.77777777778 V
gmo = 5712.35294118 µmho
β = 0.756046712803m
VDD = 21 V
VD = 10.5 V
IDQ = 225 µA
RD = 46.6666666667 kΩ
VGSQ = -3.23224990585 V
RS = 14.3655551371 kΩ
gm = 824.889108622 µmho
AV (gain) = 38.494825069
Output swing headroom (positive) = 10.5 V
IDO (ohmic) ≤ 282.182455648 µA
Output swing headroom (negative) = 6.72222222222 V
Maximum input signal before clipping = 174.626646833 mV
For those of you without a scope and only a simple DVM, this calculation for the source resistance should be VERY close to the optimal value for that JFET.
I went through most of my stash of 2N3819's and have a few near the extremes of the ranges. I'll breadboard up the circuit and inject a test signal and we'll see how close the math is to reality.
doqmemory said:Another D87 joins the world! Mic-Parts RK-87, Cinemag CM 13113 and body from chunger. It is quiet and rich sounding, complementing my other microphones nicely.