C414 EB P48 build

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Gus

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having a little think back to this mic and have deleted the switches and the other patterns, wanted someone to verify whether this would work like this?
reply 117
 

Spencerleehorton

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Success, switch works great between cardioid and fig 8, also have tweaked the volages a bit to get the ma needed and sounds much better, changed the capsule as well. i have noticed the back capsule is slightly darker than the front.
mounted the switch on the bottom of the mic for easy switching.

my next step is to try the switch all 4 patterns with a lorlin.
 

Spencerleehorton

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Sorted out 2 of the 3 mics I've built, strange that only one of them seems to have very low output, all resistors check out, have replaced a couple of the caps but will change the txf as well.
Definitely isn't the capsule, will put a scope on the working one and put a sinewave through it, then do the same on the low output one.
Should be able to diagnose then!!!
 

Spencerleehorton

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still completly lost with this low output mic!!? ive completely changed one pcb and have got slightly better output, went from 256mv to 857mv!! when compared with the other mic it outputs 3.2v at this setting.
I'll changed the other pcb and see if it improves
 

RuudNL

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Looking at your drawing:

- What is the point of the 27 M.ohm and 10 M.ohm resistors in series on the supply voltage? (R19+R20)
- The 'upper' part of the switch doesn't have any function; in both positions the 1 G.ohm resistor is connected to ground. (R17)
 

Spencerleehorton

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The 27meg and 10meg give a hyper cardioid setting.
I've ordered some more jfets as I suspect they are the problem.
Also Ive managed to get hold of some mini 4 way switches, if I solder them together and put on a small pcb they would work perfectly as a good 4 way switch, will just need to make a knob for it.
Also gonna test again with another 2:1 txf which works perfectly in another mic.
I think the problems I've got is using a 2sk30 batch which are faulty!!
Gonna try with J201, J113, 2n5457 and a 2n5458 jfets and see which come out the best after tweaking.
 

Gus

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Look at the sim screenshot and RuudNL's reply in post #172

 

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