0dbfs said:The K67 style capsules should have a pre-emphasis or "peaked high frequency" response. The U87 and U67 circuits are designed to "de-emphasize" that response and bring the capsule signal back towards "flat" while at the same time reducing HF noise. This KM84 circuit is flat with no de-emphasis so best suited for so-called "flat capsules" like C12, K47, M7 or even maybe a sony C37 style capsule if you were lucky enough to get any of those when Dale was making them.
If you use a K67 style capsule with the built-in pre-emphasis then it will seem bright and spitty but they all sound different right and you can also always EQ it too
Cheers!
-jb
0dbfs said:Yeah. CHeck out the U87 schematic and look at the signal path from top of FET (output) to C9 -to- R8 and C6 (in parallel) which then feeds to the backplate... This is the negative feedback de-emphasis part of that circuit.
IOW -
The signal coming out of the FET is fed through an eq / filter (R8 and C6) which then causes modulation on the backplate. This modulation signal is band limited due to the filter and since it's on the backplate it is opposite in polarity and therefore subtracts from the signal produced on the front diaphragm and fed into the FET... Essentially a notch filter. I don't know the exact math but you can probably google that for more specifics on the filter frequencies / etc...
Otherwise the U87 and KM84 circuits are pretty much the same with a slightly different transformer ratio and of course the pattern option differences.
You could put a BV08 in this mic and a K47 or M7 if it would fit and it's basically a "Single FET U47" (not a FET47)... I wonder if we could parallel a couple FET's similar to how the ||6028 implementation works - reducing output Z and increasing drive capability of the active device.. I might experiment with that a little but the mic body in this thread would probably be too small for the BV08
Cheers!
-j
0dbfs said:Yeah. CHeck out the U87 schematic and look at the signal path from top of FET (output) to C9 -to- R8 and C6 (in parallel) which then feeds to the backplate... This is the negative feedback de-emphasis part of that circuit.
IOW -
The signal coming out of the FET is fed through an eq / filter (R8 and C6) which then causes modulation on the backplate. This modulation signal is band limited due to the filter and since it's on the backplate it is opposite in polarity and therefore subtracts from the signal produced on the front diaphragm and fed into the FET... Essentially a notch filter. I don't know the exact math but you can probably google that for more specifics on the filter frequencies / etc...
Otherwise the U87 and KM84 circuits are pretty much the same with a slightly different transformer ratio and of course the pattern option differences.
You could put a BV08 in this mic and a K47 or M7 if it would fit and it's basically a "Single FET U47" (not a FET47)... I wonder if we could parallel a couple FET's similar to how the ||6028 implementation works - reducing output Z and increasing drive capability of the active device.. I might experiment with that a little but the mic body in this thread would probably be too small for the BV08
Cheers!
-j
elskardio said:Hi Guys,
I just wanted to share my version of this nice circuit. Have a great weekend
elskardio said:Hi Guys,
I just wanted to share my version of this nice circuit. Have a great weekend
elskardio said:Hi Guys,
I just wanted to share my version of this nice circuit. Have a great weekend
Wordsushi said:Love it! Looks fantastic. Any chance of making your boards available?
The badge looks really cool, too.
G-Sun said:Finishing my Fet847 now,
firing up to bias fet.
I have some low-fq-noise, like AC hum,
but I get some signal to hum, just like 12db or some.
Any pointers where to get rid of the noise/hum?
Oh, thanks a lot! That's good newsKhron said:If the mic body's still open, and/or the headbasket isn't installed, that's where the hum gets in.
But just for the bias adjust, that's nothing to worry about, the test-signal will be way larger in amplitude anyway.
Thanks!Khron said:Bit of a thread "necro", but here's a slight update / simplification https://groupdiy.com/index.php?topic=63889.msg853127#msg853127
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