EDIT: facepalm party... I had my scope on 10kHaz, not 1kHz!... been a long day haha....
>>>>>>
Hi all - thought I'd ask via a new thread. Let me know if I should just tack this onto the build thread.
Just finished two d-87's... pretty chuffed to be honest
...
One odd thing I couldn't quite clock in was even distortion in calibration. Just hoping someone can confirm this is either "not that odd" or "odd"!
Having just finished two other mics (Vamisound ldc84), I've seen nice clear calibration... not seeing it on my d-87, despite them sounding pretty nice.
So:
- D-87 m (blue pcb)
- Calibration is signal gen at 1k freq on the 1 gig R6 resistor, with scope direct to drain leg on FET.
- Everything wired up except capsule
*At low amp ~0.3v I get a nice clean sine.
*As I increase the upper half of the wave broadens, and the lower half thins.
* I can reduce this via trim to make it more sine like, but it then clips early on the lower half (I think... read below)
* when I increase amplitude in generator, it clips strangely... bottom hard clips, top soft clips...
Refer attached for my actual final product... looks wrong, BUT it is the point where it evenly clips, despite one half being hard and one half being soft... I.e. low amp is sine, increased amp starts to deform at the same time top and bottom, and pushed harder they deform the same amount, despite it being a different shape.
I can't actually get the top half top hard clip... it keeps that ramp shape.
Both builds are exactly the same... so not likely a dodgy part.
With capsule wired up, it actually sound pretty nice bit I'm thinking this doesn't seem right!
>>>>>>
Hi all - thought I'd ask via a new thread. Let me know if I should just tack this onto the build thread.
Just finished two d-87's... pretty chuffed to be honest
...One odd thing I couldn't quite clock in was even distortion in calibration. Just hoping someone can confirm this is either "not that odd" or "odd"!
Having just finished two other mics (Vamisound ldc84), I've seen nice clear calibration... not seeing it on my d-87, despite them sounding pretty nice.
So:
- D-87 m (blue pcb)
- Calibration is signal gen at 1k freq on the 1 gig R6 resistor, with scope direct to drain leg on FET.
- Everything wired up except capsule
*At low amp ~0.3v I get a nice clean sine.
*As I increase the upper half of the wave broadens, and the lower half thins.
* I can reduce this via trim to make it more sine like, but it then clips early on the lower half (I think... read below)
* when I increase amplitude in generator, it clips strangely... bottom hard clips, top soft clips...
Refer attached for my actual final product... looks wrong, BUT it is the point where it evenly clips, despite one half being hard and one half being soft... I.e. low amp is sine, increased amp starts to deform at the same time top and bottom, and pushed harder they deform the same amount, despite it being a different shape.
I can't actually get the top half top hard clip... it keeps that ramp shape.
Both builds are exactly the same... so not likely a dodgy part.
With capsule wired up, it actually sound pretty nice bit I'm thinking this doesn't seem right!
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I shouldn't post here while sleep-deprived...
*cough* REW *cough*
It's occasionally enough to just voice a problem, and the solution may or may not reveal itself or become obvious 
