Blue Jinn
Well-known member
Well,
Decided to do this for fun, changed the capacitor between the two 1 g resistors to 470pf, removed the emitter follower, changed the coupling cap to 1uF, and swapped transformer. Signal is very very low, and there is a bit of hum and noise. Noise I think is partially dirty fingers etc, but I'm not sure about hte hum and hte low sensitivity. I didn't use the Cinemag though, I used the KCM transformers I have which i used for the Royer. The published specs are 11.5:1, which is one turn higher then the published spec for the Cinemag, (EDIT) which itself is one turn higher then the AMI T13, so 11.5:1 vs 9.5:1. That doesn't seem an extreme difference, or does it? I'm tempted to swap out the transformer for the Cinemag, (or maybe the 8.2:1 Edcor (????) and see if that makes a difference. As always, very much open to suggestions.
EDIT: I also swapped the stock 32mm capsule for a 34mm K67 type capsule. I replaced two capacitors and removed everything after the FET, coupling the FET via a 1uF/100v poly to the 11.5:1 transformer. HOwever, I did not attempt to replace the FET or re-bias the FET. (Something I'm reluctant to do just yet, until I have a 'scope and setup a better bench environment.)
This was a late night glazy eye project, so I haven't cleaned it up at all, which I'm sure will help the noise level. I would expect some loss of gain with teh higher ratio transformer and the single amplifier stage, but the mic is basically unusable at the moment from and S/N standpoint.
Decided to do this for fun, changed the capacitor between the two 1 g resistors to 470pf, removed the emitter follower, changed the coupling cap to 1uF, and swapped transformer. Signal is very very low, and there is a bit of hum and noise. Noise I think is partially dirty fingers etc, but I'm not sure about hte hum and hte low sensitivity. I didn't use the Cinemag though, I used the KCM transformers I have which i used for the Royer. The published specs are 11.5:1, which is one turn higher then the published spec for the Cinemag, (EDIT) which itself is one turn higher then the AMI T13, so 11.5:1 vs 9.5:1. That doesn't seem an extreme difference, or does it? I'm tempted to swap out the transformer for the Cinemag, (or maybe the 8.2:1 Edcor (????) and see if that makes a difference. As always, very much open to suggestions.
EDIT: I also swapped the stock 32mm capsule for a 34mm K67 type capsule. I replaced two capacitors and removed everything after the FET, coupling the FET via a 1uF/100v poly to the 11.5:1 transformer. HOwever, I did not attempt to replace the FET or re-bias the FET. (Something I'm reluctant to do just yet, until I have a 'scope and setup a better bench environment.)
This was a late night glazy eye project, so I haven't cleaned it up at all, which I'm sure will help the noise level. I would expect some loss of gain with teh higher ratio transformer and the single amplifier stage, but the mic is basically unusable at the moment from and S/N standpoint.