Wow I am not sure if I like this circuit. Its alot like a cardiod only older u87 circuit mixed with a EF circuit like in the cheap china circuit like the v67,2001 even down to the use of a PNP transistor if I traced this right.
Notes
not having a source bypass cap, No bypass cap more noisy:However I should add it helps with making the gain of the Fet more linear Fets without feedback (soure r bypassed with a good cap) have more of a pentode curve. Remember triodes are more linear than most gain devices without feedback
EF has bad bias setup only one transistor and it is electro cap coupled to the Drain. for the picture the ef looks to be a pnp like in the china stuff.
if it was a direct coupled NPN you don't need the electro and the current in each semicondutor leg is going in opposite directions causing a more constant current draw from the Phantom supply.
The switches look to be a sensitivy control by dropping the voltage to the capsule. I see 3 part I can remove from this circuit.
Center tap on the output side is the phantom V path to the resitor on the top right in the picture of the top of the board. the to what looks like a 2.2k then a zener bypassed to ground with the FC cap last number of the zener pn might be the voltage 24 older U87 or 33 newer U87 I would guess
Then another dropping resistor to the Drain resistor the node of the two resistor bypassed with the big Jamercon cap
Looks like a 3 gig to ground on the gate. A unbypassed soure R to ground A 680pf ? to the gate the other side of the 680 to another 3 gig to ground and the red wire of the capsule.
Now the bad part IMO a elctro Jamercon? to the base of a pnp the base of the pnp to ground via a resistor no other resistor to a + V this is a way to bias not stable you should have another resistor to a more + part of the circuit power supply this can be a path for noise but with GOOD design it is not an issue.
then another electro off the emitter to the transformer I would guess a 2:1 because of the size and the cheap parts used. IIRC lower ratio transformer are not as critical with winding as higher ratios
I will say more when I get the part values and numbers. I have a few more thought out SS circuits designs forming in my head . For the cost of this microphone have a custom fet speced.
I will scan my traced schematic tomorrow.
The only original looking things with the phantom are the shock mount and the capsule IMO.
Notes
not having a source bypass cap, No bypass cap more noisy:However I should add it helps with making the gain of the Fet more linear Fets without feedback (soure r bypassed with a good cap) have more of a pentode curve. Remember triodes are more linear than most gain devices without feedback
EF has bad bias setup only one transistor and it is electro cap coupled to the Drain. for the picture the ef looks to be a pnp like in the china stuff.
if it was a direct coupled NPN you don't need the electro and the current in each semicondutor leg is going in opposite directions causing a more constant current draw from the Phantom supply.
The switches look to be a sensitivy control by dropping the voltage to the capsule. I see 3 part I can remove from this circuit.
Center tap on the output side is the phantom V path to the resitor on the top right in the picture of the top of the board. the to what looks like a 2.2k then a zener bypassed to ground with the FC cap last number of the zener pn might be the voltage 24 older U87 or 33 newer U87 I would guess
Then another dropping resistor to the Drain resistor the node of the two resistor bypassed with the big Jamercon cap
Looks like a 3 gig to ground on the gate. A unbypassed soure R to ground A 680pf ? to the gate the other side of the 680 to another 3 gig to ground and the red wire of the capsule.
Now the bad part IMO a elctro Jamercon? to the base of a pnp the base of the pnp to ground via a resistor no other resistor to a + V this is a way to bias not stable you should have another resistor to a more + part of the circuit power supply this can be a path for noise but with GOOD design it is not an issue.
then another electro off the emitter to the transformer I would guess a 2:1 because of the size and the cheap parts used. IIRC lower ratio transformer are not as critical with winding as higher ratios
I will say more when I get the part values and numbers. I have a few more thought out SS circuits designs forming in my head . For the cost of this microphone have a custom fet speced.
I will scan my traced schematic tomorrow.
The only original looking things with the phantom are the shock mount and the capsule IMO.
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