Gus

Re: TF11
« Reply #40 on: October 05, 2020, 01:41:04 PM »
red(PCB has R3 under it) looks to be a higher value resistor, one of the gates(if I have the correct dual pinout) appears to have a trace going to it.
I would guess 51meg to 3gig maybe on the lower side because of the reduced low end in the frequency graph however a lower value is higher noise so the low end could be from using a higher value cap to the transformer. THIS IS A GUESS

One electro might be a 100uf at 16VDC the other might be a 50VDC(I think I saw a 0) rating from one of the videos
the axial looks to be 2.2uf

the top one looks like 470pf polystyrene

The two blues are unknown. GUESS if they are for the capsule voltage filtering maybe .01uf GUESS

15k, 150k, 1gig(from what I could find yellow means 4%, I do not know what the PPM/C of the last band is) 100k, 2.67k, 182k, 2.2k and 5k trim

Guess
The white wire is grounded(front of capsule),

Blue wire is capsule charge and input to the 470pf

Anyone see different colors on the resistors?



analogguru

Re: TF11
« Reply #41 on: October 05, 2020, 02:19:41 PM »
red(PCB has R3 under it) looks to be a higher value resistor, one of the gates(if I have the correct dual pinout) appears to have a trace going to it.
correct
One electro might be a 100uf at 16VDC.....
This would be the source resistor+trimmer bypass capacitor.

.... the other might be a 50VDC(I think I saw a 0) rating from one of the videos
This would be the coupling capacitor from drain to the transformer.

the axial looks to be 2.2uf
Filter cap

the top one looks like 470pf polystyrene
correct

The two blues are unknown. GUESS if they are for the capsule voltage filtering maybe .01uf GUESS
Both are filter caps one for the FET (after the 2k67) and the other is for the capsule (after the 100k resistor).  I would go for a 100nF (or more).

15k, 150k, 1gig(from what I could find yellow means 4%, I do not know what the PPM/C of the last band is) 100k, 2.67k, 182k, 2.2k and 5k trim
.....
Anyone see different colors on the resistors?
I don't.
2k2 is  the source resistor in series with 5k pot to ground.  (insanely to the opposite side of the pcb the as the bypass capacitor - a skilled technician wouldn't do that).

2k67 is the power supply filtering resistor going to the 15k drain resistor and the blue capacitor beside the 182k resistor.

100k is the power supply filtering cap for the capsule connected to the second blue cap and the 1G resistor.

15k is the drain resistor, 150k and 182k are a voltage divider from drain to ground.

The red resistor is connected one one side to the midpoint of this voltage divider and on the other side to the gate and 470p capacitor.  (This is for "double biasing" the FET together with the source resistor).

The two halves of the Dual-Fet are in parallel, probably in an attempt to improve the noise performance by 3db (theoretically).

It is questionable if a voltage multiplier for a higher capsule voltage, a buffer transistor after the FET and a 1:1 transformer instead of the (probably ~ 10:1) step-down transformer would not lead to an overall better result.  I mean the costs for the extra parts shouldn't play a big role except if there would be hardcore hustlers at work.

Alltogether not an impressing "design", especially for this money.

Guess
The white wire is grounded(front of capsule),

Blue wire is capsule charge and input to the 470pf
probably
« Last Edit: October 05, 2020, 02:40:03 PM by analogguru »

Gus

Re: TF11 New
« Reply #42 on: October 05, 2020, 02:59:07 PM »
analogguru
Are you sure the JFETS are in parallel? that does not make sense because that add the gate capacitance together. That is something I would not do however, I do see both of the sources connected on the backside in one of the videos.


EDIT made a sim. I guess the dual because of the drain current
« Last Edit: October 05, 2020, 06:17:28 PM by Gus »

analogguru

Re: TF11 New
« Reply #43 on: October 05, 2020, 03:15:36 PM »
analogguru
Are you sure the JFETS are in parallel?
Yes, I am.  The gates are connected together on the component side (under the Dual-FET).
Sources are connected on the track-side and the drains too - via the the output coupling electrolytic pad, both drains go there and then to the 15k. 

... that does not make sense because that add the gate capacitance together. That is something I would not do .....
There are several things I would not do.... The first thing I would not do is the position of the 2k2 resistor which could be placed in parallel to the 5k-trimmer and connected to ground on this side (near the bypass electrolytic).

But who cares, fetishist-buyers don't think about a good design....

« Last Edit: October 05, 2020, 03:50:06 PM by analogguru »