No. Unmatched FET's are benign.
hFE for a FET? Doesn't exist.
From the Toshiba datasheet:
Note: IDSS classification GR: 2.6~6.5 mA, BL: 6.0~12 mA, V: 10~20 mA
Active ribbon-mic
- Thread starter clintrubber
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Help Support GroupDIY Audio Forum:
Note: IDSS classification GR: 2.6~6.5 mA, BL: 6.0~12 mA, V: 10~20 mA
??So what am I measuring exactly when testing the 2SK170s in my digital multimeter hFE mode?
IDK. That may (or may not) be explained in the owner's manual...?
See what mine displays.
It does not do Gm, but gives the important Vgsoff.
I haven't seen a component tester that displays directly Gm. Some of the most expensive can be connected to a PC for curve tracing, which allows determining Gm.
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Ah that! I believe its measuring the avg voltage amplification. Anyway, weird thing with my circuit, after leaving it plugged in for about 10+mins while I went to the toilet, the crackling noise seemingly disappeared.
Granted I only tested using crocodile clips between the xlr output of my interface & the booster circuit input, but i think I can say that the mods are an improvement over the initial schemo.
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That makes me suspect a capacitor.
I have purchased batches of 2SK170BL's from Asia.
I test them in my Peak Atlas DCA75 which tells me they are all back to back diodes.
Swapped them in the circuit (White source follower using real ones) and they work, albeit different bias. However I would not trust them in any noise critical application.
I test them in my Peak Atlas DCA75 which tells me they are all back to back diodes.
Swapped them in the circuit (White source follower using real ones) and they work, albeit different bias. However I would not trust them in any noise critical application.
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What a disappointment! I thought the higher price point of the DCA75 would put it in a better position.
Even genuine ones have large variations. My mentors always told me not to rely on individual transistor parameters for the correct operation of a circuit. However, in the case of mic buffers, it's almost impossibe not to, unless one is ready to make it much more complcated.
Someone on reddit mentioned that if I plan to isolate DC using transformers, I can use a center tapped tranny (maybe wire up 2 1:1 transformer in series) and do away with the 4 resistor + 1 cap along the DC path to improve headroom & noise performance (see schematic 1(a)) I could effectively wire up the transformers to make them a 1:2 step up transformer, but should I match resistor values to the impedance or winding resistance of the tranny before splitting them off to the FETs? Is there anything I should take note of when wiring it up like that? (I also plan to put a LED indicator in the path as well)
PS: is my implementation of an attenuation Pad alright for 1(a)? I'm thinking resistor values of 1-5k for this path.
In schematic 1(b), I've thought about adding a transformer pre-FET stage and using a dual-ganged pot to adjust between transformer vs direct signal. Is this impementation workable?
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You say you want a xfmr for "isolation", but in schemo 1a, the primary and secondary are connected, resulting in no "isolation" at all.
Anyway, what do you expect from "isolation"?
Schemo 1a shows bipolar transistors, not FET's, and a completely different topology. Doesn't make much sense.
The pots are useless in this configuration.
Hmm ok. It appears I did not fully understand what I drew up. Back to the drawing board it is.
If transformer colouration is what I want to add with the booster pre-transistor, I should just do away with the pots and connect the mic capsule directly to transformer primaries yes? Any good suggestion to somehow make a blend pot/switch between transformer coloration & the direct signal?
If transformer colouration is what I want to add with the booster pre-transistor, I should just do away with the pots and connect the mic capsule directly to transformer primaries yes? Any good suggestion to somehow make a blend pot/switch between transformer coloration & the direct signal?
You won't get any "transformer coloration" with mic level. You may get attenuation, loss of BandWidth, increased noise, but no color, sorry.
Ah... Thought it may be a cool idea like the transformer version of the cloudlifter (CL-X I believe)
So its just a gimmicky way of making a mic sound "cooler"?
