Input devices Output devices

I have often wondered why we don't see med power transistors as input devives in microphone preamps. Things like the easy to get in the USA devices like TIP 29s, 30s,etc and they don't cost much.

FWIW I have used tip29s as the transistor in Rangemaster type treble booster for guitar. Less noise and less gain this can be a good thing. The die is bigger so they could have less noise. I am thinking of trying this with an AMEK 2500 type circuit. I would use 2 devices and not the 8 smaller ones.


Now for output devices why do people use MOSFETS instead of Bipolars for output devices I does not make sense to me. Maybe IGBTs make sense.

PRR posted at the old TT a simple SS microphone pre Altec? I wonder how power devices might work in that circuit.

IGBTs can be fairly expensive from my experience. they are superior to either fets or transistors in their specs, uses, and durability though. I am always a big supporter of using new technology over old. I'm working with an IGBT at work that is rated at 900v/30A constant current draw, or 900v/228A pulsed current.. now that from a T0247 die is amazing to me. maybe we should just go ahead and try it since i feel that a stock answer would be to tube/iron the sucker just like all the others.. :green:



sorry, just had to rant today!

Cheers :guinness:

Now for output devices why do people use MOSFETS instead of Bipolars for output devices I does not make sense to me.

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Mosfets are easy to make into a simple output circuit that won't go into thermal runaway... also, good high power mosfets are cheap and readily available while good high power bipolars are getting harder to find and more expensive, and manufacturers are under constant pressure to add features while reducing the costs...

In certain consumer products, "mosfet output" has become a buzzword implying that the amp/circuit is more hi-tech, and since the mosfets are cost-effective, the marketers go that way for the extra sizzle...

regards, Jack

A few comments:
[quote author="AMZ-FX"]Mosfets are easy to make into a simple output circuit that won't go into thermal runaway...[/quote]
If you are referring to a MOSFETs general characteristic of lower Rds-on causing it to generate less heat, then I would agree. If you are talking about bipolar complimentary output circuits with bias, I would tend to disagree, unless you are going to go to a lot of trouble to match the devices. In my experience, MOSFET ckts generally require more attention due to their wider tolerances than BJTs.

also, good high power mosfets are cheap and readily available while good high power bipolars are getting harder to find and more expensive, and manufacturers are under constant pressure to add features while reducing the costs...

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Umm, that might depend on what you are calling "high quality". TIP35/36 are readily available and not expensive. Maybe you want MJL21134? They are more expensive but available...one thing that might be making the issue change is the demand for lower costs and to fulfill that, product manufacturers are buying components from "other" component manufacturers, with sometimes different part numbers.

In certain consumer products, "mosfet output" has become a buzzword implying that the amp/circuit is more hi-tech, and since the mosfets are cost-effective, the marketers go that way for the extra sizzle...

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MOSFET is used as a buzzword all too often. These ahve been in used in many ways for so many years now, I don't understand why its so "cool" anymore. For designs that use all N-channel pseudo-complimentary output designs, this is pretty cheap, but P-channel MOSFETs are pretty expensive to make still and require more of them since they won't handle the same amount of current as their equiv N-channel compliment.

I'm certainly not trying to pick a fight with you here, Jack. Just trying to relate that my experience seems a bit different than yours. :green:

Peace!
Charlie

yes P channels are terrible to attempt to use needing gate protection in high voltage situations to keep the gates from cooking.. n channels are fine if you can charge-pump the gate to Source+15v or so.. which is not too hard to do.