[sdiy] Mosfet Amps?

[dan snazelle]

I think those might be issues if i was trying to design an audiophile system (this is the problem I have with David self...the same author who basically calls OTA's a historical curiosity, he is great if you are looking to build HI-END low noise power amps, etc but for guitar boosters, weird distortion boxes, etc Mosfets are great! ( i think the circuits I have been able to build with one MOSFET blow any one BJT circuit out of the water for a 
clean hi-gain device.

I just want to get more info on them, instead of switching parts out randomly.



I have been wanting to buy the book you are speaking of, but it is not cheap ( i can get most electronics books used for around 1-5 dollars on amazon if i wait long enough)

so to answer your question, I am trying to make some hi-gain boxes for guitar and synth. 

I have been having fun mixing BJT's and Mosfets too


thanks



On Jul 10, 2011, at 9:39 PM, Noah Vawter wrote:

> fwiw,
> 
> Douglas Self in "Audio Power Amplifier Design Handbook" recommends against FETs in audio amps for various reasons, but nevertheless includes examples and information on them as small-signal amplifiers in Chapter 4 and power output stages in Chapter 12.
> 
> In his Disadvantages section, he cites low transconductance, and variability of conduction as issues with FETs.
> He also mentions that in the small-signal amplifier input stages, noise performance will be inferior with FETs when used with devices with low output impedance.  His guesstimate is 5kOhms.
> 
> In chapter 12, the list of disadvantages to using FETs is quite large.  7 Major items.  Here are some highlights:
> 
> poor linearity, higher gate voltage, high minimum channel resistance (I'm not sure that I buy this one.)  liability to parasitic oscillation, difficult to place devices in parallel.
> 
> however, he sums up all of the differences between FET and BJT amplifiers (power audio amplifiers) simply by saying that it's matter of cost and FETs will be 1.5-2.0 times as expensive.
> 
> 
> *By the way, this book is excellent.  I recommend it for anyone interested in advanced electronics and amplifiers.  Experts and experienced designers may already know everything, but it filled in a huge gap of knowledge for me, and nearly every designer needs to consider the metal inside of an amplifier at some point.
> 
> After studying Self's book, I'm cocky enough to ask you: How many watts are you looking to dissipate and into what?
> 
> -Noah!
> 
> 
> On Jul 10, 2011, at 6:09 PM, dan snazelle wrote:
> 
>> I have lots of electronics books. But basically none of them show how to use MOSFETS as linear amplifiers. they usually just show using Mosfets as INVERTERS (ala CMOS)
>> or as switching devices.
>> 
>> I know you can make amplifiers with them.
>> 
>> 
>> Can anyone recommend a book or a website that covers them in more depth?
>> 
>> thanks
>> 
>> 
>> 
>> 
>> 
>> 
>> 
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> 
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