mosfet

[Bucket Head]

what is mosfet in relation to pedals? wat does it do ect and what difference does it make cheers

[The Twickerman]

[quote name='Bucket Head' post='727719' date='Jan 28 2010, 03:52 PM']what is mosfet in relation to pedals? wat does it do ect and what difference does it make cheers[/quote]

MOSFET is an acronym for Metal Oxide Semiconductor Field Effect Transistor. It's a type of transistor. They are often used in amplifier or buffer
design (and make good switches too). They are quite linear and relatively easy to design with. Unlike bipolar transistors (which they largely displaced in amplifier design) they are not susceptible to catastrophic over-heating.

That's about all I can remember now (it was a long time ago I did my degree).

In am amplifier, MOSFETs can be used to provide oodles of clean power (think of Trace Elliot).

In relation to pedals, it just means the circuit designer used MOSFETs in the circuit and, in itself, doesn't really mean very much at all!

Why do you ask?

Edited January 28, 2010 by The Twickerman

[Silent Fly]

[quote name='Bucket Head' post='727719' date='Jan 28 2010, 03:52 PM']what is mosfet in relation to pedals? wat does it do ect and what difference does it make cheers[/quote]

A pedal that uses mosfet is not necessarily better or worse of other pedals that use other type of transistors.

Simplifying a lot and removing all the technical jargon:

From the functional point of view there are (more or less) two type of Mosfet: power mosfet and small signal mosfet.

Power mosfet are mainly used in power amps. Compared to standard transistors (aka BJT) offer the advantage that they self-protect against overheating.

The other mosfet type behaves more or less like a standard transistor. There are some differences: mosfet clip in a more valve-like way and they need almost no current to control the output (i.e. high input impedance).

In pedals they are used on the input stage to achieve high input impedance. They are also good for switching and clean amplification. They also saturate nicely. Last but not least, they can also be used as clipping diodes in TubeScreamer-type or DS1-type distortion pedals.

The major drawbacks in using Mosfet are that the output impedance is relatively high and that they are very sensitive to electrostatic charges.

[Bucket Head]

Thanks for the replys guys pritty informative, the reason i asked is cos i was thinking of buying a fulltone bass drive but saw some have mosfet and others dont and was worried about whether or not i would get the right one ect you know. but u recon it wont make much diffence sound wise? thanks again for the replys

[Silent Fly]

[quote name='Bucket Head' post='728138' date='Jan 28 2010, 09:37 PM']Thanks for the replys guys pritty informative, the reason i asked is cos i was thinking of buying a fulltone bass drive but saw some have mosfet and others dont and was worried about whether or not i would get the right one ect you know. but u recon it wont make much diffence sound wise? thanks again for the replys[/quote]

Mosfet or not does make a difference sound wise but using mosfet does not necessarily make a bad pedal sound good or vice versa.

I would suggest to not consider the presence (or not) of mosfet transistors when you buy a pedal. IMO, sound, connectivity, interface, construction and customer support are more important elements.

[The Twickerman]

[quote name='Silent Fly' post='728148' date='Jan 28 2010, 09:48 PM']Mosfet or not does make a difference sound wise but using mosfet does not necessarily make a bad pedal sound good or vice versa.

I would suggest to not consider the presence (or not) of mosfet transistors when you buy a pedal. IMO, sound, connectivity, interface, construction and customer support are more important elements.[/quote]

The question arises I suppose because Fulltone decided to label the redesigned pedal as the "Bass Drive MOSFET". This suggested it is a selling point. I have no idea why they would - all that matters is how it sounds.

[harvey1-8]

In the case of the Fulltone Bass Drive MOSFET, there's a switch on the top that lets you select the standard circuit or the MOSFET circuit. If there isn't a huge difference in price then you may as well go for the MOSFET version and have the best of both worlds.

[Silent Fly]

[quote name='The Twickerman' post='728170' date='Jan 28 2010, 10:08 PM']The question arises I suppose because Fulltone decided to label the redesigned pedal as the "Bass Drive MOSFET". This suggested it is a selling point. I have no idea why they would (...)[/quote]

I guess they did it to make pedal name unique. I don't know Fulltone production but they may have/had a Bass Drive that don’t use mosfet...?

[quote name='The Twickerman' post='728170' date='Jan 28 2010, 10:08 PM'](...) all that matters is how it sounds.[/quote]

+1

[umph]

i've always considered mosfets better than the standard bjt's because of their valve like qualitys

[Bucket Head]

ahhh ok ill go for the mosfet version its just cos its specifically named with mosfet and i was confused and worried i would miss out on certain features or somthing but thanks for clearning it up for me guys big thanks to all postersssssssssssss

[bigjohn]

[quote name='umph' post='728627' date='Jan 29 2010, 12:58 PM']i've always considered mosfets better than the standard bjt's because of their valve like qualitys[/quote]

which are ? [url="http://en.wikipedia.org/wiki/MOSFET"]mosfet[/url]

I thought the best thing about mosfets is that they're able to handle more heat.

Edited January 29, 2010 by bigjohn

[bigjohn]

[quote name='bigjohn' post='729252' date='Jan 29 2010, 10:04 PM']which are ? [url="http://en.wikipedia.org/wiki/MOSFET"]mosfet[/url]

I thought the best thing about mosfets is that they're able to handle more heat.[/quote]


I've been thinking the best amp would be a valve pre > mosfet powered by a lightweight switching power supply.

I do own one but it's 17kg. And it's not the mosfets that are heavy.