What exactly is MOSFET and does it have a signature sound?

pugs · « **on:** 26 May 2006, 01:28 am »

I just sold my Odyssey Mono Extremes and hooked up my old B&K ST2140 MOSFET stereo amplifier. The Odyssey's did everything technically better, but I really like the sound of the B&K. I'm going to try the CIA D-200's next but if they don't work out, I might try something else from B&K or maybe another MOSFET amplifier.

What exactly is MOSFET? Do MOSFET amplifiers have a signature sound or is it more likely that I just like the B&K sound?

Sasha · « **Reply #1 on:** 26 May 2006, 01:39 am »

Metal oxide semiconductor field-effect transistor.
Well designed amplifier with quality MOSFET transistors is in my opinion the best amplification beside well designed quality tube amplification.
Consequently I have the best sounding amplifier that there is, Linar class A with MOSFETs in output stage.

OTL · « **Reply #2 on:** 26 May 2006, 02:13 am »

Quote from: pugs

What exactly is MOSFET? Do MOSFET amplifiers have a signature sound or is it more likely that I just like the B&K sound?

J-FET, MOSFET, triode, pentode....it really doesn't matter much. Jewels and turds have been and continue to be manufactured using any and all solid state and tube technologies.

As a buddy of mine used to say, "It's not the tools, it's the craftsman".

Frank at AVA can offer considerable insight into the MOSFET thing, and he's right around the corner.

http://www.audiocircle.com/index.php?board=48

warnerwh · « **Reply #3 on:** 26 May 2006, 04:14 am »

I've owned a couple of Hafler XL amps and now the AVA 550. Compared to bipolar amps I've owned the Mosfet amps have been the better deals for the money. Seriously though I think that comparing bipolar and mosfet amps is fruitless. I wouldn't buy an amp because it had a certain type of output transistors.

pugs · « **Reply #4 on:** 26 May 2006, 08:16 am »

Do MOSFET amps tend to have a type of sound such as warm, lush, smooth, laid back, forward, detailed, etc?

GHM · « **Reply #5 on:** 26 May 2006, 12:47 pm »

I'm no expert.... from my experience with mosfets. They do seem to be a little warmer or lush sounding than bipolars. Some Classe amplifiers use a mixture of JFETs,Mosfets and Bipolars..they sound terrific!

ctviggen · « **Reply #6 on:** 26 May 2006, 05:32 pm »

A MOSFET has metal over a thin oxide over a substrate. When you apply a voltage to the metal, an electric field (the "field effect") is created in the substrate. Assuming you apply a positive voltage, electrons (carriers) will be attracted toward the oxide. A "layer" of electrons forms. On either side of the thin oxide are regions of high electron concentration called the source and drain. If you apply a voltage between the source and drain, current (electrons, in this case) will flow from the source, through the "layer" of electrons, and to/through the drain. The substrate will have a lack of electrons (made of a material having a lot of "holes" or positively charged elements). Consequently, when you remove the positive voltage from the metal, the layer of electrons collapses/goes away, leaving very few electrons (negatively charged) and many holes. Current ceases to flow between the source and drain because there's no layer (called an "inversion" layer as the layer contains carriers of opposite polarity to the elements in the substrate) to allow electron flow. Any electrons that escape from the source will be "eaten" by oppositely charged holes in the area between the source and drain.

Capice?

As to what sounds better -- I have no idea. I thought Tubes where the God-send, nirvana-to-end-all of audio? ;-)

woodsyi · « **Reply #7 on:** 26 May 2006, 05:48 pm »

Quote from: ctviggen

As to what sounds better -- I have no idea. I thought Tubes where the God-send, nirvana-to-end-all of audio?

Only SET!

Welcome back. I am glad I didn't see you posting on AC while you were on your honeymoon.

WEEZ · « **Reply #8 on:** 26 May 2006, 11:41 pm »

To me, a Mosfet amplifier (if well designed) sounds more tube-like in the mids and treble than most (not all) bipolar amps. The sound is more relaxed overall. I like my Mosfet amplifier better than any bipolar amp I've ever owned.

For the same reason that I like it, however, some will not. My amp (and most of the Mosfet amps I've owned or heard) do not have quite the 'punch' or 'slam' factor that a bipolar will have. The dynamics are certainly there- but the 'attack' is more delicate sounding. This is not for everyone.

I think a good Mosfet amp is an ideal compromise between tubes and bipolars. A Mosfet transistor operates more like a valve than like a switch. That might be one reason why they sound more like tubes. (They don't seem to have as nasty an 'edge' when driven into clipping, in my experience).

As always, YMMV, and my opinion is just that- an opinion. It might be worth exactly what you paid for it.

WEEZ

machine · « **Reply #9 on:** 27 May 2006, 12:12 am »

I'm the guy who bought pugs Odyssey Mono Extremes - I sure hope they don't SUCK!!!

Haven't been able to get much info out of pugs, or the manufacture, regarding these.

From what I read they seem to be nice, and I wish pugs success on his search for replacements.

boead · « **Reply #10 on:** 27 May 2006, 01:08 am »

Metal Oxide Semiconductor Field Effect Transistor

Did I get that right?

BobC · « **Reply #11 on:** 27 May 2006, 04:56 am »

Quote from: machine

I'm the guy who bought pugs Odyssey Mono Extremes - I sure hope they don't SUCK!!!

Trust me, they're great amps.

Enough current that they can handle almost anything you throw at them with ease.

I love mine. Only downside in my opinion is the physical size.

And look at it this way...if they don't float your boat, then they sell easily. Enjoy!

pugs · « **Reply #12 on:** 27 May 2006, 07:37 am »

Quote from: machine

I'm the guy who bought pugs Odyssey Mono Extremes - I sure hope they don't SUCK!!!

Haven't been able to get much info out of pugs, or the manufacture, regarding these.

From what I read they seem to be nice, and I wish pugs success on his search for replacements.

I didn't know you were trying to get information from me. If you have any questions, please send me a PM or email and I will give you all the information I have. I hope you have been receiveing the emails I have sent you.

If you could see my current set up, you would know why I sold them. I have no space in my 12' wide room which includes a 55" widescreen, 2 x 12" wide speakers and 18" wide subwoofer.

They definately don't suck. I've been listening to my system at relatively low levels lately. When I crank up the B&K, the sound gets a lot worse. The Odyssey's could play a lot louder than I care to listen without any distortion.

I'm trying the D200's next - a large part because of their size. If those don't work out, I think I'll try to find a good 3 channel amp.

pugs · « **Reply #13 on:** 27 May 2006, 08:10 am »

Quote from: machine

I'm the guy who bought pugs Odyssey Mono Extremes - I sure hope they don't SUCK!!!

Haven't been able to get much info out of pugs, or the manufacture, regarding these.

From what I read they seem to be nice, and I wish pugs success on his search for replacements.

Doh! It looks like your emails have been going to my spam file. Sorry about that.

G Georgopoulos · « **Reply #14 on:** 27 May 2006, 09:19 am »

What exactly is MOSFET? Do MOSFET amplifiers have a signature sound or is it more likely that I just like the B&K sound?
----------------------------------------------------------------
they do when in circuit it all comes down to a designer he has to
give his signature on it

Regards
G Georgopoulos
Analogue Designer

Doublej · « **Reply #15 on:** 27 May 2006, 03:53 pm »

pugs

What do you like better about the B&K and what is the loudness level at which it starts to go south. Are we talking ear splitting rock and roll, just above conversation level or something in between

pugs · « **Reply #16 on:** 27 May 2006, 05:49 pm »

Quote from: Doublej

pugs

What do you like better about the B&K and what is the loudness level at which it starts to go south. Are we talking ear splitting rock and roll, just above conversation level or something in between

The B&K is really smooth, and kind of lush sounding. There is no edginess at all.

The first thing I noticed when I hooked up the B&K was that the soudstage depth was really flat compared to the Odyssey's. Transparancy, soundstage, imaging, clarity, bass, impact was all better with the Odyssey's. The B&K has a lushness (maybe colored?) to the sound that is very pleasing.

I estimate that the B&K begins to sound more distorted when decibles are in the mid to high 80's. When my wife plays her rap, it is especially noticeable. She's the one really pushing for me to get new amps because she loved cranking up the music LOUD with the Odyssey's. The Odyssey's never ran out of juice.

My system is also used for HT, and with the Odyssey's in my system, my HT sounded MUCH better. It's not a fair comparison though because I had 3 Odyssey's for the front three channels and the B&K for the surrounds. Now I am using the B&K for the L & R channels, and my Denon AVR-4800 runs the center and surrounds.

I could almost settle using the B&K long term, but my HT suffers too much. I want to explore higher quality amps with a similar sound hoping to have all of the technical qualities of the Odyssey's, with the lushness of the B&K. Hopefully the D-200's will give me what I need.

I don't have a lot of experience listening to different equipment so I 'm still discovering what I like.

TheChairGuy · « **Reply #17 on:** 27 May 2006, 06:39 pm »

WEEZ really nailed my experience(s) with MOSFET's here...and more limited experiences with J-FET's in a couple preamps, too.

I find them soft and lush, but prefer the snap and slam of bipolar. Paired with a tube preamp, bipolar 'sound' relaxes a bit and largely eliminates (my) need for MOSFET's. To me, MOSFET amps sound like a poor transistor attempt at creating tube ambience...why not just use tubes and get it right to start?? Aside from maintenance issues of tube amps, they sound like tubes because they ARE tubes. MOSFET's don't sound like good tube amps

But, like all things the final decision rests with you - we can only express opinions.

Quote from: WEEZ

To me, a Mosfet amplifier (if well designed) sounds more tube-like in the mids and treble than most (not all) bipolar amps. The sound is more relaxed overall. I like my Mosfet amplifier better than any bipolar amp I've ever owned.

For the same reason that I like it, however, some will not. My amp (and most of the Mosfet amps I've owned or heard) do not have quite the 'punch' or 'slam' factor that a bipolar will have. The dynamics are certainly there- but the 'attack' is more delicate sounding. This is not for everyone.

I think a good Mosfet amp is an ideal compromise between tubes and bipolars. A Mosfet transistor operates more like a valve than like a switch. That might be one reason why they sound more like tubes. (They don't seem to have as nasty an 'edge' when driven into clipping, in my experience).

As always, YMMV, and my opinion is just that- an opinion. It might be worth exactly what you paid for it. icon_smile.gif

WEEZ

bunky · « **Reply #18 on:** 27 May 2006, 08:49 pm »

Quote from: TheChairGuy

WEEZ really nailed my experience(s) with MOSFET's here...and more limited experiences with J-FET's in a couple preamps, too.

I find them soft and lush, but prefer the snap and slam of bipolar. Paired with a tube preamp, bipolar 'sound' relaxes a bit and largely eliminates (my) need for MOSFET's. To me, MOSFET amps sound like a poor transistor attempt at creating tube ambience...why not just use tubes and get it right to start?? Aside from maintenance issues of tube amps, they sound like tubes because t ...

I am running a Pair of Symphonic Line RG 11 based Odyssey "Special order"Mono Extreme SEs with a Balanced Audio Technology VK 3i tube Linestage and i feel that it is a wonderful combination of solidstate and tube amplification. not all bipolar amplifiers are created equal. i have several friends on another forum who prefer the older bipolar Adcom power amps over the current MOSFET Adcom power amps. this topic like everything else in audio is highly subjective. i adore my bipolar monoblocks. thanks....WCW III

SWG255 · « **Reply #19 on:** 27 May 2006, 08:57 pm »

The latest generation of SS amps from Conrad-Johnson mix bipolar and MOSFET devices in a hybrid design. The bipolar devices are used as the output devices with the MOSFETs used in the input stage. This is claimed to give the best combination of low odd-order distortion that the MOSFETs can provide and the excellent speed and current delivery of the bipolar output devices. Based on what i've heard of the Premier 350, this combination is very nice indeed.

C-J's earlier SS amps often used MOSFETs throughout their circuits, and although they were remarkably smooth and "warm" for SS amps, they had rather loose bass reproduction, and with some speakers fell short of the best possible transient performance.

It took C-J over 20 years to develop the circuit they use in the Premier 350, and it is among the very best SS amplification I've ever heard. However, I feel the use of the MOSFETs is secondary to the design and implementation chosen. It fit the needs of the designer, but I don't think C-J set out to use MOSFETs and bipolars together as an absolute goal. So, I guess I fall squarely into the "it's the craftsman, not the tools, that matters" camp.