View Full Version : Stereo Amps.....please explain

05-21-2005, 03:56 PM
Could one of you audiophiles explain the difference between this Profile 4 channel amp (http://www.crutchfield.com/S-8smiE20QQjN/cgi-bin/ProdView.asp?g=120&I=489AP740) and this Rockford Fosgate amp (http://www.crutchfield.com/S-8smiE20QQjN/cgi-bin/ProdView.asp?g=120&I=575P4004) Don't understand what MOSFET is and why more than twice the price.

05-21-2005, 05:10 PM
The MOSFET, or Metal-Oxide-Semiconductor Field-Effect Transistor, is by far the most common field effect transistor in both digital and analog circuits. The MOSFET is composed of a channel of n-type or p-type semiconductor material (see article on semiconductor devices), and is accordingly called an NMOSFET or a PMOSFET. Usually the semiconductor of choice is silicon, but some chip manufacturers, most notably IBM, have begun to use a mixture of silicon and germanium (SiGe) in MOSFET channels. Unfortunately, many semiconductors with better electrical properties than silicon, such as gallium arsenide, do not form good gate oxides and thus are not suitable for MOSFETs.

The gate terminal is a layer of polysilicon (polycrystalline silicon; why polysilicon is used will be explained below) placed over the channel, but separated from the channel by a thin layer of insulating silicon dioxide. When a voltage is applied between the gate and source terminals, the electric field generated penetrates through the oxide and creates a so-called "inversion channel" in the channel underneath. The inversion channel is of the same type—p-type or n-type—as the source and drain, so it provides a conduit through which current can pass. Varying the voltage between the gate and body modulates the conductivity of this layer and makes it possible to control the current flow between drain and source.

this help?

05-21-2005, 05:26 PM
This help???? Are you kidding! :uglyhamme Let put my question another way..........would I be able to discern a difference in the sound quality of the two amps???? :D

05-21-2005, 06:14 PM
This help???? Are you kidding! :uglyhamme Let put my question another way..........would I be able to discern a difference in the sound quality of the two amps???? :D

LMFAO!!! So Bob, you want gloss or semi-gloss paint? :D

05-21-2005, 06:15 PM
To answer your question, I don't think so. If I understand you correctly you're just looking for a little more juice. RF makes great stuff and it would certainly improve your listening quality. But, I don't think on a boat under way you'll notice a considerable difference. IMO.

05-21-2005, 06:28 PM
This is going into the new truck if that makes a difference. 4 channel amp for the 4 door speakers and a 2 channel, bridged, for the sub. Or I may look into a 6 channel due to limited space to mount the amp.

05-21-2005, 07:28 PM
I couldn't open the link, but one difference in the way an amp sounds is based in how it distorts. I'm not talking about massive, overdriven distortion, but when the signal gets into the range where it starts to break up, some sound really nasty and grating. Some don't. The R-F won't sound as bad a a lot of amps. R-F amps tend to have loosely regulated power supplies and this helps it achieve high peak power ratings(along with high dB volume peaks).

There is a voltage diferential in every amplifier. For example, if the differential is 1:2, for a 1 volt input, you'll have a 2 volt output. The power supply allows the output voltage to get to a certain point and no higher. If the input voltage is too high, the signal is clipped off (this is what is meant by clipping distortion) at the peaks and distortion results.

If a power supply is tightly regulated, you get power output through a certain range, but if the music demands a higher peak, you get nothing. Think of this as hitting your head on a ceiling when you're jumping on a bed. A loosely regulated power supply is like jumping on a bed with a flexible ceiling above you.

MOS-FETs are more $, but they are better. Under high temperature situations, they also limit their own current so you aren't as likely to smoke it if you drive a low impedance load, like two 4 ohm subwoofers wired in parallel. Some amps(Soundstream) hate 2 ohm loads, regardless of what the product literature said. R-F amps don't mind, as long as the power wires and ground are adequate and the supply voltage are up to speed.

05-21-2005, 08:14 PM
:toast: Thanks for the lengthy explaination Jim....not that I fully understood it. I fixed the link on the Profile amp. Tell me honestly if you think I'll percieve any real difference in sound.

05-21-2005, 08:33 PM
The differences are easier to explain with visual aids. Personally, I don't have any experience with this brand. R-F I have installed tons of and they work really well. There are other brands out there, though. If you want to save money, I would keep shopping. I think you would notice a difference if you were able to do an A-B comparison.

05-23-2005, 12:40 AM
QUESTION -- I just purchased a set (2) of Pioneer oversized 6.5" speakers. I have four 6.5" Clarion speaker separates factory installed already. From what I understand, the installed head unit only pushes about 15 to 20 amps to each of the four speakers; they are rated at 100 watts peak and like 50 watts continuous power -- the Pioneers I just purchase are close to the same.

HERE IS MY THOUGHT -- Can I get a 4 channel amp and run the two tower speakers and the two rear speakers off the amp for improved sound performance? I would really like to hear a DRASTIC improvement. Any specific product guidance (best amp for the job) is greatly appreciated. Lehman's terms please.

05-24-2005, 01:47 PM
Disregard my previous post -- I started a new thread. I didn't mean to hi-jack this thread.

05-24-2005, 01:57 PM
Hey Mag, depending on the space you have, the JBL 6Way I have in my truck sounds great and was around $280 with simple inputs and cross overs for the four mid channel speakers and the 12" sub that I have bridged on the sub channel. You might want to check www.sounddomain.com they have a 105% price match that really can make a difference off of list. www.etronics.com is also pretty good.

I also used www.partsexpress.com for all my cables. They are in Springboro about 35 minutes from you south of D-Ton.