Author Topic: Ain't the brightest bulb in the box  (Read 9155 times)

Offline dflee

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Ain't the brightest bulb in the box
« on: February 27, 2023, 03:00:25 PM »
Is MosFet just another way of saying class "D".
When my amp died I was looking for an inexpensive one till I could decide on a permanent model.
I found a diy for sale at a decent price built with a First One board. Everything I read said MosFet so
I gave it a go. While I knew it was temporary I found it to be pretty good in most aspects. After loosing money on a couple of amps I ended up with the Musical Fidelity M6s PRX and enjoy it.
Thinking on a secondary system for the office I am pondering the little diy so I put it back into the system with the Fyne 501SP speakers and was surprised how well it did with most mids and highs but was lacking in the mid and low bass departments. I didn't really realize that until speaking with Steve (thank you sir) and discussing the sound. Man that guy knows of what he speaks. Am thinking of sending it to him to see what can be done with it but is it really worth it. If it is D is there no hope of improvement?

Thanks Guys
Don
"Enjoy pleasure, not because it is fleeting, but because it exists at all." Sacrament, Clive Barker.

Offline GDHAL

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Re: Ain't the brightest bulb in the box
« Reply #1 on: February 27, 2023, 06:02:25 PM »
I have an M6si (for many years) and it rules!  :thumb:

Take a pretty penny to best it.  8) For any 1 negative review (either "professional" or audiophile) there's a 1,000 positive reviews.

In terms of MOSFET they're ubiquitous (i.e. in certain amps, preamps, dacs, you name it).

Enjoy your M6s PRX, Don.   :)
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Offline S Clark

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Re: Ain't the brightest bulb in the box
« Reply #2 on: February 27, 2023, 06:20:47 PM »
Mosfet is a different thing from Class D.
Metal–oxide–semiconductor field-effect transistors (Mosfet) have been around a long time (1925)- so it's a variation of a transistor amp. 
There are still several around, and the Moscode 401HR is my current amp of choice in one of my systems. 
They can product high power with moderate heat.  Like all amp types, the devil is in the details. 
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Offline HAL

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Re: Ain't the brightest bulb in the box
« Reply #3 on: February 27, 2023, 07:06:08 PM »
Power MOSFET's can be used in Class A, Class AB and Class D amps, so it depends on the amplifier topology.

Class A and Class AB tend to be VFET or HEXFET styles.  The HEXFET can also be used in Class D.  The Hafler DH/XL series used VFET's along with the MOSCODE amps in the output stage along with Acoustat TNT series amps. 

GaN devices are a type of MOSFET.  It depends on the amplifier topology, but mainly used for Class D amps.  Also SiC devices another type of MOSFET can be used in Class D amps as well.

That and $5 will get you a cup of coffee. :)
« Last Edit: February 27, 2023, 07:09:54 PM by HAL »

Offline dflee

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Re: Ain't the brightest bulb in the box
« Reply #4 on: March 09, 2023, 09:02:49 AM »
Finally found some info on the unit.
Diyaudio has a section from LazyCat (designer) and states 250 W and 16 Amp continuous current. They do state it as a class A/B.

Max Power 8 Ohm   150 Watt 0.05 THD   
Max Power 4 Ohm   230 Watt 0.05 THD   
Bandwidth   3 Hz to 3 MHz (-3dB)
THD   0.0034% (100 Watt)   
IMD   0.003%
SNR   110 dB
Input Impedance   10 Kohm
Damping Factor   >2000 (4 ohm)
Year Introduction   2014
Does continuous current mean class A? And am I right assuming it's 75 per channel into 8 Ohm?
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Offline GDHAL

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Re: Ain't the brightest bulb in the box
« Reply #5 on: March 09, 2023, 09:32:31 AM »
It's not clear from your post whether or not "250 W and 16 Amp continuous current" is the amplifiers power draw, or power output.

In any case that has nothing to do with the type of amplification class.

As to the wattage output normally manufacturers state the specification in terms of each channel, if it's a two channel amplifier. So in your example it should be 150 watts per channel into 8 ohms
« Last Edit: March 09, 2023, 09:34:41 AM by GDHAL »
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Offline HAL

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Re: Ain't the brightest bulb in the box
« Reply #6 on: March 09, 2023, 12:28:54 PM »
Class AB is a linear amplifier output stage, so not totally Class A.  Usually that spec is for its continuous RMS output power per channel.  That is a lot of current for an output stage to deliver, so it has a hefty power supply!

Offline steve

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Re: Ain't the brightest bulb in the box
« Reply #7 on: April 20, 2023, 07:02:48 PM »
Finally found some info on the unit.
Diyaudio has a section from LazyCat (designer) and states 250 W and 16 Amp continuous current. They do state it as a class A/B.

Max Power 8 Ohm   150 Watt 0.05 THD   
Max Power 4 Ohm   230 Watt 0.05 THD   
Bandwidth   3 Hz to 3 MHz (-3dB)
THD   0.0034% (100 Watt)   
IMD   0.003%
SNR   110 dB
Input Impedance   10 Kohm
Damping Factor   >2000 (4 ohm)
Year Introduction   2014
Does continuous current mean class A? And am I right assuming it's 75 per channel into 8 Ohm?

Hi Don,

Describing is rather difficult, but I will try to be as clear as possible. Please bear with me.

Yes, 75 watts per Push Pull channel into 8 ohms, the current flow is ~3.06 amps per channel.
Times two channels is 6.12 amps.

Per the designer's comment 250 watts/channel rms into 4 ohms, the current flow is ~7.9 amps rms.
Times two channels is 15.8 amps rms. He is stating the power supply can power both channels to
the max without an "unscheduled disassembly" of itself.

However, what determines whether operation is Class A or Class AB is determined mainly by the
output devices and device parameters chosen (although the power supply has to be designed to power
whatever Class is chosen). (Collector voltage, bias current etc etc)

Since Class A is so inefficient, even 16 amp current rating would not provide 250 watts output
into 4 ohms. Theoretical maximum efficiency is 50%, but figure 30% plus/minus.

Operating Push Pull AB is interesting as, depending upon the idle bias, both transistors (tubes)
operate Class A over a range of X few output watts before each transistor starts to shut off over a
portion of the waveform/cycle. At that point, AB operation commences. Class A X power output depends
upon the idle current (with no signal), size of the device(s) etc etc.

Sometimes I am not very clear, but hope this helps some Don.

steve
« Last Edit: May 23, 2023, 12:21:07 PM by steve »
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