Bonkers MOSFET Amp
- Mike H
- Amstrad Tower of Power
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#1 Bonkers MOSFET Amp
You've seen Phillip's simple MOSFET amp, and Brian's "Class A from scrap", now put you hands together (and pray) and please give a big welcome to ~
Bonkers MOSFET Amp
aka "An Amplifier For Hotter Evenings" (© Andrew I [well almost])
It's bonkers because it seems like the wrong sorts of bits used in unexpected ways
Circuit's a bit bonkers as well
The amps are two version 1 FETREG module boards, modified (somewhat extensively):
Now improved with "panel mounted" controls:
The power supply is:
If nothing else it proves a IRFP240 power MOSFET can (also) be used as an audio amplifier.
Bonkers MOSFET Amp
aka "An Amplifier For Hotter Evenings" (© Andrew I [well almost])
It's bonkers because it seems like the wrong sorts of bits used in unexpected ways
Circuit's a bit bonkers as well
The amps are two version 1 FETREG module boards, modified (somewhat extensively):
Now improved with "panel mounted" controls:
The power supply is:
If nothing else it proves a IRFP240 power MOSFET can (also) be used as an audio amplifier.
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- Bonkers-MOSFET.gif (7.18 KiB) Viewed 4153 times
Last edited by Mike H on Thu Jun 30, 2011 3:50 pm, edited 1 time in total.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
- Mike H
- Amstrad Tower of Power
- Posts: 20189
- Joined: Sat Oct 04, 2008 5:38 pm
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#4
No it's an early prototype (slightly larger) VT1087 output transformer and using the 16 Ohms taps.
PS: I modified the diagram for Q2 & C1
PS: I modified the diagram for Q2 & C1
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
#5
First Watt amps are full of themIf nothing else it proves a IRFP240 power MOSFET can (also) be used as an audio amplifier.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
- Mike H
- Amstrad Tower of Power
- Posts: 20189
- Joined: Sat Oct 04, 2008 5:38 pm
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#6
PS: that means the impedance ratio is 312:1 and the Volts ratio 17.68:1, the whole thing just runs on 70 mA
Max. power o/p is a whole half a Watt r.m.s. Told you it was bonkers
Max. power o/p is a whole half a Watt r.m.s. Told you it was bonkers
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
#8
Very nice. Out of interest, does R4 help?
I thought about degeneration on mine, but didn't try simulating it with and without. The theory being that a higher open loop gain would allow better correction from the feedback loop. I think this is something to try when I get home.
Brian.
I thought about degeneration on mine, but didn't try simulating it with and without. The theory being that a higher open loop gain would allow better correction from the feedback loop. I think this is something to try when I get home.
Brian.
- Mike H
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#9
R4 allows setting the DC biased current with any kind of accuracy, as it all depends on what's flowing through Q2, which in turn depends on supply Voltage. As R1 is effectively connected to supply rail via the transformer (DCR 230 Ohms or something). So it's not like half the supply is across the primary, cos it isn't, only about 9V or so. And that because of 35 - 40 mA of Q1 drain current.
I left it unbypassed to keep the number of caps to a minimum, seems to be happy
I left it unbypassed to keep the number of caps to a minimum, seems to be happy
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
- Mike H
- Amstrad Tower of Power
- Posts: 20189
- Joined: Sat Oct 04, 2008 5:38 pm
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#11
It's worth having its own transformer now I reckon, a suitable toroid is on order as I type, as the droning fan of the bench PSU is annoying.
Bit of an ally box, IEC inlet; bridge rectifiers I got coming outa me ears, even got one on a bit of board, add on another 1,000uF, proper job.
Bit of an ally box, IEC inlet; bridge rectifiers I got coming outa me ears, even got one on a bit of board, add on another 1,000uF, proper job.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
#12
Ah, I see - makes sense now.Mike H wrote:R4 allows setting the DC biased current with any kind of accuracy, as it all depends on what's flowing through Q2, which in turn depends on supply Voltage. As R1 is effectively connected to supply rail via the transformer (DCR 230 Ohms or something). So it's not like half the supply is across the primary, cos it isn't, only about 9V or so. And that because of 35 - 40 mA of Q1 drain current.
I left it unbypassed to keep the number of caps to a minimum, seems to be happy
I tried simulating it on mine, and the distortion hardly changed until it was too big to bias properly. My supply is only 15V, so finding the 4V needed for the MOSFET gate isn't really an issue.
Brian.
#14
The zen series is a brilliant tutorial on this if anybody is interested.
http://www.firstwatt.com/articles.html
Of particular interest to the bass cos the early projects use BIG lightbulbs as load resistors....
As Nick suggests, all roads of this type eventually lead to F2.
It certainly helped me understand more about what those pesky electrons get up to.
btw Mike..has it got anything to do with simplified nemesis?
http://www.linearaudio.net/letters/Volume_0_NP.pdf
http://www.firstwatt.com/articles.html
Of particular interest to the bass cos the early projects use BIG lightbulbs as load resistors....
As Nick suggests, all roads of this type eventually lead to F2.
It certainly helped me understand more about what those pesky electrons get up to.
btw Mike..has it got anything to do with simplified nemesis?
http://www.linearaudio.net/letters/Volume_0_NP.pdf
There's nowhere you can be that isn't where you're meant to be
- Mike H
- Amstrad Tower of Power
- Posts: 20189
- Joined: Sat Oct 04, 2008 5:38 pm
- Location: The Fens
- Contact:
#15
Very interesting, nope none whatsoever, it started with what could be best to drive my 4 germanium power transistors with transformer phase splitter
Is that a fact? lol ..Nick wrote:Keep going in this direction and you will reinvent the F2
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."