I am afraid that the output power will be about 25W RMS maximum on 4ohm since most opamps are designed for +-15V power supply.
It can be done with more power, but the complexity would increase even more than if you use classic scheme.
Maching of input transistors is not so critical, especialy if they have high gain (400-1000). And if you buy transistors from one serie (they have all text on them equal), the betas will be very close usualy.
Look there for example:
http://sound.westhost.com/project3a.htm
or there for MOSFET one:
http://sound.westhost.com/project101.htm
I think these are simple enough, cheap, powerfull and high quality.
It can be done with more power, but the complexity would increase even more than if you use classic scheme.
Maching of input transistors is not so critical, especialy if they have high gain (400-1000). And if you buy transistors from one serie (they have all text on them equal), the betas will be very close usualy.
Look there for example:
http://sound.westhost.com/project3a.htm
or there for MOSFET one:
http://sound.westhost.com/project101.htm
I think these are simple enough, cheap, powerfull and high quality.
maplin made a 150 watt RMS mosfet amplifier that would suit guitar amplification, there was a bridge circuit avalable too that could boost power to 400W RMS.
It was supposed to be very reliable and the circuit is pretty basic.
If you are interested i could have a look for my schematic. and post a pic.
http://www.soton.ac.uk/~apm3/diyaudio/Maplin_MOSFET.html
Craig
It was supposed to be very reliable and the circuit is pretty basic.
If you are interested i could have a look for my schematic. and post a pic.
http://www.soton.ac.uk/~apm3/diyaudio/Maplin_MOSFET.html
Craig
These LMs are good. And simple too. And have thermal and shortcircuit protection.
I think theese are most switable for you.
0.1% distortion on their top powers looks good enough.
There should be plenty of PCBs for them on the net.
And probably will run without a problem at the moment you switch the power on.
HIGHLY RECOMENDED!!!
ok here are specs:
+ and - 50V max supply
idle current 50-100mA
150 watts RMS into 4 ohm 100 into 8
THD 0.01% @1Khz
15hz-40Khz
20V/uS
vin = 2.4v pk/pk for max o/p
Input is not op amp though, but its very simple to make.
Distortion is probably better in this circuit which uses doubled up MOSFETS. You will have to find modern equivalents for the MOSFETS and some of the bipolars but it shouldnt be difficult.
For guitar amplification such large supply caps wont be necessary if you want to skimp a bit, 6800uf per rail maybe?
I also have the bridge circuit schematic, and PCB layout.
The bridge can theoretically provide 650 watts RMS with 2 MOSFET modules attached.
But i cant be bothered to draw it up at moment
..............ok i cant attach a word document with a screen dump in it.
I need to make a picture out of my screen dump somehow first?
Craig
+ and - 50V max supply
idle current 50-100mA
150 watts RMS into 4 ohm 100 into 8
THD 0.01% @1Khz
15hz-40Khz
20V/uS
vin = 2.4v pk/pk for max o/p
Input is not op amp though, but its very simple to make.
Distortion is probably better in this circuit which uses doubled up MOSFETS. You will have to find modern equivalents for the MOSFETS and some of the bipolars but it shouldnt be difficult.
For guitar amplification such large supply caps wont be necessary if you want to skimp a bit, 6800uf per rail maybe?
I also have the bridge circuit schematic, and PCB layout.
The bridge can theoretically provide 650 watts RMS with 2 MOSFET modules attached.
But i cant be bothered to draw it up at moment
..............ok i cant attach a word document with a screen dump in it.
I need to make a picture out of my screen dump somehow first?
Craig
The input cap is sposed to be 1uF, i guess a larger value would help the LF response a bit more.
And the zobel network cap is supposed to be 100nf.
I forgot to mark on supply rails but you can tell by the big caps orientation.
enjoy!!
i have built this circuit running from 32V rails for a guitar amp a few years ago and it worked, it will need a preamp though.
sorry about the squashedness but i couldnt get it onto the forum any bigger i think its readable.
Craig
And the zobel network cap is supposed to be 100nf.
I forgot to mark on supply rails but you can tell by the big caps orientation.
enjoy!!
i have built this circuit running from 32V rails for a guitar amp a few years ago and it worked, it will need a preamp though.
sorry about the squashedness but i couldnt get it onto the forum any bigger
i think its readable.Craig
Attachments
It's perfectly feasible to use opamps for the input stage of a power amp. I am pretty sure Crown did it in the DC300 design years ago, for example. It's not clear that it buys you much of anything though, since as noted, you'll likely need some more gain/level shifting almost immediately.
As far as Hitachi Mosfets, I can supply small quantities to DIYers, matched or unmatched... inquire privately please.
_-_-bear
As far as Hitachi Mosfets, I can supply small quantities to DIYers, matched or unmatched... inquire privately please.
_-_-bear
op amp based mosfet power amplifier
Hello
I have played a mosfet power amplifier made by a company named Tube Works it was called Mosvalve 942 and this power amplifier had a op amp front -end and a mosfet output section it sound great very warm-like,but they don't make them anymore. As forthe limit of the op amp output you can put transistors in the op amp supply pin that will bring down the op amp to +/- 15 volts or so.Then you can use any voltage for the amplifier. There is a amplifier made by Vellemen the k4020 they also have a op amp in the front end but it's to complex .I like simple circuits less parts to go wrong. I think the Mosvalve power amplifier had a TL072 at the input a MPSA42 AS a driverwithHitachi mosfet for the output. It put out 250watts a channel these were very good sounding amplifier. For me less is more in componets in the amplifier. the less you have to deal with when you have to fix it.I know there are simple circuits out there that can put out high watts. so i want to thank everybody for your information and i hope somebody can find a circuit that i am looking for......so i can build it and get on with jamming.......The Blues rock -jazz-fusion thing.........PEACE
Hello
I have played a mosfet power amplifier made by a company named Tube Works it was called Mosvalve 942 and this power amplifier had a op amp front -end and a mosfet output section it sound great very warm-like,but they don't make them anymore. As forthe limit of the op amp output you can put transistors in the op amp supply pin that will bring down the op amp to +/- 15 volts or so.Then you can use any voltage for the amplifier. There is a amplifier made by Vellemen the k4020 they also have a op amp in the front end but it's to complex .I like simple circuits less parts to go wrong. I think the Mosvalve power amplifier had a TL072 at the input a MPSA42 AS a driverwithHitachi mosfet for the output. It put out 250watts a channel these were very good sounding amplifier. For me less is more in componets in the amplifier. the less you have to deal with when you have to fix it.I know there are simple circuits out there that can put out high watts. so i want to thank everybody for your information and i hope somebody can find a circuit that i am looking for......so i can build it and get on with jamming.......The Blues rock -jazz-fusion thing.........PEACE
LM chip amps
I think the Marshall guitar company in England uses a mosfet IC chip amp in their Mode Four guitar amplifier. It is a good sounding amplifier imo..350watts it also has a tube pre amp very warm tone it's a hybrid head....but i think i will stay with discret mosfet in the output section of my amplifier.......i also use a tube pre amp for the warm tone.
this is a good marriage......good overdrive and warm tone from the tube front-end.
I think the Marshall guitar company in England uses a mosfet IC chip amp in their Mode Four guitar amplifier. It is a good sounding amplifier imo..350watts it also has a tube pre amp very warm tone it's a hybrid head....but i think i will stay with discret mosfet in the output section of my amplifier.......i also use a tube pre amp for the warm tone.
this is a good marriage......good overdrive and warm tone from the tube front-end.
The Mode Four is a poor amplifier.
Check out the 6100, that is a really good amp from Marshall, it is tube though but the best ones always are.
Marshall did bring out Mosfet heads capable of 100W in the mid/late 80's i havn't looked at the schematic for a while but it had op-amp input.
http://www.drtube.com/schematics/marshall/3210.gif
Craig
Check out the 6100, that is a really good amp from Marshall, it is tube though but the best ones always are.
Marshall did bring out Mosfet heads capable of 100W in the mid/late 80's i havn't looked at the schematic for a while but it had op-amp input.
http://www.drtube.com/schematics/marshall/3210.gif
Craig
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