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Old 25th July 2005, 06:27 PM   #11
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Any help with screen dump necessary?

If you are in windows then Shift+PrnScn will dump current window. Then paste it in paintbrush, save it in JPG end you are done.
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Old 25th July 2005, 07:19 PM   #12
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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
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Old 25th July 2005, 08:56 PM   #13
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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.

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Old 25th July 2005, 09:41 PM   #14
johnnyx is offline johnnyx  United Kingdom
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I can e-mail a photocopy of Maplin's article on their MOSFET amp, which can use Exicon's modern equivalents to the Hitachi MOSFETS. A search on the forums should reveal where I've posted this before, cann't remember now. Send me an email and I'll send it by return.
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Old 26th July 2005, 03:38 AM   #15
Dusk is offline Dusk  United States
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Smile 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
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Old 26th July 2005, 04:07 AM   #16
Dusk is offline Dusk  United States
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Smile 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.
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Old 26th July 2005, 08:08 AM   #17
edl is offline edl  Hungary
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Default Re: LM chip amps

Quote:
Originally posted by Dusk
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.

Marshall uses the cheap TDA7294...
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Old 26th July 2005, 08:20 AM   #18
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And TDA7294 sucks.

LM3886 is much better.
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Old 26th July 2005, 10:08 AM   #19
Dusk is offline Dusk  United States
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Smile Marshall and the TDA7294

ouch......are you guys sure Marshall used the TDA7294 in their Mode Four model? The LM3886 is it a non-mosfet IC and don't u
have to worry about thermal-meltdown with this IC chip? LM3886. I go for the rugged mosfet at the output....but that just me.
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Old 26th July 2005, 10:20 AM   #20
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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
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