op-amp based mosfet power amplifier for guitar rig - diyAudio
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Old 30th July 2005, 08:32 PM   #1
Dusk is offline Dusk  United States
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Smile op-amp based mosfet power amplifier for guitar rig

Hello
I wentto the solid state Forum, i will try here maybe it's more guitar friendly....just kidding.....i did get some help over there. Well here goes......iam not anti-power tube but why kill el34s and 6l6s by overdriving them so, i want to build a mosfet power amplifier that has a op-amp at the front-end. Now, i was told u could use a power IC as op-amp and this sounds good but iam not an amplifier Guru.......i need a schematic. I use a tube pre amp to get overdrive sound and clean tone 12ax7 don't cost that much. The op amp based mosfet power amplifier will be the muscle in the rig 150 to 250watta side....and no power tube to replace........Something like a Tube Works Mosvalve 942 power amplifier......they don't make those now. I play guitar and i like the Blues-rock- jazz-fusion type sound........Hendrix meet Albert King at coltrains house.....type sound......so if anyone has aschematic.....please step forward.........thanks

less componts in a power amplifier less headach
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Old 30th July 2005, 08:41 PM   #2
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If it's a simple amp you are after and your power desire is more than 100W you can't use a chip as the voltages required will be too high. IMO using a chip front end requires so much additional circuitry it's not worth it.

Take a look at ESP Project 101. sound.au.com
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Old 30th July 2005, 08:53 PM   #3
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Smile Booth-strap

Hi richie00boy
Well if i use a low voltage op-amp i can boot-strap the supply lines of the op amp to get +/- 15 voltage for op-amp than i can use any voltage to power the mosfets output section....no problem. That is to get high voltage to the driver and mosfet power section.
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Old 30th July 2005, 09:30 PM   #4
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Are you sure you know what a bootstrap is? You are talking about a step down not a bootstrap Moot point anyway. The output stage will be required to have gain and this is what makes things complicated. Trust me, it's not so easy P101 is a good amp and about as simple as they get, take a look
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Old 31st July 2005, 01:01 AM   #5
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Smile Bootstrapping ???

richieooboy
Sorry for the terminology mix-up but what i ment was using transistors to match the low suppy voltage of a op-amp.anyway the amplifier you pointed out i have seen. I have the Randy Slone book on high power amplifiers and it has many many source-follower mosfet power amplifiers in it. Iam loking for something in aop-amp front-end design. This would feed apair of driver that would feed the mosfet output section. Iam no rocket scientist...they are down the coast a bit.......just guitar player
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Old 31st July 2005, 04:50 PM   #6
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Default Now three of us are confused

I am not clear about what you are looking for. You say frontend for a mosfet amp. You want an FET input stage? Much better than OP-amps as far as tone goes. You already have a mosfet power-section design you like? (I love TubeWorks) Please clarify as I think you are just looking for a nice input/driver stage. By the way, there are tons of TubeWorks amps out there for sale. They are rugged and easy to fix, should they break. I use them for EVERYTHING from PA to bass. I believe Genz-Benz is still making a few of them.
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Old 1st August 2005, 12:59 AM   #7
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Smile not confused

Iam just looking for a schematic for a mosfet power amplifier that has three stages. a op amp input stage ,alevel shifting stage and amosfet output stage....very simple set-up and low part count.I want to build it my self....i built most of my gear. I know there is lots of Tube Works stuff out there but....i like diy
I checked out Genz-Benz site they no longer make Tube Works amplifiers....to bad......its good stuff.
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Old 1st August 2005, 02:03 AM   #8
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A long time ago Elektor published a circuit that used an opamp input driving IRF p / n channel fets. It ran rails of around +/- 35 volts with zener derived voltages feeding the op amp. I think it provided an estimated output power of about 70watts into 8 ohms and 120 watts into 4 ohms.

From what I recall the circuit could be modified to handle +/- 50 or 60 volts with extra FETS to handle the power you are talking about.

I'll look for it tonight (10 hours time). In the meantime you may want to send me an email.

Cheers
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Old 1st August 2005, 08:40 AM   #9
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Grateful if you could provide more info here when you get to it
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Old 1st August 2005, 09:04 AM   #10
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Smile Elektor circuit

quasi
this amplifier in the Elektor magazine sounds like what iam looking for.....finally.......thanks
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