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Old 26th April 2004, 03:51 PM   #1
Stocker is offline Stocker  United States
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Talking Using multiple (like 40) TL074s...

I have about a jillion TL074s laying around making my fingers itch to use them. Obviously it would not be anything like a reference amplifier but...


I keep thinking it would be neat (not practical, fast or terribly easy, but neat) to make an amplifier out of these things with an ouput of several watts... like maybe 10-20W. I'm guessing i'd have to have at least one of them ( ! ) be a buffer on the front, with the rest configured as unity or low-gain followers. bridge/parallel times a whole bunch maybe. How many TL074s do you need to put out several volts across a 4-ohm speaker anyway?

aside from the obvious size and hassle, with possibly some funky capacitances and inductances in all the wiring, what other things are stupid about this?

It's a good thing I have a wife to keep me from wasting *all* my time...
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Old 26th April 2004, 03:59 PM   #2
sss is offline sss  Israel
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u can make a stereo 30 band graphic equalizer with that many op amps , u gotta be crazy triying to make a 20w amp out of them , u cant even us a heatsink
also u need a 8 (or more) layer pcb for that many op amps
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Old 26th April 2004, 04:03 PM   #3
tiroth is offline tiroth  United States
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Yes, this is totally insane. You can swing about 5V into 175 ohms, which means you need at least 44 in parallel to get ~3W. This also requires 44 DC servos.
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Old 26th April 2004, 04:17 PM   #4
Alcaid is offline Alcaid  Norway
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If they bother you that much you could always send them to me so your fingers stop itching
I might even pay the postage
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Old 26th April 2004, 06:20 PM   #5
Stocker is offline Stocker  United States
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Quote:
Originally posted by sss
u can make a stereo 30 band graphic equalizer with that many op amps , u gotta be crazy triying to make a 20w amp out of them , u cant even us a heatsink
also u need a 8 (or more) layer pcb for that many op amps
mmmmm...2x20WPC, with a 30 band eq for each... only 150 devices required...

why would I need an 8 layer PCB? I'm thinking more along the lines of a few 8-inch square pieces of veroboard! and sure I could use a heatsink...or maybe a whole BUNCH of little ones. Our good friends at Aavid Thermalloy have several DIP heatsinking options. Of course, I could make a common heat sink out of one big flat one... drill a few holes by every op-amp package, and mount all the other components on the underside of the PCB... and screw the PCB down to the heatsink with the amps inbetween, with a little white grease...about 100 screws should do it... then 60 pots for the adjustments...


Quote:
Originally posted by tiroth
Yes, this is totally insane. You can swing about 5V into 175 ohms, which means you need at least 44 in parallel to get ~3W. This also requires 44 DC servos.
Would you please explain how you arrived at this number?
as for the servos: did you miss the "offset voltage indicator" thread? I'd only need 44 little potentiometers (which I do have BTW) along with 44 or 88 LEDs (which I don't have). That, plus 45 minutes to trim out the zero on all the individual amplifiers. Then three days to tune the EQs to suit the room...along with the DIY RTA I could make out of another 15 opamps...


Quote:
Originally posted by Alcaid
If they bother you that much you could always send them to me so your fingers stop itching
I might even pay the postage
They don't itch *that* much!
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Old 26th April 2004, 06:38 PM   #6
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Default OpAmp amps are possible, though

This project might not fly, but very good amps have been built out of OpAmps. See

http://headwize2.powerpill.org/proje...meier3_prj.htm[/URL]

Norman
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Old 26th April 2004, 10:28 PM   #7
tiroth is offline tiroth  United States
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175/4 ~ 44
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Old 27th April 2004, 12:58 PM   #8
Stocker is offline Stocker  United States
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I realized today that I have more LM324s than I do TL074s... how about 90 of them for a subwoofer channel where the SQ isn't "as important" and 50 TL074 per channel for highs...

make sure they all get wired up right, though...

that other amp was cool. thanks for the link.
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Old 27th April 2004, 01:04 PM   #9
Alcaid is offline Alcaid  Norway
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Can I ask where you've gotten all these op-amps?
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Old 27th April 2004, 02:40 PM   #10
Stocker is offline Stocker  United States
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I could tell you, but then I'd have to kill you...

I get them free from work.

When a PCB fails on a customer device, It's almost never because of the opamps. So on the ones that are not surface mount, there are usually one or two (depending on model) good lm324 or tl074s. I have been saving them because I am a bit of a pack rat. I asked my boss specifically about using 'trash' devices and he doesn't care what I do with them. I can even sell them or things I put them in...but according to the nondisclosure agreement, any circuits I come up with are property of the company.
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