sss said:thats because its easy to answer dumb questions
Well golly, I'll just have to keep asking them to he'p other folks look smart!
azira said:
So then, would the output resistance be...low?
gee, maybe I'll hook up a few subwoofers in parallel for 0.5 ohms load for this bad boy!
but seriously, the open loop or closed loop gain?
Perhaps a headphone amplifier?
I'm missing something about "all the pots". If each amplifier is configured for a low gain like 1 the worst case output offset is probably a few millivolts.
Since the output offsets will never match, each output will need to be resistor isolated from all the others (no math here just a guess of probably 100 Ohms). This prevents one op-amp from trying to drive all the others to it's own idea of what represents zero. Then, one pot on the input buffer could set the sum of all outputs to as close to zero as you might like.
The biggest problem is that paralleling the Op-amps will probably not provide any improvement in the sound because the mechanisms that make multiple parallel things sound better apply to random events such as noise or D to A non-linearities. These kinds things tend to cancel or even out. With the 074 all the op-amps will have certain gain discontinuities at the same points in the waveform so probably no cancellation will take place. (Hint it wont sound as good as all the work)
The basic idea seems workable. I'll leave it to you to calculate the return on investment of labor.
I'm missing something about "all the pots". If each amplifier is configured for a low gain like 1 the worst case output offset is probably a few millivolts.
Since the output offsets will never match, each output will need to be resistor isolated from all the others (no math here just a guess of probably 100 Ohms). This prevents one op-amp from trying to drive all the others to it's own idea of what represents zero. Then, one pot on the input buffer could set the sum of all outputs to as close to zero as you might like.
The biggest problem is that paralleling the Op-amps will probably not provide any improvement in the sound because the mechanisms that make multiple parallel things sound better apply to random events such as noise or D to A non-linearities. These kinds things tend to cancel or even out. With the 074 all the op-amps will have certain gain discontinuities at the same points in the waveform so probably no cancellation will take place. (Hint
it wont sound as good as all the work)The basic idea seems workable. I'll leave it to you to calculate the return on investment of labor.
The multiple pots bit was referring to a half-joke thread a while back about manually adjusting a(ny) theoretical amplifier's offset voltage manually, plus the mention earlier in the thread about the 30-band eq possibility.
100R does seem a bit high per device to try to get multiple watts out of the whole
but how about 1.0 or 0.1?
I *know* this wouldn't be the best-sounding chip-amp around. I know. I know I know I know. That is not the point.
As for return on labor invested, my dad told me one time (about something else, but still valid): "I'ts not wasted if you're enjoying it." And isn't enjoyment the whole point of this hobby?
I will leave the ethics of using "samples" for personal, one-time use to others to argue. I will buy my chips from national or leave it alone. They're only a couple of ducks apiece.
100R does seem a bit high per device to try to get multiple watts out of the whole
but how about 1.0 or 0.1?I *know* this wouldn't be the best-sounding chip-amp around. I know. I know I know I know. That is not the point.
As for return on labor invested, my dad told me one time (about something else, but still valid): "I'ts not wasted if you're enjoying it." And isn't enjoyment the whole point of this hobby?
I will leave the ethics of using "samples" for personal, one-time use to others to argue. I will buy my chips from national or leave it alone. They're only a couple of ducks apiece.
You're determined to make me get out the calculator (and maybe even read the data sheet ). But I'll stick to guessing.
Each op-amp is good for about, what, 5 milliamps? So a 1 Ohm resistor would cause (current) saturation if one op-amp wanted it's output at +5 millivolts and some other op amps thought that -5 millvolts was dandy.
Even with 10 Ohms the offset will limit the total voltage swing on some of the op amps pretty quickly. If the output current is substantially higher than 5 milliamps then you are right, my guesses of resistor values are high.
Depending on power supply voltage there is an exact answer, but it is most likely higher than 10 Ohms.
). But I'll stick to guessing.Each op-amp is good for about, what, 5 milliamps? So a 1 Ohm resistor would cause (current) saturation if one op-amp wanted it's output at +5 millivolts and some other op amps thought that -5 millvolts was dandy.
Even with 10 Ohms the offset will limit the total voltage swing on some of the op amps pretty quickly. If the output current is substantially higher than 5 milliamps then you are right, my guesses of resistor values are high.
Depending on power supply voltage there is an exact answer, but it is most likely higher than 10 Ohms.
CALCULATOR CALCULATOR CALCULATOR CALCULATOR CALCULATOR Break out the datasheet! From the horses' mouths:
http://focus.ti.com/lit/ds/symlink/tl074.pdf
And don't forget the bass drivers!
http://www.national.com/ds/LM/LM324.pdf
Product folders...
http://focus.ti.com/docs/prod/productfolder.jhtml?genericPartNumber=TL074
http://www.national.com/pf/LM/LM324.html
There was a whole flurry of Op-amp evaluations for audio some years back. All of the TL0.. series were considered pretty much OK but (and memory grows dim) I seem to recall the 324 was thought to be a true stinker.
The headphone idea would allow evaluatiion with considerably less time investment. Headphones, headphones, anyone? Anyone at all?
The headphone idea would allow evaluatiion with considerably less time investment. Headphones, headphones, anyone? Anyone at all?
a 44 op amp/channel power amp?
http://headwize2.powerpill.org/projects/showproj.php?file=meier3_prj.htm
http://headwize2.powerpill.org/projects/showproj.php?file=meier3_prj.htm
I was talking to an engineer friend of mine after church last night and he surprised me by not thinking this was all that crazy an idea. I proposed using the LM324s as drivers and TL074s as active feedback chips, and he said that I'd have to be careful. Since the 324s are bipolar and 074s are CMOS the 074s might pick up switching noise from the power supply rails from the 324s loading it... "Careful bypassing will be required".
That stumped me until I remembered my pile of voltage regulators...Put them on different power supplies altogether. Figure 14 LM324s and maybe 50 TL074s per 7815/7915 combination. and 0.1uF caps like candy all over the place...
For ease of signal wiring I was thinking of alternating 324s and 074s, driver, feedback, driver, feedback etc. all the way across...
"Careful bypassing will be required". That stumped me until I remembered my pile of voltage regulators...Put them on different power supplies altogether. Figure 14 LM324s and maybe 50 TL074s per 7815/7915 combination. and 0.1uF caps like candy all over the place...
For ease of signal wiring I was thinking of alternating 324s and 074s, driver, feedback, driver, feedback etc. all the way across...
Still noodling this...
The positive rail of the TL07x is included in the common mode range, so separate power supplies are out, but careful (read: lots of caps) bypassing should take care of it. The bigger problem may be ground loops with such long rails, but a fat ground rail or a ground plane may cure that.
I have heard that the TL07x has a 15mA wire-bond limit and I have also heard 18mA. Seems better to shoot for 12mA to be on the safe side.
I never knew large sheets of proto board were so expensive!
I generated a spreadsheet based on some simple algebra and it's pretty useful if you want to parallel any number of amplifiers. Let's see if anyone has some comments on it.
The positive rail of the TL07x is included in the common mode range, so separate power supplies are out, but careful (read: lots of caps) bypassing should take care of it. The bigger problem may be ground loops with such long rails, but a fat ground rail or a ground plane may cure that.
I have heard that the TL07x has a 15mA wire-bond limit and I have also heard 18mA. Seems better to shoot for 12mA to be on the safe side.
I never knew large sheets of proto board were so expensive!
I generated a spreadsheet based on some simple algebra and it's pretty useful if you want to parallel any number of amplifiers. Let's see if anyone has some comments on it.
I was looking for something else and found this thread. What a gas!
Anyhow, all this fuss was about DC offsets and one time an engineer told me something like...if you aren't amplifying DC, why not just use a cap? duh.
Good thing he didn't tell me that when I was thinking of doing this mess!
also, the 15mA wire-bond current-limit was a misheard 50mA which seems more like a thermal dissipation limit with any sort of moderate output voltage!
Anyways, please join me in rolling your eyes (at me)
Anyhow, all this fuss was about DC offsets and one time an engineer told me something like...if you aren't amplifying DC, why not just use a cap?
duh.Good thing he didn't tell me that when I was thinking of doing this mess!
also, the 15mA wire-bond current-limit was a misheard 50mA
which seems more like a thermal dissipation limit with any sort of moderate output voltage!Anyways, please join me in rolling your eyes (at me)
I for one applaud your adventurousness! So many naysayers... ignore them.
Using a capacitor to block DC offset per op-amp is a good idea, but you would still need a resistor to account for differences in gain between op-amps. Using matched resistor arrays would alleviate that problem a bit.
Hmmm... perhaps you could try making a 40-phase class D amplifier instead. There's a thought...
Using a capacitor to block DC offset per op-amp is a good idea, but you would still need a resistor to account for differences in gain between op-amps. Using matched resistor arrays would alleviate that problem a bit.
Hmmm... perhaps you could try making a 40-phase class D amplifier instead. There's a thought...
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