Using multiple (like 40) TL074s...
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 Chip Amps Amplifiers based on integrated circuits

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sss
diyAudio Member

Join Date: Jul 2003
Location: Israel , haifa
Quote:
 Originally posted by Stocker I am beginning not to be surprised at how willing people here are to answer even dumb questions. Very helpful.
thats because its easy to answer dumb questions

azira
diyAudio Member

Join Date: Dec 2003
Location: Near Seattle
Quote:
 Originally posted by tiroth Well, we know the voltage output is10V @ 2k (5mA) 5V @ 175R (28.5mA) deltaI = 28.5 - 5 = 23.5mA deltaV = 5V R= V/I = 5V/23.5mA ~ 212R So 200 in parallel will be about 1 ohm output impedance, or a damping factor of 4.
Interesting, the datasheet shows about 200 ohms of impedance at the output also.
However, the output resistance should be divided by the open loop gain in a feedback amplifier, so you'll have 1/200th of an extremely low output resistance or... extremely low...
--
Danny

Stocker
diyAudio Member

Join Date: Dec 2003
Location: Austin
Quote:
 Originally posted by sss 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!

Quote:
 Originally posted by azira Interesting, the datasheet shows about 200 ohms of impedance at the output also. However, the output resistance should be divided by the open loop gain in a feedback amplifier, so you'll have 1/200th of an extremely low output resistance or... extremely low...
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?
__________________
Jesus loves you.

 28th April 2004, 12:48 PM #24 tiroth   diyAudio Member   Join Date: Dec 2001 Location: Pittsburgh, PA, USA Azira is correct, the apparant output impedance will be reduced due to feedback. The actual output impedance, though, cannot be altered by feedback and has a profound effect on the amount of current that can be supplied to the load.
 28th April 2004, 02:46 PM #25 Stocker   diyAudio Member   Join Date: Dec 2003 Location: Austin oooookaaay... So what use is an apparent output impedance when it is different from the actual output impedance? The bit about the current limiting, I knew. __________________ Jesus loves you.
azira
diyAudio Member

Join Date: Dec 2003
Location: Near Seattle
Quote:
 Originally posted by Stocker oooookaaay... So what use is an apparent output impedance when it is different from the actual output impedance? The bit about the current limiting, I knew.
Voltage damping factor...

Think of it as your output impedance and your load are in series to GND. If sourced voltage changes, then it forms a voltage divider between the apparent output impedance and the load.
--
Danny

 28th April 2004, 04:15 PM #27 hermanv   diyAudio Member   Join Date: Apr 2004 Location: Northern California 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.
tiroth
diyAudio Member

Join Date: Dec 2001
Location: Pittsburgh, PA, USA
Quote:
 Originally posted by hermanv 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).
Did you miss the fact that he is trying to get multiple watts out of this?

 28th April 2004, 04:37 PM #29 breguetphile   diyAudio Member     Join Date: Mar 2003 Location: Indiana, USA It's been mentioned, but if you just want to build something because you have a free opamp, get a few samples of the LM3875TF from National. They don't output much heat, there's tons of info on them and the sq won't be half bad. __________________ Dawn: When men of reason go to bed. ~Ambrose Bierce
 28th April 2004, 04:46 PM #30 Stocker   diyAudio Member   Join Date: Dec 2003 Location: Austin 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. __________________ Jesus loves you.

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