question 1: I was looking at the NE5532 datasheet and I can see typical supply current is around 8mA. (30V(?) * 8mA = .24W each)
assuming I have 30 NE5532 chips in the circuit, I somehow doubt I only need a <15W transformer (with headroom added in)?
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question2: is there a better specced drop-in alternative that's still inexpensive? (example: I saw that the OPA1612 is also a bipolar input that may be ok BUT it's like 8-10x the price as well)
Thanks for the assistance.
assuming I have 30 NE5532 chips in the circuit, I somehow doubt I only need a <15W transformer (with headroom added in)?
------------
question2: is there a better specced drop-in alternative that's still inexpensive? (example: I saw that the OPA1612 is also a bipolar input that may be ok BUT it's like 8-10x the price as well)
Thanks for the assistance.
The idle supply current is spec'd at 8mA but you probably want some audio output which could be 38mA each, so for 30 op-amps that would be 30*0.038*30V(+/-15)=34.2 Watts.
Others have done this but it's a better idea to buffer the output of one op-amp with real power transistors or use a chip-amp.
Others have done this but it's a better idea to buffer the output of one op-amp with real power transistors or use a chip-amp.
Well depends what you mean by a better idea - the parallel opamp design has extremely low distortion, no requirements for biasing or offset adjustment, is bomb-proof (withstands indefinite short-circuit, no issue of secondary breakdown), and uses the PCB as the heatsink, so its got a lot of advantages.
By contrast an opamp driven class-B output stage will have much higher distortion than the opamp alone, even when correctly biased, and can be blown up by short circuit or overload.
Granted. But if you don't mind 30 op-amps then a few extra bits for output protection is no big deal. And the gain can be moved to a ~pre-amp, so that more OLG is available for the output, ie less distortion. And 8/38mA is 21% idle, which is seriously class-A. 30x38mA=1.14A max output, ~= 5.2W rms. Driving 8 Ohms to 15V is 49, 50 op-amps and 14 Wrms. The circuit I posted is as simple as it can be, so not a great example. Running a pair of TO-3P transistors at 1.14A peak or even 15/8=1.875 Amps would be a cake walk, (~400mA idle) in class-A territory, and a power supply fuse could be all the protection it needs. A dozen transistors just seems a much better idea to me than 50 op-amps (30 not enough).
The parallelled devices have gain +1 so that parallelling is accurate, allowing low value output resistors for the current sharing. Otherwise you'd need precision gain resistors for every opamp. A single opamp stage can act as input and VAS. You can even make this into a composite topology I suspect, though I've not tried.
64 NE5532 dual opamps are about £10, BTW, enough for two amps. 5532's can drive 500 ohms, 500/64 = 7.8ohms. And you can do all SMT which commercially is a big advantage.
64 NE5532 dual opamps are about £10, BTW, enough for two amps. 5532's can drive 500 ohms, 500/64 = 7.8ohms. And you can do all SMT which commercially is a big advantage.
One could consider the LM4562 in that application. It's more expensive than the NE5532, but then again so is just about any opamp. The LM4562 can go closer to the rail and drive a heavier load at much lower distortion than the NE5532.
If my math holds up, you're looking at about 4 W dissipated in the amp and 1 W (average) dissipated in the load when you drive the amp to clipping with music signal (14 dB CF), 8 Ω load, and ±15 V power supply. So you need at least 5 W (per channel) from the power supply.
Of course, the peak output current will be around 1.8 A (per channel) so your power supply needs to be able to provide that in the short term.
If you were to drive the amp to clipping with a sine wave, you'd get about 14 W to the 8 Ω load and dissipate 4.4 W in the amp. So the supply would need to provide at least 18.4 W, per channel.
I give you all the necessary math here: https://neurochrome.com/pages/power-supply-design I use the LM3886 as an example, but you can just change the numbers to match your opamp of choice. I used the LM4562 in my math above.
Tom
If my math holds up, you're looking at about 4 W dissipated in the amp and 1 W (average) dissipated in the load when you drive the amp to clipping with music signal (14 dB CF), 8 Ω load, and ±15 V power supply. So you need at least 5 W (per channel) from the power supply.
Of course, the peak output current will be around 1.8 A (per channel) so your power supply needs to be able to provide that in the short term.
If you were to drive the amp to clipping with a sine wave, you'd get about 14 W to the 8 Ω load and dissipate 4.4 W in the amp. So the supply would need to provide at least 18.4 W, per channel.
I give you all the necessary math here: https://neurochrome.com/pages/power-supply-design I use the LM3886 as an example, but you can just change the numbers to match your opamp of choice. I used the LM4562 in my math above.
Tom