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LM386 oscillator challenge

Started by bitrex October 26, 2015
On 27/10/2015 17:40, bitrex wrote:
> Jasen Betts <jasen@xnet.co.nz> Wrote in message: >> On 2015-10-26, bitrex <bitrex@de.lete.earthlink.net> wrote: >>> So here's a schematic of a standard LM386 power oscillator: >>> >>> http://www.interfacebus.com/lm386-square-wave-oscillator-circuit.jpg >>> >>> I have an idea for a thing where what I'd like to have is a second LM386 >>> oscillating at the same frequency and amplitude, but opposite phase as >>> the first one, for push-pull drive. But I'd like to not use any further >>> active parts other than the second LM386, if that's possible. >>> >>> I know there are other chips that could probably do what I want more >>> easily, but this is just for a little breadboard experiment and I happen >>> to have a bunch of these sitting around. >> >> Just wire the second one's inputs antiparallel to the first. (connect >> it to the first inputs bu swap + amd -) LM386 has gain fixed internally >> to 10, so doing this is not like running an op-amp open-loop. >> >> -- >> \_(?)_ >> > > I'm not sure how this is helpful. The first LM386 is configured as > a relaxation oscillator.
If you attach the other as a basic amplifier to the inputs of the first 386 oscillator but with + & - inputs swapped and the same gain then the second amplifier will thrash from rail to rail in the opposite direction to the first effectively abusing it as a comparator. -- Regards, Martin Brown

"Martin Brown" <|||newspam|||@nezumi.demon.co.uk> wrote in message 
news:n0ouuv$uo1$1@speranza.aioe.org...
> On 27/10/2015 17:40, bitrex wrote: >> Jasen Betts <jasen@xnet.co.nz> Wrote in message: >>> On 2015-10-26, bitrex <bitrex@de.lete.earthlink.net> wrote: >>>> So here's a schematic of a standard LM386 power oscillator: >>>> >>>> http://www.interfacebus.com/lm386-square-wave-oscillator-circuit.jpg >>>> >>>> I have an idea for a thing where what I'd like to have is a second >>>> LM386 >>>> oscillating at the same frequency and amplitude, but opposite phase as >>>> the first one, for push-pull drive. But I'd like to not use any further >>>> active parts other than the second LM386, if that's possible. >>>> >>>> I know there are other chips that could probably do what I want more >>>> easily, but this is just for a little breadboard experiment and I >>>> happen >>>> to have a bunch of these sitting around. >>> >>> Just wire the second one's inputs antiparallel to the first. (connect >>> it to the first inputs bu swap + amd -) LM386 has gain fixed internally >>> to 10, so doing this is not like running an op-amp open-loop. >>> >>> -- >>> \_(?)_ >>> >> >> I'm not sure how this is helpful. The first LM386 is configured as >> a relaxation oscillator. > > If you attach the other as a basic amplifier to the inputs of the first > 386 oscillator but with + & - inputs swapped and the same gain then the > second amplifier will thrash from rail to rail in the opposite direction > to the first effectively abusing it as a comparator.
In the TDA2822 appnote example BTL amplifier; the minus input of the stage fed with input signal is coupled via a capacitive potential divider to the minus input of the "slave" stage, coupling is 10uF and shunt is 10nF. The plus input of the slave is grounded. It may well depend on the exact structure of the input stage as to whether it works with other chips. There is a simplified schematic on the datasheet, the minus input is actually labeled; NF, and has an internal resistor from the junction of the output pair. If this resistor doesn't exist in the 386 - it can probably be added externally.