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LM386 oscillator challenge

Started by bitrex October 26, 2015
Use a single transistor inverter to inject a small amount of inverted signal into the second oscillator..  Thus injection locking the slave. Crude, but effective.. 

Steve 
On 10/26/2015 3:46 PM, Tim Wescott wrote:
> On Mon, 26 Oct 2015 14:30:06 -0400, bitrex 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. > > Rig up one as the oscillator, the other as an amplifier with a gain of -1. >
I could give it a shot, but the problem is the LM386 only comes in two configurations - an "open loop" gain of 20 or an "open loop" gain of 200 with bypassing. It has an internal feedback loop and internal 50k resistors to ground on the inputs as well. I'm not sure how well a standard inverting op-amp virtual ground configuration will work with such low "open loop" gain.
On 10/26/2015 3:46 PM, Tim Wescott wrote:
> On Mon, 26 Oct 2015 14:30:06 -0400, bitrex 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. > > Rig up one as the oscillator, the other as an amplifier with a gain of -1. >
I'm also not sure that it would be unity-gain stable in such a configuration.
sroberts6328@gmail.com wrote:
> Tim, > see http://www.proaudiodesignforum.com/images/pdf/ti_20150901004_09292015_eol.pdf
It sort of looks like they're shutting down a 6" wafer fab. I wonder how old that production line is, and if they have computers running DOS running it.
On Mon, 26 Oct 2015 17:03:15 -0400, bitrex wrote:

> On 10/26/2015 3:46 PM, Tim Wescott wrote: >> On Mon, 26 Oct 2015 14:30:06 -0400, bitrex 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. >> >> Rig up one as the oscillator, the other as an amplifier with a gain of >> -1. >> >> > I could give it a shot, but the problem is the LM386 only comes in two > configurations - an "open loop" gain of 20 or an "open loop" gain of 200 > with bypassing. It has an internal feedback loop and internal 50k > resistors to ground on the inputs as well. > > I'm not sure how well a standard inverting op-amp virtual ground > configuration will work with such low "open loop" gain.
Then run it at 26dB of gain and let it whack into the stops like the master oscillator. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
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. -- \_(&#12484;)_
On Mon, 26 Oct 2015 11:51:10 -0700, sroberts6328 wrote:

> LM386 just went on lifetime buy... > > Steve
Go figure, I'm still doing stuff with germanium transistors and a package of miniature tubes is coming from Russia:)
On Mon, 26 Oct 2015 19:57:37 +0000, Ian Field wrote:

> Even if it were a problem - there are other similar chips that could do > the job.
This. TDA2822 (cheap and dual) comes to mind. For music reproduction I can't but endorse those small and cheap D class amplifier modules (PAM8403 etc), their fidelity is astounding. Too bad they're often alredy bridged (ie. output is not to ground hence not usable for headphones amps) and there's no mono version.
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. -- ----Android NewsGroup Reader---- http://usenet.sinaapp.com/

"asdf" <asdf@nospam.com> wrote in message 
news:n0nupr$h2t$1@speranza.aioe.org...
> On Mon, 26 Oct 2015 19:57:37 +0000, Ian Field wrote: > >> Even if it were a problem - there are other similar chips that could do >> the job. > > > This. TDA2822 (cheap and dual) comes to mind.
I already mentioned that yesterday - the appnote shows a way to hook up the inputs for anti-phase drive that might make the bridge oscillator dead easy.