"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.
Reply by Martin Brown●October 27, 20152015-10-27
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
Reply by Ian Field●October 27, 20152015-10-27
"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.
Reply by bitrex●October 27, 20152015-10-27
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/
Reply by asdf●October 27, 20152015-10-27
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.
Reply by asdf●October 27, 20152015-10-27
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:)
Reply by Jasen Betts●October 27, 20152015-10-27
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.
--
\_(ツ)_
Reply by Tim Wescott●October 26, 20152015-10-26
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
Reply by Cydrome Leader●October 26, 20152015-10-26
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.
Reply by bitrex●October 26, 20152015-10-26
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.