I built myself and audio amplifier circuit to play music from an old
phone through to a speaker.This worked fine for a while, then the phone
stopped playing to the amplifier. The sound was still coming from the
phone speaker even when a stereo audio lead was plugged into the phone's socket. I tried 2 other leads but still the same result.

I then tried the same with another old phone , and the same thing
happened. The phone will play music but not out through the audio leads.

I don't have a headphone set to plug in to the 2 different phones, as I
only used bluetooth headphones.

I haven't tried pluging into a stereo system as I don't have one now but
I could plug in my Alexa device??

The amplifier is a home built one , nothing serious at the moment , more
just a try it and see, and is powered by a 9v DC power source from a
benchtop power supply.

I haven't done much else, as neither phone goes mute? when a stereo
audio lead is plugged in, but they did at first. That is what normally
happens , doesn't it.

Thanks

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 10/03/2022 09:22, RobH wrote:

I built myself and audio amplifier circuit to play music from an old
phone through to a speaker.This worked fine for a while, then the phone stopped playing to the amplifier. The sound was still coming from the
phone speaker even when a stereo audio lead was plugged into the phone's socket. I tried 2 other leads but still the same result.

I then tried the same with another old phone , and the same thing
happened. The phone will play music but not out through the audio leads.

I don't have a headphone set to plug in to the 2 different phones, as I
only used bluetooth headphones.

I haven't tried pluging into a stereo system as I don't have one now but
I could plug in my Alexa device??

The amplifier is a home built one , nothing serious at the moment , more
 just a try it and see, and is powered by a 9v DC power source from a benchtop power supply.

I haven't done much else, as neither phone goes mute? when a stereo
audio lead is plugged in, but they did at first. That is what normally happens , doesn't it.

Thanks

The following might answer it, you'll have to dig. I'll warn you, Quora
answers are not known for being entirely accurate.

[https://www.quora.com/How-do-phones-detect-headsets]

On Android phones, on iOS devices, and on HD Audio PCs, no mechanical
switches in the socket are used.

Instead, the headphone socket has 4 contacts instead of 3, and accepts
both 4-contact headsets and 3-contact headphones. The sleeve of the 3-
contact headphone audio jack connects two of the socket contacts together.

One of the contacts is responsible for microphone and usually feeds
1.5-3.3v of voltage through a current limiting resistor (2-10 kOhm),
which is necessary to bias a JFET transistor in the microphone capsule
of a headset. DC resistance measurement between the microphone pin and
the ground pin of the socket can be used to detect the kind of device
plugged in - it will be 0 Ohm for a headphone, infinitely high for no
device connected, and about 2 kOhm thereabouts for a headset with
microphone.

The bias current limiting resistor forms a part of voltage divider
network, with the other part being the above mentioned DC resistance.
Voltage measurement on the microphone pin is taken to both determine
the sound pressure on the microphone (through a 100hz high pass filter thereabouts) and the kind of jack or device inserted (through a low pass
filter or noise rejection logic), allowing this design to be implemented without extra parts, if the filters are implemented digitally.
Corresponding to the above DC resistances, you will measure about 0V on
the microphone pin if headphone is connected, the full mic bias voltage
in case nothing is connected, and something in between in case a headset
is connected.

Switches in the audio jack like in the answer above were common in older electronics, but are incompatible with headsets and are just too bulky
for a high-tech handset.

--
Adrian C

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 10/03/2022 10:41, Adrian Caspersz wrote:

he bias current limiting resistor forms a part of voltage divider network,

Quora posters steal ...

https://electronics.stackexchange.com/questions/95575/how-does-the-phone-detect-if-3-5-mm-jack-circuit-is-closed

--
Adrian C

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

In article <j8tuagF3dn0U2@mid.individual.net>, rob@despammer.com says...

I built myself and audio amplifier circuit to play music from an old
phone through to a speaker.This worked fine for a while, then the phone stopped playing to the amplifier. The sound was still coming from the
phone speaker even when a stereo audio lead was plugged into the phone's socket. I tried 2 other leads but still the same result.

I then tried the same with another old phone , and the same thing
happened. The phone will play music but not out through the audio leads.

I don't have a headphone set to plug in to the 2 different phones, as I
only used bluetooth headphones.

I haven't tried pluging into a stereo system as I don't have one now but
I could plug in my Alexa device??

The amplifier is a home built one , nothing serious at the moment , more
just a try it and see, and is powered by a 9v DC power source from a benchtop power supply.

I haven't done much else, as neither phone goes mute? when a stereo
audio lead is plugged in, but they did at first. That is what normally happens , doesn't it.

Thanks

You could just get a Bluetooth receiver (with its own battery, e.g.
Bluetooth® Audio & Hands-free Receiver AV:Link BTR1; Item ref: 100.590UK
~£10) and plug the amplifer into that. It's what I did...

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 10/03/2022 10:41, Adrian Caspersz wrote:

On 10/03/2022 09:22, RobH wrote:

I built myself and audio amplifier circuit to play music from an old
phone through to a speaker.This worked fine for a while, then the
phone stopped playing to the amplifier. The sound was still coming
from the phone speaker even when a stereo audio lead was plugged into
the phone's socket. I tried 2 other leads but still the same result.

I then tried the same with another old phone , and the same thing
happened. The phone will play music but not out through the audio leads.

I don't have a headphone set to plug in to the 2 different phones, as
I only used bluetooth headphones.

I haven't tried pluging into a stereo system as I don't have one now
but I could plug in my Alexa device??

The amplifier is a home built one , nothing serious at the moment ,
more   just a try it and see, and is powered by a 9v DC power source
from a benchtop power supply.

I haven't done much else, as neither phone goes mute? when a stereo
audio lead is plugged in, but they did at first. That is what normally
happens , doesn't it.

Thanks

The following might answer it, you'll have to dig. I'll warn you, Quora answers are not known for being entirely accurate.

[https://www.quora.com/How-do-phones-detect-headsets]

On Android phones, on iOS devices, and on HD Audio PCs, no mechanical switches in the socket are used.

Instead, the headphone socket has 4 contacts instead of 3, and accepts
both 4-contact headsets and 3-contact headphones. The sleeve of the 3- contact headphone audio jack connects two of the socket contacts together.

One of the contacts is responsible for microphone and usually feeds
1.5-3.3v of voltage through a current limiting resistor (2-10 kOhm),
which is necessary to bias a JFET transistor in the microphone capsule
of a headset. DC resistance measurement between the microphone pin and
the ground pin of the socket can be used to detect the kind of device
plugged in - it will be 0 Ohm for a headphone, infinitely high for no
device connected, and about 2 kOhm thereabouts for a headset with
microphone.

The bias current limiting resistor forms a part of voltage divider
network, with the other part being the above mentioned DC resistance.
Voltage measurement on the microphone pin is  taken to both determine
the sound pressure on the microphone (through a 100hz high pass filter thereabouts) and the kind of jack or device inserted (through a low pass filter or noise rejection logic), allowing this design to be implemented without extra parts, if the filters are implemented digitally.
Corresponding to the above DC resistances, you will measure about 0V on
the microphone pin if headphone is connected, the full mic bias voltage
in case nothing is connected, and something in between in case a headset
is connected.

Switches in the audio jack like in the answer above were common in older electronics, but are incompatible with headsets and are just too bulky
for a high-tech handset.

If it makes any difference, both phones are quite old, with 1 being on
Android 5.0.2, and the other being on Android 5.1, and both about 7
years old now.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 10/03/2022 11:35, Mike Coon wrote:

In article <j8tuagF3dn0U2@mid.individual.net>, rob@despammer.com says...

I built myself and audio amplifier circuit to play music from an old
phone through to a speaker.This worked fine for a while, then the phone
stopped playing to the amplifier. The sound was still coming from the
phone speaker even when a stereo audio lead was plugged into the phone's
socket. I tried 2 other leads but still the same result.

I then tried the same with another old phone , and the same thing
happened. The phone will play music but not out through the audio leads.

I don't have a headphone set to plug in to the 2 different phones, as I
only used bluetooth headphones.

I haven't tried pluging into a stereo system as I don't have one now but
I could plug in my Alexa device??

The amplifier is a home built one , nothing serious at the moment , more
just a try it and see, and is powered by a 9v DC power source from a
benchtop power supply.

I haven't done much else, as neither phone goes mute? when a stereo
audio lead is plugged in, but they did at first. That is what normally
happens , doesn't it.

Thanks

You could just get a Bluetooth receiver (with its own battery, e.g. Bluetooth® Audio & Hands-free Receiver AV:Link BTR1; Item ref: 100.590UK ~£10) and plug the amplifer into that. It's what I did...

Could I plug the amp into my Alexa device, as I don't want to damage
that, as I may have fried the audio circuitry in both phones.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 10/03/2022 11:35, Mike Coon wrote:

In article <j8tuagF3dn0U2@mid.individual.net>, rob@despammer.com says...

I built myself and audio amplifier circuit to play music from an old
phone through to a speaker.This worked fine for a while, then the phone
stopped playing to the amplifier. The sound was still coming from the
phone speaker even when a stereo audio lead was plugged into the phone's
socket. I tried 2 other leads but still the same result.

I then tried the same with another old phone , and the same thing
happened. The phone will play music but not out through the audio leads.

I don't have a headphone set to plug in to the 2 different phones, as I
only used bluetooth headphones.

I haven't tried pluging into a stereo system as I don't have one now but
I could plug in my Alexa device??

The amplifier is a home built one , nothing serious at the moment , more
just a try it and see, and is powered by a 9v DC power source from a
benchtop power supply.

I haven't done much else, as neither phone goes mute? when a stereo
audio lead is plugged in, but they did at first. That is what normally
happens , doesn't it.

Thanks

You could just get a Bluetooth receiver (with its own battery, e.g. Bluetooth® Audio & Hands-free Receiver AV:Link BTR1; Item ref: 100.590UK ~£10) and plug the amplifer into that. It's what I did...

Do mean 1 like this:

https://www.ebay.co.uk/itm/132242665044?hash=item1eca46ee54:g:9SQAAOSwOMdZU8LB

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

In article <j8u7gbF55n2U1@mid.individual.net>, RobH <rob@despammer.com> wrote:

Could I plug the amp into my Alexa device, as I don't want to damage
that, as I may have fried the audio circuitry in both phones.

I think you should first take a look at your amplifier design, and see
whether it's capable of accidentally back-feeding a voltage spike into
whatever you have plugged it into.

If, for example, it's a single-sided power supply design, and has a capacitor-coupled input, there's a chance that "hot-plugging" it into
a device (or turning on its power when it's already plugged in) could
send a pulse of current into the phone, as the DC-blocking input
capacitor charges up. A device with e.g. a 12-volt power supply,
which was capacitor-blocking half that much voltage, could put what
amounts to a 6-volt spike into the phone output. This might have
damaged the "headphone detect" circuitry in the phone.

One possibly-damaged phone could be an accident. Two,
possibly-damaged with the same symptoms, leads me to suspect that
the amp may indeed be at fault and could potentially damage other
devices.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 10/03/2022 18:52, Dave Platt wrote:

In article <j8u7gbF55n2U1@mid.individual.net>, RobH <rob@despammer.com> wrote:

Could I plug the amp into my Alexa device, as I don't want to damage
that, as I may have fried the audio circuitry in both phones.

I think you should first take a look at your amplifier design, and see whether it's capable of accidentally back-feeding a voltage spike into whatever you have plugged it into.

If, for example, it's a single-sided power supply design, and has a capacitor-coupled input, there's a chance that "hot-plugging" it into
a device (or turning on its power when it's already plugged in) could
send a pulse of current into the phone, as the DC-blocking input
capacitor charges up. A device with e.g. a 12-volt power supply,
which was capacitor-blocking half that much voltage, could put what
amounts to a 6-volt spike into the phone output. This might have
damaged the "headphone detect" circuitry in the phone.

One possibly-damaged phone could be an accident. Two,
possibly-damaged with the same symptoms, leads me to suspect that
the amp may indeed be at fault and could potentially damage other
devices.

As I am only an amateur just doing basic circuits I watch videos on
things I am interested in doing and this is the circuit I have used.

I await your verdict on it.

https://www.circuitbasics.com/wp-content/uploads/2015/04/Build-a-Great-Sounding-Audio-Amplifier-with-Bass-Boost-from-the-LM386-Amplifier-With-Gain-Schematic.png

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

In article <j8v4r2Fanu2U1@mid.individual.net>, RobH <rob@despammer.com> wrote:

As I am only an amateur just doing basic circuits I watch videos on
things I am interested in doing and this is the circuit I have used.

I await your verdict on it.

https://www.circuitbasics.com/wp-content/uploads/2015/04/Build-a-Great-Sounding-Audio-Amplifier-with-Bass-Boost-from-the-LM386-Amplifier-With-Gain-Schematic.png

I don't see a problem with it, if the LM386 is working correctly and
the circuit is wired up accurately. The data sheet for the LM386 has
some very similar application circuits, and the data-sheet notes and
schematic both show the inputs being biased down at ground voltage.
No input capacitor is required, and the circuit you show doesn't have
one. So, the sort of turn-on pulse I was concerned about ought not
to occur.

As a check - if you have a voltmeter, try powering the amp up (when
not connected to anything) and then measure the DC voltage between the
two input leads (e.g. the ground shell and the tip connector on the
jack). You shouldn't read more than a small fraction of 1 volt
(just a few millivolts) at any time.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

In article <j8unf8F87nrU1@mid.individual.net>, rob@despammer.com says...

On 10/03/2022 11:35, Mike Coon wrote:

In article <j8tuagF3dn0U2@mid.individual.net>, rob@despammer.com says...

I built myself and audio amplifier circuit to play music from an old
phone through to a speaker.This worked fine for a while, then the phone
stopped playing to the amplifier. The sound was still coming from the
phone speaker even when a stereo audio lead was plugged into the phone's >> socket. I tried 2 other leads but still the same result.

I then tried the same with another old phone , and the same thing
happened. The phone will play music but not out through the audio leads. >>
I don't have a headphone set to plug in to the 2 different phones, as I
only used bluetooth headphones.

I haven't tried pluging into a stereo system as I don't have one now but >> I could plug in my Alexa device??

The amplifier is a home built one , nothing serious at the moment , more >> just a try it and see, and is powered by a 9v DC power source from a
benchtop power supply.

I haven't done much else, as neither phone goes mute? when a stereo
audio lead is plugged in, but they did at first. That is what normally
happens , doesn't it.

Thanks

You could just get a Bluetooth receiver (with its own battery, e.g. Bluetooth® Audio & Hands-free Receiver AV:Link BTR1; Item ref: 100.590UK ~£10) and plug the amplifer into that. It's what I did...

Do mean 1 like this:

https://www.ebay.co.uk/itm/132242665044?hash=item1eca46ee54:g:9SQAAOSwOMdZU8LB

Exactly. Sorry the price has crept up!

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 10/03/2022 23:48, Dave Platt wrote:

In article <j8v4r2Fanu2U1@mid.individual.net>, RobH <rob@despammer.com> wrote:

As I am only an amateur just doing basic circuits I watch videos on
things I am interested in doing and this is the circuit I have used.

I await your verdict on it.

https://www.circuitbasics.com/wp-content/uploads/2015/04/Build-a-Great-Sounding-Audio-Amplifier-with-Bass-Boost-from-the-LM386-Amplifier-With-Gain-Schematic.png

I don't see a problem with it, if the LM386 is working correctly and
the circuit is wired up accurately. The data sheet for the LM386 has
some very similar application circuits, and the data-sheet notes and schematic both show the inputs being biased down at ground voltage.
No input capacitor is required, and the circuit you show doesn't have
one. So, the sort of turn-on pulse I was concerned about ought not
to occur.

As a check - if you have a voltmeter, try powering the amp up (when
not connected to anything) and then measure the DC voltage between the
two input leads (e.g. the ground shell and the tip connector on the
jack). You shouldn't read more than a small fraction of 1 volt
(just a few millivolts) at any time.

I put a voltmeter between the 2 input leads, GND and tip, and the
reading was .002 VDC at maximum volume on the 10k pot. Nothing was
connected to the amplifier circuit.

Thanks

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

In article <j8u7gbF55n2U1@mid.individual.net>, rob@despammer.com says...

On 10/03/2022 11:35, Mike Coon wrote:

In article <j8tuagF3dn0U2@mid.individual.net>, rob@despammer.com says...

I built myself and audio amplifier circuit to play music from an old
phone through to a speaker.This worked fine for a while, then the phone
stopped playing to the amplifier. The sound was still coming from the
phone speaker even when a stereo audio lead was plugged into the phone's >> socket. I tried 2 other leads but still the same result.

I then tried the same with another old phone , and the same thing
happened. The phone will play music but not out through the audio leads. >>
I don't have a headphone set to plug in to the 2 different phones, as I
only used bluetooth headphones.

I haven't tried pluging into a stereo system as I don't have one now but >> I could plug in my Alexa device??

The amplifier is a home built one , nothing serious at the moment , more >> just a try it and see, and is powered by a 9v DC power source from a
benchtop power supply.

I haven't done much else, as neither phone goes mute? when a stereo
audio lead is plugged in, but they did at first. That is what normally
happens , doesn't it.

Thanks

You could just get a Bluetooth receiver (with its own battery, e.g. Bluetooth® Audio & Hands-free Receiver AV:Link BTR1; Item ref: 100.590UK ~£10) and plug the amplifer into that. It's what I did...

Could I plug the amp into my Alexa device, as I don't want to damage
that, as I may have fried the audio circuitry in both phones.

Don't see why not. I assume the problem with my phone is just the audio
socket rather than "circuitry". An "Alexa device" should have a safe
input. Only you know about your amplifier input!

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 11/03/2022 10:07, Mike Coon wrote:

In article <j8unf8F87nrU1@mid.individual.net>, rob@despammer.com says...

On 10/03/2022 11:35, Mike Coon wrote:

In article <j8tuagF3dn0U2@mid.individual.net>, rob@despammer.com says... >>>>

I built myself and audio amplifier circuit to play music from an old
phone through to a speaker.This worked fine for a while, then the phone >>>> stopped playing to the amplifier. The sound was still coming from the
phone speaker even when a stereo audio lead was plugged into the phone's >>>> socket. I tried 2 other leads but still the same result.

I then tried the same with another old phone , and the same thing
happened. The phone will play music but not out through the audio leads. >>>>
I don't have a headphone set to plug in to the 2 different phones, as I >>>> only used bluetooth headphones.

I haven't tried pluging into a stereo system as I don't have one now but >>>> I could plug in my Alexa device??

The amplifier is a home built one , nothing serious at the moment , more >>>> just a try it and see, and is powered by a 9v DC power source from a >>>> benchtop power supply.

I haven't done much else, as neither phone goes mute? when a stereo
audio lead is plugged in, but they did at first. That is what normally >>>> happens , doesn't it.

Thanks

You could just get a Bluetooth receiver (with its own battery, e.g.
Bluetooth® Audio & Hands-free Receiver AV:Link BTR1; Item ref: 100.590UK >>> ~£10) and plug the amplifer into that. It's what I did...

Do mean 1 like this:

https://www.ebay.co.uk/itm/132242665044?hash=item1eca46ee54:g:9SQAAOSwOMdZU8LB

Exactly. Sorry the price has crept up!

Yes, no doubt it has like everything else. The price is now £11.49, oh
well. Ive ordered it and await its' delivery.

thanks

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 11/03/2022 10:07, Mike Coon wrote:

In article <j8unf8F87nrU1@mid.individual.net>, rob@despammer.com says...

On 10/03/2022 11:35, Mike Coon wrote:

In article <j8tuagF3dn0U2@mid.individual.net>, rob@despammer.com says... >>>>

I built myself and audio amplifier circuit to play music from an old
phone through to a speaker.This worked fine for a while, then the phone >>>> stopped playing to the amplifier. The sound was still coming from the
phone speaker even when a stereo audio lead was plugged into the phone's >>>> socket. I tried 2 other leads but still the same result.

I then tried the same with another old phone , and the same thing
happened. The phone will play music but not out through the audio leads. >>>>
I don't have a headphone set to plug in to the 2 different phones, as I >>>> only used bluetooth headphones.

I haven't tried pluging into a stereo system as I don't have one now but >>>> I could plug in my Alexa device??

The amplifier is a home built one , nothing serious at the moment , more >>>> just a try it and see, and is powered by a 9v DC power source from a >>>> benchtop power supply.

I haven't done much else, as neither phone goes mute? when a stereo
audio lead is plugged in, but they did at first. That is what normally >>>> happens , doesn't it.

Thanks

You could just get a Bluetooth receiver (with its own battery, e.g.
Bluetooth® Audio & Hands-free Receiver AV:Link BTR1; Item ref: 100.590UK >>> ~£10) and plug the amplifer into that. It's what I did...

Do mean 1 like this:

https://www.ebay.co.uk/itm/132242665044?hash=item1eca46ee54:g:9SQAAOSwOMdZU8LB

Exactly. Sorry the price has crept up!

If you have the same receiver I have just bought, do you get a voice
message when you power it it up or down, as per the instructions. I
don't and it doesn't show up in the list of devices on my phone.
The blue light on the receiver is flashing, but that is all.

Thanks

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)