I am looking at a number of FM transmitter circuits, purely as a
project, but all of them use electret microphones as input. Would it
be possible to replace this with an audio input for my iPod?

On Feb 15, 10:45 am, "Dave.H" <the19...@googlemail.com> wrote:
> I am looking at a number of FM transmitter circuits, purely as a
> project, but all of them use electret microphones as input. Would it
> be possible to replace this with an audio input for my iPod?

I found a circuit that does use a regular audio input, but I can't
find a couple of capacitor values at Dick Smith. The caps have to be
ceramic. I can find a 3.3 pF for the 3 pF, but I can't find a 10 nF
ceramic unit. Would it be OK to just parallel 10 1 nF caps, until I
can find a 10 nF unit?

On Thu, 14 Feb 2008 15:45:31 -0800 (PST), "Dave.H"
<the1930s@googlemail.com> wrote:

>I am looking at a number of FM transmitter circuits, purely as a
>project, but all of them use electret microphones as input. Would it
>be possible to replace this with an audio input for my iPod?

Of course. You wouldn't have stereo with a simple one or two
transistor transmitter - so you may also want to combine both channels
going in.

Electret's have built in preamplifiers or impedance matching amps and
they usually impress a DC voltage on the audio connection to the
electret mic.. You just need to disconnect that resistor and not use
it.

There also may be a need for a capacitor to couple audio in without
upsetting the DC bias of the transmitter.
--

On Feb 15, 1:08 pm, "Dave.H" <the19...@googlemail.com> wrote:
> On Feb 15, 10:45 am, "Dave.H" <the19...@googlemail.com> wrote:
>
> > I am looking at a number of FM transmitter circuits, purely as a
> > project, but all of them use electret microphones as input. Would it
> > be possible to replace this with an audio input for my iPod?
>
> I found a circuit that does use a regular audio input, but I can't
> find a couple of capacitor values at Dick Smith. The caps have to be
> ceramic. I can find a 3.3 pF for the 3 pF, but I can't find a 10 nF
> ceramic unit. Would it be OK to just parallel 10 1 nF caps, until I
> can find a 10 nF unit?

Forgot the link: http://www.techlib.com/Karen/radio.htm#FM%20Transmitter

default wrote:
> On Thu, 14 Feb 2008 15:45:31 -0800 (PST), "Dave.H"
> <the1930s@googlemail.com> wrote:
>
> >I am looking at a number of FM transmitter circuits, purely as a
> >project, but all of them use electret microphones as input. Would it
> >be possible to replace this with an audio input for my iPod?
>
> Of course. You wouldn't have stereo with a simple one or two
> transistor transmitter - so you may also want to combine both channels
> going in.
\

I understand that, but my radio receiver is a mono type anyway, so I'm
not looking for a stereo version.
> --

On Thu, 14 Feb 2008 18:08:48 -0800 (PST), "Dave.H"
<the1930s@googlemail.com> wrote:

>On Feb 15, 10:45 am, "Dave.H" <the19...@googlemail.com> wrote:
>> I am looking at a number of FM transmitter circuits, purely as a
>> project, but all of them use electret microphones as input. Would it
>> be possible to replace this with an audio input for my iPod?
>
>I found a circuit that does use a regular audio input, but I can't
>find a couple of capacitor values at Dick Smith. The caps have to be
>ceramic. I can find a 3.3 pF for the 3 pF, but I can't find a 10 nF
>ceramic unit. Would it be OK to just parallel 10 1 nF caps, until I
>can find a 10 nF unit?

Yeah the 3.3 is good enough. Isn't 10 nano farad just another way of
saying .01 microfarad? .01 microfarad is very common.
--

On Thu, 14 Feb 2008 18:15:00 -0800 (PST), "Dave.H"
<the1930s@googlemail.com> wrote:

>
>
>default wrote:
>> On Thu, 14 Feb 2008 15:45:31 -0800 (PST), "Dave.H"
>> <the1930s@googlemail.com> wrote:
>>
>> >I am looking at a number of FM transmitter circuits, purely as a
>> >project, but all of them use electret microphones as input. Would it
>> >be possible to replace this with an audio input for my iPod?
>>
>> Of course. You wouldn't have stereo with a simple one or two
>> transistor transmitter - so you may also want to combine both channels
>> going in.
>\
>
>I understand that, but my radio receiver is a mono type anyway, so I'm
>not looking for a stereo version.
>> --
sorry I somehow got the idea that the Ipod would be the music source.
--

"Dave.H" (the1930s@googlemail.com) writes:
> default wrote:
>> On Thu, 14 Feb 2008 15:45:31 -0800 (PST), "Dave.H"
>> <the1930s@googlemail.com> wrote:
>>
>> >I am looking at a number of FM transmitter circuits, purely as a
>> >project, but all of them use electret microphones as input. Would it
>> >be possible to replace this with an audio input for my iPod?
>>
>> Of course. You wouldn't have stereo with a simple one or two
>> transistor transmitter - so you may also want to combine both channels
>> going in.
> \
>
> I understand that, but my radio receiver is a mono type anyway, so I'm
> not looking for a stereo version.

But if you don't combine the two channels at the receiver, you'll only
be getting some of the content.

IN order for there to be stereo, there has to be difference between the
channels. How it's arranged can be quite complicated and depends on
what was recorded and how the recording engineer felt things should sound.

If you only have one channel of a stereo signal, you will lose content.
So that trumpet over in the right channel that is only on the right channel
to give a sense of space, will be missing if all you feed into the transmitter
is the left channel. Other things may still be there, but lacking in volume
because the intent was to place it somewhere between the two channels.

Michael

"Dave.H" (the1930s@googlemail.com) writes:
> On Feb 15, 10:45 am, "Dave.H" <the19...@googlemail.com> wrote:
>> I am looking at a number of FM transmitter circuits, purely as a
>> project, but all of them use electret microphones as input. Would it
>> be possible to replace this with an audio input for my iPod?
>
> I found a circuit that does use a regular audio input, but I can't
> find a couple of capacitor values at Dick Smith. The caps have to be
> ceramic. I can find a 3.3 pF for the 3 pF, but I can't find a 10 nF
> ceramic unit. Would it be OK to just parallel 10 1 nF caps, until I
> can find a 10 nF unit?

10nF is .01.

1nF= .001
10nF=.01

Thus you need the extremely common .01uF capacitor. And I suspect
that's not even critical, such a large value is bound to be a bypass
capacitor and hence something around that value will do fine.

Michael

On Feb 15, 1:20 pm, default <defa...@defaulter.net> wrote:
> On Thu, 14 Feb 2008 18:15:00 -0800 (PST), "Dave.H"
>
>
>
> <the19...@googlemail.com> wrote:
>
> >default wrote:
> >> On Thu, 14 Feb 2008 15:45:31 -0800 (PST), "Dave.H"
> >> <the19...@googlemail.com> wrote:
>
> >> >I am looking at a number of FM transmitter circuits, purely as a
> >> >project, but all of them use electret microphones as input. Would it
> >> >be possible to replace this with an audio input for my iPod?
>
> >> Of course. You wouldn't have stereo with a simple one or two
> >> transistor transmitter - so you may also want to combine both channels
> >> going in.
> >\
>
> >I understand that, but my radio receiver is a mono type anyway, so I'm
> >not looking for a stereo version.
> >> --
>
> sorry I somehow got the idea that the Ipod would be the music source.
> --

iPod is the music source, it will be broadcasting to the mono radio. I
will use that circuit I linked to before, seems to have the audio
channels combined by 10K resistors so I don't have to worry about
that. Even though I've already got a device that combines left and
right with 1.8K resistors.

On Feb 15, 1:28 pm, et...@FreeNet.Carleton.CA (Michael Black) wrote:
> "Dave.H" (the19...@googlemail.com) writes:
> > On Feb 15, 10:45 am, "Dave.H" <the19...@googlemail.com> wrote:
> >> I am looking at a number of FM transmitter circuits, purely as a
> >> project, but all of them use electret microphones as input. Would it
> >> be possible to replace this with an audio input for my iPod?
>
> > I found a circuit that does use a regular audio input, but I can't
> > find a couple of capacitor values at Dick Smith. The caps have to be
> > ceramic. I can find a 3.3 pF for the 3 pF, but I can't find a 10 nF
> > ceramic unit. Would it be OK to just parallel 10 1 nF caps, until I
> > can find a 10 nF unit?
>
> 10nF is .01.
>
> 1nF= .001
> 10nF=.01
>
> Thus you need the extremely common .01uF capacitor. And I suspect
> that's not even critical, such a large value is bound to be a bypass
> capacitor and hence something around that value will do fine.
>
> Michael

I somehow managed to read the chart wrong @ http://www.justradios.com/uFnFpF.html
Handy chart to have by the way.

On Thu, 14 Feb 2008 18:38:55 -0800 (PST), "Dave.H"
<the1930s@googlemail.com> wrote:

>On Feb 15, 1:20 pm, default <defa...@defaulter.net> wrote:
>> On Thu, 14 Feb 2008 18:15:00 -0800 (PST), "Dave.H"
>>
>>
>>
>> <the19...@googlemail.com> wrote:
>>
>> >default wrote:
>> >> On Thu, 14 Feb 2008 15:45:31 -0800 (PST), "Dave.H"
>> >> <the19...@googlemail.com> wrote:
>>
>> >> >I am looking at a number of FM transmitter circuits, purely as a
>> >> >project, but all of them use electret microphones as input. Would it
>> >> >be possible to replace this with an audio input for my iPod?
>>
>> >> Of course. You wouldn't have stereo with a simple one or two
>> >> transistor transmitter - so you may also want to combine both channels
>> >> going in.
>> >\
>>
>> >I understand that, but my radio receiver is a mono type anyway, so I'm
>> >not looking for a stereo version.
>> >> --
>>
>> sorry I somehow got the idea that the Ipod would be the music source.
>> --
>
>iPod is the music source, it will be broadcasting to the mono radio. I
>will use that circuit I linked to before, seems to have the audio
>channels combined by 10K resistors so I don't have to worry about
>that. Even though I've already got a device that combines left and
>right with 1.8K resistors.

You have a better idea of what you are doing than I do. The Ipod
output has to (should) be mixed to drive the transmitter with the
contents of both channels. That can be as simple as two resistors
from each channel to a common input.

Not aware of the circuit you linked to before. You aren't referring
to the one where you ground the two signals to control volume are you?
--

On Feb 15, 1:52 pm, default <defa...@defaulter.net> wrote:
> On Thu, 14 Feb 2008 18:38:55 -0800 (PST), "Dave.H"
>
>
>
> <the19...@googlemail.com> wrote:
> >On Feb 15, 1:20 pm, default <defa...@defaulter.net> wrote:
> >> On Thu, 14 Feb 2008 18:15:00 -0800 (PST), "Dave.H"
>
> >> <the19...@googlemail.com> wrote:
>
> >> >default wrote:
> >> >> On Thu, 14 Feb 2008 15:45:31 -0800 (PST), "Dave.H"
> >> >> <the19...@googlemail.com> wrote:
>
> >> >> >I am looking at a number of FM transmitter circuits, purely as a
> >> >> >project, but all of them use electret microphones as input. Would it
> >> >> >be possible to replace this with an audio input for my iPod?
>
> >> >> Of course. You wouldn't have stereo with a simple one or two
> >> >> transistor transmitter - so you may also want to combine both channels
> >> >> going in.
> >> >\
>
> >> >I understand that, but my radio receiver is a mono type anyway, so I'm
> >> >not looking for a stereo version.
> >> >> --
>
> >> sorry I somehow got the idea that the Ipod would be the music source.
> >> --
>
> >iPod is the music source, it will be broadcasting to the mono radio. I
> >will use that circuit I linked to before, seems to have the audio
> >channels combined by 10K resistors so I don't have to worry about
> >that. Even though I've already got a device that combines left and
> >right with 1.8K resistors.
>
> You have a better idea of what you are doing than I do. The Ipod
> output has to (should) be mixed to drive the transmitter with the
> contents of both channels. That can be as simple as two resistors
> from each channel to a common input.
>
> Not aware of the circuit you linked to before. You aren't referring
> to the one where you ground the two signals to control volume are you?
> --

No, the one @ http://www.techlib.com/Karen/radio.htm#FM%20Transmitter

On Feb 15, 2:18 pm, "Dave.H" <the19...@googlemail.com> wrote:
> On Feb 15, 1:52 pm, default <defa...@defaulter.net> wrote:
>
>
>
> > On Thu, 14 Feb 2008 18:38:55 -0800 (PST), "Dave.H"
>
> > <the19...@googlemail.com> wrote:
> > >On Feb 15, 1:20 pm, default <defa...@defaulter.net> wrote:
> > >> On Thu, 14 Feb 2008 18:15:00 -0800 (PST), "Dave.H"
>
> > >> <the19...@googlemail.com> wrote:
>
> > >> >default wrote:
> > >> >> On Thu, 14 Feb 2008 15:45:31 -0800 (PST), "Dave.H"
> > >> >> <the19...@googlemail.com> wrote:
>
> > >> >> >I am looking at a number of FM transmitter circuits, purely as a
> > >> >> >project, but all of them use electret microphones as input. Would it
> > >> >> >be possible to replace this with an audio input for my iPod?
>
> > >> >> Of course. You wouldn't have stereo with a simple one or two
> > >> >> transistor transmitter - so you may also want to combine both channels
> > >> >> going in.
> > >> >\
>
> > >> >I understand that, but my radio receiver is a mono type anyway, so I'm
> > >> >not looking for a stereo version.
> > >> >> --
>
> > >> sorry I somehow got the idea that the Ipod would be the music source.
> > >> --
>
> > >iPod is the music source, it will be broadcasting to the mono radio. I
> > >will use that circuit I linked to before, seems to have the audio
> > >channels combined by 10K resistors so I don't have to worry about
> > >that. Even though I've already got a device that combines left and
> > >right with 1.8K resistors.
>
> > You have a better idea of what you are doing than I do. The Ipod
> > output has to (should) be mixed to drive the transmitter with the
> > contents of both channels. That can be as simple as two resistors
> > from each channel to a common input.
>
> > Not aware of the circuit you linked to before. You aren't referring
> > to the one where you ground the two signals to control volume are you?
> > --
>
> No, the one @http://www.techlib.com/Karen/radio.htm#FM%20Transmitter

The article linked to previously mentioned using a 5-20 pF trimmer cap
instead of a fixed capacitor. What capacitor do I need to replace to
install a 4.2pF-20pF trimmer? This would make it easier to tune.

On Feb 16, 12:16 am, default <defa...@defaulter.net> wrote:
> On Fri, 15 Feb 2008 04:56:18 -0800 (PST), "Dave.H"
>
>
>
> <the19...@googlemail.com> wrote:
> >On Feb 15, 2:18 pm, "Dave.H" <the19...@googlemail.com> wrote:
> >> On Feb 15, 1:52 pm, default <defa...@defaulter.net> wrote:
>
> >> > On Thu, 14 Feb 2008 18:38:55 -0800 (PST), "Dave.H"
>
> >> > <the19...@googlemail.com> wrote:
> >> > >On Feb 15, 1:20 pm, default <defa...@defaulter.net> wrote:
> >> > >> On Thu, 14 Feb 2008 18:15:00 -0800 (PST), "Dave.H"
>
> >> > >> <the19...@googlemail.com> wrote:
>
> >> > >> >default wrote:
> >> > >> >> On Thu, 14 Feb 2008 15:45:31 -0800 (PST), "Dave.H"
> >> > >> >> <the19...@googlemail.com> wrote:
>
> >> > >> >> >I am looking at a number of FM transmitter circuits, purely as a
> >> > >> >> >project, but all of them use electret microphones as input. Would it
> >> > >> >> >be possible to replace this with an audio input for my iPod?
>
> >> > >> >> Of course. You wouldn't have stereo with a simple one or two
> >> > >> >> transistor transmitter - so you may also want to combine both channels
> >> > >> >> going in.
> >> > >> >\
>
> >> > >> >I understand that, but my radio receiver is a mono type anyway, so I'm
> >> > >> >not looking for a stereo version.
> >> > >> >> --
>
> >> > >> sorry I somehow got the idea that the Ipod would be the music source.
> >> > >> --
>
> >> > >iPod is the music source, it will be broadcasting to the mono radio. I
> >> > >will use that circuit I linked to before, seems to have the audio
> >> > >channels combined by 10K resistors so I don't have to worry about
> >> > >that. Even though I've already got a device that combines left and
> >> > >right with 1.8K resistors.
>
> >> > You have a better idea of what you are doing than I do. The Ipod
> >> > output has to (should) be mixed to drive the transmitter with the
> >> > contents of both channels. That can be as simple as two resistors
> >> > from each channel to a common input.
>
> >> > Not aware of the circuit you linked to before. You aren't referring
> >> > to the one where you ground the two signals to control volume are you?
> >> > --
>
> >> No, the one @http://www.techlib.com/Karen/radio.htm#FM%20Transmitter
>
> >The article linked to previously mentioned using a 5-20 pF trimmer cap
> >instead of a fixed capacitor. What capacitor do I need to replace to
> >install a 4.2pF-20pF trimmer? This would make it easier to tune.
>
> The 12 pf cap is the tank circuit tuning cap; spreading or
> compressing the coil will also tune it.
>
> The 3 pf is a feedback cap and gets it oscillating. The .01 is a
> bypass cap and not critical to anything. The 1 nf on the base is a
> bypass but will affect audio frequency's as well.
> --

So if I got this right, I replace the 12 pF?

On Fri, 15 Feb 2008 04:56:18 -0800 (PST), "Dave.H"
<the1930s@googlemail.com> wrote:

>On Feb 15, 2:18 pm, "Dave.H" <the19...@googlemail.com> wrote:
>> On Feb 15, 1:52 pm, default <defa...@defaulter.net> wrote:
>>
>>
>>
>> > On Thu, 14 Feb 2008 18:38:55 -0800 (PST), "Dave.H"
>>
>> > <the19...@googlemail.com> wrote:
>> > >On Feb 15, 1:20 pm, default <defa...@defaulter.net> wrote:
>> > >> On Thu, 14 Feb 2008 18:15:00 -0800 (PST), "Dave.H"
>>
>> > >> <the19...@googlemail.com> wrote:
>>
>> > >> >default wrote:
>> > >> >> On Thu, 14 Feb 2008 15:45:31 -0800 (PST), "Dave.H"
>> > >> >> <the19...@googlemail.com> wrote:
>>
>> > >> >> >I am looking at a number of FM transmitter circuits, purely as a
>> > >> >> >project, but all of them use electret microphones as input. Would it
>> > >> >> >be possible to replace this with an audio input for my iPod?
>>
>> > >> >> Of course. You wouldn't have stereo with a simple one or two
>> > >> >> transistor transmitter - so you may also want to combine both channels
>> > >> >> going in.
>> > >> >\
>>
>> > >> >I understand that, but my radio receiver is a mono type anyway, so I'm
>> > >> >not looking for a stereo version.
>> > >> >> --
>>
>> > >> sorry I somehow got the idea that the Ipod would be the music source.
>> > >> --
>>
>> > >iPod is the music source, it will be broadcasting to the mono radio. I
>> > >will use that circuit I linked to before, seems to have the audio
>> > >channels combined by 10K resistors so I don't have to worry about
>> > >that. Even though I've already got a device that combines left and
>> > >right with 1.8K resistors.
>>
>> > You have a better idea of what you are doing than I do. The Ipod
>> > output has to (should) be mixed to drive the transmitter with the
>> > contents of both channels. That can be as simple as two resistors
>> > from each channel to a common input.
>>
>> > Not aware of the circuit you linked to before. You aren't referring
>> > to the one where you ground the two signals to control volume are you?
>> > --
>>
>> No, the one @http://www.techlib.com/Karen/radio.htm#FM%20Transmitter
>
>The article linked to previously mentioned using a 5-20 pF trimmer cap
>instead of a fixed capacitor. What capacitor do I need to replace to
>install a 4.2pF-20pF trimmer? This would make it easier to tune.

The 12 pf cap is the tank circuit tuning cap; spreading or
compressing the coil will also tune it.

The 3 pf is a feedback cap and gets it oscillating. The .01 is a
bypass cap and not critical to anything. The 1 nf on the base is a
bypass but will affect audio frequency's as well.
--

On Fri, 15 Feb 2008 05:21:19 -0800 (PST), "Dave.H"
<the1930s@googlemail.com> wrote:

>On Feb 16, 12:16 am, default <defa...@defaulter.net> wrote:
>> On Fri, 15 Feb 2008 04:56:18 -0800 (PST), "Dave.H"
>>
>>
>>
>> <the19...@googlemail.com> wrote:
>> >On Feb 15, 2:18 pm, "Dave.H" <the19...@googlemail.com> wrote:
>> >> On Feb 15, 1:52 pm, default <defa...@defaulter.net> wrote:
>>
>> >> > On Thu, 14 Feb 2008 18:38:55 -0800 (PST), "Dave.H"
>>
>> >> > <the19...@googlemail.com> wrote:
>> >> > >On Feb 15, 1:20 pm, default <defa...@defaulter.net> wrote:
>> >> > >> On Thu, 14 Feb 2008 18:15:00 -0800 (PST), "Dave.H"
>>
>> >> > >> <the19...@googlemail.com> wrote:
>>
>> >> > >> >default wrote:
>> >> > >> >> On Thu, 14 Feb 2008 15:45:31 -0800 (PST), "Dave.H"
>> >> > >> >> <the19...@googlemail.com> wrote:
>>
>> >> > >> >> >I am looking at a number of FM transmitter circuits, purely as a
>> >> > >> >> >project, but all of them use electret microphones as input. Would it
>> >> > >> >> >be possible to replace this with an audio input for my iPod?
>>
>> >> > >> >> Of course. You wouldn't have stereo with a simple one or two
>> >> > >> >> transistor transmitter - so you may also want to combine both channels
>> >> > >> >> going in.
>> >> > >> >\
>>
>> >> > >> >I understand that, but my radio receiver is a mono type anyway, so I'm
>> >> > >> >not looking for a stereo version.
>> >> > >> >> --
>>
>> >> > >> sorry I somehow got the idea that the Ipod would be the music source.
>> >> > >> --
>>
>> >> > >iPod is the music source, it will be broadcasting to the mono radio. I
>> >> > >will use that circuit I linked to before, seems to have the audio
>> >> > >channels combined by 10K resistors so I don't have to worry about
>> >> > >that. Even though I've already got a device that combines left and
>> >> > >right with 1.8K resistors.
>>
>> >> > You have a better idea of what you are doing than I do. The Ipod
>> >> > output has to (should) be mixed to drive the transmitter with the
>> >> > contents of both channels. That can be as simple as two resistors
>> >> > from each channel to a common input.
>>
>> >> > Not aware of the circuit you linked to before. You aren't referring
>> >> > to the one where you ground the two signals to control volume are you?
>> >> > --
>>
>> >> No, the one @http://www.techlib.com/Karen/radio.htm#FM%20Transmitter
>>
>> >The article linked to previously mentioned using a 5-20 pF trimmer cap
>> >instead of a fixed capacitor. What capacitor do I need to replace to
>> >install a 4.2pF-20pF trimmer? This would make it easier to tune.
>>
>> The 12 pf cap is the tank circuit tuning cap; spreading or
>> compressing the coil will also tune it.
>>
>> The 3 pf is a feedback cap and gets it oscillating. The .01 is a
>> bypass cap and not critical to anything. The 1 nf on the base is a
>> bypass but will affect audio frequency's as well.
>> --
>
>So if I got this right, I replace the 12 pF?

Yes, put a variable in place of it. The plate of the variable that
the adjustment screwdriver touches should be the ground side so the
adjustment tool doesn't cause it to change freq..

Just look at the cap to determine which side should be ground, It is
normally obvious.
--

On Feb 16, 12:27 am, default <defa...@defaulter.net> wrote:
> On Fri, 15 Feb 2008 05:21:19 -0800 (PST), "Dave.H"
>
>
>
> <the19...@googlemail.com> wrote:
> >On Feb 16, 12:16 am, default <defa...@defaulter.net> wrote:
> >> On Fri, 15 Feb 2008 04:56:18 -0800 (PST), "Dave.H"
>
> >> <the19...@googlemail.com> wrote:
> >> >On Feb 15, 2:18 pm, "Dave.H" <the19...@googlemail.com> wrote:
> >> >> On Feb 15, 1:52 pm, default <defa...@defaulter.net> wrote:
>
> >> >> > On Thu, 14 Feb 2008 18:38:55 -0800 (PST), "Dave.H"
>
> >> >> > <the19...@googlemail.com> wrote:
> >> >> > >On Feb 15, 1:20 pm, default <defa...@defaulter.net> wrote:
> >> >> > >> On Thu, 14 Feb 2008 18:15:00 -0800 (PST), "Dave.H"
>
> >> >> > >> <the19...@googlemail.com> wrote:
>
> >> >> > >> >default wrote:
> >> >> > >> >> On Thu, 14 Feb 2008 15:45:31 -0800 (PST), "Dave.H"
> >> >> > >> >> <the19...@googlemail.com> wrote:
>
> >> >> > >> >> >I am looking at a number of FM transmitter circuits, purely as a
> >> >> > >> >> >project, but all of them use electret microphones as input. Would it
> >> >> > >> >> >be possible to replace this with an audio input for my iPod?
>
> >> >> > >> >> Of course. You wouldn't have stereo with a simple one or two
> >> >> > >> >> transistor transmitter - so you may also want to combine both channels
> >> >> > >> >> going in.
> >> >> > >> >\
>
> >> >> > >> >I understand that, but my radio receiver is a mono type anyway, so I'm
> >> >> > >> >not looking for a stereo version.
> >> >> > >> >> --
>
> >> >> > >> sorry I somehow got the idea that the Ipod would be the music source.
> >> >> > >> --
>
> >> >> > >iPod is the music source, it will be broadcasting to the mono radio. I
> >> >> > >will use that circuit I linked to before, seems to have the audio
> >> >> > >channels combined by 10K resistors so I don't have to worry about
> >> >> > >that. Even though I've already got a device that combines left and
> >> >> > >right with 1.8K resistors.
>
> >> >> > You have a better idea of what you are doing than I do. The Ipod
> >> >> > output has to (should) be mixed to drive the transmitter with the
> >> >> > contents of both channels. That can be as simple as two resistors
> >> >> > from each channel to a common input.
>
> >> >> > Not aware of the circuit you linked to before. You aren't referring
> >> >> > to the one where you ground the two signals to control volume are you?
> >> >> > --
>
> >> >> No, the one @http://www.techlib.com/Karen/radio.htm#FM%20Transmitter
>
> >> >The article linked to previously mentioned using a 5-20 pF trimmer cap
> >> >instead of a fixed capacitor. What capacitor do I need to replace to
> >> >install a 4.2pF-20pF trimmer? This would make it easier to tune.
>
> >> The 12 pf cap is the tank circuit tuning cap; spreading or
> >> compressing the coil will also tune it.
>
> >> The 3 pf is a feedback cap and gets it oscillating. The .01 is a
> >> bypass cap and not critical to anything. The 1 nf on the base is a
> >> bypass but will affect audio frequency's as well.
> >> --
>
> >So if I got this right, I replace the 12 pF?
>
> Yes, put a variable in place of it. The plate of the variable that
> the adjustment screwdriver touches should be the ground side so the
> adjustment tool doesn't cause it to change freq..
>
> Just look at the cap to determine which side should be ground, It is
> normally obvious.
> --

Thanks, I don't really like the idea of fiddling with the coil, I like
to leave coils alone. The trimmer I'm going to use is a PCB mount
one, from Dick Smith of course Cat # R2945

On Feb 16, 12:32 am, "Dave.H" <the19...@googlemail.com> wrote:
> On Feb 16, 12:27 am, default <defa...@defaulter.net> wrote:
>
>
>
> > On Fri, 15 Feb 2008 05:21:19 -0800 (PST), "Dave.H"
>
> > <the19...@googlemail.com> wrote:
> > >On Feb 16, 12:16 am, default <defa...@defaulter.net> wrote:
> > >> On Fri, 15 Feb 2008 04:56:18 -0800 (PST), "Dave.H"
>
> > >> <the19...@googlemail.com> wrote:
> > >> >On Feb 15, 2:18 pm, "Dave.H" <the19...@googlemail.com> wrote:
> > >> >> On Feb 15, 1:52 pm, default <defa...@defaulter.net> wrote:
>
> > >> >> > On Thu, 14 Feb 2008 18:38:55 -0800 (PST), "Dave.H"
>
> > >> >> > <the19...@googlemail.com> wrote:
> > >> >> > >On Feb 15, 1:20 pm, default <defa...@defaulter.net> wrote:
> > >> >> > >> On Thu, 14 Feb 2008 18:15:00 -0800 (PST), "Dave.H"
>
> > >> >> > >> <the19...@googlemail.com> wrote:
>
> > >> >> > >> >default wrote:
> > >> >> > >> >> On Thu, 14 Feb 2008 15:45:31 -0800 (PST), "Dave.H"
> > >> >> > >> >> <the19...@googlemail.com> wrote:
>
> > >> >> > >> >> >I am looking at a number of FM transmitter circuits, purely as a
> > >> >> > >> >> >project, but all of them use electret microphones as input. Would it
> > >> >> > >> >> >be possible to replace this with an audio input for my iPod?
>
> > >> >> > >> >> Of course. You wouldn't have stereo with a simple one or two
> > >> >> > >> >> transistor transmitter - so you may also want to combine both channels
> > >> >> > >> >> going in.
> > >> >> > >> >\
>
> > >> >> > >> >I understand that, but my radio receiver is a mono type anyway, so I'm
> > >> >> > >> >not looking for a stereo version.
> > >> >> > >> >> --
>
> > >> >> > >> sorry I somehow got the idea that the Ipod would be the music source.
> > >> >> > >> --
>
> > >> >> > >iPod is the music source, it will be broadcasting to the mono radio. I
> > >> >> > >will use that circuit I linked to before, seems to have the audio
> > >> >> > >channels combined by 10K resistors so I don't have to worry about
> > >> >> > >that. Even though I've already got a device that combines left and
> > >> >> > >right with 1.8K resistors.
>
> > >> >> > You have a better idea of what you are doing than I do. The Ipod
> > >> >> > output has to (should) be mixed to drive the transmitter with the
> > >> >> > contents of both channels. That can be as simple as two resistors
> > >> >> > from each channel to a common input.
>
> > >> >> > Not aware of the circuit you linked to before. You aren't referring
> > >> >> > to the one where you ground the two signals to control volume are you?
> > >> >> > --
>
> > >> >> No, the one @http://www.techlib.com/Karen/radio.htm#FM%20Transmitter
>
> > >> >The article linked to previously mentioned using a 5-20 pF trimmer cap
> > >> >instead of a fixed capacitor. What capacitor do I need to replace to
> > >> >install a 4.2pF-20pF trimmer? This would make it easier to tune.
>
> > >> The 12 pf cap is the tank circuit tuning cap; spreading or
> > >> compressing the coil will also tune it.
>
> > >> The 3 pf is a feedback cap and gets it oscillating. The .01 is a
> > >> bypass cap and not critical to anything. The 1 nf on the base is a
> > >> bypass but will affect audio frequency's as well.
> > >> --
>
> > >So if I got this right, I replace the 12 pF?
>
> > Yes, put a variable in place of it. The plate of the variable that
> > the adjustment screwdriver touches should be the ground side so the
> > adjustment tool doesn't cause it to change freq..
>
> > Just look at the cap to determine which side should be ground, It is
> > normally obvious.
> > --
>
> Thanks, I don't really like the idea of fiddling with the coil, I like
> to leave coils alone. The trimmer I'm going to use is a PCB mount
> one, from Dick Smith of course Cat # R2945

The website also mentions replacing a 10K resistor, with a pot. Would
I need this if I drive the transmitter from an ipod headphone output,
and if so, what resistor should be removed? There are 5 10k units
there.

On Sat, 16 Feb 2008 03:01:28 -0800 (PST), "Dave.H"
<the1930s@googlemail.com> wrote:

>
>The website also mentions replacing a 10K resistor, with a pot. Would
>I need this if I drive the transmitter from an ipod headphone output,
>and if so, what resistor should be removed? There are 5 10k units
>there.

You see the vertical resistor just on the input where the LR channels
come together? Put a 10K pot in place of it, with the junction of the
LR 10K's to the full clockwise position and ground on the CCW
position. Change the position of the 100 nf to the wiper of the pot
so it connects there and nowhere else.


--

On Feb 17, 12:28 am, default <defa...@defaulter.net> wrote:
> On Sat, 16 Feb 2008 03:01:28 -0800 (PST), "Dave.H"
>
> <the19...@googlemail.com> wrote:
>
> >The website also mentions replacing a 10K resistor, with a pot. Would
> >I need this if I drive the transmitter from an ipod headphone output,
> >and if so, what resistor should be removed? There are 5 10k units
> >there.
>
> You see the vertical resistor just on the input where the LR channels
> come together? Put a 10K pot in place of it, with the junction of the
> LR 10K's to the full clockwise position and ground on the CCW
> position. Change the position of the 100 nf to the wiper of the pot
> so it connects there and nowhere else.
>
> --

OK thanks, I assume it doesn't matter if I use a linear taper or audio
taper? I want to use a linear taper.

On Feb 17, 12:35 am, "Dave.H" <the19...@googlemail.com> wrote:
> On Feb 17, 12:28 am, default <defa...@defaulter.net> wrote:
>
>
>
> > On Sat, 16 Feb 2008 03:01:28 -0800 (PST), "Dave.H"
>
> > <the19...@googlemail.com> wrote:
>
> > >The website also mentions replacing a 10K resistor, with a pot. Would
> > >I need this if I drive the transmitter from an ipod headphone output,
> > >and if so, what resistor should be removed? There are 5 10k units
> > >there.
>
> > You see the vertical resistor just on the input where the LR channels
> > come together? Put a 10K pot in place of it, with the junction of the
> > LR 10K's to the full clockwise position and ground on the CCW
> > position. Change the position of the 100 nf to the wiper of the pot
> > so it connects there and nowhere else.
>
> > --
>
> OK thanks, I assume it doesn't matter if I use a linear taper or audio
> taper? I want to use a linear taper.

I've got a 10K audio taper pot. Will that also work.

On Sat, 16 Feb 2008 05:35:17 -0800 (PST), "Dave.H"
<the1930s@googlemail.com> wrote:

>On Feb 17, 12:28 am, default <defa...@defaulter.net> wrote:
>> On Sat, 16 Feb 2008 03:01:28 -0800 (PST), "Dave.H"
>>
>> <the19...@googlemail.com> wrote:
>>
>> >The website also mentions replacing a 10K resistor, with a pot. Would
>> >I need this if I drive the transmitter from an ipod headphone output,
>> >and if so, what resistor should be removed? There are 5 10k units
>> >there.
>>
>> You see the vertical resistor just on the input where the LR channels
>> come together? Put a 10K pot in place of it, with the junction of the
>> LR 10K's to the full clockwise position and ground on the CCW
>> position. Change the position of the 100 nf to the wiper of the pot
>> so it connects there and nowhere else.
>>
>> --
>
>OK thanks, I assume it doesn't matter if I use a linear taper or audio
>taper? I want to use a linear taper.

It doesn't matter to me . . . Seriously: If you anticipate using it
frequently to adjust volume you might be happier with an audio taper
pot. If you set it once and forget about it, it hardly matters.

The question is how constant is the volume from the 'pod? If you
think the control on your receiver is good enough to compensate use a
linear.

It doesn't matter one way or the other - it just "feels" right when
you use an audio pot for audio signals. I put a linear pot into a
stereo I built at my office/shop where I was working. It had 50 W a
channel and was too much for the little office but everyone who used
the control said it "didn't have enough volume." Never bothered me
though.
--

On Sat, 16 Feb 2008 05:46:44 -0800 (PST), "Dave.H"
<the1930s@googlemail.com> wrote:

>I've got a 10K audio taper pot. Will that also work.

It will
--

On Feb 17, 12:52 am, default <defa...@defaulter.net> wrote:
> On Sat, 16 Feb 2008 05:46:44 -0800 (PST), "Dave.H"
>
> <the19...@googlemail.com> wrote:
> >I've got a 10K audio taper pot. Will that also work.
>
> It will
> --

OK. I hope to get this transmitter up and running today. I will post
here with the results.