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 Post subject: Almost successful aux. input on 1968 Philco-Ford 8TPO
PostPosted: Nov Fri 27, 2020 7:58 pm 
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I've avoided coming for help as long as I could, but at this point I'm going in circles on this problem.

Long story short, a long time ago when I knew much less about radios I wired an auxiliary input into the stock AM radio in my daily driver 1968 Ford Falcon. But I didn't do it right in several aspects, and it's taken me 8 years to get back around to trying to fix it and wire it up the "correct" way.

The problem is, I cannot figure out the "correct way." The wiring in this radio is a mix of point to point and circuit boards, which makes it more difficult to mess with since I'm used to older vacuum tube stuff.

There is a small board soldered directly to the volume and tone pots, and I have tried tapping into all of the wires coming from it. The Black wire is the ground, which I have connected to the ground on a switching 3.5mm TS socket. The White wire just goes straight from the wiper of the volume pot to the amplifier circuitry on the main board, this is what I had connected the tip of the TS socket to years ago, which did produce listenable volume, but obviously made the volume and tone controls on the radio ineffective when the aux was plugged in. The only wire left going to the volume control panel is the Green wire, which seems to me that it should be the wire carrying the signal from the AM radio circuitry to the volume control. But when I spliced the TS connector into this wire so that plugging a cable in would disconnect the AM circuit and switch to my iPhone, I can only very faintly hear why is playing on the iPhone, and the volume is completely unaffected by the volume knob.

What the heck am I doing wrong?

Here's pictures of everything.

Image

Image

Image

This is how I currently have the audio jack hooked up to the wires between the volume board and the main board, and it doesn't work at all.

Image


I think I probably shouldn't be sharing the wiring diagram, so I'll delete those images when I get this working or get an answer. EDIT: I did take the wiring diagram images down since I'm shelving this project for the moment.


Last edited by GreyHawkins on Dec Tue 01, 2020 11:49 pm, edited 2 times in total.

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 Post subject: Re: Almost successful aux. input on 1968 Philco-Ford 8TPO
PostPosted: Nov Fri 27, 2020 8:25 pm 
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You need a switch to isolate the radio.

Disconnect the green. The common of the switch goes to the volume board, the NC and NO go to the green and iPhone signals.

If you don't use the radio, disconnect the green and connect the iPhone signal to the volume board where the green was.

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 Post subject: Re: Almost successful aux. input on 1968 Philco-Ford 8TPO
PostPosted: Nov Fri 27, 2020 10:11 pm 
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If you are using a stereo source, like a smart phone or i-pod, you need to combine L and R channels to create a mono source to go to the switch Steve mentioned.
Two 20 ohm resistors will work for this.

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 Post subject: Re: Almost successful aux. input on 1968 Philco-Ford 8TPO
PostPosted: Nov Sat 28, 2020 12:57 am 
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I do have the L and R channels tied together with 100 Ω resistors in a separate dongle I made that plugs into the audio socket on the radio, so there shouldn't be an issue with a stereo signal.

If I'm understanding SHenion correctly, I think the way I have it wired up now is functionally the same as what you're describing. The audio socket i have wired in right now is a switching one. So with nothing plugged in the signal on the green wire passes unobstructed, but when something is plugged in the signal from the main board is disconnected and the positive signal from the (mono converted) iPhone signal is fed into the volume board instead.

With it set up that way though, I can only faintly hear the audio from the iPhone, and volume pot has no effect on the very low volume. It seems like this should be the easy solution, but it doesn't work for some reason.


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 Post subject: Re: Almost successful aux. input on 1968 Philco-Ford 8TPO
PostPosted: Nov Sat 28, 2020 2:54 am 
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Your description of how it should work sounds correct. What is happening may be something else. Do you have a way to trace an audio signal through the circuit?
I like to use the audio test tone app I have on my phone (freebee) for testing auxiliary inputs circuits.
You could load the app on your device and use a digital voltmeter on AC volts to see where you are losing the signal.

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 Post subject: Re: Almost successful aux. input on 1968 Philco-Ford 8TPO
PostPosted: Nov Sat 28, 2020 3:49 am 
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I would:
a) interrupt the white instead of the green. You are already bypassing the volume control, so it's no surprise the volume is having no effect. If you pull the jack out while it's on there will be a full-blast pop.
b) as the schematic suggests for testing, decouple your input with a .1uF cap, if you don't already have one in your dongle.
The way you have it connected should have worked somewhat, but it appears from your drawing you may have the two greens backwards - connecting the tip back to the volume board instead of the input of the amplifier.

Joe


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 Post subject: Re: Almost successful aux. input on 1968 Philco-Ford 8TPO
PostPosted: Nov Sat 28, 2020 3:58 am 
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I think Joe is right. Looking at the schematic, the volume control works a little differently then most old tube radios, where you would break the signal lead at the high side of the volume control. On this car radio, you need to come in through the wiper of the VC, which is the white lead.

I think you should try connecting it like shown below.

Attachment:
Aux in.jpg
Aux in.jpg [ 172.77 KiB | Viewed 683 times ]

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Last edited by processhead on Nov Sat 28, 2020 6:17 pm, edited 2 times in total.

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 Post subject: Re: Almost successful aux. input on 1968 Philco-Ford 8TPO
PostPosted: Nov Sat 28, 2020 4:03 am 
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The schematic does not match the board.

The white goes to the wiper of the pot, the green goes to one end. Look at the bottom view.

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 Post subject: Re: Almost successful aux. input on 1968 Philco-Ford 8TPO
PostPosted: Nov Sat 28, 2020 11:02 pm 
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Okay I think I've got something to go on now. I was so fixated on the idea that the signal went from the wiper to the amplifier that I misread the rest of the circuit. So what you're saying - and what I'm seeing now that I'm looking at it with fresh eyes - is that the signal actually comes into the volume board through the wiper, and goes to the amplifier circuit through the green wire.

I'll try wiring it up that way to see if it works.

When I decouple the input with .1uF caps, should I use ones on the positive and negative leads, or just one on the positive? I'll have to see if I have extras sitting around, I generally buy caps on a per-project basis.


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 Post subject: Re: Almost successful aux. input on 1968 Philco-Ford 8TPO
PostPosted: Nov Sun 29, 2020 1:18 am 
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You'll only need a cap on the positive lead. Anything near that value should work fine - .22, .47 up to 1uf.

Joe


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 Post subject: Re: Almost successful aux. input on 1968 Philco-Ford 8TPO
PostPosted: Nov Sun 29, 2020 1:38 am 
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Probably 99% radio will need at least the three section filter cap, likely all electrolytics.
The 9TPO in my '69 Fairlane would cut all sorts of shenanigans till it was replaced.

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 Post subject: Re: Almost successful aux. input on 1968 Philco-Ford 8TPO
PostPosted: Nov Sun 29, 2020 4:22 am 
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Great, good to know. Thanks.

I'm prepared to tackle recapping this radio when the time comes. So far it still performs well when it's playing just AM. It has developed a quiet engine speed related buzz, and if replacing the filter capacitor in the engine bay doesn't fix it I suppose I will be digging into the electrolytics in the radio itself. I've got one on the way so I'll be finding out soon.


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 Post subject: Re: Almost successful aux. input on 1968 Philco-Ford 8TPO
PostPosted: Nov Sun 29, 2020 8:22 pm 
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A new development. I wired it up like processhead suggested, and it still doesn't produce any sound when the jack is plugged in. However, it does play the iPhone's audio clearly when the jack is plugged in just enough to be grounded and make contact with the white wire, but not disconnect the radio circuit from the volume board. As soon as it goes into the socket enough to fully switch the input all audio stops.

Basically if the iPhone is trying to play over top of the radio signal, it works. But it doesn't work if the radio is disconnected and the iPhone is the only source.

I tried decoupling the input with an old leaky .1uf capacitor I had laying around, and the behavior of the whole thing was exactly the same other than that the tone was a little tinnier and the iPhone signal played a little better with the volume knob. But it still didn't work unless the iPhone was being played over top of the radio signal.

I have no idea why the iPhone has to be played over top of the radio signal, and why all audio stops if I disconnect the radio circuit.

processhead wrote:
I think Joe is right. Looking at the schematic, the volume control works a little differently then most old tube radios, where you would break the signal lead at the high side of the volume control. On this car radio, you need to come in through the wiper of the VC, which is the white lead.

I think you should try connecting it like shown below.

Attachment:
Aux in.jpg


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 Post subject: Re: Almost successful aux. input on 1968 Philco-Ford 8TPO
PostPosted: Nov Sun 29, 2020 11:15 pm 
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GreyHawkins wrote:
A new development. I wired it up like processhead suggested, and it still doesn't produce any sound when the jack is plugged in. However, it does play the iPhone's audio clearly when the jack is plugged in just enough to be grounded and make contact with the white wire, but not disconnect the radio circuit from the volume board. As soon as it goes into the socket enough to fully switch the input all audio stops.

Basically if the iPhone is trying to play over top of the radio signal, it works. But it doesn't work if the radio is disconnected and the iPhone is the only source.

I tried decoupling the input with an old leaky .1uf capacitor I had laying around, and the behavior of the whole thing was exactly the same other than that the tone was a little tinnier and the iPhone signal played a little better with the volume knob. But it still didn't work unless the iPhone was being played over top of the radio signal.

I have no idea why the iPhone has to be played over top of the radio signal, and why all audio stops if I disconnect the radio circuit.

processhead wrote:
I think Joe is right. Looking at the schematic, the volume control works a little differently then most old tube radios, where you would break the signal lead at the high side of the volume control. On this car radio, you need to come in through the wiper of the VC, which is the white lead.

I think you should try connecting it like shown below.

Attachment:
Aux in.jpg


Sounds like progress.

Is it possible the switch in the 3.5 mm jack you are using is not connected properly or possibly malfunctioning? The ones I use have multiple contacts and using the wrong combination won't disconnect the radio audio and properly couple through the auxiliary input audio.

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 Post subject: Re: Almost successful aux. input on 1968 Philco-Ford 8TPO
PostPosted: Nov Mon 30, 2020 6:23 pm 
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The switch itself is connected properly, I even double checked it by just hooking everything up with alligator clips and skipping the 3.5mm jack, and the behavior was the same. AM circuit connected to the volume board, and AM radio plays. AM circuit and iPhone connected to the volume board, and both play on top of each other. AM circuit disconnected and iPhone connected, no sound at all.

I got tired of the hole in my dashboard so I put the radio back together and put it back in. I'm going to keep thinking through this problem "on paper" until I feel like taking the radio out again. I'm going over the schematic over and over again trying to figure out why sending a signal from my phone to the amplification circuit is any different than when the AM circuit does the same. There are only two wires/traces connecting the amplification circuit to the rest of the radio circuitry. The green wire that brings an audio signal from the volume board, and a 9.8v trace that looks like the power supply to the radio circuitry. I tried bypassing the volume board entirely, disconnected the green wire from the volume board and hooked my iPhone up to the green wire, grounded it to the panel ground, and wasn't able to get any sound at all even going straight into the amplifier.


I have a few questions to help me continue:

The voltage leaving the N4 filter, heading through the white wire to the volume board is listed as 0. Is that because the schematic specifies that all voltages listed are with no signal? The expectation is that with any signal there would be measurable voltage there I assume.

I've been grounding the 3.5mm jack to the panel ground. I assumed that was correct, rather than grounding it to the chassis. I was afraid of damaging something if I tried grounding it to the chassis. Is there anything else I could try grounding to? I think that sounds like a dumb question, but I've tried most of my first guesses.

Am I wrong about the direction current is flowing in the wires around the volume control panel? I was assuming current flowed from the AM circuit to the volume board by the white wire, and from the volume board to the amplifier by the green amplifier. Looking at the schematic though, it's showing the resting voltage on the white wire as 0v, and the green wire as 0.6v, which makes it look like current flows to the volume board from both ends which doesn't make sense.


Sorry, I'm talking in circles because this should be such a simple thing to figure out but it's totally stumping me.


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 Post subject: Re: Almost successful aux. input on 1968 Philco-Ford 8TPO
PostPosted: Nov Mon 30, 2020 7:34 pm 
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GreyHawkins wrote:


I have a few questions to help me continue:

The voltage leaving the N4 filter, heading through the white wire to the volume board is listed as 0. Is that because the schematic specifies that all voltages listed are with no signal? The expectation is that with any signal there would be measurable voltage there I assume.

Almost all of the voltages listed on the schematic are DC voltages and not signal (AC) voltages.



I've been grounding the 3.5mm jack to the panel ground. I assumed that was correct, rather than grounding it to the chassis. I was afraid of damaging something if I tried grounding it to the chassis. Is there anything else I could try grounding to? I think that sounds like a dumb question, but I've tried most of my first guesses.

You are correct to use the ground on the volume control board, that's what you want


Am I wrong about the direction current is flowing in the wires around the volume control panel? I was assuming current flowed from the AM circuit to the volume board by the white wire, and from the volume board to the amplifier by the green amplifier. Looking at the schematic though, it's showing the resting voltage on the white wire as 0v, and the green wire as 0.6v, which makes it look like current flows to the volume board from both ends which doesn't make sense.

No DC current flows through the volume control board. As mentioned above, the voltages shown are DC voltages. The Signal flow (AC) through the volume control flows in through the white wire and out through the green wire.


Sorry, I'm talking in circles because this should be such a simple thing to figure out but it's totally stumping me.

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