A/c/r speaker question.

[Tinman]

This is regarding some alarm clock radios I have (I collect various models).
They're all from the late 70s & early 80s.
For some reason when some (not all) of the AM/FM radio alarms go off, they have an initial pop sound through the speaker.
I've recapped them and tried a 10uf cap on the speaker to try and filter the pop out, it does lessen it but it's still there.
I've had numerous radios and boomboxes do this when powered on but it's less noticeable when you're already awake.
The all work well but this is an annoyance I'd like to get rid of if possible.
I'm assuming it's an initial surge to the speaker that needs to be bled off.
Does anyone have any ides what would cause the pop and/or what I could do to get rid of it?

 

[Ken]

This is regarding some alarm clock radios I have (I collect various models).
They're all from the late 70s & early 80s.
For some reason when some (not all) of the AM/FM radio alarms go off, they have an initial pop sound through the speaker.
I've recapped them and tried a 10uf cap on the speaker to try and filter the pop out, it does lessen it but it's still there.
I've had numerous radios and boomboxes do this when powered on but it's less noticeable when you're already awake.
The all work well but this is an annoyance I'd like to get rid of if possible.
I'm assuming it's an initial surge to the speaker that needs to be bled off.
Does anyone have any ides what would cause the pop and/or what I could do to get rid of it?

It depends. When you hear the POP, where is the volume control set? Try it with the volume control off. If you still hear a POP, then it is likely in the output stages of the amp. If you don't hear a POP with the volume turned down, its likely the problem originates in the pre-amp stages. Most radios and stereos have a relay and delay so that the sound doesn’t come on until the amp is powered up, you turn on the amp, it’s silent for a few seconds, then the volume comes on at whatever level it is set to and you don’t hear the sudden charge of a capacitor. If that relay/delay is malfunctioning you will get that POP you speak of. You might be stuck with it as normal operation of the particular circuit design as a clock radio isn’t going to have a lot of high quality parts, especially after the years yours are from. The Japanese economy started its current mess in the early 80s, and its first and foremost effect for most of us was the beginning of the use in manufacturing of electronic parts that were of far less quality, to lower productio costs.
For instance, that 100 ohm resistor with a tolerance of +/- 1% became a 100 ohm resistor with a tolerance of +/- 10%.
Thats why audio components before the mid 80s are so valuable and sought after. They are simply made of better, more accurate, discrete components.

That’s why what we collect is of such value. It’s not that boomboxes aren’t made any more, it’s that they CAN’T be made anymore, at least at anything less than an astronomical price point. It’s also why with what someone like me considers to be a tiny bit of work, they sound like they are brand new.

 

[Tinman]

The pop is when the volume is at normal listening level, none when completely off.
I keep it a little lower to wake up to.
I've read about there being a delay in some equipment, makes sense.
I'm wondering:
If I use a physically larger capacitor in the speaker path (C62 and C60), would that do anything to dissipate some of the pop better than a physically smaller cap?
The schematic is of the one model of radio that has a resistor (R61) and I assume the coil of wire around it is labeled "part of R61".
I've never seen a resistor like that (pic of R61 below).
The other model has the speaker connected directly to ground and it doesn't pop like the one with R61 resistor.

 

[hopey]

does it have a pot with power switch included? could be bad contacts try to bypass.

 

[Tinman]

does it have a pot with power switch included? could be bad contacts try to bypass.

No, it doesn't.
I did try the two larger size caps on my last radio and it isn't popping on start up.
I can't say for sure if the larger caps are why but I have another radio and I'm going to try them again.
C60 is the small cap below R61 in the pic above.

 

[hopey]

Ground fault loop. Good luck.