Unkey TX speaker pop

[Shockwave]

If the delay were electronically controlled we could suspect things like a bad electrolytic. In these cases the delay is much more simple than that. It's a mechanical delay in the mic switch through the alignment of the contacts. This allows the RX connection to be broken before the transmit is turned on and the transmit connection to be broken before the speaker is connected.

The delay is controlled by how fast you can move your finger on the key switch rather than the charge or discharge time of a cap. The fix here is rather simple since you only have a pop when you unkey and not like a Tram where it's when you key and unkey. Just add another small single pole relay to control the receive mic wire that the roger beep is wired to now.

Wire the coil directly across the coil on the roger beep BUT place a diode in SERIES with the coil so current can only flow into the second coil. Now add an electrolytic between 47 and 220 uf across the second coil to delay its turn off with the receive control wire connected to the N.C. contacts. This first diode stops the cap from keeping the original TX relay on the roger beep keyed during the delay time so only the new relay is delayed. Add the normal inductive kickback diode across the second relay coil too.

 

[darklife]

If the delay were electronically controlled we could suspect things like a bad electrolytic. In these cases the delay is much more simple than that. It's a mechanical delay in the mic switch through the alignment of the contacts. This allows the RX connection to be broken before the transmit is turned on and the transmit connection to be broken before the speaker is connected.

The delay is controlled by how fast you can move your finger on the key switch rather than the charge or discharge time of a cap. The fix here is rather simple since you only have a pop when you unkey and not like a Tram where it's when you key and unkey. Just add another small single pole relay to control the receive mic wire that the roger beep is wired to now.

Wire the coil directly across the coil on the roger beep BUT place a diode in SERIES with the coil so current can only flow into the second coil. Now add an electrolytic between 47 and 220 uf across the second coil to delay its turn off with the receive control wire connected to the N.C. contacts. This first diode stops the cap from keeping the original TX relay on the roger beep keyed during the delay time so only the new relay is delayed. Add the normal inductive kickback diode across the second relay coil too.

Glad you understand what is going on and thank you everyone else for the tips and help.
Yeah I knew it had something to do with the time between the RX and TX contact in the mic jack since the original mic had a bit of space between going directly from TX to RX in the switch contacts which was fine with normal hand operation but if releasing the switch quickly on the PTT on the stock mic would have the same issue as the later installed relay in the roger beep.
For being a Uniden built radio they sure were not expecting any mods. All the internal TX/RX switching is done via diodes instead of the older relay method in 70s radios and earlier.
I reduced the thump of the speaker greatly to almost inaudible by just adding some resistance across the speaker to quiet it and compensate by increasing the volume which is fine with me because the internal speaker is far too loud for desk listening anyways even at low volume.

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One more thing and sorry if off topic but does anyone know any interesting mods to do to this old radio?
So far I added the roger two tone beep as mentioned (along with a thread about it here..), changed the primary audio stage transformer to something more beefy with the same ohm specs to increase the AF range on both receive and transmit for hifi sound. Original transformer covered 300hz to 3khz but outside of that it fell quickly, new transformer covers 100hz to around 5khz with the cutoff beginning at the IF filter in RX. So TX now covers <100hz to >5khz with some fall off outside. Sounds great using outboard compression and audio limiting with a bit of EQ at the mic end.
I can get decent HIFI AF out of this rig on both TX/RX.
Going to change the original lights with natural LEDs since the original bulbs are flaking out.
Added channel 24 by soldering in a chunk of wire across the slot in the tuner selector where the "blank" channel is.
Thinking about adding in a switch with a crystal socket on the butt for the LO freq. to increase channel coverage beyond the 24
channels.

One last time just to reduce confusion, the original issue the thread is about existed BEFORE any mods.

This is just a fun side project. I know there are far better radios to screw with but I am getting joy out of hotrodding this old rig.

 

[Osscott]

Glad you understand what is going on and thank you everyone else for the tips and help.
Yeah I knew it had something to do with the time between the RX and TX contact in the mic jack since the original mic had a bit of space between going directly from TX to RX in the switch contacts which was fine with normal hand operation but if releasing the switch quickly on the PTT on the stock mic would have the same issue as the later installed relay in the roger beep.
For being a Uniden built radio they sure were not expecting any mods. All the internal TX/RX switching is done via diodes instead of the older relay method in 70s radios and earlier.
I reduced the thump of the speaker greatly to almost inaudible by just adding some resistance across the speaker to quiet it and compensate by increasing the volume which is fine with me because the internal speaker is far too loud for desk listening anyways even at low volume.

--------------------------------------

One more thing and sorry if off topic but does anyone know any interesting mods to do to this old radio?
So far I added the roger two tone beep as mentioned (along with a thread about it here..), changed the primary audio stage transformer to something more beefy with the same ohm specs to increase the AF range on both receive and transmit for hifi sound. Original transformer covered 300hz to 3khz but outside of that it fell quickly, new transformer covers 100hz to around 5khz with the cutoff beginning at the IF filter in RX. So TX now covers <100hz to >5khz with some fall off outside. Sounds great using outboard compression and audio limiting with a bit of EQ at the mic end.
I can get decent HIFI AF out of this rig on both TX/RX.
Going to change the original lights with natural LEDs since the original bulbs are flaking out.
Added channel 24 by soldering in a chunk of wire across the slot in the tuner selector where the "blank" channel is.
Thinking about adding in a switch with a crystal socket on the butt for the LO freq. to increase channel coverage beyond the 24
channels.

One last time just to reduce confusion, the original issue the thread is about existed BEFORE any mods.

This is just a fun side project. I know there are far better radios to screw with but I am getting joy out of hotrodding this old rig.

Well this post is about a decade late but I thought I would share my solution to the popping sound when keying and unkeying. It reduced the volume to such a low level I consider it a very acceptable solution.

I tried many of the posted solutions but most addressed the symptom instead of root cause - at least in my use case. i.e. add resistors or caps in series or parallel with the speaker circuit. They all had marginal impact and mostly just reduced audio quality (low pass filter, etc.) which IMHO made them unacceptable solutions.

Our radios have an AF Power Amplifier IC. Mine was the Sanyo LA4422. They are typically mounted to a heat sink. It's input comes from the CB/PA audio circuit and the volume potentiometer controls the input signal. It's output goes to the speaker circuit.

I noticed, like others, that the pop volume was constant, irrespective of the volume control setting. So, that got me thinking if I could reduce the output gain of this amp, that should have the effect of also reducing the pop. Then, as with the posted solutions above, I would compensate with more input gain (increase the volume control).

I also noticed I could barely open the volume control, before the volume was actually too loud to which to listen. I could never open the volume more than 15% without distortion. That didn't seem right. This excessive AF amp output gain also appeared to impact the squelch in that when the squelch threshold was reached and the volume should be 100% attenuated, I could still hear the audio, albeit much lower, but not 100% silent. AF was still bleeding through a bit.

So, here is my solution....

These AF Amp ICs typically have an external control for AF output gain. In my case, the LA4422 uses pin 5 in this capacity. Similar amps will have some sort of control pin or may even use varying the Vcc input voltage in this regard.

The designer of the Pacific SSB-800, the radio I corrected, apparently thought it best to not add any resistance here at all. This left the amp at wide open maximum AF output gain voltage. I suspected this may have caused the many issues noted above.

I cut the PCB between pin 5 and the electrolytic cap which went to ground and inserted a 10K potentiometer to find the "sweet spot" resistance.

- At 0K it was full volume as expected.
- At 3.8K the AF gain was clearly reduced, and to a level of my liking.
- Past 5K this introduced distortion and noise. The amp didn't like that.

So now the test at 3.8K:

- The volume knob at 30% open now provided a good listening level and could go as high as 60% open before distortion was noticed.
- When the squelch reached the cut off threshold, AF was 100% attenuated.
- And the most important part.... YES, THE POP WAS REDUCED BY 90%. Very livable and something one could consider acceptable.
- I should also note there was no change to the frequency response curve of the AF signal. Bass and treble response at this output AF level remained consistent with full AF output gain before the mod.

I replaced the potentiometer with a 1/4 watt 3.8K resistor and called it a day.

Hope this helps someone with a similar problem. Maybe this will inspire those of you who settled with addressing the symptom to take another stab at eliminating the pop this way.

Good luck to all!