Transmission has too much bass

I am being told that I have too much bass in my transmission. I have a Yeasu 2 meter FT221R transmitter. What should I look for that can cause this problem. When I got this radio it didn't come with a mic and the manual states that the mic should be 600 ohms, so I looked through my box of mics and found one very close to 600 ohms. I was told that the radio sounded good. I came home from a trip and no one could hear me, so I checked my freq. and the off set freq. and that was right on. I made a transmission and listen with my scanner and I sounded like trash. I checked the mic and cable, looked good. I removed the mic amplifier card from the radio and replaced two coupling caps in the front of the amplifier card and now I have my audio back but I am told now that I have too much bass in it. I used the same size caps that I removed. So now I am not sure where to look to remove the bass sound.
Thanks for any help.

Robert
KB4HVO

 

Do you have a schematic of the caps you replaced ? Scope to see audio response ?

You can put a small value cap in series with the audio line to limit the low frequencies that are passed. Caps going to ground kill high frequency response, Removing them should help.

You may have to experiment to find the best cap value. A O-scope is nice for that.

Good Luck.

 

How close are you to the microphone when talking? Many microphones have a bass-emphasis proximity effect when speaking directly next to the microphone.

Back off by a hands-width and see if it’s any better.

 

Cap values can changes the low end response so that's one thing to try. If you are eating the Mic, don't !! Like AED said, it will boost the Bass a lot. You said you have other Mics? If so, try another one. Ham radio lost Art, is trying other mics to find one that works best. The stock mics were always crappy 30 years ago, and Heil Sound was born. I have the FT 225RD and its not bassy - stock mic. Not great either! Those radios were the last of the ( built like a Tank ) rigs. Good luck.

 

Hi Robert.
The 221R uses a crystal filter in its SSB generation so the frequency response is affected by the alignment of the USB and LSB carrier crystals.
I would check these first as if set correctly, the crystal filter should cut off all response below 300Hz.

Frank

 

If you are trying to listen on a Scanner to FM, that may be a problem in itself.
Might be over loading the monitor creating the bad audio you hear.
Put the radio on a 50 ohm dummy load to minimize the power the Scanner has to deal with.
Take the antenna off the Scanner to further reduce the signal.
When your sure this in not an issue, then procced to work out the transmit audio.

 

To reduce bass, I hold him a different way.

 

That fish is all about the bass, 'bout the bass, no treble.

 

Now, if you really want lots of bass...

 

I hear (no pun intended) that helium works wonders.

TOM K8ERV Montrose Colo

 

Changing the capacitance of the audio circuit does change it's 'tone'. The trick is to find the -right- capacitance to get things 'normal' again, it ain't simple/easy! And then, just how bassy is your voice? There are ways of changing that too, but I ain't going there...

 

You guys are all looking at the wrong thing. Clearly it not being too bassy, microphones are not intrinsically "too bassy". I'm sure he has other radios and sounds fine, so it's not his voice or proximity effect or any other things mentioned here. It's most likely that the high frequencies are attenuated in the mic element due to failure or decrepitude. The problem likely lies in the untested junkbox microphone.

Electronics 101: Verify the source first, before moving into the circuit further. If you have a microphone that you know sounds OK on other radios, that is reasonably low impedance (don't worry about the value so much, just as long as it isn't like 10K or something higher for this test), try that and see if your reports on being bassy go away. Then you know it's the junkbox mic. Don't go messing around inside the radio until you know for sure the microphone (the source) is working properly. Thinking the mic worked fine two years ago (or even last week) is not verification, it's guessing.

Most mic elements, especially dynamics, when they go south usually lose their high-frequency response first if they haven't failed completely. Microphones can suddenly lose response from a variety of causes. Getting jarred or dropped hard, moisture or spit, corrosion of the elements mechanical components, a tear in the diaphragm, and the list goes on and on.

 

So do I.

TOM K8ERV Montrose Colo

 

If the radio came with a crystal mic, A dynamic will most likely not work properly.

I would guess the highs are just not there.

 

Hi Robert,

That is strange. Did you save the old caps and can you put them back in to see of that makes a difference? Can you measure their value? I assume you replaced C24 and C25. The schematic shows them as 10uF. Is that the value which was in there?

Basically, I don't see any tone-shaping with how they connect the mike. There are just some pF value caps to check RF, then the coupling caps; and 10uF is way too high to make any difference in audio. Often you can see 1uF used with no effect too, and maybe when it gets down to 0.1uF, then you could here some difference (it depends on input impedance though).

Those rigs use plug in cards, so I would clean up the PCB traces where the wire spring connectors mate, and maybe use a droplet of deoxit on each side and slide the card in and out a few times. Make sure too, that the connector wires are all in the correct place when the card is in. Sometimes they get shifted off a trace to one side or the other.

73,


Mark