Audio bass level "mitigation".

[garys]

I received the caps and modified two speakers. The first was a Speco 8ohm speaker in a fairly large enclosure. That worked pretty well, so I did a Motorola RSN4001A next. I had to wire the cap into the speaker wire as I couldn't find a way to open the enclosure without breaking it. It sounds pretty good, but I found out afterwards that it's a 4 ohm speaker. As it happens, I have a 4024A, which is 8 ohms. I'll test the 4001A in my truck and if I don't like the sound, I'll modify the other one.

In that case, go for it.

One caveat: I'm assuming your speakers are 8-ohm. If they are some other impedance, the capacitor value has to change accordingly. For a 16-ohm speaker, a 50uF capacitor (47 being the closest commonly available value) would be the correct value. For a 4-ohm speaker, you'd need a 200uF capacitor.

 

[jonwienke]

I received the caps and modified two speakers. The first was a Speco 8ohm speaker in a fairly large enclosure. That worked pretty well, so I did a Motorola RSN4001A next. I had to wire the cap into the speaker wire as I couldn't find a way to open the enclosure without breaking it. It sounds pretty good, but I found out afterwards that it's a 4 ohm speaker. As it happens, I have a 4024A, which is 8 ohms. I'll test the 4001A in my truck and if I don't like the sound, I'll modify the other one.

For a 4-ohm speaker, just use two capacitors in parallel.

 

[garys]

Thanks. I was a bit concerned about using a 4ohm speaker on a radio with an 8 ohm output. That aside I'm going to put one of the capacitors on the 4024 which has a heavier magnet anyway. Once I find one I like, I'll settle on that.

For a 4-ohm speaker, just use two capacitors in parallel.

 

[jonwienke]

You're right, a 4-ohm speaker isn't really a good idea for a Uniden scanner. But if you're having a similar problem with a different radio, 2 caps in parallel is what you'd need.

 

[Anderegg]

My SDS200 has enough wattage power to drived the 8ohm 7.5 watt Mototola speakers withoutany noticable distortion...loud enough for in car use in my working news enviornment.

Paul

 

[garys]

I'm going to try the SPECO 8 ohm speaker and see if I like it. If not, I'll modify the 8 ohm Motorola speaker I have on my shelf.

 

[maus92]

Does the audio frequency response between digital and analog systems match better now? I.e. digital has more bass normally because it goes down to 100Hz compared to 300Hz for most analog systems (you appear to have some exceptions).

The SmartZone system I monitor has a noticeable disconnect tone (~160Hz) when being played through my studio monitors (speakers,) when using ProScan or UT2. You cannot hear the tone when played through an external communications speaker (Moto or Vertex) or via the radio's speaker.

 

[Anderegg]

The SmartZone system I monitor has a noticeable disconnect tone (~160Hz) when being played through my studio monitors (speakers,) when using ProScan or UT2. You cannot hear the tone when played through an external communications speaker (Moto or Vertex) or via the radio's speaker.

Did you throw a ProScan 160Hz notch filter at it? I use Equalizer APO to notch all the CTCSS tones coming in through my mic/line in jack on my PC.

Paul

 

[maus92]

Did you throw a ProScan 160Hz notch filter at it? I use Equalizer APO to notch all the CTCSS tones coming in through my mic/line in jack on my PC.

Paul

It's not really an issue for me since I use the communications / internal speakers - it's just something I noticed.

 

[Mike_G_D]

That is the wrong answer when the caps sold are too small. And you'll still fry polarized caps with reversed polarity if you run AC through two of them in series, unless you add the additional complexity of a bias circuit tied to the center connection.

While you're right about reducing the capacitance when in series, I suspect the "large electronics store" will likely have much larger regular polarized caps that can be seriesed together to get something close to 100 uF. For this application it is not critical and not a magic number anyway. Something close is good enough. Couple of regular 150uF's in series to get 75uF is probably good enough though slides the response a tad. And I wouldn't worry about putting two polarized caps in series tied at the negative - that is a very common method of getting a non polarized equivalent. Essentially that's what a non-pol electrolytic is. We used to try blowing electrolytics for fun in lab reverse polarized ("party streamers";-)). Takes some continuous wrong polarity DC to do it. In AC especially with varying audio phases and frequencies and amplitudes your average in the wrong direction isn't very likely to add up quick enough before being rapidly discharged on the reverse swings.

 

[jonwienke]

We used to try blowing electrolytics for fun in lab reverse polarized ("party streamers";-)). Takes some continuous wrong polarity DC to do it. In AC especially with varying audio phases and frequencies and amplitudes your average in the wrong direction isn't very likely to add up quick enough before being rapidly discharged on the reverse swings.

It's still not good practice, especially if you decided to mod the scanner speaker, and a blown capacitor would decorate the interior with aluminum foil and electrolyte. Multiple large-value capacitors in series are also going to take up more space than a non-polarized cap with a reasonable voltage rating.

 

[Ubbe]

The AC power supply for Uniden scanners only delivers 750mA as max current and most of it goes to the RF and CPU electronics and perhaps half of it are left for the loudspeaker amplifier. So probably not enough current flowing to blow up a capacitor. A 220uF 25v polarised cap are 10x20mm and 470uF 16V have the same size. I believe the chemicals in el-lyt's will make them self biasing in this configuration in series with the negatives connected together. Seems to be a common practice when needing a non-polarising cap with a high uF value.

/Ubbe

 

[garys]

After I got the SPECO speaker modified and installed in my truck, I found a replacement Motorola 8ohm replacement speaker on my "speaker' shelf. I took about the RSN4001a, swapped out the speaker, and did the modification. Tomorrow, I'll put the Motorola speaker in because it sounds much better than the SPECO.

Anyone need a 4ohm Motorola replacement speaker?