Hifi question

[Ratfink]

Anyone know how to hifi the 148/2000 platform without loosing sideband? I have a gentleman I know thy wants the sound but doesn't want to lose sideband when you direct inject your procesing gear.

 

[9C1Driver]

I would tell him to let the 148/2000 be what it is, one of the best cb sets ever made. If he wants to play the rack gear Hi Fi game go buy a Kenwood or Yeasu.

 

[Robb]

From the 'Goldfinger' tech and 'Deep South Radio Forum':

Cobra 148/2000/Grant XL

TX circuit audio improvements:

C46 Change to 2.2uf mylar/polyester film or non-polarized electrolytic
C101 Change to 1.5uf tantalum 16 to 50 volt
C102 Change to a 910pf ceramic disc
C104 Change to 2.2uf tantalum 16 to 50 volt
C108 Change to 1uf to 2.2 uf tantalum 16 to 50 volt
I found that if you have a very deep voice start with 1uf on C108
and work up if need be.
If you need more highs on tx Change C 105 to .001 to .0001uf mylar/polyester film The smaller you go the more highs you get.

RX circuit audio improvements:

C71 Change to 1uf mylar/polyester film or non-polarized electrolytic
C75 Change to .001 to .0001uf this will give you more highs on rx
optional
C76 Change to 2.2uf mylar/polyester film or non-polarized electrolytic
C182 Change to .001 to .0001 for more highs on rx and tx
optional
C183 Change to 2.2uf mylar/polyester film or non-polarized electrolytic
C187 Change to 2.2uf mylar/polyester film or non-polarized electrolytic
With C75 and C182 you can start with no Change to them, then if you feel you want more highs then change them out

I've done this mod to a President/Uniden Grant. The results were xlnt. So I know it works. No re-alignment needed for this mod.

And . . .
Cobra 2000 BIG AUDIO!!! at silicon two one two dot org

Removing this deactivates the modulation limiters in all modes. Use the front panel mic gain (aka Dynamike) control to set the modulation percentage. Replace the following 10k resistors with 1/4 watt, 4.7k resistors: R126, R124 (both located near the VR3 Squelch range trimpot). If you do not wish to remove TR24, you may add a 1.5k resistor in series with the middle leg of TR24 (the collector). Replace R131 (10k) with a 4.7k resistor (only if you do not remove TR24). My own note: Removing TR26 or R131 will disable the AMC in the AM mode but leave the limiter intact for SSB usage. Since this is a primarily AM mod, and delimiting modulation in SSB is a bad thing for SSB audio clarity, this is the personal route I would take.

The bold type is the consideration for SSB integrity by keeping TR24 intact.

If you don't have the alignment gear, the experience, or the know-how for this mod ('difficult'); then - forgetaboutit . . .


Do your own research; these are just tips.
You must take ALL responsibility for ANY of the work done!

 

[Ratfink]

From the 'Goldfinger' tech and 'Deep South Radio Forum':


I've done this mod to a President/Uniden Grant. The results were xlnt. So I know it works. No re-alignment needed for this mod.

And . . .
Cobra 2000 BIG AUDIO!!! at silicon two one two dot org



The bold type is the consideration for SSB integrity by keeping TR24 intact.

If you don't have the alignment gear, the experience, or the know-how for this mod ('difficult'); then - forgetaboutit . . .


Do your own research; these are just tips.
You must take ALL responsibility for ANY of the work done!

That's alot of work vs direct injecting.

 

[Ratfink]

Maybe Dirt will chime in here.

 

[Robb]

That's alot of work vs direct injecting.

Direct injecting is not do all/fix all solution to real audio improvements. It is definitely more complex than that; but not so hard as to be unobtanium if each step is followed through correctly.

Direct injection IIRC only bypasses the mic amp in the radio. Has NOTHING to do with expanding the freq response that a radio is capable of if improved upon. Suppose that all depends on just how far you want to take it . . .

 

[Shockwave]

If you like the simplicity of the direct modulation to the series pass modulator for hi-fi AM, why not do the same thing for SSB? You just feed the balanced modulator directly in SSB. You might need a switch to change the audio feed from the series pass modulator in AM to the balanced modulator on SSB unless you modify the existing transistor switch.

 

[Captain Kilowatt]

Direct injecting is not do all/fix all solution to real audio improvements. It is definitely more complex than that; but not so hard as to be unobtanium if each step is followed through correctly.

Direct injection IIRC only bypasses the mic amp in the radio. Has NOTHING to do with expanding the freq response that a radio is capable of if improved upon. Suppose that all depends on just how far you want to take it . . .

In most cases bypassing the microphone amp does result in increased fidelity because the mic amp has bandwidth limits designed for voice comms. the degree of which is variable depending on the radio. Amateur gear sees a BIG difference when feed the modulator directly.IMHO it is pretty useless to TX wideband audio when 99.999% of the receivers out there can't take full advantage of it anyway due to RX IF bandwidth.

 

[Ratfink]

If you like the simplicity of the direct modulation to the series pass modulator for hi-fi AM, why not do the same thing for SSB? You just feed the balanced modulator directly in SSB. You might need a switch to change the audio feed from the series pass modulator in AM to the balanced modulator on SSB unless you modify the existing transistor switch.

Well It would be a SSB radio only he doesn't talk on am. Do you have any info on what to do and where on the 148/2000's ?

 

[985chicago]

Being able to hear your "over the air audio " for me is what i think is missing with all these CB audio mods.How do you eq. Tweek the audio with out being able to hear whats going over the air.How do you monitor it ? I know of only a few radios that have a accurate monitor . TS870'950sdx are best i am aware of.Even these will only pass the audio on ssb.only.Without a accurate monitor you can only guess where to tweek your eq. This is a major problem imo.
985chicago

 

[bob85]

best way imho is to use a second radio and closed back headphones.

 

[Shockwave]

Being able to hear your "over the air audio " for me is what i think is missing with all these CB audio mods.How do you eq. Tweek the audio with out being able to hear whats going over the air.How do you monitor it ? I know of only a few radios that have a accurate monitor . TS870'950sdx are best i am aware of.Even these will only pass the audio on ssb.only.Without a accurate monitor you can only guess where to tweek your eq. This is a major problem imo.
985chicago

There is a simple diode detector I found on this forum a while back. I've installed it to feed the headphone jack on several radios. This allows me to hear my audio on transmit and the receiver still drives the headphones in RX. Allowing continuous monitoring while using the rig. If your radio has been modified to pass hi-fi in receive, you can use the detector to feed the input of the volume control potentiometer since it will pass the bandwidth, be louder, and work with the volume control. Use a switch to open the feed when using the radio without headphones.

The one thing the simple diode detector was lacking is forward bias. The circuit on this forum was easy to modify by reversing the diodes in the circuit. The detector still functions the same way but now you can forward bias the detector diode with a positive voltage rather than a negative voltage. Needless to say that makes things easier in most radios. By adjusting how much RF feeds the detector and the amount of bias, you can remove nearly all distortion from the diode detector. If you're installing this in an HF rig, don't use a cap to couple the RF into the detector since its impedance and the amount of RF it passes with change with frequency. Use a 1000 ohm 2 watt resistor for the 100 watt HF rig. All of this is for AM only.

 

[ExitThirteen]

Tagging this thread. Might do these mods on a Cobra 2000 I have laying around.... see if it actually works or not. LOL



~Cheers~