|
|
Post by brownbomber72 on Sept 5, 2022 17:27:06 GMT -5
Just got this rig and it came with a cheap powered hand mic. Was told it sounded pinched up and my voice nasally on transmit. Some even said at times I even sounded off frequency. After lots of adjusting the mic gain on radio and amp the only way I could get it to sound halfway decent was to hold the mic about 3 feet away from my mouth. Today I wired up a Astatic 636 for it and at first was getting the same audio reports as I was with the powered mic. Finally got it to talk halfway decent with the mic gain on the radio barely cracked open. Does this sound like a mic issue or something wrong inside the radio? I kind of wonder if this rig just does not like a dynamic mic.....
|
|
|
|
Post by 2600 on Sept 6, 2022 0:43:04 GMT -5
Hmmm. A 44 year-old radio. Everything in it might be perfect, good as new.
Might not. Pinched audio quality is one kind of symptom caused by age alone. Not so much the age of the radio as the age of the aluminum electrolytic capacitors sprinkled all about the radio's circuits, especially the audio circuits. Those go bad from age alone, frequently after no more than 15 or 20 years. It would be a borderline miracle if every one of them in this radio were performing perfectly after this many years.
This issue of age is what's behind the practice of "re-capping" old radios. Removing every electrolytic capacitor and installing a new replacement.
All of them.
This radio presents an extra issue for anyone who considers undertaking that project. The circuit board is more sophisticated than most CB radio circuit boards. The norm is a circuit board with foil on one side, and the parts on the other side. This model is built with foil traces on both sides of the laminate. This simplifies things for the designer of the radio, but creates a hazard when removing parts. Every hole in the board has what's called a "plate-through" metal sleeve inside the hole. It serves to connect foil on the top side to the foil on the bottom side at that hole. It's too easy to suck the solder off of a capacitor's two lead wires, and then pull out the old part before all the solder is removed. Any remaining solder that 'glues' a lead wire to that sleeve risks pulling it out of the board altogether. Creates a new fault where there was none before.
One thought I skipped would be the modulation limiter adjustments. People will tweak them to slam the wattmeter harder. But this usually screws up the audio quality. Could be it's just turned up too high. Could be that a 44 year-old radio has more than one issue developed in all that time.
73
|
|
|
|
Post by brownbomber72 on Sept 6, 2022 18:21:04 GMT -5
Would have to find some one to recap it. Im afraid I would mess something up.
|
|
Sandbagger
Administrator/The Boss 
Posts: 6,250 
|
Post by Sandbagger on Sept 6, 2022 18:59:28 GMT -5
Just got this rig and it came with a cheap powered hand mic. Was told it sounded pinched up and my voice nasally on transmit. Some even said at times I even sounded off frequency. After lots of adjusting the mic gain on radio and amp the only way I could get it to sound halfway decent was to hold the mic about 3 feet away from my mouth. Today I wired up a Astatic 636 for it and at first was getting the same audio reports as I was with the powered mic. Finally got it to talk halfway decent with the mic gain on the radio barely cracked open. Does this sound like a mic issue or something wrong inside the radio? I kind of wonder if this rig just does not like a dynamic mic..... CPI makes one of the finest SSB CB radios. It really will perform well on SSB. However, on AM, the transmit modulation was never loud or punchy. The reason for this is that the radio uses a low level modulation scheme, similar to what Amateur HF radios do. If you have too much modulation for the amount of carrier, the modulation peaks will "mush up" and not sound good. Inside the radio there are adjustments for both modulation level and carrier level. Those need to be in balance. Set the carrier for the desired level, and then set the modulation level for 100% on the scope. At that point, the modulation should sound good. But remember, it will never get "loud", but it should be clean. But, as was mentioned before, caps and other parts can drift with age, which can cause these adjustments to go out of balance. As can an over enthusiastic screwdriver tech trying to get more out of the radio. |
|
|
|
Post by cbrown on Sept 7, 2022 11:42:13 GMT -5
Most people that I know who had one wired a Turner Super Sidekick and stayed on SSB (for the most part). They were great SSB rigs.
|
|
|
|
Post by brownbomber72 on Sept 7, 2022 18:06:37 GMT -5
Wish I had known it was not a great AM talker. Would have passed it up.
|
|
|
|
Post by brownbomber72 on Sept 8, 2022 18:28:19 GMT -5
Where are the carrier and modulation adjustments located inside the radio? |
|
Sandbagger
Administrator/The Boss
Posts: 6,250
|
Post by Sandbagger on Sept 9, 2022 19:42:01 GMT -5
Most people that I know who had one wired a Turner Super Sidekick and stayed on SSB (for the most part). They were great SSB rigs. The Super Side kick was the best match for that radio, both on AM and SSB. When set up properly, the CPI 2000 sounded decent on AM. Not an audio monster, but clean and natural sounding. But SSB is where it really shined. Next to the Stoner Pro-40, the CPI was probably the best Part 95 SSB CB radio made. |
|
Sandbagger
Administrator/The Boss
Posts: 6,250
|
Post by Sandbagger on Sept 9, 2022 21:47:26 GMT -5
Where are the carrier and modulation adjustments located inside the radio? It's been over 15 years since I last worked on a CPI 2000, so my recollection of these adjustments is foggy. But here is a link to the manual from CB tricks including an alignment procedure. Follow that and you should be ok. CPI-2000 |
|
|
|
Post by brownbomber72 on Sept 9, 2022 22:08:07 GMT -5
Thanks. Speaking of SSB I finally got to make some contacts with it on sideband today and was told it sounded great.
|
|
|
|
Post by narfedwards2 on Sept 10, 2022 18:32:54 GMT -5
also not unusual to need very little mic gain on the CPI...specially if yer using compression
|
|
|
|
Post by narfedwards2 on Sept 10, 2022 18:33:06 GMT -5
also not unusual to need very little mic gain on the CPI...specially if yer using compression
|
|
|
|
Post by cbrown on Sept 14, 2022 14:11:03 GMT -5
Wish I had known it was not a great AM talker. Would have passed it up. They are fine talkers on AM, just not the audio monsters other rigs are. In my opinion they are fine on AM. As for your other questions, I had this saved from a conversation a bunch of years ago. Use at your own risk: Step 1: Peak L204, L202, L203, L205, and L201 in that order for maximum power output on CH 20. Adjust 8205 to maintain 4-watt carrier output. Check output power balance on Ch 1, 20, and 40. If this power varies more than 0.5 watts from Ch 1 to 40 complete the following. Slightly adjust L204 for maximum power on Ch 1 and L205 on Ch 40. Check power balance. Re-check 4-watt level and adjust 8205 if required.
Step 2: Turn to LSB mode and check power level with limiting 1 kHz modulation. It should be at least l0 watts.
Step 3: Set front panel meter to read 4w with no modulation on AM, Ch 20 using TX MTR CAL pot 8557 located on the Interface Board (73043). There is a small hole through the circuit board to allow adjustment from the backside. |
|
