December 2012, 17:45 PM
Hello every one. Im brand new to this forum. I use others a lot but have noticed some interesting threads from Google. I've been working on a radio as an on going project and its coming out pretty well. It's a cobra 29lx that I installed the rfx75 and done several other upgrades as well. With a germanium diode replacing the modulation limiter with vr4 set at 40% it's peaking at 65 watts or so. Right now I have the dk set to 2 watts because it's going to drive an amp I'm building later. I've got several projects under my belt. 2 amps, radio mods rfx.. and I also work on guitar amps.
I used the cobra power Mic upgrade schematic from cbtricks on a piece of Vero board. It uses 2x 2n3904 stages and supposedly gets like 40db. I whipped up the circuit and put the board INSIDE the radio right after the Mic input. And got some massive drive. I added an attenuation pot to the end of the circuit. (Remember this question coming. I have to attenuate it quite a bit or it will squel like a biotech. Also with an amp behind it it causes feedback, I think through talk back. I'm powering the circuit from the radios 12+v and grounding to a near by variable coil. Let me add also that this heats up the fets too..I cut the wires and replaced with Teflon silver coated thick wire and added 3 turns on an 1/8in type 61 ferrite choke on v+ input and output to try and filter the circuit out some.... with amp still squeals.. did help with no amp though although the key it's low. There it's 3 seperate ferrite btw.. I also added some heatsink compound to the fets of rfx.
My questions are:
1: is it appropriate to use ferrite in this manner on input, output, and v+ or am I overkill?
2. The attenuation pot, should it be on the input instead of output? The dynamic would adjust the output, correct? Or should I add a trimmer to the emitters and adjust gain?
3. Is it possible I'm clipping the radios lil Mic amp built in? It's there away to bypass this transistor or should I lower voltage off my circuit?
4. Any ideas about shielding this circuit m because I'm sure it floating in the radio subjects it to feedback although it's actually working pretty good I just want to perfect it.
5. The way the dynamic is setup would it effect the input or output of my circuit? I'm having trouble decyphering this section off the schematic. Mine it's directly connected to the Mic plug pin and output in to the board where it is just spliced in.
Please understand this is not an emergency I'm just making adjustments. I've thought of ditching the transistors and using opamp s. But I'm not good at designing gain stage for this freq. Thanks in advance
Friday, 07 December 2012, 19:01 PM
Also in a lil bit I'm going to post pics. The circuit I'm talking about is cbtricks, microphone manuals and schematics, cobra, last link on page. I will post pics in a lil while and add avtar
9Lives
NEW DUCK
Posts: 1
Joined: Friday, 07 December 2012, 15:21 PM
Name: grant
Cell Phone: 6543336788
Hello every one. Im brand new to this forum. I use others a lot but have noticed some interesting threads from Google. I've been working on a radio as an on going project and its coming out pretty well. It's a cobra 29lx that I installed the rfx75 and done several other upgrades as well. With a germanium diode replacing the modulation limiter with vr4 set at 40% it's peaking at 65 watts or so. Right now I have the dk set to 2 watts because it's going to drive an amp I'm building later. I've got several projects under my belt. 2 amps, radio mods rfx.. and I also work on guitar amps.
I used the cobra power Mic upgrade schematic from cbtricks on a piece of Vero board. It uses 2x 2n3904 stages and supposedly gets like 40db. I whipped up the circuit and put the board INSIDE the radio right after the Mic input. And got some massive drive. I added an attenuation pot to the end of the circuit. (Remember this question coming. I have to attenuate it quite a bit or it will squel like a biotech. Also with an amp behind it it causes feedback, I think through talk back. I'm powering the circuit from the radios 12+v and grounding to a near by variable coil. Let me add also that this heats up the fets too..I cut the wires and replaced with Teflon silver coated thick wire and added 3 turns on an 1/8in type 61 ferrite choke on v+ input and output to try and filter the circuit out some.... with amp still squeals.. did help with no amp though although the key it's low. There it's 3 seperate ferrite btw.. I also added some heatsink compound to the fets of rfx.
My questions are:
1: is it appropriate to use ferrite in this manner on input, output, and v+ or am I overkill?
2. The attenuation pot, should it be on the input instead of output? The dynamic would adjust the output, correct? Or should I add a trimmer to the emitters and adjust gain?
3. Is it possible I'm clipping the radios lil Mic amp built in? It's there away to bypass this transistor or should I lower voltage off my circuit?
4. Any ideas about shielding this circuit m because I'm sure it floating in the radio subjects it to feedback although it's actually working pretty good I just want to perfect it.
5. The way the dynamic is setup would it effect the input or output of my circuit? I'm having trouble decyphering this section off the schematic. Mine it's directly connected to the Mic plug pin and output in to the board where it is just spliced in.
Please understand this is not an emergency I'm just making adjustments. I've thought of ditching the transistors and using opamp s. But I'm not good at designing gain stage for this freq. Thanks in advance
Friday, 07 December 2012, 19:01 PM
Also in a lil bit I'm going to post pics. The circuit I'm talking about is cbtricks, microphone manuals and schematics, cobra, last link on page. I will post pics in a lil while and add avtar
9Lives
NEW DUCK
Posts: 1
Joined: Friday, 07 December 2012, 15:21 PM
Name: grant
Cell Phone: 6543336788
