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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Feb Mon 05, 2018 6:35 pm 
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Thanks for the info Tube Radio, I suspected that was the issue but wasn't sure what to do about it. I had tried having the audio jacks only hooked only to my external ground on the breadboard and couldn't get it to transmit (was running the ground to a baseboard heater that dosen't get used). If a guy could find some large coils similar to whats used in the Sstran on the audio jacks, would that have the same effect?

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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Feb Mon 05, 2018 6:57 pm 
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Retrotube wrote:
Thanks for the info Tube Radio, I suspected that was the issue but wasn't sure what to do about it. I had tried having the audio jacks only hooked only to my external ground on the breadboard and couldn't get it to transmit (was running the ground to a baseboard heater that dosen't get used). If a guy could find some large coils similar to whats used in the Sstran on the audio jacks, would that have the same effect?


You're welcome.

If the coils are such that they do some sort of isolation of the ground then they should work.

The transformer is nice though as you can wire up the transformer to a DPDT switch and use a source with a balanced output or flip the switch and the input is unbalanced.


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Feb Wed 07, 2018 6:41 am 
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I checked into the transformer brand you mentioned, Tube Radio. They look nice, especially the advertised frequency range. I went a head and ordered one for my self to play with, I'll link it. Looks like they have the same same one on a PCB with screw terminals too but don't give info on how to wire it. Could you tell me if the schematic in the link is wired for balanced or unbalanced on the in/output? Also how would the wiring be for the opposite?

https://www.edcorusa.com/pc6400

Thanks

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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Feb Wed 07, 2018 1:08 pm 
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The input is actually wired for stereo so one channel would connect to pin 1, ground to pin 2 and the other stereo channel to pin 3.

For the output to be unbalanced you either use pins 5 and 6 or 6 and 7 for a step down or use pins 5 and 7 for the full output voltage. If you wanted a balanced output pins 5 and 7 carry the signal while pin 6 is ground.

I recommend installing the transformer in the transmitter case if at all possible. If the case is too small you will need a bigger case.

The output of the transformer gets wired directly to the level control.

The reason you want the transformer in the case is so the wiring from it to the level control is as short as possible to minimize any effects that could be caused by the required audio cable you would have used if the transformer is mounted externally.

Now if no room on the inside of the case you could cut the necessary holes for the terminals and screws to go through and mount the transformer on the outside of the case.

Far as the one on the PC board if it is the same transformer, the wiring will be the same.


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Feb Sun 11, 2018 5:39 am 
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Thanks Tube Radio, Space won't be a problem as I'm going to be using it in a new build. I have a few other changes I'm making too and want to keep my first one as it is.

On my first build I have a 10k pot and 2k resistors. Which sounded better than a 5k/1k combo with my phone. Am I correct in thinking that that the input on the transformer will replace 10k of that resistance and I should use a smaller pot. Also, does the input on the LM386 call for the balanced or unbalanced signal?

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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Feb Wed 14, 2018 2:37 am 
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The pot used with the transmitter should be no lower in resistance than the impedance of the secondary of the transformer.

The LM-386 takes an unbalanced signal.


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Sep Tue 25, 2018 6:10 pm 
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I've built a (very) slightly modified version of the transmitter and thought I'd post the changes for general consumption. I'm a ham and run everything in my shack off 12V dc (really more like 13-13.8), so I simplified the power supply to use a 7810 linear voltage regulator, which gives me 8.3 V after the diode. I'm used to ugly bug construction from ham projects and have found that it really helps in taming ground noises, so that's what I used here. I connected my shack's rf ground to circuit common, but still had some problems with noise feeding back into the audio inputs, especially a high birdie that I'd guess was up around 10k Hz. A couple of 10 uF caps on the inputs have tamed that problem and I now have a pretty good system going.

I'm in Hampton Roads, VA where 1000 and 1228 kHz conflict with strong local stations. Ecliptek oscillators for 1544 kHz are still available at "that" auction site for a few bucks. I picked up a pack of 4 for $10.

Many thanks to 35Z5 for all the work putting this project together. It's truly amazing what a handful of parts can do.


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