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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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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Mar Tue 05, 2019 6:21 pm 
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I'm finally getting to building one of these after a couple years of distraction. All parts are on hand and ready to go, but I'm not sure which value to pick for L1? how does a value at the low or high range of the listed 150-680 µH effect the signal? Or is that simply a range in which it will always work, and the value is very much non-critical within that range? I understand that L2 is critical based on frequency of the oscillator, and based on length of antenna and value of tuning cap for the antenna.


Thanks in advance!
jon

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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Mar Wed 06, 2019 5:50 pm 
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Quote:
how does a value at the low or high range of the listed 150-680 µH effect the signal?
You won't see or hear any difference. Much higher values, say around 1mH or higher, can affect audio high frequency response but within the range you asked about there is no problem. I'd pick between 150 or 220 if available in your stash.

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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Mar Wed 06, 2019 11:52 pm 
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ok, thanks! I have a whole range of them that I bought when originally getting parts for the transmitter. looking for where I put the enclosures that I have in a box somewhere before I build, though it might be faster at this point to build an enclosure than to look for one.

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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Mar Thu 14, 2019 4:10 am 
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bbuszard wrote:
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.
What is that? Redundant ground wires?

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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Mar Thu 14, 2019 4:45 am 
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Seems to be an issue with pictures this evening. Not only the OP in this thread but also the OP in a few others.. images are not showing up.


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Mar Thu 14, 2019 5:13 am 
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Minicowman wrote:
Seems to be an issue with pictures this evening. Not only the OP in this thread but also the OP in a few others.. images are not showing up.

I just posted one in another thread and had NP;
viewtopic.php?f=15&t=355810

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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Mar Sun 17, 2019 6:32 am 
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Hello Guys,
I really seen some nice builds here great job


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Sep Mon 07, 2020 4:33 am 
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Hello folks, meant to stay active in the community here after all the help building my last transmitter. Long story short I lost my transmitter and pretty much everything else in a flood last summer and have just lately been getting around to replacing my transmitter.

Not to go making this thread any longer but I've spent a good bit of time on this and thought I would share. I'm not quite finished tweaking it just yet so the values haven't been entered yet, none fall in line with the original. The noise suppression is insane on this bad boy, so much so that a early version didn't have any high-hats or verbal "S" sounds in songs. No separate audio compressor/limiter needed. I don't know anything about scopes and don't have one but I can hear 6th gen and later Intel processors singing from 2 ft away. That being said when I get one of these on a board I'd like to send it to someone to check it out with a scope if they'd be interested, possibly Tom? I'll get bake next week with a final design and parts values, waiting on some things from Digikey.

Dan


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File comment: LM386 Tx
LM386.PNG
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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Sep Mon 07, 2020 6:51 pm 
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I don't know whether any will be interested in this, but it is an idea to build an AM MW transmitter using only an LM386.

It is actually a regenerative receiver with the regeneration control removed so it always oscillates.

The inductor connected to input Pin 3 can be a standard transistor 455 KHz IF transformer with its internal capacitor crushed so that it may be tuned by a variable capacitor. A red local oscillator transformer may also be used.

As a regenerative receiver the capaciively coupled choke from Pin 1 creates a high reactance to RF. A resistor of about 330 Ohms can likely be used instead of the choke. The choke and the 10 uF capacitor create an extremely high gain audio output stage which may not be required when used as a transmitter.

Connecting a 220 pF capacitor from Pin 1 to ground creates a Colpitts oscillator using the internal transistors connected to Pin 3 with their intrinsic Base-Emitter capacitance as the second required Colpitts feedback capacitance across the tank.

There are number of ways of modulating the oscillator. One way is to use a high level audio input capacitively coupled to Pin 7. The internal voltage divider connected to Pin 7 using the 15K resistors determines the output voltage on Pin 5. Applying audio into Pin 7 will amplitude modulate the transmitter. If this technique is used Pins 2 and 3 may be connected together for more output. Another technique is the manner shown in the first schematic below. Another alternative is to use the choke to isolate the audio input from the oscillator as shown in the fourth schematic.

Although I have built too many receivers in this configuration to count which do radiate into nearby MW receivers, I HAVE NOT TRIED THIS CIRCUIT AS A MODULATED TRANSMITTER. I thought that some might find it interesting. For any willing to experiment i would first try the simplest third schematic.

In general it is not good design practice to modulate an oscillator, but its simplicity would suggest that it might be useful for its intended purpose.


Attachments:
LM386 Transmitter.png
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LM386-Schematic (1).jpg
LM386-Schematic (1).jpg [ 76.45 KiB | Viewed 528 times ]
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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Sep Sat 12, 2020 7:05 am 
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Location: Colorado Springs, CO 80917
Is anyone still building the LM386N + oscillator module transmitters?
I just bought a bunch of modules at a surplus store. There's a LOT of 1544KHz ones, some 1536KHz, a bunch of 1120KHz and some 614.4KHz frequencies. Haven't yet tested them for whether they modulate okay but if they do, that seems a handy selection of channels to be able to find a local clear spot.


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Sep Sat 12, 2020 8:18 pm 
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These made for the OKC Radio club members. Very easy and work with most available crystals/frequencies including SMD's. Many, many Chinese parts go into these for compactness.

Dale

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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Sep Sun 13, 2020 12:52 am 
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Mini 386.


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Sep Wed 23, 2020 7:20 am 
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To follow up on my last post, here is an updated schematic. I think it sounds good, especially on my ZTO G500 that seems to pickup a lot of HF noise. Not sure what's up with my inductance (osc or ant wire) but it's the same for the original design in my current setup.

A 10pf can be used in place for C1 for a slight frequency change on the high end. Anything in between 10 - 1000pf (that i have) adds some funkiness on the scope.

C3 can be swapped for .1uf for a slight frequency change on the low end.

C4 can be a 10 or 47uf, I liked 22uf or 47uf.


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LM386.2.PNG
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IMG_3527.JPG
IMG_3527.JPG [ 915.64 KiB | Viewed 244 times ]

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