Woohoo! great, Larry - glad you got it going. I too am thinking of building another transmitter, just for the enjoyment of building.

-Sam T.

Now that I've had it running all day I have a couple questions. I have tried various different OTR recordings as well as MP3 music files using the USB stick in the built-in MP3 player. I have listened to it using different radios and receivers ranging from a Hallicrafters S-20R to a Zenith 10S669 and there are two issues. Issue one is the antenna. I'm using 10' of 14 gauge multi-strand and am having difficulty peaking with the trimmer. There is a very, very slight difference from fully tight to 1/4 turn backed off. However, if I grab ahold of the antenna wire with my hand the reception immediately gets louder on the radio. Antenna too short?

Second, everything comes through with too much bass, almost to the point of being muffled. That's with VR1 set at about 70%. Now it's possible some of this is due to the MP3 player and perhaps some adjustments need to be made by changing caps or resistors in the circuit? Anybody else running this MP3 player?

Larry

Hi Larry

Do you have a scope or some other method of determining a RF output peak??? If not AVC voltage can be measured on a radio(or eye tube observed)... Also tube plate current can be measured(meter must be between coil & B+), and set for minimum... If current is falling at max capacitance but no dip reached, you can try hanging a 47-68pf across the trimmer, then try again... If it's dipping but no max reached while backing off the trimmer, then you possibly have the incorrect coil installed... A scope probe clipped to the antenna insulation is by far the easiest & quickest way to find out what's going on...

I'd think 70% on the gain is going to be far too much and it's over modulating, of course that depends on output of the Mp3 player and I have zero experience with those...

Tom

I've been experimenting with some tweaks (?). First, I had originally twisted together the left and right outputs from the MP3 and had run it through just one resistor (R1). I seperated them and ran each through it's own resistor (R1/R2) to help reduce input. I replaced the 12AV6 with a 12AT6 which, I believe, reduces the gain a bit. The only 12AV6 I have in stock to try is an IEC Service Master (Japan). Good/bad? I also replaced C1 (.05) with a .0089 cap, and extended the antenna to 16'. With the pot set at about 55% it sounds much better now. I think the issue is the MP3 player's output. I would be interested to hear from anyone else who installed the USB MP3 player.

Larry

Hi Larry,
Guess I got lucky when installing the mp3 player, never had any trouble from it.
I did install two resistors in the audio circuit in order to combine stereo channels.
My transmitter has been running 24/7 for months and sounds fine.

-Sam T.

Do you process your MP3s before loading them onto the USB stick?

Larry

You may want to try feeding it with a known good source(CD player, computer, etc) to be sure the Tx is up to snuff...

Tom

There wasn't enough room between the trimmer and the wall of the cabinet to allow the trimmer to function. My bad. I made tiny spacers for the retaining screws and now it works. I shouldn't work on these things unless I've had at least 2 cups of coffee in me.

Larry

Yes, I use MP3Gain to level the gain of all files before moving them onto the thumbdrive.

-Sam T.

Tom, I'm working on adding an audio input to the cabinet and running both the audio input and the MP3 player through a DPCO switch making it input selectable. Once I get that done I can plug in a CD player and see how it plays then.

Easy, thanks for the info on the software.

Larry

I've got a question for the guys running the MP3 player using a thumbdrive; how does it remember where it's at even if the transmitter is unplugged overnight? Two nights in a row I've been playing a thumbdrive of OTR and both times that I plugged the transmitter back in the next night it started to play right where it had left off the night before. How's it do that without a battery backup?

Larry

Same way the thumb drive remembers all those MP3s you put on it without a battery backup.

It's not the same thing. The thumbdrive is just a mem stick that gets data written to it and stores it. It has no idea what that data is or represents. The software reading that data, in this case the MP3 player, determines what it is and how to interpret it. I'm asking how the MP3 player remembers where it was amongst all those files stored on the thumbdrive when the power is turned off and then back on later. For a tiny little piece of hardware this thing is quite sophisticated. It must have some sort of storage capacity on board to store either the address or file name of the file it was playing.

Larry

Actually, it is. Data is data. I'm simply saying the MP3 player apparently has non-volatile storage just like the memory stick is non volatile storage. In fact, if they were 'clever' they might use the memory stick for it. All it needs to do is write a "where we is" value.

Agreed, Larry - the Chinese MP3 players are sophisticated, especially considering the price and physical size.
I still have a wish-list, though. Mainly better documentation and the ability to read playlists, or at least a shuffle feature.

-Sam T.

Data is data but that's not the issue and it is not the same thing. Look, I've been building computers, trouble-shooting computers, and writting software since 1979 so I do know something about data and how it's stored and accessed. The software that accesses it is what keeps track of where it is/was at any given time, certainly not the data itself. So, the MP3 player itself is keeping track, even when unplugged electrically, and I was curious as to whether anyone had spent the time to figure out how considering documentation is virtually non-existent. If it wrote it to the stick then it would still be there even after removing and replacing the stick, which it isn't, so that's not the answer. You're right in that it's being stored somehow by the MP3 player but that doesn't answer the question of how, which is what I was asking.

Larry

Tom, I added a 1/8" audio input to the box and ran both the input and the MP3 player thru a DPCO switch so now I can just flip a switch to change from an external player to the built-in MP3. I hooked up an external CD player and she's sounds real good. Part of the problem, I think, has been that it's overwhelming the Zentih 10S669 that's just 4 feet from the antenna so I went to the living room and tried my Philco 40-180 (about 35' away). The very slight distortion I'm hearing in the Zenith is not present in the Philco so I think that answers the question.

I put a .05 cap back at C1 and even with the pot turned all the way up it still sounds real good with the external cd player.

Thanks to everybody for the help and guidance on this, much appreciated.

Larry

I have you beat by 10 years

Assuming it remembers, as you describe, then it's obvious they store 'where it was' in non-volatile memory or else it couldn't recall the information after having power removed but, no, I don't have details on their code.

I can think of a number of ways to store information on the memory stick that would not be normally visible when removed but near as I can tell from deciphering translated Chinese the controller/decoder is likely to have something on the order of 512k bit on-board flash. What I meant by 'the same thing' is that, in both the memory stick and MP3 player case, data is stored in flash memory, either on-board or on the memory stick, hence neither need 'power' to retain the information.

It might be interesting to try two different memory sticks and see if it remembers 'where it was' on each but, judging by user comments on web sites selling those things, I suspect they're not quite that clever.

The MP3 player that I discussed in the other recent thread, has a small amount of on board flash memory that is used to remember which song was playing, and a few other settings.

To answer flippers question, once the thumbdrive is removed and reinserted the MP3 player starts over from the first file whether the xmitter was still plugged in or not. I know some have mentioned that they wish it had play-list capability but as for me, I just wish it played the files alphabetically. That, at least, would give me some control over establishing a playing order. Right now the only way is to write the files out to the stick one file at a time in the order you'd like them to play, rather than batch copy. But, for less than $10 you can't complain.

Larry