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I. Dimov (Overrider)
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Username: Overrider

Post Number: 91
Registered: 12-2005
Posted on Saturday, August 19, 2006 - 9:59 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Does the LM386 amplifier on the site need a preamplifier? Also, are there any ultra special precautions I have to take to prevent oscillation? I kinda made a radio, so it like doesn't work at all, so I was like, y'know thinking of posting here, so here is the radio:

I can live with the radio having no reception (there are no radio stations in the AM Band around), but it seems to be the amplifier bit that isn't working (all my connections are fine, the battery is fresh and OK, but no Voltage/Current whatsoever). I changed the IC (I'm using a socket), and the problem persists, I've followed the 1 watt integrated circuit amplifier circuit without doing any modifications (apart from the pcb).
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scott (Ichyc)
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Username: Ichyc

Post Number: 79
Registered: 6-2006
Posted on Saturday, August 19, 2006 - 2:04 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

No the lm386 dosent need a preamplifer for what you are using it for the problem may be in the lm386 circuit but it is more likely that the radio circuit is the problem take the schematic and check every part and connection.
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I. Dimov (Overrider)
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Username: Overrider

Post Number: 92
Registered: 12-2005
Posted on Saturday, August 19, 2006 - 4:01 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

I am sure the amplifier isn't working anyways, because, I tested it with my stereo.
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scott (Ichyc)
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Username: Ichyc

Post Number: 81
Registered: 6-2006
Posted on Saturday, August 19, 2006 - 5:21 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Then you should of fixed it rather than posting it here.They are prity simple circuits so it should be pritty simple to fix,if you need help just post it here.
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Alex Roberts (Whoo_mythbusters)
Senior Member
Username: Whoo_mythbusters

Post Number: 136
Registered: 9-2005
Posted on Saturday, August 19, 2006 - 11:11 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

That is why he is posting it here, he needs help.

Go back and check your circuit with the one on the site. if everything checks out then go over each part to make sure the parts are not faulty.

Pretty is not spelled with an I
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I. Dimov (Overrider)
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Username: Overrider

Post Number: 93
Registered: 12-2005
Posted on Sunday, August 20, 2006 - 2:33 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Well, I don't know, how to check the continuity of the caps (they block dc, so my multimeter doesn't register anything).
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I. Dimov (Overrider)
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Username: Overrider

Post Number: 94
Registered: 12-2005
Posted on Sunday, August 20, 2006 - 4:16 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

I cut off the wires between the radio and the amp, and plugged the amp in me stereo, and I raised the volume to the max, and put the speaker next to my ear, and I was able to hear what I was playing , but very faintly. I checked the output with my multimeter, and it was hovering around 0.20 volts, and the current was in nanoamps (!) probably.
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Alex Roberts (Whoo_mythbusters)
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Username: Whoo_mythbusters

Post Number: 139
Registered: 9-2005
Posted on Sunday, August 20, 2006 - 10:59 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

What kind of resistors are you using? Are they the right value, because it sounds like you are using to "strong" of resistors. But, if that is not the case you might want to consider just buying a pre-amplifier chip and using it. I'm not sure if Radio Shack sells these.
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I. Dimov (Overrider)
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Username: Overrider

Post Number: 95
Registered: 12-2005
Posted on Sunday, August 20, 2006 - 3:29 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

all resistors are the correct value (taken directly from the site), and they are all 0.25 w. How much power would a preamp require? Also, the amp doesn't get any power from the battery (I still heard it after unclipping it, and the volume didn't fall, it was really quiet anyways).
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Alex Roberts (Whoo_mythbusters)
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Username: Whoo_mythbusters

Post Number: 140
Registered: 9-2005
Posted on Sunday, August 20, 2006 - 3:55 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Well the amplifier on the site requires a 9 volt battery for it only, which means that if you are using the radio from the site a AA battery is needed for the radio its self.

The amount of power a Pre-amplifier chip needs would depend on what you get. Most small ones would not require anymore than 9 volts.
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I. Dimov (Overrider)
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Username: Overrider

Post Number: 96
Registered: 12-2005
Posted on Sunday, August 20, 2006 - 6:12 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

I'm using an un-powered crystal radio.
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Alex Roberts (Whoo_mythbusters)
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Username: Whoo_mythbusters

Post Number: 141
Registered: 9-2005
Posted on Sunday, August 20, 2006 - 6:31 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Ok, the radio may not need power, but the amplifier still does.
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I. Dimov (Overrider)
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Username: Overrider

Post Number: 97
Registered: 12-2005
Posted on Monday, August 21, 2006 - 7:45 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

You're so not understanding me. The battery is clipped on but the amplifier doesn't recieve any power (the signal from the headphones jack of my stereo is recieved prperly, but the sound isn't pleasing and realistic ( I have followed the circuit EXACTLY).
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Alex Roberts (Whoo_mythbusters)
Senior Member
Username: Whoo_mythbusters

Post Number: 145
Registered: 9-2005
Posted on Monday, August 21, 2006 - 1:23 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

I'm sorry for the confusion I was looking at the wrong amplifier on the main site. So you have checked the circuit and it is exactly correct, then it either sounds like (somehow) you are either connecting the IC incorrectly, or ,more likely, the IC is faulty, but you said you changed it in the very first post, but maybe somehow you got two faulty chips. If that is not the case I am not sure what to do.
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I. Dimov (Overrider)
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Username: Overrider

Post Number: 98
Registered: 12-2005
Posted on Monday, August 21, 2006 - 6:00 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Well, I went and asked a local radio-electritian, and according to him I would need a preamp. However there is something about that amplifier, that just isn't letting power get to it :-(
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Alex Roberts (Whoo_mythbusters)
Senior Member
Username: Whoo_mythbusters

Post Number: 146
Registered: 9-2005
Posted on Monday, August 21, 2006 - 7:52 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Yeah, the chip is bad, but a pre-amp for an amplifier? No, that makes it redundant and why would you make an amplifier that needs a pre-amplifier. It just doesnt make sence.
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I. Dimov (Overrider)
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Username: Overrider

Post Number: 100
Registered: 12-2005
Posted on Tuesday, August 22, 2006 - 4:07 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

The IC amp on the site needs a preamplifier for a crystal radio ( a X-tal radio, not a MK848 radio), to be able to drive low-Z earphones.
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Simon Quellen Field (Sfield)
Senior Member
Username: Sfield

Post Number: 1441
Registered: 12-2004
Posted on Tuesday, August 22, 2006 - 11:13 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

The LM386 amplifier is often used as a preamplifier for larger
amplifiers that have low impedance inputs.

The input impedance is 50,000 ohms, which is quite adequate for
amplifying crystal radios, whose output impedance is less than
that by quite a bit, usually around 2,000 ohms.

Your stereo can output many watts of power when the volume is
turned up to the maximum, and it has a low output impedance
(probably 8 ohms) so it can drive a signal through a brick. It
is easy to see how you could hear a signal from it coming through
a dead LM386 or an LM386 circuit that was unpowered or wired
incorrectly.

The spec sheet for the LM386 can be found at National Semiconductor's web page,
and will show you the schematics for the circuit.

The properly constructed amplifier should be able to amplify
the crystal radio with no trouble, especially if the bypass
capacitor is added to increase the gain to 200.


(Message edited by sfield on August 22, 2006)

(Message edited by sfield on August 22, 2006)
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Simon Quellen Field (Sfield)
Senior Member
Username: Sfield

Post Number: 1442
Registered: 12-2004
Posted on Tuesday, August 22, 2006 - 11:31 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

To Scott, Alex, and Overrider:

I just fixed a spelling error in my post that got by because I forgot
to click on the spell-check button in the Google Toolbar before submitting.

But, since typos are common, I later remembered and went back to use the
spell checker and it found the single 'l' that I was sure I typed twice ;-).

The spell checker is free, and will make you look much smarter in all of
your postings, here and elsewhere. It can correct errors in words like
"electrician" and "sense", and is particularly good at protecting people
who correct other people's spelling from making embarassing errors. ;-)

I strongly suggest that everyone download the Google Toolbar and use the
spell checker on every post. It also makes it much easier to find things
when searching, since searching is much easier when everyone agrees on
the spelling.
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Alex Roberts (Whoo_mythbusters)
Senior Member
Username: Whoo_mythbusters

Post Number: 148
Registered: 9-2005
Posted on Tuesday, August 22, 2006 - 2:08 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

I do have the Google tool bar and use the spell check button all the time. I miss things like that because I type to quickly and the spell checker does not pick up things like "sence" and "sense". I read over each posting a few times but I still miss them.
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Simon Quellen Field (Sfield)
Senior Member
Username: Sfield

Post Number: 1444
Registered: 12-2004
Posted on Tuesday, August 22, 2006 - 2:16 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

I just typed "sence" and the spell checker flagged it just fine.
So, I suspect that, like me, you just forgot to check that time.

But this thread should be about amplifiers and radios.
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Alex Roberts (Whoo_mythbusters)
Senior Member
Username: Whoo_mythbusters

Post Number: 149
Registered: 9-2005
Posted on Tuesday, August 22, 2006 - 3:58 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Yes, this should be about radios and amplifiers so this will be the last thing I say about this, I must have an older version than you, because when I type "sence" it does not mark it. I need to get a newer version. But, who cares its just a word.
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I. Dimov (Overrider)
Senior Member
Username: Overrider

Post Number: 101
Registered: 12-2005
Posted on Tuesday, August 22, 2006 - 4:24 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

*NOTE* I made such and amp, and it worked ( a while ago), on my stereo, but I missed the small jumper wire, between pins 2&4 I think, and it worked for a couple of hours, I unplugged it, and voila, next day it didn't. So because I copied the circuit from the one I first built, and missed the jumper wire again, and started to run it, is it possible, to brick the chip I did that on? (the second was used in a correct version).
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I. Dimov (Overrider)
Senior Member
Username: Overrider

Post Number: 102
Registered: 12-2005
Posted on Wednesday, August 23, 2006 - 4:18 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

I have a couple of questions:
1. Will I be able to use an impedance transformer, instead of the entire amply/x-tal earphone thingy? (i.e. the one for the am voice transmitter, or a 2000:8 O one)
2. Is there anyway, I can get a tachometer IC to display, the frequency I'm on on a small lcd display ( if yes, please point me to a good ic/screen combination)?
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I. Dimov (Overrider)
Senior Member
Username: Overrider

Post Number: 103
Registered: 12-2005
Posted on Thursday, August 24, 2006 - 4:56 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Ooops, didn't mean tachometer. So is there any display-driver, that'll let me display frequency, (to 4 digits after the decimal point, idealy).

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