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PostPosted: 26 May 2010, 08:43 
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Joined: 13 Apr 2010, 10:39
Posts: 37
Location: Dallas, Texas, USA
I'm guessing possibly the pins might be wired up incorrectly.

For the LM317 (PDF Datasheet: http://www.national.com/ds/LM/LM117.pdf), when it's sitting on it's 'back', it's:
1. ADJ
2. Voltage OUT
3. Voltage IN

Alternatively, the Bill of Materials specifies only a 10 ohm, 1/4 watt resistor, which ought to be fine, but I think I used a 1/2 watt. But double-check the LM317 pinout first, it's easy to get incorrect - the LM780X's have a pinout of 'OUT, ADJ, IN', and I think I've seen other regulators have a pinout of 'IN, ADJ, OUT', so it's always easy to get these wrong. My bet is the LM317 is ok and unharmed by the 'experiment'.

Mike Y
Dallas, Texas

crippledlemming wrote:
So I finished the build tonight and powered up the amp and the 10ohm resistor on the right channel immediately started smoking. I checked all my solder joints and the circuit nothing looks out of place, any ideas on what could cause this?


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PostPosted: 27 May 2010, 20:37 
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Joined: 11 Apr 2010, 01:54
Posts: 8
Location: Tel Aviv, Israel
Hi.
Finished to build the amp today. In first test with cheap earbuds amp works well I can hear music, but in the 10 seconds my earbuds starts to produce heat. Strange.
Is this DC leak problem? First thought was it is because of non stabilized power supply, I have tried to connect to battery power supply instead... same problem.
Which part in the schematics may produce the problem and what I need to check to solve this?

Thanks in advance.
Dan.


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PostPosted: 28 May 2010, 05:30 
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Joined: 15 May 2010, 10:01
Posts: 6
crippledlemming, the same thing happened when we wired the input power the wrong way. Magic smoke immediately. Check that you have + on + and - on -.

Cheers

/Jonas


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PostPosted: 31 May 2010, 21:15 
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Joined: 03 Aug 2008, 20:22
Posts: 386
Location: Denver, Colorado
AndrAKondrA wrote:
Finished to build the amp today. In first test with cheap earbuds amp works well I can hear music, but in the 10 seconds my earbuds starts to produce heat. Strange.
Is this DC leak problem? First thought was it is because of non stabilized power supply, I have tried to connect to battery power supply instead... same problem.
Which part in the schematics may produce the problem and what I need to check to solve this?

Dan, First thing I can think is that you have the output coupling capacitors backward, in this configuration they will not block DC to the headphones. Check the output with a dvm, if you have ~6v to the earbuds, replace the capacitors. Once the caps have been reversed they are most likely damaged. The good thing is you used some cheap phones for testing. Let us know what you find, as some other builders may run into the same problem.

Also download and verify your voltage regulator pinout. National Semiconductor pinout for the LM317 is Adjust Vout Vin. The tab is Vout as well.

Rogers


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PostPosted: 01 Jun 2010, 17:48 
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Joined: 01 Jun 2010, 17:22
Posts: 4
Hi, I'm new to the board. I've been looking at the design and I'm getting the parts to build it. It looks straight-forward, but There isn't a big explanation on how the potentiometer is wired. (I got mine from Radio Shack and it has 3 prongs on it)

I believe the board is sending wired from the input to the potentiometer. I have a potentiometer with three prongs, do I need one with six? (3 for input to go into, 3 to output into the circuit board?). I'm also not too familiar with potentiometers and I cannot find a decent explanation about which prong is wired to the "L" or "R" side of the circuit board and if the third is wired to the "ground" and which to which.
Attachment:
Alps-Potentiometer-12AU7-IRF510-Headphone-Amp.jpg

I've provided the image file with annotations on it about what I'm confused about. Any help would be appreciated :P


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PostPosted: 02 Jun 2010, 00:15 
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Joined: 15 May 2010, 10:01
Posts: 6
Hi

I'm no expert so don't take my words too seriously. We bought a two chanel potentiometer, one for left and one for right chanel. What you do is you measusre what two pind the resistans goes down over when you turn the pot clock wise. Those two pins are for the signal (in signal we wired to the pot) and the third one for each chanel goes to ground. It works fine for us.

Cheers

/Jonas


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PostPosted: 02 Jun 2010, 05:53 
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Joined: 17 Apr 2010, 16:07
Posts: 39
Location: Huddersfield ,West Yorkshire,UK
This is how the majority of pots are wired up with some exceptions. The picture shows a dual gang for stereo applications

Image

The wiper being the output

you can also wire it in reverse the wiper being input

ground stays the same position

if you only have 1 ground say from a jack short the 2 grounds together on the pot and attach one side
its generaly prefered to keep the grounds seperate for each channel but depends on the circuit

hope this helps

i still need to get around to getting more parts to build one of these .My gainclone chassis is taking way too much time ;)

Koogar :smoking:

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PostPosted: 03 Jun 2010, 18:24 
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Joined: 11 Apr 2010, 01:54
Posts: 8
Location: Tel Aviv, Israel
First of all thanks for the response.

The output DC leakage was the "mistake of the beginners" the main circuit was double checked and the output caps soldered after that. And the mistake was - forgot to cut foil strip the between the legs of caps in the strip board = shortcut of the legs, like no capacitor at all.

After overall happiness of finding the mistake another problem rises.

When I reach 7 volt in (U in) the amp started to produce strange hum. First thought was I'm too close to source of 50 hz interference. Screening the amp doesn't help. Maybe my stabilizer doesn't work? After double check all seems to be OK. I have clear output voltage. Hm....
Connected 2 DVMs and oscilloscope to find the problem. See the pictures of measures.
The amplifier has no input signal.
Little DVM shows the input voltage.
Big DVM - the voltage before output capacitor.
Oscilloscope shows output signal (before capacitor).


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Last edited by AndrAKondrA on 03 Jun 2010, 19:19, edited 1 time in total.

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PostPosted: 03 Jun 2010, 19:16 
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Joined: 11 Apr 2010, 01:54
Posts: 8
Location: Tel Aviv, Israel
Until I reach 7 volt zone i can hear music clearly (with Electro Harmonics tube, JJ tube heaters in this low voltage not produce enough heat to start Thermo-emission). After 7 volt strong hum noise. :(
After many thoughts of what can produce the problem and double checking the circuit. Disconnected the amp from the stabilizer and checked the input voltage with the oscilloscope - from 1-12 volt i see strait line no ripple in 5mv resolution. Seems the power line is OK. Second step - replacing the tube and checking the bias voltages - doesn't help. Same hum in same voltage Strange very strange.
Connected the amp to the battery - here is the place the solution comes. 7-9-10 volt I hear the music without hum. OK it's supply voltage problem. Changing cheap AC/DC adapter to better quality adapter helps. But, still why until 7 volt zone i didn't hear the hum noise? Connected again the cheap adapter and oscilloscope to the output of the LM317 regulator. If the amp is disconnected no ripple seen in output voltage, when I connect the amp to the regulator I see ripple (after 7 volt zone) in the input voltage!

Bottom line:
1. I think its some sort of resonance between the amp and cheap power source.
2. Stay away from very cheap adapters they are unpredictable!

Dan.
P.S Sorry for my English.


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PostPosted: 03 Jun 2010, 20:17 
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Joined: 28 May 2008, 21:53
Posts: 4580
Location: Winnipeg, CANADA
I would start with the power supply. Fill out the resistor values for the regulator circuit so we can check it.

Also, check the voltage from your DC supply (before the regulator). You need >14.5V into the regulator (under load).

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