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PostPosted: 15 Dec 2010, 15:17 
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Joined: 17 Apr 2010, 16:07
Posts: 39
Location: Huddersfield ,West Yorkshire,UK
SmittyHalibut wrote:
gofast wrote:
while assembling this particular one, i connected the PS wrong once and saw some smoke from either power-regulator or the transistor. it was just a few seconds and didn't seem to have damaged any of them....but do you think one of them might be damaged and causing the distortion?

If you let out the "magic smoke," that's almost certainly the problem. I'd replace all four components: the 510s and the 317s. Smoke is never a good thing.

Its not just reverse polarity or getting the legs too hot the mosfets are sensitive to static also so ground yourself on something metal like a radiator first before handling just as a precaution :)

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PostPosted: 15 Dec 2010, 15:21 
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Joined: 30 Nov 2010, 15:35
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thanks for your advices!

i've seen my share of magic smoke escape from transformers before....not a good feeling.


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PostPosted: 16 Dec 2010, 03:06 
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Joined: 30 Nov 2010, 15:35
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built the second one and hooked it up to the battery from the first build. sounds simply excellent!

no hum, noise, or distortion!

now only if i can get the wall wart supply with RC filter figured out.....

one interesting thing i experienced is that different tubes require a large adjustment in resistance. after setting the voltage right at 6.30v on a RCA 12au7, sylvania measured 8.20v!! and GE ripped gray plate at 7.14v. i need to figure out a way to adjust the resistance from outside when tube rolling.

few more pictures.

Image
Image


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PostPosted: 18 Dec 2010, 14:08 
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Location: Winnipeg, CANADA
Hi gofast, looking good. What is the the other tube gear in the back?
gofast wrote:
now only if i can get the wall wart supply with RC filter figured out.....

Best bet is to get a 16-20VDC supply and run it through a 7812 (make sure it it rated at 1A) or a LM317 regulator circuit.
Cheers

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PostPosted: 18 Dec 2010, 20:00 
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Joined: 18 Sep 2010, 12:48
Posts: 81
you can also go look for a 12V wall wart... regulated or switch mode...

then let it through a row of capacitors to remove ripples.

This is what I do for mine. :P


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PostPosted: 19 Dec 2010, 20:38 
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Joined: 30 Nov 2010, 15:35
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santik wrote:
you can also go look for a 12V wall wart... regulated or switch mode...

then let it through a row of capacitors to remove ripples.

This is what I do for mine. :P



Gio wrote:
Hi gofast, looking good. What is the the other tube gear in the back?
gofast wrote:
now only if i can get the wall wart supply with RC filter figured out.....

Best bet is to get a 16-20VDC supply and run it through a 7812 (make sure it it rated at 1A) or a LM317 regulator circuit.
Cheers

thanks.
it's a bottlehead "crack" headphone amp. output tranyless with 6080 tube. sounds quite nice.

yeah...i'm planning one building some of those filter circuits. or if i can get those 12v batteries for cheap somewhere, i'd love to build half a dozen of these little amps. maybe i'll pass them out to my friends as xmas gifts. :D


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PostPosted: 19 Dec 2010, 21:03 
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Joined: 27 Nov 2010, 02:18
Posts: 34
Location: Arroyo Grande, CA, US
Classes are done for the quarter, holiday parties thrown, wife and daughter watching Christmas movies... I finally had some downtime to finish building my amp. Here are some pictures I tweeted earlier today:

http://yfrog.com/h05fjcaj
http://yfrog.com/h8cp9hjj
http://yfrog.com/h6mbdj
http://yfrog.com/h7ypmj
http://yfrog.com/h2wu7kj

I've made a few minor modifications to the circuit:
- I added a 1k resistor to the input before the volume pot and DC blocking cap. This gives your source a bit of a load so it has something to drive, and also pulls some current through the cable which raises the signal-to-noise ratio (more signal, constant noise, better ratio.) Also, when nothing is connected to the amp, it ties the input to near-ground (1k to ground on a 100k impedance input is ALMOST ground) so you don't get the annoying buzzing.

Rather than just use a 1k static resistor, I decided to use a 10 turn pot instead which allows you to trim down the maximum volume on the amp. On larger mixers, this is usually called a pad. If your input is too hot such that you can only use a little bit of your volume knob's full range, you can turn down the input here giving you full range use of the volume knob again.

- I put the volume knob in the circuit diagram (between the pad described above, and the DC blocking cap). It's a dual 10k audio taper indexed pot. The "indexed" means it clicks as you turn it. I like that. :-)

- I upped C1 from 2.2uF to 5.6uF (the largest film cap I could find at my local electronics supply store). This should help with the low frequency response. It seems to have, though I haven't used my "good" headphones yet.

- I also made several components "connectors" on the board. That is, audio comes in through a removable connector, hits the pad, then leaves again through another connector to go to the volume pot, then comes back to go through the DC blocking cap and 100k load resistor, then hits another connector to go to the tube (which is not mounted directly to the board; see the pictures above.). Then when it comes back from the tube, everything else is directly on the board until its ready to go out the 1/4" headphone connector. My schematic includes all these connectors. I included a block at the top of the diagram with all to components put back into the circuit (not connectors) so you can see it a bit easier.

- I added a 2200uF power supply cap between +B and GND. I figure a touch more filtering won't hurt (though I'm not really noticing power supply noise), and the added power for bass kicks would be good too.

I'm listening to it right now and am quite pleased with how its turned out. :-D


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PostPosted: 22 Dec 2010, 18:25 
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Joined: 22 Dec 2010, 18:18
Posts: 9
This is my first diy amp project and I did pretty miserably in my college engineering circuits class (I am a coe, definitely not ee). Anyway, I am a bit confused about the wiring in several spots. First, I do not understand why the wiring on the trim pots differs between the channels. On the left channel, the tube output is tied to pin 3, whereas on the right channel the tube output is tied to pin 3 and pin 2. Also pin 1 on the left channel's trimpot is tied to its pin 2 and the pin 1 on the right side's trimpot is tied directly to the 12V power source.

The next problem I have is that the right channel's 100uF capacitor's positive end is tied directly to the ground, whereas the left channel's 100uF capacitors negative end is tied to the ground. And this then changes which side of the capacitor is tied to the tube (positive to tube's pin 8 on left and negative to tube's pin 3 on the right).


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PostPosted: 22 Dec 2010, 20:22 
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Joined: 22 Nov 2010, 19:57
Posts: 1
Location: Quincy, MA
Finally had a day off to put my amp together:
Attachment:
CoasterAmp.jpg

Setting the bias i maxed out the trimpots and just barely got it to 6.5V on both channels. I'm powering it with a 12V SLA battery and get zero hiss or pops when the input is disconnected. Sounds great so far, i've connected it to a pair of ATH-M50's and it is PLENTY loud. Just need to get an enclosure and tidy it all up.


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PostPosted: 23 Dec 2010, 06:22 
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Joined: 22 Dec 2010, 18:18
Posts: 9
SmittyHalibut wrote:
- I also made several components "connectors" on the board. That is, audio comes in through a removable connector, hits the pad, then leaves again through another connector to go to the volume pot, then comes back to go through the DC blocking cap and 100k load resistor, then hits another connector to go to the tube (which is not mounted directly to the board; see the pictures above.). Then when it comes back from the tube, everything else is directly on the board until its ready to go out the 1/4" headphone connector. My schematic includes all these connectors. I included a block at the top of the diagram with all to components put back into the circuit (not connectors) so you can see it a bit easier.

Funny, I had the exact same approach with the connectors -- though I only made a connector from tube to main board.


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