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Old 11th September 2012, 09:00 PM   #1
tipetu is offline tipetu  Norway
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Default 12AU7 stereo SE mini-amp build!

Click the image to open in full size.

Look at this tiny thing. It`s a super simple 12AU7 single ended stereo amplifier. The tiny egg-sized output trannys are reverb transformers.

I`ll post more when I build it these days!
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Old 12th September 2012, 08:53 AM   #2
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Can you show the schematic ?
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Old 12th September 2012, 09:05 AM   #3
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Schematic whould be nice.
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Old 12th September 2012, 10:18 AM   #4
airegin is offline airegin  Italy
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nice toy, should be something like this, around 200mW:

Last edited by Pano; 12th September 2012 at 03:56 PM. Reason: schematic removed
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Old 12th September 2012, 12:53 PM   #5
tipetu is offline tipetu  Norway
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No schematic yet, but it`s quite similar to the one posted earlier here. Perhaps I`ll put some bigger caps in the powersupply. I`ll probably finish it today or tomorrow.
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Old 12th September 2012, 01:14 PM   #6
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[QUOTE=airegin;3161682]nice toy, should be something like this, around 200mW:




Something wrong with the schematic: You cannot run the thing straight from the power line - there has to be a power transformer.

Cheers,
Martin

Last edited by Pano; 12th September 2012 at 03:57 PM. Reason: schematic removed
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Old 12th September 2012, 02:04 PM   #7
palmas is offline palmas  Portugal
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Quote:
Originally Posted by bayermar View Post
Something wrong with the schematic: You cannot run the thing straight from the power line - there has to be a power transformer.

Cheers,
Martin
Actually you CAN, but you shouldn't!

Still seems a lot of feedback. No oscilation with those trafs?
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Old 12th September 2012, 02:25 PM   #8
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Quote:
Originally Posted by palmas View Post
Actually you CAN, but you shouldn't!

Still seems a lot of feedback. No oscilation with those trafs?
if the input has a transformer and the output (without feedbacK) and ground ofc. didnt they use power transformer less designs for PA systems?
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Old 12th September 2012, 02:30 PM   #9
palmas is offline palmas  Portugal
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Quote:
Originally Posted by ruben alstad View Post
if the input has a transformer and the output (without feedbacK) and ground ofc. didnt they use power transformer less designs for PA systems?
You just need to not connect anything to the power ground (AC supply power ground), as most single phase AC have the neutral connected to ground (and you'd have a big BANG)
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Old 12th September 2012, 03:13 PM   #10
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Quote:
Originally Posted by ruben alstad View Post
if the input has a transformer and the output (without feedbacK) and ground ofc. didnt they use power transformer less designs for PA systems?
They used to do a lot of these things in low cost systems decades ago (e.g. guitar amplifiers, record players etc).
You cannot do this nowadays - for good reason.
(of course there are modern transformerless designs but they use other means of protection).
I strongly recommend not to post these kind of schematics without warning on internet forums, because there will always be a kid who knows how to solder but not what he is doing... (actually if you check the forum rules the moderators think quite along the same line).

Cheers,
Martin
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