Tube Headphone Amp

Mar 09, 2008 8 Replies
D

Hi, I'm interested in building a simple tube stereo headphone amp, I found a circuit but have a few questions.



Link to circuit (Site is in Japanese, but schematic is perfectly readable)

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First, the schematic calls for a 117 volt/12.6 volt transformer across what I think is the output, I can only find a 115 volt/12.6 volt 2.5 amp transformer. Will this work? Another question is about the numbering of tube pins on the 12AU7A, there's two sets of numbers. Which ones am I supposed to read? Last question is regarding the 12AU7A itself, will I regular 12AU7 work here? Thanks for your help.



Thanks in advance.



Dave


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D

Forgot one thing, all the ground connections, are they going to signal ground, or B-?

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D

Specs for the transfomrer is as follows: * Primary 115 VAC, 60 Hz. * Center tapped secondary. * Enclosed, 4 hole chassis mount. * Minimum 6" long leads. * Dual bobbin design - no electrostatic shield required. * Class B insulation (130 degrees, C) * Hi-Pot test of 2,000 V RMS. * UL listed (# E50394) & CSA certified (# LR3902).

Specifications Rating: 12.6 VCT, 2.5 A Mounting Centers: 1.5" x 1.56", vertical

Or another transformer I found

TRANSFORMER, POWER, 125 V, 15 mA

Primary: 117 volt, 50/60 Hz Secondary: 125 V, 15 mA Filament winding: 12.6 volt, 0.3 amp Mounting centers: 2", U-bracket

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E

Well, it's certainly a close enough match to the specified part for sure, but using a MAINS transformer as the output transformer will assure truly dismal audio quality.

Sorry to tell you but many (most) hobby projects of this ilk are truly dreadfully designed and will assure at best mediocre results that somewhat defeat their original purpose.

Graham

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E

Hello ! Ting ting ! Wakey wakey ! The 12AU7 / ECC82 is a DUAL triode. One set of numbers refers to the first triode and the second to the err .. second triode.

Have you been using valves long ?

Yes, a 12AU7 works very well in a socket designed for a 12AU7.

If you mean 12AX7 or 12AT7 then the answer is NO.

Graham

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E

Read the thread on grounding and star points in rec.audio.tubes. It's very recent.

Graham

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M

Yes, it's the same thing. But you might be happier with the results if you use real audio output transformers.

The two numbers refer to the first and second sections of the tube. Use the first set of numbers for one channel and the second set for the other channel.

Yes, no problem.

Mike

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T

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has audio transformers that'll work much better than mains transformers. You can start with mains transformers, but as Eeyore so diplomatically mentioned, your sound quality may suffer.

Tim Wescott Control systems and communications consulting http://www.wescottdesign.com Need to learn how to apply control theory in your embedded system? "Applied Control Theory for Embedded Systems" by Tim Wescott Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
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