I'm eager to learn about tube amps and build kits for guitar, hifi and maybe amateur radio, so I figured why not order a $10 Chinese preamp/headphone amp kit and see what happens?
Well it turned out "good." I put my headphones (47 ohms) into my cell phone (handiest audio source), listen to music and various volumes. Then I feed the phone audio into the amp, listen to the headphones.
Results:
Sounds better through the amp, I don't think placebo, I especially notice the clarity of percussion (drums, symbols) and distinct voices of the instruments through the amp.
However, I'd like to listen a little louder, but with the output on the phone and the amp volume all the way up, it is still not nearly as loud as the phone itself is capable of driving the same headphones. Is that normal? What can I do to make it louder? Am I mistaken to think this is a headphone amp, i.e. is it meant to just be an input for some other amp? Could it be intentionally limited? What does the term buffer mean?
I know I haven't given much to go on here, but I do have an oscilloscope and multimeter, are there some measurements I can take to see if this is normal? It's a 12vac input with 6J1 tubes: Amazon.com: DDIY Valve Preamp Buffer Tube Amplifiers Audio Preamplifier 6J1 Electronic Soldering Project: Home Audio & Theater
Thanks for any guidance.
Well it turned out "good." I put my headphones (47 ohms) into my cell phone (handiest audio source), listen to music and various volumes. Then I feed the phone audio into the amp, listen to the headphones.
Results:
Sounds better through the amp, I don't think placebo, I especially notice the clarity of percussion (drums, symbols) and distinct voices of the instruments through the amp.
However, I'd like to listen a little louder, but with the output on the phone and the amp volume all the way up, it is still not nearly as loud as the phone itself is capable of driving the same headphones. Is that normal? What can I do to make it louder? Am I mistaken to think this is a headphone amp, i.e. is it meant to just be an input for some other amp? Could it be intentionally limited? What does the term buffer mean?
I know I haven't given much to go on here, but I do have an oscilloscope and multimeter, are there some measurements I can take to see if this is normal? It's a 12vac input with 6J1 tubes: Amazon.com: DDIY Valve Preamp Buffer Tube Amplifiers Audio Preamplifier 6J1 Electronic Soldering Project: Home Audio & Theater
Thanks for any guidance.
It probably is not able to drive the 50 ohm load. Most preamps cannot, especially tube.
Buffer means no voltage gain (0dB), meaning with the proper load, output = input.
Buffer means no voltage gain (0dB), meaning with the proper load, output = input.
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This particular one is intended to tube-ify the sound.
A real buffer unloads the previous circuit, and better drives the following circuit.
A real buffer unloads the previous circuit, and better drives the following circuit.
Sounds like it's sort of a transformer, changing some input impedence to some different expected output impedence? Is there some way I can measure or otherwise know what I could feed this into?
Also, is this buffer (zero gain) a characteristic of these tubes, or could I make some modifications to the circuit to get a little more gain? I figure if that is possible, it would a) be a good learning experience about different tube circuits, and b) make the board more usable as a headphone amp until I build a more challenging project. It was $10 off of amazon and like an hour or so of soldering, so I don't mind experimenting.
It just came with a bag of parts, curious if this is a common, well known circuit where the schematic and mods might be found online?
The output drive ability of this circuit is probably around 1k ohm or even higher.
I doubt you could easily modify this board to be a good headphone amp.
Small audio tubes in general won't do that very well, at least without a transformer.
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