Vacuum Tube Preamp Circuit for MP3 Players
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- Опубліковано 6 жов 2024
- A short video on how to design a basic, easy to build and tweak 1-tube preamp to boost the output of your MP3 player. This will add enough gain to be able to drive a tube amplifier direct, when you don't want to use a separate preamp.
Dear Tony, thank you for this video! It's very helpful for the beginners. Greetings from Belarus!
I'm sure everyone watching these series is waiting for the schematics of the preamp you've shown in previous series (with tone controls). Or a video would be a killer :)
Tony, I see that you are looking at the 12AX7 tubes... Ever thought about trying out the EF86 Pentode? I don't have personal experience (yet) but I have seen other UA-camr's state that the 12AX7 tubes tend to peak around the mid frequencies, where the EF86 has a flatter frequency response. Not to mention the gain of around 180, it even looks prettier too!... It's probably got the best datasheet, most datasheets that I have are usually only one page jobs but not the EF86... They really went to town on that one... Once again, I'm no expert but it's what I have gathered so far. Everyone else seems to concentrate on the output stage of tube amplification but very little is covered on the preamp section so I was happy to see this video! You really did an amazing job on the explanation of a topic that I believe is neglected...
HI Tony , the mu of a triode is only theoretci based on an infinite load.........SO 100 for an ECC83/12AX7 is in real use far lower.
The 12AU7 is usualy a better sounding tube than the AX7 , besides exceptions ....
for low impedance drive and lower B+ voltages on following amp the 6DJ7 /ECC88 family may be a good choice ( as seen on different commercial line level amps )
Anyway any of these tubes can indeed do the job .....just beware of not applying max operation conditions for long life and correct filament voltages !;
So useful to me...cheers!
Nice video, thanks! Seems simpler than solid state. I would use it as a output stage for a DAC I've build. The only thing holding me back to try it is the cost of the high voltage supply, aren't these expensive?
Marcel,
Good question. I will do a short follow-up video on how you can build an inexpensive power supply for this project. I'm sure others would be interested in this as well. Stay tuned!
That would be great! Looking forward to it.
Actually.. If you swap out the tube for a transistor and use a low voltage transformer instead, you will find that it's literally the same but cheaper... If you disregard the heater, you are essentially looking at the base, emitter and collector of a solid state transistor... Hope this helps 😊
John Audio Tech built a stereo preamp using a 12 volt battery
Low (“line”) output level .. also true for Bluetooth receivers ...
The first thing you should do is get a TUBE MANUAL. In it you will find a section of tubes that can be used for AUDIO AMPLIFIERS. The manual has values that may be used for a given gain. It will also tell you of HOW to design tube AUDIO AMPLIFIERS. Just putting values to a circuit does not teach you much of anything. Yes there rules of thumb you can use, but for me I like to know why I am using such values.
The tube manuals have a wealth of information .
@Henry Hopkinson
Yep. No real explanation of grid biasing, no grid stopper etc.
I already have 1 12AX7 now. all I need now is a power supply
How do you characterize the impedance of the MP3 palyer. should that not be taken into account?
I see there are 3 filament pins which two would be bridged?
good ideas.I was thinking to build this preamp as a portable to use on old tube radios with a phono input so a record player with a modern (low voltage output) cartridge.Any ideas for a power supply? Thanks,Art.
Check out the next video for a power supply. You may have to tweak the design a bit to get the gain you want from the circuit. Different cartridges have different outputs. You can play with the values of the cathode resistor and then add or remove a cathode bypass capacitor to get the gain you want. Good luck!
If you're listening to MP3s, you don't need a fancy preamp. Just use any old one.
Now where is the fun in doing that?
This may be perfect for me to start with. DO you still need a preamp stag in the amp before this preamp? My amp is just 6sn7 and 4 6v6 tubes. Leslie organ amp model-44W
If you use this circuit with the 12AX7 and the 1.8K cathode resistor, you should be fine.
what are the wattages on the resistors?
They are usually 1/2 watt. But you can get away with a 1/4 watt for the cathode bias resister. If you put a 1 watt, you won’t hurt nothing. It just costs more
Could this be used for a headphone amp ?
Impedance will be wrong
Total caos.