Tube preamp kit FE-6J1-2.0B

A valve amplifier or tube amplifier is a type of electronic amplifier that uses vacuum tubes to increase the amplitude or power of a signal. In audio applications, valves continue to be highly desired by most professional users, particularly in recording studios’ equipment and guitar amplifiers. Among stereo enthusiasts, there is a subgroup of audio buffs who advocate the use of tube amplifiers for home listening; they argue that tube amplifiers produce a “warmer” or more “natural” valve sound. Tube sound (or valve sound) is the characteristic sound associated with a vacuum tube-based audio amplifier.

Before the rise of the transistor in the 1950s, all amps used vacuum tubes. Still the audible significance of tube amplification on audio signals is a subject of continuing debate among audio enthusiasts. Audiophiles disagree on the relative merits of tube vs solid state amplification. Tube amplifiers have retained a loyal following amongst some audiophiles and musicians. Some musiciansprefer the distortion characteristics of tubes over transistors for electric guitar, bass, and other instrument amplifiers.

Today tubes are the incandescent light bulb of the audio world: an older, relatively inefficient technology that consumes a good deal of energy to output a modest amount of power. For power amplifiers solid state designs can be manufactured without output transformers and are therefore immune to speaker-dependent impedance mismatches and transforer effects. I have been long the person who has usef transistors for hifi applications and considered they to be better for hifi amplifiers.

Tubes have their place in audio processing where you want to add to the sound the “warm tube distortion” sound (for example in guitar amplifiers). For preamplifer use tubes can work well. To get the idea of tube sound and how tube preamps works, I got this cheap kit for experimenting: AC12V/1A Stereo 2.0 Pre Amplifier Headphone Module Amplifier Buffer Board. It is a preamplifer that is suitable for conntrolling volume of line level audio signals (attenuate or amplify) and maybe add some magic tube sound to audio. Cheap way though of experiencing ‘tube sound’!

Specifications:

Type: FE-6J1-2.0B
Channel type: 2.0/ stereo
Power input: AC12V 1A / 5.5*2.5 plug
Knob function: Power switch / volume control
Size: 76 x 74 x 20mm
Pre-amp tube diameter: 18mm

Everything was packed to a plastic bags.


There seem to be some small LEDs in the center of tube sockers. Those are blue LEDs that make the tubes to glow in blue color.

One tube installed.


Two tubes installed.

The volume control in this board is combined volume control and power switch: The knob rotates counterclockwise to reduce the volume, when the volume to the hour, continues to rotate, until the “tick” sound, then power off, lights out.

A look to the connectors…

On the left side: Audio signal input terminals that can be connected to mobile phones, computers, MP3, MP4, and other music player.

On the right side: The output terminal of the audio signal can be connected to an audio signal input terminal of a power amplifier and a power amplifier board. And next to them power input (12V AC 1A).

When I powered the amplifier, it did what it promised. It worked OK as a preamplifier.

Voltage amplification can be controlled from zero to around 6 times (around 15 dB).

The output worked on testing well to over 2Vpp input signal amplitudes at maximum amplitude without noticeable distortion on oscilloscope screen starting to appear.

The signal output impedance is around 3 kilo-ohms. That works well as line level signal preamplifier that drives power amplifier. This circuit is not headphone amplifier that drives headphones (if you thing if that from product name), it would would be pretty non-ideal headphone amplifier for low impedance headphones.

Does what it describes as preamplifier for audio signals. It sounds good, but I can’t find it to be adding any magic “tube sound” to the audio. The circuit adds some slight huming though (at more than about 1/3rd volume).

Note on powering: you need an (not DC) 12V plugpack or transformer. The kit says it needs 12V 1A power supply, so that what I used (I did not measure the actual power this circuit takes).

Ti get better idea how this circuit amplifier works, a circuit diagram would be nice. With some Googling I found that there are several pages that tell about this or very similar tube amplifiers:

http://www.head-fi.org/t/661823/mercator-6j1-very-inexpensive-chinese-2-x-6j1-tube-pre-amp-head-fi-amp-consensus-is-that-this-is-not-an-ld-clone

https://www.circuitlab.com/circuit/9vnehk/fever-6j1-tube-pre-amp-circuit/

http://www.diyaudio.com/forums/tubes-valves/286349-6j1-tube-buffer-circuit-diagram.html

The best circuit diagram I could found was this at https://www.circuitlab.com/circuit/9vnehk/fever-6j1-tube-pre-amp-circuit/

 

tubepre

It seems to be mostly correct (shows only one channel), but has some small details that do not seem to be correct (for example connection of resistor on amplifier output should be connected to ground and not -28V). By the way the circuit diagram can be edited at https://www.circuitlab.com/editor/#?id=9vnehk

As you can see in the circuit diagram the power supply part converts the 12V AC input to +28V and -28V power rails that are used to power the tube. This means that the tube is run at 56V voltage (which is quite low voltage for an audio tube circuit, they typically operate at 100-300V voltage depending on tube type). This 56V voltage is good for safety – it does not hurt too much if you accidentally come in contact with this voltage when you test the board before putting it to case.

The power supply circuit consists of voltage multiplier + rectifier circuit followed with filter capacitors, some transistor circuitry (emitter follower with current limiting, somewhat resembles gyrator circuit) and more filter capacitors.

The tube heaters are directly powered from input 12V AC (two 6.3V heating coils in series can be powered from 12V AC).

Information on the 6J1  tube used can be found at http://www.radiomuseum.org/tubes/tube_6j1.html and http://greatsound168.pixnet.net/blog/post/254453398-%E4%BA%8C%E5%8F%B06j1%E7%B7%A9%E8%A1%9D%E7%B4%9A%E7%9A%84%E5%88%86%E6%9E%90

Another preamp circuit using 6J1 tube at http://www.yunwt.net/1mydiy/qt14.htm

The basic design of this AC12V/1A Stereo 2.0 Pre Amplifier Headphone Module Amplifier Buffer Board seems to be sensible. If I had designd this I would maybe had designed few things slightly differently (for example power supply filtering and maybe tube heating) – that could have maybe reduced the slight mains humming on the output. Anyways as it isC12V/1A Stereo 2.0 Pre Amplifier Headphone Module Amplifier Buffer Board seems to be good quality cheap tube preamplifier.

 

12 Comments

  1. Tomi Engdahl says:

    The technical specifications said that the module uses 12V AC 1A power supply.

    I tested my premap with current meter, and found out that it takes around 200 mA current from 12V AC 50 Hz power source.

    Reply
  2. Tomi Engdahl says:

    Now is the Golden Age of Artisanal, Non-Traditional Tube Amps
    http://hackaday.com/2016/09/24/now-is-the-golden-age-of-artisanal-non-traditional-tube-amps/

    Earlier in the month, [Elliot Williams] quipped that it had been far too long since we saw a VFD-based amplifier build. Well, that dry spell is over. This week, [kodera2t] started showing off his design for a VFD headphone amp.

    Here’s the thing, this isn’t using old surplus vacuum fluorescent displays. This is actually a new part. We first covered it about 18 months ago when Korg and Noritake announced the NuTube. t’s the VFD form factor you would find in old stereo and lab equipment, but housed in the familiar glass case is a triode specifically designed for that purpose.

    Amplifier project by Nutube, a new vacuum tube!
    You know VFD, but may not know this VFD. It can amplify signal!! Yes, it is a TRIODE!!
    https://hackaday.io/project/15023-amplifier-project-by-nutube-a-new-vacuum-tube

    VFD is well known as digit display but not a amplifying device. A Japanese company Noritake and KORG made a incredible device by VFD technology. It looks like VFD but it works as a TRIODE.

    Most of vacuum tune requires high voltage but VFD is just around 12V. Moreover it is quite compact compared to general vacuum tube!

    Tubes on a Chip
    http://hackaday.com/2015/02/02/tubes-on-a-chip/

    For 40 years, there really haven’t been many advances in tube technology. Now, at last, there’s something new.

    The Nutube 6P1, as this curious invention is called, is a full triode or half of a 12ax7 you’ll find in just about every tube amp ever. Unlike the 12ax7, it consumes 2% of the power required of a normal tube, is 30% of the size of the normal tube, and lasts for 30,000 hours.

    This new tube-chip thing was brought to life by Korg, makers of fine musical equipment and Noritake Co., manufacturers of vacuum fluorescent displays. There’s no word on what these tubes will be used in and there’s no data sheet.

    Reply
  3. Tomi Engdahl says:

    Fleming patents vacuum tube, November 16, 1904
    http://www.edn.com/electronics-blogs/edn-moments/4401607/Fleming-patents-vacuum-tube–November-16–1904?_mc=NL_EDN_EDT_EDN_today_20161116&cid=NL_EDN_EDT_EDN_today_20161116&elqTrackId=52a02361c21142d7be1f11f0b95ed9d3&elq=2cc3a21a761e407391818a97c2957f71&elqaid=34807&elqat=1&elqCampaignId=30382

    English engineer John Ambrose Fleming received a patent for the thermionic valve, better known as the vacuum tube, on November 16, 1904.

    The two-electrode vacuum-tube rectifier, which Fleming called the oscillation valve, and some peers called the Fleming valve, was a major breakthrough. However, whether the breakthrough actually belonged to Fleming was debated in and out of court.

    The United States Supreme Court eventually invalidated the patent because of an improper disclaimer and maintained that the technology in the patent was known art when filed.

    Even still, Fleming continued to work on his diode and saw its use in radio receivers and radars for many decades afterward, until it was superseded by solid state electronic technology.

    Reply
  4. Tomi Engdahl says:

    Dave reverse engineers the XuanZu X2-U808 Hi-Fi Headphone Amplifier to see if the valves actually do anything.

    EEVblog #837 – Reverse Engineering A Valve Headphone Amplifier
    https://www.youtube.com/watch?v=coSt5HWRvv4

    Reply
  5. Tomi Engdahl says:

    Another valve amplifier design:

    The Muffsy BSTRD – Valve Preamp
    https://hackaday.io/project/16944-the-muffsy-bstrd-valve-preamp

    An open source Class-A valve preamplifier and regulated PSU, complete with Eagle project files and detailed Bill of Materials

    Reply
  6. Tomi Engdahl says:

    The Muffsy BSTRD – Valve Preamp
    https://hackaday.io/project/16944-the-muffsy-bstrd-valve-preamp

    An open source Class-A valve preamplifier and regulated PSU, complete with Eagle project files and detailed Bill of Materials

    View Gallery
    1.5k 0 1 3
    Team (1)

    skrodahl

    Join this project’s team
    completed project
    hardware
    PREAMP MUFFSY Valve tube eagle files gerbers hifi BSTRD The bastard Ny Elektronik psu POWERSUPPLY TL783 LM317 6J5 6S2S
    This project is submitted for

    Hackaday.com Tip Line

    This project was created on 10/31/2016 and last updated 2 minutes ago.
    Description
    The BSTRD iis a simple Class-A valve preamplifier, complete with Eagle project files in the files area of this project. The preamp has been built and tested, so it’s perfectly safe to order the PCBs from the fab house of your choice.

    The project is fully open source, no strings attached.

    Reply
  7. Tomi Engdahl says:

    Tube amp project:
    Dumpster Dive Speaker Results In Tube Amplifier
    http://hackaday.com/2017/03/18/dumpster-dive-speaker-results-in-tube-amplifier/

    [Michael] found a nice reference design of an OTL amplifier for a 620 ohm single speaker. He decided to use the same design but because these speakers were about 300 ohm each, he would have to wire his two speakers in series.

    A regular halogen lamp 12V transformer takes care of the heater power supply for all the tubes, and a second, smaller 12V transformer is wired backwards to provide the 300V needed for the plate supply.

    Output-Transformer-Less Tube Guitar Amplifier
    https://acidbourbon.wordpress.com/2017/03/08/output-transformer-less-guitar-amplifier/

    I did a bit of research on the radio (Philips Jupiter 463) and the speakers online and I found out that there were some radio receivers that in fact did not possess an output transformer. That is possible because they had high impedance speakers (I assume thin coil wire, many windings). The speakers have a DC resistance of 300 Ohms each. The amplifiers to drive these speakers are consequently called OTL (Output-Transformer-Less) amplifiers.

    Reply
  8. Tomi Engdahl says:

    The Muffsy BSTRD – Valve Preamp
    https://hackaday.io/project/16944-the-muffsy-bstrd-valve-preamp

    An open source Class-A valve preamplifier and regulated PSU, complete with Eagle project files and detailed Bill of Materials

    The BSTRD iis a simple Class-A valve preamplifier, complete with Eagle project files in the files area of this project. The preamp has been built and tested, so it’s perfectly safe to order the PCBs from the fab house of your choice.

    The project is fully open source, no strings attached. Use the attached files as you like, for what you like. I’d appreciate if I were credited, but I don’t require it.

    The circuit is modified version of a the line amp from a preamp published in the Danish magazine Ny Elektronik: http://www.nisbeth.dk/carrotman/files/Bastard.pdf

    Reply
  9. Tomi Engdahl says:

    Amplifier project by Nutube, a new vacuum tube!
    You know VFD, but may not know this VFD. It can amplify signal!! Yes, it is a TRIODE!!
    https://hackaday.io/project/15023-amplifier-project-by-nutube-a-new-vacuum-tube

    VFD is well known as digit display but not a amplifying device. A Japanese company Noritake and KORG made a incredible device by VFD technology. It looks like VFD but it works as a TRIODE. I cannot avoid it and quickly designed a headphone amplifier.

    Most of vacuum tune requires high voltage but VFD is just around 12V. Moreover it is quite compact compared to general vacuum tube!

    As same as general vacuum tube, Nutube has high input and output impedance. For driving headphone, some impedance converter is required and I simply added voltage follower. As a place holder, I used TL072 but in the real device I will use NJM8920 (MUSES8920)

    http://korgnutube.com/en/

    Reply
  10. Tomi Engdahl says:

    The Best Stereo Valve Amp In The World
    http://hackaday.com/2017/08/16/the-best-stereo-valve-amp-in-the-world/

    There are few greater follies in the world of electronics than that of an electronic engineering student who has just discovered the world of hi-fi audio. I was once that electronic engineering student and here follows a tale of one of my follies. One that incidentally taught me a lot about my craft, and I am thankful to say at least did not cost me much money.

    Nowadays, building a valve amp is a surprisingly straightforward process, as there are many online suppliers who will sell you a kit of parts from the other side of the world. Transformer manufacturers produce readily available products for your HT supply and your audio output matching, so to a certain extent your choice of amp is simply a case of picking your preferred circuit and assembling it.

    Reply

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