FX Audio 6j1 tube preamp - a $31 wonder

[kriss75]

Hello from Paris I received the FX Audio Tube 01 from AliExpress a week ago.

I'm using it solely as a buffer between a Kenwood KA 7100 (power stage restored with Elna Silmic and Nichicon capacitors). Cambridge Audio Azur DACmagic (Panasonic, Elna Silmic, and Nichicon capacitors) is connected to a linear power supply 12v 2a. My speakers are JBL L19 (with new foam of course, and capacitors Jentzen Z Superior crossovers). I won't mention the cables...

I tried it directly with the matched Voskhod 6J1P-EV tube and a basic Mean Well 12V 2A power supply. It was good at first, but not quite as good. I've been breaking in the tubes and components for about a hundred hours.
It does add some tube-like harmonics, but nothing spectacular. A bit artificial. The sound is even slightly degraded across the board. Oddly, there's a certain coldness, a harshness in the treble and upper midrange, and the bass is a bit muffled. The midrange is warmer and more rounded.

The device is sensitive to the power supply polarity. Important! I tested it with a raw power supply (an old 12V 1.5A transformer). It's better, more musical, but there's noise around 50Hz. The potentiometer is poor quality, the right channel is less bright. After some forceful manipulation by pulling on it, the problem is solved…

Okay, so why not try the Japanese version (J)? Found it on Amazon Japan. As seen in the comments, no, the Japanese version is different. The -6dB, of course. But apparently, the circuit board is of better quality, made of copper… Shematic is also the same, but components slightly better: Rubycon and Elna, and better filtering, but coupling capacitors are so ridiculous...Nfj japan sell special parts about this subject. And the board bigger different soldering points.

I'm going to replace the four coupling capacitors with Vishay MKT 1813, which have the biggest impact on the sound. Alps potentiometer Two 330uF capacitors Nichicon FG. Raw power supply with a Fosi Audio filter (another cheap Chinese product). And we'll stop there, otherwise we'll be looking at another product…

Here's a photo japan inside (low quality). The Chinese version is on the diyaudio website. I've noticed that the people on that site really want to improve things, but sometimes they do stupid things that ruin the first material...

Maybe it's funny sometimes, but i don't thing is fabulous on a good system already.

Wait and listen in two weeks

Less is more

Ahah sometimes I wonder about these so-called audiophiles. "To each their own tastes and to each their own ears"

I can repost better picture quality

Sorry, the french translate from google

 

[50 Green]

Hello from Paris I received the FX Audio Tube 01 from AliExpress a week ago.

I'm using it solely as a buffer between a Kenwood KA 7100 (power stage restored with Elna Silmic and Nichicon capacitors). Cambridge Audio Azur DACmagic (Panasonic, Elna Silmic, and Nichicon capacitors) is connected to a linear power supply 12v 2a. My speakers are JBL L19 (with new foam of course, and capacitors Jentzen Z Superior crossovers). I won't mention the cables...

I tried it directly with the matched Voskhod 6J1P-EV tube and a basic Mean Well 12V 2A power supply. It was good at first, but not quite as good. I've been breaking in the tubes and components for about a hundred hours.
It does add some tube-like harmonics, but nothing spectacular. A bit artificial. The sound is even slightly degraded across the board. Oddly, there's a certain coldness, a harshness in the treble and upper midrange, and the bass is a bit muffled. The midrange is warmer and more rounded.

The device is sensitive to the power supply polarity. Important! I tested it with a raw power supply (an old 12V 1.5A transformer). It's better, more musical, but there's noise around 50Hz. The potentiometer is poor quality, the right channel is less bright. After some forceful manipulation by pulling on it, the problem is solved…

Okay, so why not try the Japanese version (J)? Found it on Amazon Japan. As seen in the comments, no, the Japanese version is different. The -6dB, of course. But apparently, the circuit board is of better quality, made of copper… Shematic is also the same, but components slightly better: Rubycon and Elna, and better filtering, but coupling capacitors are so ridiculous...Nfj japan sell special parts about this subject. And the board bigger different soldering points.

I'm going to replace the four coupling capacitors with Vishay MKT 1813, which have the biggest impact on the sound. Alps potentiometer Two 330uF capacitors Nichicon FG. Raw power supply with a Fosi Audio filter (another cheap Chinese product). And we'll stop there, otherwise we'll be looking at another product…

Here's a photo japan inside (low quality). The Chinese version is on the diyaudio website. I've noticed that the people on that site really want to improve things, but sometimes they do stupid things that ruin the first material...

Maybe it's funny sometimes, but i don't thing is fabulous on a good system already.

Wait and listen in two weeks

Less is more

Ahah sometimes I wonder about these so-called audiophiles. "To each their own tastes and to each their own ears"

I can repost better picture quality

Sorry, the french translate from google

I have a couple of these Tube 01. I've replaced all the electrolytic caps and resistors with better quality (forget which - it's been years) and input/output caps w/ polypropylene. Also replaced the potentiometers (again forget which.) I prefer the sound of Mullard tubes in them, with Voskhod second (out of about 5-6 makes of NOS tubes I tried.) I use a linear PS for power.

That said, I haven't used either in years, since I tried the Nobsound E6, direct heated tube preamp that FlaCharlie mentioned in this thread and here. The E6, with NOS Soviet tubes (ebay from Ukraine) has a better sound to my ears.

 

[path4play]

I'm going to join the party. I'm waiting on a FX-Audio Tube 03J+ and FX-Audio Tube 01 just bought off feeBay. I run WiiM Airplay 2 to Rolls SX45 (to Fosi MC-331 amp to Dali Oberon 3s) and (to Cambridge Audio Mini X201). Went ahead and upgraded to Fosi ZA3 amp, so needed a tube pre-amp and going to try both. Also, grabbed a MUSES02 to try in the 03J+. Let's see what happens - was going for improved 3D holographic and "tube rolling" flavor. Any suggestions welcome, I'll come back to post "what i hear."

 

[path4play]

I'm going to join the party. I'm waiting on a FX-Audio Tube 03J+ and FX-Audio Tube 01 just bought off feeBay. I run WiiM Airplay 2 to Rolls SX45 (to Fosi MC-331 amp to Dali Oberon 3s) and (to Cambridge Audio Mini X201). Went ahead and upgraded to Fosi ZA3 amp, so needed a tube pre-amp and going to try both. Also, grabbed a MUSES02 to try in the 03J+. Let's see what happens - was going for improved 3D holographic and "tube rolling" flavor. Any suggestions welcome, I'll come back to post "what i hear."

Correction WiiM Airplay 2 to Fosi ZD3 DAC to Rolls SX45 (to Fosi MC-331 amp to Dali Oberon 3s) and (to Cambridge Audio Mini X201). Adding ZD3 and FX-Audio Tube 03J+ and FX-Audio Tube 01 to replace MC-331

 

[path4play]

few more tubes to play with:

LM Ericsson, Dumont and WE and another mysterious one

What was your final judgement on the Ericsson's? I have a pair of early 50's Ericsson 5591's. They are nickel plated, D getters like folks have mentioned here. I like them. To me, they are floaty, sparkly - dreamy and clear. They are at top my flavor rotations.

 

[path4play]

Sorry to be peppering the thread with the newbie questions, but reading back about this reverse polarity. Am I correct then that I'll want (or need to) flip the +/- inputs on my Dali's for both the FX-Audio Tube 03J+ and the FX-Audio Tube 01? I would assume then I would reverse the sub phase as well. Else, I'll hear loss of punch on bass as its sucking in, not pushing out?

 

[drjohnnyfeva]

I'm going to join the party. I'm waiting on a FX-Audio Tube 03J+ and FX-Audio Tube 01 just bought off feeBay. I run WiiM Airplay 2 to Rolls SX45 (to Fosi MC-331 amp to Dali Oberon 3s) and (to Cambridge Audio Mini X201). Went ahead and upgraded to Fosi ZA3 amp, so needed a tube pre-amp and going to try both. Also, grabbed a MUSES02 to try in the 03J+. Let's see what happens - was going for improved 3D holographic and "tube rolling" flavor. Any suggestions welcome, I'll come back to post "what i hear."

I've upgraded my Tube03's with Muses 8820's. The Muses 02's were a little rich for my blood with such an inexpensive unit. Altho, I researched many opamps to change, like Burstons? and other similarly priced options, I was very pleased with both the Muses 8920D's and, my preference, the 8820's. I have them in each of my three units.

I think you'll really enjoy the addition of the Tube03. I have them vintage units, but it really made a really nice difference on the Class D Fosi A07 when I was using it.

Also, there are a lot of tubes that will work on this unit. I went down the rabbit hole on tubes a while back based on @NZVinylFan's work on this thread in identifying tubes that "work." Look for post #51 on the link below.

REDUX and more - FX Audio 6j1 tube preamp - a $31 wonder

 

[path4play]

I've upgraded my Tube03's with Muses 8820's. The Muses 02's were a little rich for my blood with such an inexpensive unit. Altho, I researched many opamps to change, like Burstons? and other similarly priced options, I was very pleased with both the Muses 8920D's and, my preference, the 8820's. I have them in each of my three units.

I think you'll really enjoy the addition of the Tube03. I have them vintage units, but it really made a really nice difference on the Class D Fosi A07 when I was using it.

Also, there are a lot of tubes that will work on this unit. I went down the rabbit hole on tubes a while back based on @NZVinylFan's work on this thread in identifying tubes that "work." Look for post #51 on the link below.

REDUX and more - FX Audio 6j1 tube preamp - a $31 wonder

Thanks Dr. The 03J+ is taking for ever to ship from Japan, and its not $31 anymore either lol. I won't able to try the Muses02 for awhile longer. I'm trying to expand the holographic 3D "sparkle" while also keeping it non-fatiguing (wrapped in a warm blanket with hot cocoa type thing). Will see - I put a Burson Classic in my DAC and didn't like it before so went back to the original so I suppose that's want rolling them all about. I presume I DO NOT want one MUSES02 in the DAC and another in the Tube-FX. A lot of questions in my mind how I presume three op amps in a chain (Fosi DAC, FX-Tube and Fosi Amp) layer with each other. I have been living in the tube rabbit hole actually myself 7 months now, have all sorts of brands and eras... Thanks, I'll check out the link for sure.

 

[path4play]

Step one, swapped the Fosi-MC331 with fosi ZD3 and at same time added a FX-TUBE 01 - definitely feels more solid, bassy and detailed (I have 403B's in for tubes right now). Its interesting when you notice things in a song you never noticed before. It also seems like "loud" isn't as loud when its clearer or crisp, but one thing I am learning with each upgrade, great songs sound better, but old mp3's of poorly recorded songs start to sound worse.... I have a lot of experimenting ahead of me. ZD3 without FX-Tube, try Spotify lossless, the FX-Tube 03J+ when it arrives... op amps... different tubes... Dual Hi-Fi Ultra-Low Noise Linear Power Supply.... probably too much at once, but fun.

 

[drjohnnyfeva]

Step one, swapped the Fosi-MC331 with fosi ZD3 and at same time added a FX-TUBE 01 - definitely feels more solid, bassy and detailed (I have 403B's in for tubes right now). Its interesting when you notice things in a song you never noticed before. It also seems like "loud" isn't as loud when its clearer or crisp, but one thing I am learning with each upgrade, great songs sound better, but old mp3's of poorly recorded songs start to sound worse.... I have a lot of experimenting ahead of me. ZD3 without FX-Tube, try Spotify lossless, the FX-Tube 03J+ when it arrives... op amps... different tubes... Dual Hi-Fi Ultra-Low Noise Linear Power Supply.... probably too much at once, but fun.

The addition of a tube preamp with any of the Class D is what some like @Frank Sol called the necessary addition to any chip amp. I have an Aimiya A07 that sounds ok on its own, but sings with either the 03 or 01 I have. The 403's are sweet tubes. I have a pair of those in a Little Bear preamp that gives the feed from my PC just the right amount of gain and tubiness I need and appreciate.

On the distinction between the 03, 01, and 01j, the j is the Japanese version that I believe has either an internal switch or external button, that gives you some gain control. That detail is in this thread early on. The 01j and 01 do not have opamps; the 03 does have opamps. I don't have any experience with the j models, but I do have three - 03's and one - 01. I've moded one or two of the 03's with film caps and all of them with different opamps. The 01 I've left as stock. You can still get the 03 and 01 on Ali. I don't know about the j's, but I've heard they are available on ebay... where I think you said you got them. Might be available on Ali too, but not sure.

The other thing I did for my 03's and 01 is the linear power supply. I almost forgot about it, because I have it behind things and don't often see it. lol That made a pretty quick and noticeable improvement.

 

[path4play]

The addition of a tube preamp with any of the Class D is what some like @Frank Sol called the necessary addition to any chip amp. I have an Aimiya A07 that sounds ok on its own, but sings with either the 03 or 01 I have. The 403's are sweet tubes. I have a pair of those in a Little Bear preamp that gives the feed from my PC just the right amount of gain and tubiness I need and appreciate.

On the distinction between the 03, 01, and 01j, the j is the Japanese version that I believe has either an internal switch or external button, that gives you some gain control. That detail is in this thread early on. The 01j and 01 do not have opamps; the 03 does have opamps. I don't have any experience with the j models, but I do have three - 03's and one - 01. I've moded one or two of the 03's with film caps and all of them with different opamps. The 01 I've left as stock. You can still get the 03 and 01 on Ali. I don't know about the j's, but I've heard they are available on ebay... where I think you said you got them. Might be available on Ali too, but not sure.

The other thing I did for my 03's and 01 is the linear power supply. I almost forgot about it, because I have it behind things and don't often see it. lol That made a pretty quick and noticeable improvement.

Three -01's and one -03 - if that is not confirmation they are way to go (at least without full class A tube preamp) then I don't know what is?

 

[macgolf]

@path4play I've had a 01 in and out of my system for many years. I love the WE 403B's and RCA silver plate 6AK5's. I have a week on my 1st Class D amp in the form of a 3255 based Ampapa D1. The D1 probably wouldn't be staying without the 01, a 5670 based SA-1000 or my Douk Audio 12AX7 based P7. A linear power supply is a very nice upgrade for the 01. I'm grateful the 01 started my journey down the tube pre-amp rabbit hole. Enjoy your new additions!

 

[path4play]

@path4play I've had a 01 in and out of my system for many years. I love the WE 403B's and RCA silver plate 6AK5's. I have a week on my 1st Class D amp in the form of a 3255 based Ampapa D1. The D1 probably wouldn't be staying without the 01, a 5670 based SA-1000 or my Douk Audio 12AX7 based P7. A linear power supply is a very nice upgrade for the 01. I'm grateful the 01 started my journey down the tube pre-amp rabbit hole. Enjoy your new additions!

This whole thing was a bit predictable/trouble for me lol. I collect golden age comics, then had a couple years in a roman coin phase, even had a rock tumbling phase. As soon as I bought the MC-331 I was off to the races buying different E95/6AK5 class tubes (bulk lots included), rolling weekly to find the magic. Once I started thinking "can this sound even better" I started changing out parts of my chain, first was speakers to Dali Oberon's, then Bluetooth to wifi etc., but didn't want to leave that tube class because I sort of married into it with all these tubes. Coming up with music in late 70s and early 80s, I may have gotten more fond of "warm analog" type sounds than crystal clear clinical. In retrospect, for another $1k I might have just gone WiiM Ultra and Willsenton R8 and been done with it - this hobby makes one a little crazy. Did I make right choice, am I really already thinking of next steps before I even have these steps in the house? I'm committed to take this current "final" set up with FX-TUBE 03J+ when it all arrives at least a solid year and see where my thinking is at then. Presumably, the FX-Tube is a "more tubey" step up over the Fosi-MC331. You mentioned a couple of others - perhaps nothing is a clear "best." Interesting to see so many of these hybrid tube amps out there. As Johnny Fever (I'm old enough to rememer WKRP) hinted at, must be part of the rise of class D amps and want/need to add some warmer flavor overlay.

​

 

[macgolf]

This whole thing was a bit predictable/trouble for me lol. I collect golden age comics, then had a couple years in a roman coin phase, even had a rock tumbling phase. As soon as I bought the MC-331 I was off to the races buying different E95/6AK5 class tubes (bulk lots included), rolling weekly to find the magic. Once I started thinking "can this sound even better" I started changing out parts of my chain, first was speakers to Dali Oberon's, then Bluetooth to wifi etc., but didn't want to leave that tube class because I sort of married into it with all these tubes. Coming up with music in late 70s and early 80s, I may have gotten more fond of "warm analog" type sounds than crystal clear clinical. In retrospect, for another $1k I might have just gone WiiM Ultra and Willsenton R8 and been done with it - this hobby makes one a little crazy. Did I make right choice, am I really already thinking of next steps before I even have these steps in the house? I'm committed to take this current "final" set up with FX-TUBE 03J+ when it all arrives at least a solid year and see where my thinking is at then. Presumably, the FX-Tube is a "more tubey" step up over the Fosi-MC331. You mentioned a couple of others - perhaps nothing is a clear "best." Interesting to see so many of these hybrid tube amps out there. As Johnny Fever (I'm old enough to rememer WKRP) hinted at, must be part of the rise of class D amps and want/need to add some warmer flavor overlay.

​

Sounds like your having fun and to me that is what hobbies are about. The journey should be fun. You've given yourself a lot of flexibility to dial in a sound signature that's fit for your equipment, music and listening environment.

Right now I'm listening to a 3W/channel 6P1P/6J1 tube amp fronted by a 5670 tube based pre in near field. That set up is driving a pair of 6" full range drivers in .8 cu ft ported cabs. I gave the Class D Ampapa D1 amp 2 full days with that set up and wasn't sold. I was totally surprised to find I enjoyed the D1 fronted with the Douk 12AX7 P7 driving a pair of 65 YO E-V Aristocrats @ 9'. I usually reserve those speakers for my all tube units as they just don't like SS power. The Douk was added as a phono pre but also has a line in for my streaming/CD's. Strange pairing but surprisingly pleasing. In another week or so I'll rotate the TUBE-01 back in for the 5670 based one and compare. Synergy is where you find it.

 

[FlaCharlie]

This whole thing was a bit predictable/trouble for me lol. . . . Once I started thinking "can this sound even better" I started changing out parts of my chain . . . am I really already thinking of next steps? . . . must be part of the rise of class D amps and want/need to add some warmer flavor overlay.

It sounds like you're heading toward the DIY rabbit hole! Here's my approach . . .

Thread 'The Flow Pre4D - A DIY Tube Preamp'

Apr 15, 2025

I’m always encouraging people to build something themselves that uses tubes. My most recent amp threads feature simple designs that don’t even require the use of solder. And they use a SMPS (switch mode power supply), which also simplifies the DIY process.

Here I’m presenting a similar DIY project for those who are interested in tube preamps.

The popularity of tube preamps has been steadily rising for years now. Perhaps the best proof of this on AK is the massive thread over on the New Gear - Values forum about the little Chinese FX Tube 01 preamp and its various spin-off...

• FlaCharlie
• Replies: 45
• Forum: Tube Audio

• 

 

[path4play]

It sounds like you're heading toward the DIY rabbit hole! Here's my approach . . .

Thread 'The Flow Pre4D - A DIY Tube Preamp'

Apr 15, 2025

I’m always encouraging people to build something themselves that uses tubes. My most recent amp threads feature simple designs that don’t even require the use of solder. And they use a SMPS (switch mode power supply), which also simplifies the DIY process.

Here I’m presenting a similar DIY project for those who are interested in tube preamps.

The popularity of tube preamps has been steadily rising for years now. Perhaps the best proof of this on AK is the massive thread over on the New Gear - Values forum about the little Chinese FX Tube 01 preamp and its various spin-off...

• FlaCharlie
• Replies: 45
• Forum: Tube Audio

• 

Very cool and interesting Charlie. I certainly have a list of features and aspects I would want in a custom build, have gone through this journey.

 

[path4play]

The FX-TUBE 03J+ arrived yesterday. To be upfront, this “review” may not be incredibly useful, as I didn't perform a "clean analysis." I just wanted to max out the potential immediately, so I popped in my premium tubes (Western Electric 6069) and the Muses02, replacing the FX-TUBE 01 I was using as a placeholder.

To my ears and through my system chain, there is no way to separate the individual parts of this "effect." I suppose I could work backward later, but I digress.

On "Tin Pan Alley" the shout and shot are clear guitar plucks and drum booms. "Riders on the Storm" featured legitimate lightning crack with a high, wide rumble and that great ghostly overdub; I could almost sense the rain dripping off a rooftop. On Yes’s Changes I hear a proper drum kick not a "heartbeat" sound. Spanish Harlem featured clear “she’s” and “garden” vocals without sounding shrill. It tamed the organ on Jimmy Smith’s "Hi-Heel Sneakers" and—OMG—"Chocolate Chip Trip" swung wide to the far left and right of my ears.

"Bubbles" is back, baby! And she even brought along a click in the upper right ear that I don’t recall ever noticing before. While it's not a reference song, 10cc’s "I'm Not In Love" played randomly, and it felt like hearing a new song for the first time.

The sound is warm—thicker, maybe—but not mushy; it remains clean. To my 58 year old ears w/tinitus, it feels like barefoot on the grass or a silk nightgown as opposed to a “cold steel rail.”

The only things I don’t like: the LED lights on the FX-TUBE 03J+ are a "piss yellow," for lack of a better term. Why not match the orange of the tube filament? Also, the gain and tone switches on the bottom are so tiny I had to use the head of a needle to move them (I have them all set to "off").

So this is best I've heard so far on this journey. I haven't tapped anyone with a killer system to hear what a premo set up sounds like. Am I at the top of my mountain? I don't know? LPS still on its way... Going to let this settle in and see how long I can go without another swap - I'm already thinking maybe dump the WiiM mini, ZD3 DAC and Rolls SX45 and plug in a WiiM Ultra? Too soon?

 

[path4play]

Day 2, I put the OPA1656 in the ZD3 DAC. So my impression is first off, surprised the OPA1656 (now first in chain) really was able to "overwhelm" or change the Muses02 sound so much. I suppose they are in synergy, combination but I felt I couldn't "hear" Muses02 anymore. Second, its certainly clearer, smoother and yes, more beautiful sounding, perhaps romantic - even "happier" if that can be a thing. However, after going through the reference songs, it also seemed each song got more generic or similar to each other. I didn't "taste" immersion quite as much or notice "all the things" I felt I noticed without OPA1656 (aka stock chips and Muses02 only in FX-TUBE). Like Tin Pan Alley Muses02 only I 'felt' the pain and struggle and sort of ugly grittiness more. Maybe could "hear" the string plucks more defined. So frankly I'm not sure here - I "like" them both but different ways I guess. If these op amps were tubes, I'd say with OPA1656 for "all day listening" and without (let Muses02 dominate) for like, feeling I'm right in a jazzy, smoke filled room? Mmmmm? I know this isn't an op amp thread, but the FX-Tube is involved. I'm actually considering reversing the op amps, give the Muses02 more dominance at start of chain and put the OPA1656 in the FX-Tube. Anyone have thoughts on this?

 

[path4play]

Ok, for folks following the saga. I got it dialed in and wow! I don't think its even just my ears or preferences at this point it is so dramatic. 100% Muses02 in ZD3 DAC and OPA1656 in the FX-Tube (w/Western Electric 6069 tubes). Got the drama and emotion along with the sparkles and happy rainbows delivery all within the 3D holographic, toe tapping, face squinting, air guitaring on the string picks, swaying presence. This thing is dialed in (still without LPS). After that, I have reference and can start rolling tubes.

 

[drjohnnyfeva]

Ok, for folks following the saga. I got it dialed in and wow! I don't think its even just my ears or preferences at this point it is so dramatic. 100% Muses02 in ZD3 DAC and OPA1656 in the FX-Tube (w/Western Electric 6069 tubes). Got the drama and emotion along with the sparkles and happy rainbows delivery all within the 3D holographic, toe tapping, face squinting, air guitaring on the string picks, swaying presence. This thing is dialed in (still without LPS). After that, I have reference and can start rolling tubes.

Nice! Mixing opamps across devices and even within a device is not something I've done. I think every device with opamps I've ever gotten has had that ubiquitous NE4355? from Texas Instruments. Every opamp I tried in replacing them sounded different. Some were brighter, others too smeary... I settled on the Muses, but I may go back and play with the 1656's in conjunction with them to see what happens.

Depending on the overall sound you're going for, the WE tubes are highly thought of. They sound great. No loss of detail and they have that tubey thing about them. The RCA's are similar. The Voskhod Rockets are great too. I used them where I need a little more gain.