FX Audio 6j1 tube preamp - a $31 wonder

Nice explanation. Using a 6bq5 amp with the pre. Does have more bass now n sounds much better in combo with Yamaha ns 1000's. Was going to return the pre, but will keep it, now. Mids n tweets r doing a better job at producing subtle sounds not heard before. Nice pre.
 
got another pre: SUCA AUDIO 6k4 tubes, socketed NE5532's
DC 12V/1.5A, 20HZ -20KHZ((±3dB), SNR: 98DB, THD: 0.1%
same as fx with cheaper components: screws, caps, plastic tube sockets, inputs, pwr adpter no pwr supply shield...
haven't heard it, yet; certainly needs upgrades. hearing it...sounds like asss; dull. mfr. says wait 2- days. for tubes or cap break in? tubes broken in. maybe caps.
 

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changed 1uf caps associated with input jacks to MPPIMG_20220609_121102765.jpg IMG_20220609_121051077.jpg n added 2.7uf(total 3.7) to tubes, left it on overnight using the supplied 6k4 tubes and it's gone up in sound quality from a 1 to an 8. bass is not to my liking, though. lacks the gain the others have, as well; even with a 12v/ 3a pwr adapter.
 
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raycarr00 said:
changed 1uf caps associated with input jacks to MPPView attachment 2588526 View attachment 2588527 n added 2.7uf(total 3.7) to tubes, left it on overnight using the supplied 6k4 tubes and it's gone up in sound quality from a 1 to an 8. bass is not to my liking, though. lacks the gain the others have, as well; even with a 12v/ 3a pwr adapter.
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The function of the cap at the input is to block any DC voltage that might be coming from the source. The music signal is AC. Many sources already have a cap on their output so this is added "just in case". There is nothing to be gained by increasing the value/size of this cap.

The cap should be installed between the input and the volume pot, not after the volume pot as it seems to be in some of these preamps. That way it protects the pot from DC, which can lead to a scratchy volume control.

The other cap comes off the plate of the tube and, along with the following 100k resistor forms a high pass filter. The stock 1uf / 100k combo has a -3db rolloff point of 1.59 Hz. That's plenty low enough.

The reason it's that low, even though there is no music frequency that low, is because you can sometimes have phase issues at frequencies up to 10x the rolloff point. Such phase issues are measurable but not necessarily audible. The musical spectrum is generally considered to be 20Hz to 20kHz but there is very little, often no, musical information that low or that high. The lowest note on a 4 string bass is 40Hz and it's 31Hz on a 5 string bass.

It's also very unlikely that your speakers can reproduce frequencies that low, unless you're using a sub. And you may also not be able to hear that low or, especially, that high. Find an online tone generator and listen.

Increasing the cap from 1uf to 3.7uf drops the -3db point to 0.43 Hz. Since there is no music down that low or even 10x that low, from a technical standpoint there's really nothing to gain by doing this. It is possible that the cap is better quality but having a -3db point of 0.43 Hz vs 1.59 Hz will not affect anything within the audible frequency range.
 
I have been using my FX Audio 01J in between my Sansui AU-7700’s preamp outs and main ins. It creates a very pleasant hybrid sound with the vintage SS integrated amp, by adding vacuum tube gain in the middle of the amp.
The nickel plated RCA 6AK5’s offer the best combination of performance for the FX Audio 01J. I use an larger external power supply than is really necessary because I picked it up off Craigslist for only $40. I consider this little preamp to be among the best audio buys I have ever made.
 
Dr. Ears said:
I have been using my FX Audio 01J in between my Sansui AU-7700’s preamp outs and main ins. It creates a very pleasant hybrid sound with the vintage SS integrated amp, by adding vacuum tube gain in the middle of the amp.
The nickel plated RCA 6AK5’s offer the best combination of performance for the FX Audio 01J. I use an larger external power supply than is really necessary because I picked it up off Craigslist for only $40. I consider this little preamp to be among the best audio buys I have ever made.
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I checked with QRX-Restore the Sansui restoration experts before inserting my FX Audio 01J, in between my SS Sansui’s preamp outs and main ins, it’s a neat way of adding a little vacuum tube gain to the vintage SS integrated amp. There is no issue in running the two preamps together, I just set the integrated’s volume control then adjust the FX Audio to add the desired amount of vacuum tube gain. BTW, I have at least 40 pairs of tubes for the FX Audio, most people will enjoy the nickel plated RCA 6AK5’s, I have a slight preference for the EF-95, made in Holland tubes.
 
I am using a pair of GE 5654W and they sound fine .. -- is there really a noticeable difference with either the EF-95's or 6AK5's ? Also - are either of these tubes in current production, or all NOS ? Here I go down the rabbit hole ...
 
kappclark said:
I am using a pair of GE 5654W and they sound fine .. -- is there really a noticeable difference with either the EF-95's or 6AK5's ? Also - are either of these tubes in current production, or all NOS ? Here I go down the rabbit hole ...
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I liked both much better and they are only NOS.
 
Kaval said:
What's your take on Mullard M8100 tubes?

Are any users here?
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The ones I have created a sound floor. Didn't like them. They were the second pair of tubes I got after the GE's. I like the Voshkods, RCA, and Motorola the best. They are not expensive and they sound great.
 
Dr. Ears said:
I think RCA made the Motorola’s.
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When I first started rolling tubes, I read an article about how to read the tubes to determine manufacturer and date of production. I think you may be right on the Motorolas. They sound very similar to the RCA's. Honestly, sometimes I just buy tubes because they come in an original box. I've started collecting those as much or more than the tubes themselves. I have about a dozen pairs now and many of them came in boxes. I think the packaging is pretty neat, so if I get a cool box with an alternate pair of tubes that I can use if one of my preferred pairs conks-out, I'm pretty happy! :)

And since I'm on, I might as well post that I ordered another set of opamps. I got them the other day and plugged them in today. I have to admit, I was VERY skeptical with the order. I've posted a link to another forum where a well-known user there compared the opamps we've mentioned numerous times... MUSES, LME-- among others. But the one that was on par with the Sparkos and Bursons according to him was the OPA627AU. Actually he rated the Bursons V6 Vivid and the OPA627AU equal. So I started looking for them. They are Burr-Brown opamps.

Low and behold I found the OPA627AU's were single channel chips. That lead me to looking for them dual, but the price for a single on Mouser was $35, iirc. I read how to combine two singles to make a dual, but that was too much fine soldering for my skill level. I was only able to find them in dual from a source selling for around $110 for a pair maybe 6 months ago. Anyway, I also found a place out of the Phillipines, on the bay, making duals and selling for a modest 5.65 a pair. I said it must be cheap knock off, imitation crap, but then there were others popping up in Google searches selling for $20 or so for a pair of dual channel over the past few months. So I finally put the order in on the bay the other day and ordered the original OPA627AU's I saw in my initial search figuring, what the hell.

They sound great! I won't lie that I'm absolutely shocked. I put them in wanting to scoff and complain, but I have to admit that they sound fantastic. I'm going to keep them in and I feel like I'm going to continue wanting to hate them, but just not being able to. lol. Really pleasantly surprised by this little expenditure and shot in the face of reason.
 
Had to register an account after lurking extensively. this thread is the ****! thank you to everyone who provided your intense insight and observations, it was truly helpful. I wanted to ask to anyone here who will know better than me, even though I think I've gotten enough info from past posts.

I recently bought a used NAD 3020i locally. the original owner bought it new in the 90s and never used it extensively. Even after a brief audition, where everything seemed to work just fine, I just sent it in for a recap – figured it didn't hurt to make sure it doesn't fail on me so soon.

The whole discourse around AIYIMA/FX/SUCA and cheap tube amps got me interested, as i've never used one in my life (cheap or expensive). but i'm game to try it out just to see how it plays with my DAC (Fiio E10k). I intend to use my NAD 3020i as a desktop amp for speakers and headphones, and ordered a Tube-03 a while ago to use with it. In the middle of a move so I'll only get to setting it up this weekend.

I will be using my NAD to control input and volume, so it seems that the gain control on the Tube-03 is of no use to me. I've read that removing the op-amps will be beneficial in this case, as I'm plugging it into an integrated. I just wanted to check if there's any risk leaving the op-amps in and essentially running my DAC through two preamps? (Tube-03 and 3020i preamp section). It seems op-amp removal will solve this, but if there's no harm done, I'm fine leaving them in - or even replacing them with better ones along the way.

I'll try out the tape loop option so I can A/B test, but if I were to put the Tube-03 between the main-in and pre-out, will it also feed the headphone signal? Or will it be bypassed and headphones will only receive the signal fed from the 3020i preamp? I'm still grasping the terminology used here so excuse me for the cluttered language!

Funnily enough, I ordered a pair of Voskhod Rocket 6J1P-EVs to try tube rolling, and they've arrived before the tube amp lol
 
Welcome.

Don't be so quick to remove the opamps. You've gotten superior tubes already over the stock ones. It might be of benefit initially to do the tape loop in deciding. Then you can go the Main-in/Pre-out route, where everything will be colored with the Tube 03, including the phones, I believe (but someone else might want to chime in on that).

I would not change any of the settings you presently have on the NAD. Insert the Tube 03 using the tape loop and set the tone controls on the Tube 03 at neutral, which I believe is 12 o'clock. Back the volume of the Tube 03 all the way off and gradually bring it on to your normal listening level. See how it sounds in and out of the loop. Play with the tone controls a little until you find what you like. If it's neutral that you like best, then you can remove the the tone opamp. It does provide a little gain so you're going to have to bump the volume of the NAD a bit to compensate. Also, before removing either of the opamps, experiment with bumping the volume up a little on the Tube 03 and backing off the NAD a little to see if you get more color from the Tube 03. If you like the sound with the tone controls, tho, there are superior opamps to the stock ones that with a small investment can improve the sound a lot. There are some that have mixed the brands of opamps, even; and others who have removed just the tone opamp and left the volume one or simply removed both. Lots of options and investigation for you.

Lastly, almost everyone on here has a linear power supply. Something like this:

https://www.amazon.com/Universal-Co...=1659361255&sprefix=pyramid+po,aps,168&sr=8-2

Small investments in tubes, opamps, and a power supply have turned this gem that PG began discussing years ago into a powerhouse. Good luck.
 
drjohnnyfeva said:
Welcome.

Don't be so quick to remove the opamps. You've gotten superior tubes already over the stock ones. It might be of benefit initially to do the tape loop in deciding. Then you can go the Main-in/Pre-out route, where everything will be colored with the Tube 03, including the phones, I believe (but someone else might want to chime in on that).

I would not change any of the settings you presently have on the NAD. Insert the Tube 03 using the tape loop and set the tone controls on the Tube 03 at neutral, which I believe is 12 o'clock. Back the volume of the Tube 03 all the way off and gradually bring it on to your normal listening level. See how it sounds in and out of the loop. Play with the tone controls a little until you find what you like. If it's neutral that you like best, then you can remove the the tone opamp. It does provide a little gain so you're going to have to bump the volume of the NAD a bit to compensate. Also, before removing either of the opamps, experiment with bumping the volume up a little on the Tube 03 and backing off the NAD a little to see if you get more color from the Tube 03. If you like the sound with the tone controls, tho, there are superior opamps to the stock ones that with a small investment can improve the sound a lot. There are some that have mixed the brands of opamps, even; and others who have removed just the tone opamp and left the volume one or simply removed both. Lots of options and investigation for you.

Lastly, almost everyone on here has a linear power supply. Something like this:

https://www.amazon.com/Universal-Compact-Bench-Power-Supply/dp/B00069RB1Q/ref=sr_1_2?crid=14NECRYY0K7ZQ&keywords=pyramid+power+supply+12v&qid=1659361255&sprefix=pyramid+po,aps,168&sr=8-2

Small investments in tubes, opamps, and a power supply have turned this gem that PG began discussing years ago into a powerhouse. Good luck.
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Appreciate the rundown! Can't wait to tinker with it.

I'm not exactly sure how a linear power supply works but will definitely look into it. Power has always been the least of my concerns when it comes to audio (just not properly informed + the added cost) but if it does have an effect I don't see the harm in trying.
 

Having tried and used the FX 03 with and without opamps....I sonically preferred it without the opamps and just tube rolling....As the opamps are a great feature and well implemented, but are primarily there to control the tone and volume control functions.... and therefore do add their different sonic flavours to the circuit and mix...which is fun as there are great opamps out there to upgrade to!

Therefore you can keep the opamps in and set the controls to suit your tastes and then leave it alone.... and just control the tone and volume from your main source or external amps..as and when or if possible

However without the opamps it becomes just a fixed tube only circuit .. with no additional tone and volume or opamp influences or interferences.

So the great thing is... you can try and compare both way...with or without opamps..as its very easy to do, with zero cost or problems.
 
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