FX Audio Tube 01 Mods

[suzziman]

Dear Members, after reading a lot about cheap NJ Fx Audio Tube 01 hence got one and upgrading the Caps and Tubes.

The result is 50% better sound stage than stock unit so its definitely a good pre and can be used as buffer too.

Upgraded film caps to Rifa with 2% tolerance, went with Rubycon or Nichicon 330uf caps and didnt touch the 470uf on Psu as they seemed okay.

Definitely change to a better 12v power supply than stock, GE5654 tubes and wow the bass and tube effect is worth enjoying.

[Kay Pirinha]

Although MKT's might not be the best capacitors for audio use, I'd keep my hands off of Rifa's due to bad experience I've gathered during the last decades. They're prone to emulate firecrackers.
Better go for MKP's if there's enough space in your PCB.
Best regards!

[Tjrep]

I have just bought the same Model 01 with the Jan 5664 tubes. It's still in the burn-in phase, so hard to say what it will sound like, but even now it sounds pretty decent for the money.

The problem I have is that it has way too much gain. With my Cambridge Dacmagic 100 directly coupled to the input and the Model 01 feeding into my Harman Kardon PA2200 , I get really high volume after the third click of the volumepot, the first two clicks doing absolutely nothing.

Has anyone had a look at which resistors set the gain in this pre-amp?

Best regards.

[Kay Pirinha]

Please show the schematics to us and most probably we may tell.
Best regards!

[Tjrep]

Originally Posted by Kay Pirinha

Please show the schematics to us and most probably we may tell.
Best regards!

I wish I could. I've been scouring the Internet but schematics are virtually unobtanium. I can't locate them anywhere so I wondered if someone over here has had more luck.
Best regards.

[FlaCharlie]

Originally Posted by Tjrep

I've been scouring the Internet but schematics are virtually unobtanium. I can't locate them anywhere so I wondered if someone over here has had more luck.

There seem to be a few variations of this design, which is sold under a wide variety of brand names with slightly different features. These units are not buffers, they have gain, and most modern sources put out enough signal that a simple attenuator is all that's really necessary.

There is a mega-thread about these preamps over on the AK forum. Some posts on there include schematics.

There are at least two different power supply designs but, ultimately, the various brands seem to use the same operating points for the tubes. Those operating points are far from optimal.

I was in the process of breadboarding a very basic preamp and was trying a variety of tubes so I tried these tubes using the stock operating points. I used a traditional PS, however, so I was able to experiment. I found that they sounded much better when operated at higher voltages with different operating points. I posted about all this in the AK thread.

FX Audio 6j1 tube preamp - a $31 wonder | Page 66 | Audiokarma Home Audio Stereo Discussion Forums

[Tjrep]

Originally Posted by FlaCharlie

There seem to be a few variations of this design, which is sold under a wide variety of brand names with slightly different features. These units are not buffers, they have gain, and most modern sources put out enough signal that a simple attenuator is all that's really necessary.

There is a mega-thread about these preamps over on the AK forum. Some posts on there include schematics.

There are at least two different power supply designs but, ultimately, the various brands seem to use the same operating points for the tubes. Those operating points are far from optimal.

I was in the process of breadboarding a very basic preamp and was trying a variety of tubes so I tried these tubes using the stock operating points. I used a traditional PS, however, so I was able to experiment. I found that they sounded much better when operated at higher voltages with different operating points. I posted about all this in the AK thread.

FX Audio 6j1 tube preamp - a $31 wonder | Page 66 | Audiokarma Home Audio Stereo Discussion Forums

Thanks, I'll have a look over there.
Best Regards.

[suzziman]

Originally Posted by Kay Pirinha

Although MKT's might not be the best capacitors for audio use, I'd keep my hands off of Rifa's due to bad experience I've gathered during the last decades. They're prone to emulate firecrackers.
Better go for MKP's if there's enough space in your PCB.
Best regards!

Thanks for feedback, I was originally looking for WIMA 1uf Caps but couldnt lay my hands on them, these Rifa are measured to precision and time will tell. Moreover gain thing is pretty loud, using as Pre on a 80wpch ss power amp this baby doesnt even need to go above 8oclock.

[Burnedfingers]

Originally Posted by Tjrep

I have just bought the same Model 01 with the Jan 5664 tubes. It's still in the burn-in phase, so hard to say what it will sound like, but even now it sounds pretty decent for the money.

The problem I have is that it has way too much gain. With my Cambridge Dacmagic 100 directly coupled to the input and the Model 01 feeding into my Harman Kardon PA2200 , I get really high volume after the third click of the volumepot, the first two clicks doing absolutely nothing.

Has anyone had a look at which resistors set the gain in this pre-amp?

Best regards.

You need to take a look at the Dacmagic and see what its output is before you set blame on the 01 unit. Does the 01 have gain or is it a straight buffer? I would suggest testing the units and if the 100 has too much output simply pad it down.

[umut1001]

Hi.I searched a lot but could not find an information.What is input and output impedance of this buffer?