FX Audio 6j1 tube preamp - a $31 wonder

the Yaqin's cd1 , cd2 and cd3 try to do that

I like my cd2 and cd3 -- I know many if not most 'audiophiles' dont
 
This is so unscientific I'm reluctant to post it (not really)

my FX has Mullard 6j1 equivalent tubes , my CD2 Voskhod 6J1P-EV - all are well 'burned-in'

one night I switched the units in and out only once - they were between a Passive Pre and an Amp

I could hear somewhat (goodness) what we claim the FX brings to a system with the CD2 in the FX's place -- I didnt match Vol technically and of course there were the different tubes

Generally I prefer the FX but there are most likely hard fact reasons why as mentioned above
 
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This is so unscientific I'm reluctant to post it (not really)

my FX has Mullard 6j1 equivalent tubes , my CD2 Voskhod 6J1P-EV - all are well 'burned-in'

one night I switched the units in and out only once - they were between a Pre and an Amp

I could hear somewhat (goodness) what we claim the FX brings to a system with the CD2 in the FX's place -- I didnt match Vol technically and of course there were the different tubes

Generally I prefer the FX but there are most likely hard fact reasons why as mentioned above
Did you factor in polarity inversion with the FX vs not with CD2?
 
What "polarity inversion" ? :D

I just switched the units in/out and made sure the right/left ch were correct


On edit: I know the terms are different but I also checked to make sure speakers were in phase
 
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This is so unscientific I'm reluctant to post it (not really)

my FX has Mullard 6j1 equivalent tubes , my CD2 Voskhod 6J1P-EV - all are well 'burned-in'

one night I switched the units in and out only once - they were between a Pre and an Amp

I could hear somewhat (goodness) what we claim the FX brings to a system with the CD2 in the FX's place -- I didnt match Vol technically and of course there were the different tubes

Generally I prefer the FX but there are most likely hard fact reasons why as mentioned above

I too had my cd-2 in the same location as you and it worked fine but decided to move it back into the tape loop with the rest of my processing units. That way I knew I would never overload the input of the cd-2 buffer.

My FX TUBE-03 is currently located between my smartphone (streaming device) and pre amp input.
 
What "polarity inversion" ? :D

I just switched the units in/out and made sure the right/left ch were correct


On edit: I know the terms are different but I also checked to make sure speakers were in phase
Discussed earlier, the FX flips the polarity of the input, up for down. Because distinctive natural sounds are generally not polar symmetrical, some will sound different or wrong if inverted from their natural polar state. It may be audible as a dullness, lacking life to some if not most listeners.
 
Discussed earlier, the FX flips the polarity of the input, up for down.


Thanks... did more reading with search feature

(sorry for the redundancy) So... to correct this the speaker wires on both left and right side should be reversed (+ from amp goes to - on speaker) ??

I remember having a reverse polarity button on an Adcom CDP once... most times could not hear a difference engaged or not
 
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Thanks... did more reading with search feature

(sorry for the redundancy) So... to correct this the the speaker wires on both left and right side should be reversed (+ from amp goes to - on speaker) ??

I remember having a reverse polarity button on an Adcom CDP once... most times could not hear a difference engaged or not
That is correct for a typical system. Some examples of program material may be itself inverted to confuse things further. The usual correct practice is to ensure the entire chain at both ends is non-inverting en toto.
 
One question for the circuit knowledgeable folks on this forum. This preamp seems to have quite a bit of gain compared to my Mapletree 2ASE (6SN7 point to point wired preamp)which has 10 db gain, The FX Audio seems to have maybe twice as much gain? Is this gain from the tubes or is there an OP amp hiding in there somewhere? I looked at the picture of the bare preamp but it's all Chinese to me :)
You are very close, the 6SN7 has a gain factor of 20, as does the 12AU7, which replaced it, the 6AK5 can have a gain factor of 50 to 200, depending on the voltage.
Here is a partial explanation of why tubes with gold pins and silver (nickel) plates were developed.
Many of these types had gold-plated base pins and special heater configurations inside the nickel cathode tube designed to reduce hum pickup from the A.C. heater supply, and also had improved oxide insulation between the heater and cathode so the cathode could be elevated to a greater voltage above the heater supply. (Note that elevating the cathode voltage above the average heater voltage, which in well-designed equipment was supplied from a transformer with an earthed center-tapped secondary, was less detrimental to the oxide insulation between heater and cathode than lowering the cathode voltage below the heater voltage, helping to prevent pyrometallurgical electrolytic chemical reactions where the oxide touched the nickel cathode that could form conductive aluminium tungstate and which could ultimately develop into a heater-cathode short-circuit.)
 
The gain of the 6AK5 in triode will be fairly low, lower with cathode degeneration. Heater bias can also reduce heater/cathode differential for cathode follower stages, the cathode will be at a 1/2 anode voltage in such service.
 
The gain of the 6AK5 in triode will be fairly low, lower with cathode degeneration. Heater bias can also reduce heater/cathode differential for cathode follower stages, the cathode will be at a 1/2 anode voltage in such service.
I can answer two issues that have come up, when I said these ,"toys" are getting pricey, I was referring to the Japanese version , I paid $68 without the wall wart, but I saw the same unit for as high as $169. The Japanese version, the FX Audio 01J, features a switch which toggles between zero gain or minus 6 db.
 
So the wall wart PS that comes with this unit is 12V 1.5amp. Does the PS contain a voltage regulator?
 
How is the CD3 compared to the FX Audio, I have wanted to try it because I have a huge collection of 6SN7's and equivalents? I went back in time to the single triode per bottle tubes using
6J5 + 6J5 = 6SN7 adapters, each 6J5 equals exactly one half of a 6SN7.
 
I was listening to a random review, and youtube automatically jumped to this video next. I kept listening to it not for the purpose of comparing sounds but because the music sounded so good through my modded superlux 668 headphones (32 bucks), liquid spark, fx audio pre (32 bucks), and a Fiio dac (10 bucks) Anyways the video might be worth a listen just for the song and it is played through the RME ADI-2 DAC and some Mytek (the speakers are MANGERS which are kinda big in Europe and Asia but not in North America. I listened to an older model of it years ago in Yerevan of all places):


AqLnYy1.jpg
 
MY FX Audio 01J, the Japanese version arrived today.
It does exactly what I hoped it would do, with the gain switch set at minus 6 db, it allows me to turn my receiver's pot all the way up, which takes it out of the circuit.
The volume control on the 01J is great and feels exactly like the Chinese version.
The LED's on this unit are yellow colored, which disappear easier and are more pleasant to look at than the red ones.
BTW: The paperwork on the box clearly indicates that this unit was shipped from Japan.
 
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