FX Audio 6j1 tube preamp - a $31 wonder

Forgot to mention I've swapped out all the tubes.
I have NOS WE 403B's in the FX and GE 5654W's with a Raytheon 832A in the amp.
Now to just get a proper power supply for the FX.

And the Raspberry Pi is set up to boot from an msata and has an Iqaudio Pi-DAC Pro. I keep a lot of ripped music on it and also stream from it.
 
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About the FX's gain

Can be excessive on many amps without attenuators

Even with those ^ amps careful speaker matching can help (lower db SPL). Something in the 80s
 
OK, just to be a stick in the mud, also very impressed at the sound from this little preamp but now I'm wondering if it isn't just the fact that it has so much gain that it sounds louder than just about any other preamp I have and the settings on the volume control are such that they are big steps from one notch to the next so that I can't actually match the sound level from my other preamps. I think that its been shown that the louder sound will typically be preferred in an A/B comparison (within reason).
 
It is a fair point about the gain. I use mine with 12db Harrison attenuators on the output side, and I'm running MMGs so not so efficient.I have also tried it in the tape loop of my SS pre with the FX volume wide open and with the 12db attenuators. I have a Foreplay II line stage and like PG, I think this little pre outshines it.
 
On the FX Audio 6j1-03 (with tone controls) why is there an opamp next to each tube? Is the tube functioning to its full extent ... or is the opamp "supporting" the tube in some way?
However, in the FX Audio 6j-01 version, there are no such opamps (that I can see).
 
It is a fair point about the gain. I use mine with 12db Harrison attenuators on the output side, and I'm running MMGs so not so efficient.I have also tried it in the tape loop of my SS pre with the FX volume wide open and with the 12db attenuators. I have a Foreplay II line stage and like PG, I think this little pre outshines it.

And I used to think my Foreplay III hung the moon. :idea:
 
the two opamps in that model provide the tone controls for the unit.

you can opamp roll along with the tube rolling. in some pix, they are
5532 and the unit has sockets for the opamps.

Is there some easy way to change the gain in the unit, by modifying the internals? The 5x is becoming a bit annoying for me in my Dilvpoetry.

I looked at the pricing of Harrison attenuators and would not want to go that way...yet...
 
you have a couple of choices, all of which require some circuit analysis and the use
of a soldering iron. if that's OK with you:

1. adjust the volume control. its usually a log taper, so measure the pot's resistance at the
maximum volume setting you'd like. this is from the input signal to the wiper. then replace
the pot with a value that is the difference from the original pots maximum resistance to that
maximum resistance you just measured. then add to the top of the new pot the new
resistance you measured. not perfect but it will be a good start. this leaves the loading alone
2. use the tone controls (not sure it can or cannot be defeated or set to unity gain) and
lower the gain at the opamps. usual formula that sets the gain with two resistors - just replace
3. use a resistor network at the output to lower the output level. start with pot and adjust it
to taste, then replace with two resistors that match the pot settings.
4. easiest: lower the outputs of your sources. if more than more use a linestage with an
output control and adjust accordingly - no design change, no soldering. just an extra
component
5. remove fx-audio. or lower its output volume.

post your results - I am sure you're not the only one with this issue.
 
I have this connected between a phono pre amp to a line in,I don't want to make a broad statement but I've been using a selection of cartridges on used records all which have been through a spin clean,with used records it is what it is,though Ive noticed that an amount of background noise has dropped.
Is it me or has anyone else noticed?
Or is Witchcraft?Its still going on around here.
 
Out of interest,using say Audacity has anyone done an A/B test comparing recordings made with and without this device?
I'm asking as I have the equipment but I wouldn't know how to analyze the findings.
I'm very happy with this in its stock form though I intend to add a better power supply and valves in stages and it would be informative if I could compare results in a graphic form.

I did here :
 
Am considering getting a 6J1 to try since the cost is so low. How does it sound (different/better) than the 3 tube 6N3 board? I like my 6N3 using external volume pot.

Or maybe I upgrade to something like the XiangSheng 728A with 12AT7/AU7 tubes, nice looking preamp with input selector.
 
Am considering getting a 6J1 to try since the cost is so low. How does it sound (different/better) than the 3 tube 6N3 board? I like my 6N3 using external volume pot.

Or maybe I upgrade to something like the XiangSheng 728A with 12AT7/AU7 tubes, nice looking preamp with input selector.

The stock volume pot on the 6n3 is it's weak point. The FX's pot is far better and I counted 40 steps on it. They're small clicks but they're there.
 
The stock volume pot on the 6n3 is it's weak point. The FX's pot is far better and I counted 40 steps on it. They're small clicks but they're there.
Is it an indexed track or switch point pot? Indexed track would be a regular wiper on track pot with "clicks".
 
you have a couple of choices, all of which require some circuit analysis and the use
of a soldering iron. if that's OK with you:

1. adjust the volume control. its usually a log taper, so measure the pot's resistance at the
maximum volume setting you'd like. this is from the input signal to the wiper. then replace
the pot with a value that is the difference from the original pots maximum resistance to that
maximum resistance you just measured. then add to the top of the new pot the new
resistance you measured. not perfect but it will be a good start. this leaves the loading alone
2. use the tone controls (not sure it can or cannot be defeated or set to unity gain) and
lower the gain at the opamps. usual formula that sets the gain with two resistors - just replace
3. use a resistor network at the output to lower the output level. start with pot and adjust it
to taste, then replace with two resistors that match the pot settings.
4. easiest: lower the outputs of your sources. if more than more use a linestage with an
output control and adjust accordingly - no design change, no soldering. just an extra
component
5. remove fx-audio. or lower its output volume.

post your results - I am sure you're not the only one with this issue.

Thanks. I can not solder, so that's out of the equation.

Now I am thinking of putting a passive preamp volume control nob between the Dilvpoetry and Emotiva SA-250 main amp (with 23.5k Ohm input impedance). I am thinking of basically cranking up the volume on Dilvpoetry tube preamp to eg. 12PM and then use the passive pre for actual volume control.

I'm looking at some reasonably priced FV3 units on the bay. I am confused about the impedance though, should I get 10k or 50k version? And should I go with ALPS RK27 or RK168 potentiometer?

ALPS specs:
https://www.alps.com/prod/info/E/HT...otentiometers/RotaryPotentiometers_list1.html
 
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