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6J1 China preamp thoughts
6J1 China preamp thoughts
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Old 23rd July 2017, 03:36 PM   #11
spendorite is offline spendorite  Canada
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I got the FX Audio 6J1 fully assembled preamp with case recently. I really didn't need another preamp,
I already have three preamps, two built from kits and the third purchased fully assembled. These cost
between $180 and $350. I like all three and two of them I like very much.

I purchased the FX Audio on EBay just to hear what these dirt cheap Chinese preamps sound like.
It was only CAD $38 including shipping, about USD $28 at the current exchange rate and I didn't have
to pay Pay Pal the exchange rate fee because it was listed in Canadian dollars.

It arrived well packed in cardboard box with moulded foam padding
The package contained the preamp in its case, the two 6J1 tubes and the power adapter.

I hooked it up to my Tubelab SSE via a direct input connection and powered up.
Firstly I should mention that this preamp is practically dead quiet, with the vol. pot. at maximum there
is just a barely audible wisp of electronic noise with my ears pressed against the speaker.

For USD $28 this little preamp sounds quite impressive, it sounds almost as good as my other much more
expensive preamps. There is quite good detail and clarity of sound and it matches very well with my Tubelab SSE.
There is no schematic, just a slip of paper with "some instructions". I'm sure the two tubes are essential to the
circuit and are not there for show. I'm not too appreciative of the LED lights in the tube sockets that light up on power on.

So, to sum up, if you don't have the money to spend on an expensive preamp or if you just want to hear what a
dirt cheap Chinese preamp sounds like then this preamp would be a suitable choice.
Attached Images
File Type: jpg FX Audio 01.jpg (297.3 KB, 1845 views)
File Type: jpg FX Audio 01 board.jpg (377.7 KB, 1774 views)
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Old 24th July 2017, 05:35 AM   #12
azazello is offline azazello  Bulgaria
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6J1 has linear good mode with +B more 100-150V /+U about 250V, after plate resistor on the tube +B will about 100-150V, inner resistance of 6J1 in triode is big and Your headphones must be with res. about 1-2 kohm, ....headphones with 30-300 ohm are not suitable.Your headphones must have res. about 2-3 times more inner res. of tubes. If +B is 12-20 V, mode is not linear/. Amp for 28 $ will sound for 28 $....
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Projects: SE GK71, SE 12BQ6, PP KT88, OTL-OCL 6AS7 Gen. Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, E84L Siemens, E236L Telefunken, headphone ampl. OTL Loftin White 6AS7 RCA,...

Last edited by azazello; 24th July 2017 at 05:54 AM.
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Old 24th July 2017, 06:31 AM   #13
rotaspec is offline rotaspec  New Zealand
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It's a preamp not a headphone amp.
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Old 24th July 2017, 10:58 AM   #14
azazello is offline azazello  Bulgaria
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Never mind....The mode for preamp is not linear with 12-28 V!
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Projects: SE GK71, SE 12BQ6, PP KT88, OTL-OCL 6AS7 Gen. Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, E84L Siemens, E236L Telefunken, headphone ampl. OTL Loftin White 6AS7 RCA,...
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Old 24th July 2017, 06:52 PM   #15
azazello is offline azazello  Bulgaria
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The same PCB, but headphones amp....
Valve 6J1 DIY Tube Amplifier Preamp AMP Pre-Amplifier Board Headphone Buffer Kit
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Projects: SE GK71, SE 12BQ6, PP KT88, OTL-OCL 6AS7 Gen. Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, E84L Siemens, E236L Telefunken, headphone ampl. OTL Loftin White 6AS7 RCA,...
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Old 25th July 2017, 08:29 PM   #16
azazello is offline azazello  Bulgaria
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It seems this is a new 6J1 PCB preamp with 200 V AC, that is better variant:
DIY Tube Preamplifier PCB Board PRT-01A-6J1
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Projects: SE GK71, SE 12BQ6, PP KT88, OTL-OCL 6AS7 Gen. Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, E84L Siemens, E236L Telefunken, headphone ampl. OTL Loftin White 6AS7 RCA,...
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Old 25th July 2017, 08:42 PM   #17
audiowize is offline audiowize  United States
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It's impossible to say much without seeing a schematic (they should provide one anyway to aide in debugging). Having said that, your odds of getting something that isn't a total POS are much higher when the power supply voltage isn't insanely low.
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Old 25th July 2017, 09:07 PM   #18
azazello is offline azazello  Bulgaria
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The schem is shown on the plate....seeing nominal of resistors, tracks, inputs AC 200V, 6-9 V, connectors....rectifier is other for 200 V.
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Old 26th July 2017, 03:09 AM   #19
audiowize is offline audiowize  United States
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Can we call it a preamp if the output impedance is close to 10K?
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Old 26th July 2017, 06:34 PM   #20
pcan is offline pcan  Italy
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6J1 China preamp thoughts
This is the schematic dragram of the board on the picture at the beginning of the this thread.
Fever 6j1 Tube Pre-amp Circuit - CircuitLab
It is clearly a preamplifier. I paid 7 euro and 19 cents for mine (DIY kit without case); the two tubes and the shipping cost from China are included in the price. It is still on transit so I dont'have tried it yet. The total B+ voltage would be just right for a dry battery radio tube, it is fairly low for a regular 6J1. By the way, the coupling capacitors seems to be way too big.
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