Just came across this thread, looking for a tube preamp with a gain of 10 (20db)
Looks like there is a more recent 6J1 preamp equipped with a step-up dc/dc converter, have a look below. Hope this is useful, I don’t know the seller so at your own risk.
Audio Mini 6J1 Valve Vacuum Tube Pre Amplifier Stereo HiFi Buffer Preamp Newest | eBay
BR
Eric
Looks like there is a more recent 6J1 preamp equipped with a step-up dc/dc converter, have a look below. Hope this is useful, I don’t know the seller so at your own risk.
Audio Mini 6J1 Valve Vacuum Tube Pre Amplifier Stereo HiFi Buffer Preamp Newest | eBay
BR
Eric
you are welcome Whelkie but there is still a problem with hum. as long as i have a fairly low impedance connected to the input i have no hum. with a high impedance like a guitar or nothing connected and the volume turned up the left channel hums quite a bit but i have found the problem. they ran ac voltage traces to the switch all aroung pin 1 of the left tube which is the grid or the input. really stupid. i am going to cut traces and mount an external switch. when i get it done i will post a pic
Thank you very much for your help. Your picture and notes make
it clear! I will do those mods!
re post 100% working fever 6j1 tube preamp hum removal
these mods will remove 100% of the hum in the fever 6j1 tube preamp. it took a little more than i originally thought. the first post had a pic but i am reposting it because you only have to add one cap to the 47 ohm resistor junctions and it is for the neg side of the supply because the neg supply bias's the grids and noise here becomes part of the signal and gets amplified. still need the extra heater supply cap. the second pic posted has the mod to fix the ac traces running too close to the grid pin 2 on the left channel tube which causes a lot of hum on the left channel.
the mods in red are required to remove the hum for normal use and is going to be good enough for most all situations. the mods in blue is for use in a situation where a very high gain amp is used after the preamp. also the bypass caps not only remove a little noise but it increases the gain from about 8.5 to 10.5 and gives a flat frequency response from 45 hz to 50 khz. the shields tied to pin 2 only works well if you use bypass caps. i had to do the full mod because i am running a compressor which uses a variable gain op amp with a max gain of x56 and now no noise at all.
i have built this preamp using this board in about a 6 x 7 x4 box it has tube inputs, 2 compressors, 2 pt2399 delays and 2 3band eq's 2 separate channels it works great. another thought the tube preamps will accept a 20 milli volt up to 2.5 volt signal with out clipping or distortion so you could take the right output and tie to the left input and get a higher gain 2 stage single channel tube amp. just a thought.
these mods will remove 100% of the hum in the fever 6j1 tube preamp. it took a little more than i originally thought. the first post had a pic but i am reposting it because you only have to add one cap to the 47 ohm resistor junctions and it is for the neg side of the supply because the neg supply bias's the grids and noise here becomes part of the signal and gets amplified. still need the extra heater supply cap. the second pic posted has the mod to fix the ac traces running too close to the grid pin 2 on the left channel tube which causes a lot of hum on the left channel.
the mods in red are required to remove the hum for normal use and is going to be good enough for most all situations. the mods in blue is for use in a situation where a very high gain amp is used after the preamp. also the bypass caps not only remove a little noise but it increases the gain from about 8.5 to 10.5 and gives a flat frequency response from 45 hz to 50 khz. the shields tied to pin 2 only works well if you use bypass caps. i had to do the full mod because i am running a compressor which uses a variable gain op amp with a max gain of x56 and now no noise at all.
i have built this preamp using this board in about a 6 x 7 x4 box it has tube inputs, 2 compressors, 2 pt2399 delays and 2 3band eq's 2 separate channels it works great. another thought the tube preamps will accept a 20 milli volt up to 2.5 volt signal with out clipping or distortion so you could take the right output and tie to the left input and get a higher gain 2 stage single channel tube amp. just a thought.
Attachments
That's brilliant. Thank you so much for all the work you've done explaining this. Gonna go and try these mods now. What sort of switch do you recommend for the cut ac traces?
hey Montrealer, i reposted a new fix for the china 6j1 preamp. it is 100% working for complete hum removal. 6J1 China preamp thoughtsThank you very much for your help. Your picture and notes make
it clear! I will do those mods!
@gmcdonld - Hi and thanks i just now saw your post.. ok so one of the caps has positive going to ground and the other has negative going to ground? i will change mine. its been making some weird noises now and then on 1 channel.. thank you for clarifying this . ill do it by the picture you posted .. thanks
@6V6dude - Hi, i would like to use my main transformer 15v ac output to power this instead of 12v .. what resistor do i need to change and how do i determine what value to use to get the heater voltage to stay at 6.3v ? any help would be appreciated
@6V6dude - Hi, i would like to use my main transformer 15v ac output to power this instead of 12v .. what resistor do i need to change and how do i determine what value to use to get the heater voltage to stay at 6.3v ? any help would be appreciated
From the schematic, there should be a 2.2 ohms resistor next to the Diode that rectify the heater AC. You want to drop 15-12.6V = 2.4V to get 6.3V per filament. R = 2.4V / 170ma = 14 ohms. If you add that 2 ohm back that make it to 16 ohms. Power = 170mA * 2.4V or 0.4W. So replace that 2.2 ohm with a 1 to 2W 16 ohms resistor should do the job.
@Alllensoncanon - hi and thank you.. i got a couple of 8ohm 2w resistors.. ill just series them.. will this be safer than just the 8.2ohm resistor the op posted?
@e_fortie - pretty cool.. i wonder if they sell one without the case.. i shall lookie
@gmcdonld - ? on the bypass caps, do they need to be non polarized and/or a specific kind aka ceramic/electro etc.. if i use polarized which way do they connect ? please forgive my newbieness is that even a word?
@e_fortie - pretty cool.. i wonder if they sell one without the case.. i shall lookie
@gmcdonld - ? on the bypass caps, do they need to be non polarized and/or a specific kind aka ceramic/electro etc.. if i use polarized which way do they connect ? please forgive my newbieness
is that even a word?I've been reading this thread with a lot of interest but I can't seem to fix my hum problem. I got an FX-Audio Tube-01 rev 1.2. It does add a very nice sound to my tpa3116 board as well as some gain but there's a hum and I don't really know what to do about it. The board has been posted here, but not as one of the mods. Can someone explain to me what to do so the hum gets less or is gone?
The best cure for your problem is to throw the 6J1P thingy into the trash can
This is genuine advice , I've had a few of these 6J1P-based £35 disaster gadgets on my bench . The cheesy power supplies that these arrive with should be replaced at the earliest possible opportunity . All seem to have major design flaws such as poorly mounted valve sockets , as well as noisy power supplies and susceptibility to interference originating from wifi and mobile phones . Some valves hum , some don't so if you have replaced the stock valves , fit the originals back in just in case
If you have a wifi access point or any other equipment nearby , switch it off or move the FX-Audio thingy and see if it makes a difference to your hum problem .
316a
This is genuine advice , I've had a few of these 6J1P-based £35 disaster gadgets on my bench . The cheesy power supplies that these arrive with should be replaced at the earliest possible opportunity . All seem to have major design flaws such as poorly mounted valve sockets , as well as noisy power supplies and susceptibility to interference originating from wifi and mobile phones . Some valves hum , some don't so if you have replaced the stock valves , fit the originals back in just in case
If you have a wifi access point or any other equipment nearby , switch it off or move the FX-Audio thingy and see if it makes a difference to your hum problem .
316a
@316a
Thanks for your honest advice. I'm happy I didn't take it entirely because it is now doing very well in my setup. You did point me towards the solution though. I bought mine without a power supply, stupidly thinking I could just use any 12v PSU I had around. It turns out it's very picky about that, which means you were right about the poor design. Fortunately for me though, I had a bunch lying around so I tried some until it was silent. A decent 12v LED PSU did the trick very well. I will look into additional grounding as it may benefit from it.
Could it be that the circuit doesn't much like switching PSUs?
Thanks for your honest advice. I'm happy I didn't take it entirely because it is now doing very well in my setup. You did point me towards the solution though. I bought mine without a power supply, stupidly thinking I could just use any 12v PSU I had around. It turns out it's very picky about that, which means you were right about the poor design. Fortunately for me though, I had a bunch lying around so I tried some until it was silent. A decent 12v LED PSU did the trick very well. I will look into additional grounding as it may benefit from it.
Could it be that the circuit doesn't much like switching PSUs?
The trick to eliminate hum is to get rid of single rail 12 volt converting to voltage doubler. Use a 15-0-15 trafo, and a diode and twocap, derive a dual power supply of +/- 22 volt, and feed it to the transistor based gyrator. use a 7812 regulator and 1 ohm 5 watt resistor for filament supply. with this setup, i have done a clone of this without a pcb..( just with perfboard for the powersupply, and thick short wires for the valves. it is extremely hum free in this set up.