I have built one of these Chinese pre-amps and I must say I quite like it. I'm new to valves/tubes so can anyone tell me why so much of the circuitry in these amps is taken up with providing current limiters on the + & - supplies? (The limiters kick in at 14ma but the valves only draw 4mA ish) Are they essential for a valve amp?
That's absolutely terrible. Such a low load on that poor little 6J1 is going to make all sorts of distortion and will have poor drive capabilities.
There's also a bit of an error in the schematic, since as its drawn, there'd be -28V present at the output of the preamp (why not ground the -28V rail and get rid of the coupling cap at the input?
It's also a little odd that the cathode resistor isn't bypassed; that isn't doing them any favors.
YGWYPF
The schematic is wrong. The 100K load resistor does in fact go to ground.
I guess the consensus is that these poor little tubes would be working in a more linear region when supplied with a higher plate voltage and higher cathode current? (more linear = less distortion?)
I'm still puzzled by the inclusion of the current limit circuits though.
I guess the consensus is that these poor little tubes would be working in a more linear region when supplied with a higher plate voltage and higher cathode current? (more linear = less distortion?)
I'm still puzzled by the inclusion of the current limit circuits though.
Not headphone buffer. This can only work when connected to amplifier and headphones from the amplifier. I tried to connect headphones to mine and the output level is next to nothing. See the connectors ion photos - RCA.
I agree 6V6dude, these kits are a great way to get into experimenting with valves/tubes.
I too have another kit on the way on which I will experiment to try and improve the performance and learn a little on the way. (Although I'm really pleasantly surprised at the sound of this thing straight out of the box/jiffy bag!)
Any thoughts on the importance of the current limit circuits?
I too have another kit on the way on which I will experiment to try and improve the performance and learn a little on the way. (Although I'm really pleasantly surprised at the sound of this thing straight out of the box/jiffy bag!)
Any thoughts on the importance of the current limit circuits?
Just trying things, I've put Baxandal between the two 6J1 boards. It makes one fine tone control. Sounds as good as my 300V 12AU7 tone control with about the same gain. I'm quiet impressed. Just to think I could have saved days building one. But than again what I've build will last for ever. The 6J1 one is just a board with everything cramped on it, transistors for voltage trippler and I don't like the series heater setup because it drifts over time or if tubes aren't well matched. But yes it does work very well for tone control regardless.
An externally hosted image should be here but it was not working when we last tested it.
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Thanks for the link PuffinI have also bought this version of 6j1 tube preamp/buffer.It gets 12V DC and it has a dc-dc step up module inside for creating positive or negative rails .I cant find a schematic for this version.Do you have one?
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I too have bought the FX Audio valve pre-amp and use this one on my hobby room system. It sounds fine and exhibits minimal hum. The circuit for the amplifier part is pretty much identical to the 6J1 kit (with the voltage doubler type of supply). I do not have the circuit for the DC-DC converter. Would like to find a similar module to drive my 6J1 kit and replace the voltage doubler. I run mine with a pair of GE5654W's.
i just dissasembled the preamp.The dc-dc converter gives +-31.1V. I dont know what would be better as a power supply: a dc dc converter or a voltage doubler followed by a cap multiplier.I am trying to draw the schematic now.
How does the pair of GE5654W's sounds compared to 6J1's?
I only have 6j1 tubes at the moment.I like how it sounds but i have the impression that there is some loss at high frequencies or they are just smoothed out...
How does the pair of GE5654W's sounds compared to 6J1's?
I only have 6j1 tubes at the moment.I like how it sounds but i have the impression that there is some loss at high frequencies or they are just smoothed out...
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I've found that the voltage doubler/multiplier combination hums annoyingly. I much prefer the DC converter!
I must admit that I've not done a strict comparison between the 6J1 and the 5654's. The 6J1's sounded fine but for a few pounds I thought I'd try a pair of 5654's which come highly recommended.
I must admit that I've not done a strict comparison between the 6J1 and the 5654's. The 6J1's sounded fine but for a few pounds I thought I'd try a pair of 5654's which come highly recommended.
Mine is waiting for a box. Had to rearrange a bit, so all of the tubes will be visable. It's a fun volume regulator for me, nothing more nothing less, so to speak
How did you raise the tubes?
Could someone explain what is occurring in this buffer? Is it simply adding some distortion or gain as well?
i have this one which came assembled:
AC 12V 6J1 Valve Pre-amp Tube PreAmplifier Board DIY KIT Headphone Buffer +Case | eBay
I plan on purchasing a 12.6v 1a transformer for it to be used with a D-class amp.
i have this one which came assembled:
AC 12V 6J1 Valve Pre-amp Tube PreAmplifier Board DIY KIT Headphone Buffer +Case | eBay
I plan on purchasing a 12.6v 1a transformer for it to be used with a D-class amp.
Mine seems to give a small amount of gain as well as the fabled 2nd order harmonic distortion valve magic ;-) (To be honest I just like the way it glows!)
This article makes interesting reading concerning tubes/valve amps.
Why Tubes Sound Better
This article makes interesting reading concerning tubes/valve amps.
Why Tubes Sound Better