Purchased one of these $20 wonders from China. Sounds real good between my dac and SS amp but too much output so I converted it to a cathode follower.
R13 and R19 stay connected but are lifted from the -28 volt buss. R15 is removed and replaced with a short. R15 is then connected from the junction of R13 and R19 to the -28 volts. The output is then taken from the junction of those three resistors and through C10 which has been disconnected from the plate.
Very simple conversion and sounds good. Much lower output.
Question about the schematic. What is the purpose of R16, the 100k resistor?
R13 and R19 stay connected but are lifted from the -28 volt buss. R15 is removed and replaced with a short. R15 is then connected from the junction of R13 and R19 to the -28 volts. The output is then taken from the junction of those three resistors and through C10 which has been disconnected from the plate.
Very simple conversion and sounds good. Much lower output.
Question about the schematic. What is the purpose of R16, the 100k resistor?
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R16 is incorrectly drawn in the schematics, its just output to ground.
Otherwise you would be killing your next stage with -28 volts.
I am surprised you like it, it sounded bad to me, and it had still some hum. That tube needs bigger voltage. I rebuilt circuit to buffer, pure sound.
You have not searched.
Otherwise you would be killing your next stage with -28 volts.
I am surprised you like it, it sounded bad to me, and it had still some hum. That tube needs bigger voltage. I rebuilt circuit to buffer, pure sound.
You have not searched.
That schematic I posted is the generic version of this common Chinese gizmo. It doesn't really reflect 100% this particular board. As you know there are several variations of this product out there. I'm not hearing any hum with this one.
Hi ! thank you very much for the kind and helpful reply.
In the meantime i think i have found it and bought one
1pc VALVOLA 6J1 Pre-AMP TUBE PREAMPLIFICATORE kit assemblato bordo AUDIO fai da te | eBay
i have already some ef95 type tubes to try out (Mullard, Vozkhod ... )
I just need a simple buffer to color the sound
I come from a similar preamp, the fx audio tube 01 ... impossible to work on it because of a very small board. This looks quite bigger
The caps quality looks a little suspicious ... anyway nothing that cannot be cured
I like Nichicon for instance
Thanks a lot again.
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Yes that's the same one I have. I also tried one of the smaller versions of this circuit and likewise found it impossible to work on. This board is roomy and much easier to trace the wiring. Also the filament rectifier supply has a couple of 1000 mfd caps in the filter so I am not hearing any hum.
However, if you use it as is, it has a high output and could be noisy going straight into an amp with no volume control. Converting it to a cathode follower was very simple as I described in the opening message and now works perfectly for me. I use solid state amplification and find this combination of tubes into solid state very musical.
The plate voltage is 2 x 24 or about 50 volts. That's not a lot but I hear no glaring problems. You could increase the voltage rating of all the capacitors and drop the filament voltage down if a higher voltage AC transformer is used but I don't see the need.
If I were to build my own I would use a more conventional tube like a 12AU7 but how can I complain for $20? Building from scratch would cost several times as much and maybe more.
I will be interested in how this works out for you.
Hi ! please excuse me for my late reply. Family issues.
Just one question ... you say
The less mods to the stock unit the easiest for me ...
I gues all the resistors values should be recalculated ? i understand that this tube works better at higher voltages
I need to get retired asap ... then the fun will start seriously
Lately i have become fascinated by the hybrid option ... i.e. using a tube buffer or a low gain and Zout tube preamp with solid state power amps.
I love what can come out a lot ...
Thanks a lot again.
very good and thank you very much. The same here ... i like more space on the board to work more easily.
yes and also the Zout can be high. I am using solid state power amps with Zin around 10K .... for this reason i am interesting in the buffer conversion
Just one question ... you say
is this really needed ? i always see a resistor on the plate in the various schematic
The less mods to the stock unit the easiest for me ...
i like the idea but i have no clue how to do it. So all the bjts in the power supply do not fix the voltage out ? they just increase the dc voltage coming from the rectification ? i wonder if it would be possible to use 2 transformer ... a 12VAC for the tubes heaters and a let's say 24V for the tubes plates
I gues all the resistors values should be recalculated ? i understand that this tube works better at higher voltages
money is not a problem for me ... i am my problem. My skills my time my space are very limited ... now
I need to get retired asap ... then the fun will start seriously
Lately i have become fascinated by the hybrid option ... i.e. using a tube buffer or a low gain and Zout tube preamp with solid state power amps.
I love what can come out a lot ...
That is sure. Hope soon. I would also try to increase plate voltages ... if only i knew how to calculate the new resistors.
Thanks a lot again.
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The only thing I know is what I wrote at the beginning of this thread. Rather than make all those modifications buy a kit designed as a tube buffer. Here is one.
Class A tube buffer kit using 6DJ8/6922/6N11stereo X-10D !! | eBay
Class A tube buffer kit using 6DJ8/6922/6N11stereo X-10D !! | eBay
thanks for the very interesting link. I am still waiting to receive the kit of the topic I would like to listen to the modded kit first Maybe it will be already good enough I just want to add some dimension to the sound.