As things are, I just came across a link ("Goldpoint pre-attenuation") that describes what I posted yesterday... with better words and schematics.
Pre-Attenuation
They even have that -20dB example and also recommended resistor values depending on what pot (impedance) you may want to use. It is all there...
I hope this is of some help
Claude
Pre-Attenuation
They even have that -20dB example and also recommended resistor values depending on what pot (impedance) you may want to use. It is all there...
I hope this is of some help
Claude
Hi
i am getting 0.01mv out from output, thats a enough to make my rel sub not to go in standby. i have no voltage if i disconnect my ifi dac.
measure att output korg and f6, both turned off.
is there anything i can do with this problem without always disconnecting my dac?
Andreas
i am getting 0.01mv out from output, thats a enough to make my rel sub not to go in standby. i have no voltage if i disconnect my ifi dac.
measure att output korg and f6, both turned off.
is there anything i can do with this problem without always disconnecting my dac?
Andreas
KB1 is AC coupled, and 0.01mV is value on which your DVM is inaccurate anyway, besides fact that it is so low value that no piece of gear is seeing it as anything else than 0 offset
problem is somewhere else, not in KB1
problem is somewhere else, not in KB1
Yes the BG sound nice, played for 250 hours+ now.
Maby they settle soon ( ;
Frank
Tanx everyone! I will try bouth singel resistor and L-pad right before pot.
The pot is TKD 601/S.
I will alsotry my 20K Glasshouse stepped series atteunator ( used in my B1 ).
Frank
The pot is TKD 601/S.
I will alsotry my 20K Glasshouse stepped series atteunator ( used in my B1 ).
Frank
Another B1 Finished
Without a doubt it's a lot easier to buy the kit version of the B1 preamp. Even though some of the parts may not be exotic. Only took me 2 - 3 days to build instead of months with my previous project the VFet CSX1.
I've been reading plenty about the tube being microphonic. So I salvaged these rubber isolation mounts from a Zalman HD heat pipe cooler.
I did not use the included pads with the Nutube as I found them too thin, so I went with the much thicker ones.
I don't prefer to have bare wires soldered direct through the PCB so used soldered pins. The red resistors are supposedly 'audio grade' that came with the kit. I noticed in previous batches of the kit had different coloured resistors etc. The 1000uF electrolytic are of unknown brand but 105C higher temps for better durability. The 10uF caps are Nichicon Fine Gold so slightly exotic.
In tradition, I replaced the green power LED light with a blue one and the signal wires with 28awg Tefzel (Teflon insulated over silver wire). The ethernet CAT TP wires for power are OK but in my experience, the insulation reacts with the bare copper (oxidation) and solder DOES NOT stick, the solution is scrape it with the razor blade so that the wire is shiny.
My current setup and can't give a verdict on how the B1 performs. The issue is the VFET CSX1 has been balanced XLR configured with the the BLS Preamp (I built 20 years ago). So going over to single ended (2 jumper pins on the CSX1) and the buffered Toshiba JFETs come alive. But it changes the sound and from previous memory testing the VFET amp I found balanced sounded better. But the B1 is not this kind of preamp that you want to achieve accuracy. Likewise with using tube amps. The CSX1 amp low gain means the B1 has to drive more (crank up the dial more clockwise) but of course with my KHorn speakers, I can hear a different in sound character at different volume levels. At higher SPL it seems more depth, perhaps due to the increase distortion beyond 1v output.
T7 / T8 voltages - i've tested at over 13 volts and low at 7.5 volts and my ears don't like it. At the moment I have it at 9.0V. Won't jump to conclusions so will need to spent more time moving voltages around again with more extended playing time. But I have a feeling I may be missing the accuracy I liked with XLR balanced - hrm. issues and more issues to wonder about.
Without a doubt it's a lot easier to buy the kit version of the B1 preamp. Even though some of the parts may not be exotic. Only took me 2 - 3 days to build instead of months with my previous project the VFet CSX1.
I've been reading plenty about the tube being microphonic. So I salvaged these rubber isolation mounts from a Zalman HD heat pipe cooler.
I did not use the included pads with the Nutube as I found them too thin, so I went with the much thicker ones.
I don't prefer to have bare wires soldered direct through the PCB so used soldered pins. The red resistors are supposedly 'audio grade' that came with the kit. I noticed in previous batches of the kit had different coloured resistors etc. The 1000uF electrolytic are of unknown brand but 105C higher temps for better durability. The 10uF caps are Nichicon Fine Gold so slightly exotic.
In tradition, I replaced the green power LED light with a blue one and the signal wires with 28awg Tefzel (Teflon insulated over silver wire). The ethernet CAT TP wires for power are OK but in my experience, the insulation reacts with the bare copper (oxidation) and solder DOES NOT stick, the solution is scrape it with the razor blade so that the wire is shiny.
My current setup and can't give a verdict on how the B1 performs. The issue is the VFET CSX1 has been balanced XLR configured with the the BLS Preamp (I built 20 years ago). So going over to single ended (2 jumper pins on the CSX1) and the buffered Toshiba JFETs come alive. But it changes the sound and from previous memory testing the VFET amp I found balanced sounded better. But the B1 is not this kind of preamp that you want to achieve accuracy. Likewise with using tube amps. The CSX1 amp low gain means the B1 has to drive more (crank up the dial more clockwise) but of course with my KHorn speakers, I can hear a different in sound character at different volume levels. At higher SPL it seems more depth, perhaps due to the increase distortion beyond 1v output.
T7 / T8 voltages - i've tested at over 13 volts and low at 7.5 volts and my ears don't like it. At the moment I have it at 9.0V. Won't jump to conclusions so will need to spent more time moving voltages around again with more extended playing time. But I have a feeling I may be missing the accuracy I liked with XLR balanced - hrm. issues and more issues to wonder about.
I'm having really horrible microphonics with the Nutube. I've read about some of the solutions for this and have tried hot gluing the included foam pads on the bottom and top of the tube. It made an improvement to the point where I can actually listen to it now without the constant high pitched ringing noise. I love the sound quality of this pre amp but the ringing noise seems to sporadically happen without even touching the chassis. When I first set up the pre amp, I made the mistake of leaving the amp on when I went outside for a second and the ringing noise grew so loud that it I could hear it from outside my apartment building. I have the pre amp on some vibrapods but it doesn't seem to help much. Any suggestions or should I just buy a new Nutube?
What is your B1K chassis look like ?
Does make high pitch whistle with top plate closed ?
Any photo ?
Does make high pitch whistle with top plate closed ?
Any photo ?
I think it would be a worthwhile experiment if we swapped another Nutube into
a situation like this and see what happens.
a situation like this and see what happens.
Tape the latex eraser to the top of the NuTube. Or glop silicon caulk on top like Tom did. It’s the single best cure for the particularly noisy ones.
I’ve got one that bad, it took all the tricks to get it listenable...
Or, as Nelson suggests, replace it.
I’ve got one that bad, it took all the tricks to get it listenable...
Or, as Nelson suggests, replace it.
I'd love to buy a couple too - happy to get 4 or more if that makes the cost of getting them made cheaper etc. Thanks for the offer mate!
Thanks, I think I'll try the eraser trick and if that doesn't work I'll replace it. Silicon caulk sounds like it could get too messy. I'm already dreading removing the hot glue if/when I have to replace the tube. Love the sound though, really incredible that it's so good considering how simple it is. I just wish I could get rid of the ringing. Also as someone else asked, I tried it with the lid on at the very beginning but since it was so microphonic I kept the lid off to try and trouble shoot it.
I'm not a fan of smearing silicon all over the NuTube and wanted to exhaust all other ways first. I have no microphonic sound on my very highly sensitive 104db/w/m speakers and I think it's all due to the rubber isolation mounts that the PCB sits on. I need a hard flick with my finger nail on the chassis to get that 'tingggggg...' sound and it just goes away. Perhaps some of this microphonics is due to 'resonant frequency' ?
Also using a thicker soft padding meant I soldered the legs of the NuTube near the very end (requiring no snipping after solder). My thought is vibration is more noticeable if the tube leads are close to the PCB vs having longer lead length. Maybe it doesn't make much difference - I have seen in other applications of the NuTube a separate board and individual wires to make the connection (de-couples the vibration connection).
I should add that in my previous post, turn on thump very noticeable = a 'thump - thump' so power on this preamp 1st before power amp.
@ 6L6 - thx, i'm not fussy with power supply caps - my CSX1 separate power supply is full of the Chinese Rover caps (touted to be 'Audio Grade'). I do have some Japanese TDK Epcos ones just in case they were the Rovers were bad, so will save them for a later project.
I used a dampening material stuck to the bottom of the lid. The top panel was very resonant. I used some water sealing tape type material that is relatively thick. It was enough to dampen my Nutube. However mine wasn't very bad.
Before the tape, when I clapped my hands hard next to the preamp, I could hear a ring that would then die off.
If you had something like dynamat, that would likely work even better.
Before the tape, when I clapped my hands hard next to the preamp, I could hear a ring that would then die off.
If you had something like dynamat, that would likely work even better.
I think I didn't put any rubber isolation mounts when installing the board to the chassis. Any suggestions on where I would find these? Hardware store or would I have to order online? Dynamat sounds like a good idea, I'll have to see if I can buy a small amount locally.
There are links to rubber mounts and sound damping in post #5291. (That's pg. 530 with the posts per page configuration on my computer, don't know about yours.) I used both of the items suggested there with very good results.
Hope this helps.
Thanks, morrism, for the initial links.
Hope this helps.
Thanks, morrism, for the initial links.