Hi Zen Mod
Whaou... No badaboom, no sound degradation, no current going in all directions... so you can that easily split outputs that way and get away with it, treating the 2 problems separately ?
If really so then first "real" working good idea I had on this project, sounds so simple (???) and so cost effective...
Many thanks once again
Claude
PS: I assume you were serious, still can't believe it, I should take the train more often LOL
Whaou... No badaboom, no sound degradation, no current going in all directions... so you can that easily split outputs that way and get away with it, treating the 2 problems separately ?
If really so then first "real" working good idea I had on this project, sounds so simple (???) and so cost effective...
Many thanks once again
Claude
PS: I assume you were serious, still can't believe it, I should take the train more often LOL
I didn't get any responses to my original post so thought I might try one more time. I have gone ahead and ordered another NuTube from the store - hopefully will be here tomorrow and I can swap the part out.
Does anybody have any other theories as to what I might check? All the other measurements from the FirstWatt article mentioned are within spec.
Also - what would be the best way to implement an LED to indicate power on/off?
Heh, Heh, I watched the NuTube segment of the Papa talk at 2017 BA. NuTube puts out 1.7mW. I suppose the output buffer might fill things in with more current as 6L6 mentioned, but that means high efficiency headphones with low to medium impedance if you want to use this for that purpose.
My headphones (100db/mW efficient, 30 and 80 ohms) sounded great with this using an output headphone adapter.
My headphones (100db/mW efficient, 30 and 80 ohms) sounded great with this using an output headphone adapter.
At 11.34 point, he said "1.7 mW of power" and showed that on the curve, but thanks for the double check. That would still be enough for very efficient headphones in the lower impedance ranges.
I suppose one could measure any additional power contribution of the output buffer.
I suppose one could measure any additional power contribution of the output buffer.
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Reply to MEPER
Sorry it has taken so long for my response. I just built the Pete Millett NuTube headphone amp which is designed for a PCB mounted volume control. My construction layout required a remote chassis mounted volume pot so I first tried a twisted pair connection. I had some noticeable hum. That almost completely went away when I switched to shielded coax. Compared to the B1 Korg circuit, additional filtering of the regulated 24vdc supply is limited to a single RC to the plates and some extra C for the 3-pin filament regulator and grid bias circuit. So maybe there is just more hum from the power supply in this design.
The circuit called for a 10K input pot so I used a 10K audio taper blue ALPS. Those pots are spec'd for channels to track within 0.3 dB of each other. This is the first one I have used that was noticeably noisy at both ends of the rotation, much more so at the "off" end. Maybe this is just a bad pot. I tried cleaning it with D5 to no avail. I will try a 50K and see how that goes.
I did not like the way the Millett design sounded. I set bias at 9.5 V. It sounded way too hot and hard, even though the design has 475K plate resistors which seems like theoretically less tube gain. I switched to Papa's B1 recommended 332K plate resistors and readjusted the bias. Much improved. Must be the extra plate current. Tube gain did not seem to change much, if at all. Final tweek I preferred was around 9.75 V. You can really hear the difference in real time adjustment using headphones! Next step is to get rid of the bipolar input buffers and switch them to JFETS. Also add extra power supply filtering.
By the time I am done, I could have just added the output opamps to a B1 Korg board, although the Millet board has a turn on delay relay circuit that helps with getting rid of the turn on pop - but turn off still pops a bit. Maybe a cap across the switch will fix that.
Oh, regarding the chassis screws, I always seem to have one or two that are problematic. Lining them up with the nuts, holding the driver in place and flipping things over so the nut drops fully down onto the threads does get a bit old. I'll give your solution a try next time.
Sorry it has taken so long for my response. I just built the Pete Millett NuTube headphone amp which is designed for a PCB mounted volume control. My construction layout required a remote chassis mounted volume pot so I first tried a twisted pair connection. I had some noticeable hum. That almost completely went away when I switched to shielded coax. Compared to the B1 Korg circuit, additional filtering of the regulated 24vdc supply is limited to a single RC to the plates and some extra C for the 3-pin filament regulator and grid bias circuit. So maybe there is just more hum from the power supply in this design.
The circuit called for a 10K input pot so I used a 10K audio taper blue ALPS. Those pots are spec'd for channels to track within 0.3 dB of each other. This is the first one I have used that was noticeably noisy at both ends of the rotation, much more so at the "off" end. Maybe this is just a bad pot. I tried cleaning it with D5 to no avail. I will try a 50K and see how that goes.
I did not like the way the Millett design sounded. I set bias at 9.5 V. It sounded way too hot and hard, even though the design has 475K plate resistors which seems like theoretically less tube gain. I switched to Papa's B1 recommended 332K plate resistors and readjusted the bias. Much improved. Must be the extra plate current. Tube gain did not seem to change much, if at all. Final tweek I preferred was around 9.75 V. You can really hear the difference in real time adjustment using headphones! Next step is to get rid of the bipolar input buffers and switch them to JFETS. Also add extra power supply filtering.
By the time I am done, I could have just added the output opamps to a B1 Korg board, although the Millet board has a turn on delay relay circuit that helps with getting rid of the turn on pop - but turn off still pops a bit. Maybe a cap across the switch will fix that.
Oh, regarding the chassis screws, I always seem to have one or two that are problematic. Lining them up with the nuts, holding the driver in place and flipping things over so the nut drops fully down onto the threads does get a bit old. I'll give your solution a try next time.
if you read article , you'll see them at schematic
or go back one page in this very thread , look at schmtc with voltages I posted
Tape loop?
I have an elderly Antique Sound Lab autoformer volume control box that has been in and out of my system at various points, for various reasons - mostly convenience. Several inputs, multiple parallel outputs, and, important in my case, a known good working device for when I screw up other alternatives.
I've been looking for a way to incorporate the B1 Korg in my current system, and my first thought was to put it in the ASL box, but the board is just too big. The ASL does have, however, what is now a somewhat quaint feature: a switchable tape loop. May I assume that I could just put the B1 Korg board in an outboard box, with 50k resistors across the inputs, and have a convenient, versatile preamp with switchable gain and H2, along with, given the autoformers, the iron component that ZM suggests from time to time?
I have an elderly Antique Sound Lab autoformer volume control box that has been in and out of my system at various points, for various reasons - mostly convenience. Several inputs, multiple parallel outputs, and, important in my case, a known good working device for when I screw up other alternatives.
I've been looking for a way to incorporate the B1 Korg in my current system, and my first thought was to put it in the ASL box, but the board is just too big. The ASL does have, however, what is now a somewhat quaint feature: a switchable tape loop. May I assume that I could just put the B1 Korg board in an outboard box, with 50k resistors across the inputs, and have a convenient, versatile preamp with switchable gain and H2, along with, given the autoformers, the iron component that ZM suggests from time to time?
Possibly, but on my Mac laptop, that is not true. I just checked. I'm thinking that the posts per page varies depending upon the screen and resolution. Perhaps the best approach is to cite to post number, as that should always be fixed. I've seen a lot of other posters refer to that and I did think it was inconvenient, but now I think I see why they adopted that approach: makes it the most accurate way of referencing a post for the user.
Anyway, I was posting just to make it easer for the poster to find your diagram, which is, BTW, very good. Thank you for all you have done in the past to help us!
Thank you for pointing me in the correct direction, H and B voltages measure 8.99
