The Korg Nutube B1 will do exactly what you are looking for.
https://diyaudiostore.com/collections/b1-buffer-w-korg-triode-pre-amplifier/products/korg-nutube-b1
https://diyaudiostore.com/collections/b1-buffer-w-korg-triode-pre-amplifier/products/korg-nutube-b1
Or this:
https://www.diyaudio.com/community/threads/h2-v2-build.376337/post-6767740
No tubes needed.
https://www.diyaudio.com/community/threads/h2-v2-build.376337/post-6767740
No tubes needed.
When I did this, I posed some questions to answer before embarking on the design.
I came up with:
1. 10k ohms (powered speakers)
2. 1k ohms or lower, so input impedance shoud be >10k ohms (I ended up using a 50k ohm pot for the volume control).
3. I needed very little gain, only 6 to 9 dB.
I ended up with an inverting amplifier with shunt NFB from out to grid.
If you need more gain and can work with a higher Zout, you could possibly use a single triode-wired 6V6GT per channel, like the Salas 6V6 preamp. Or a single 12B4A per channel.
There are quite a few ways to skin this cat.
- What is the load impedance to be driven by the preamp?
- What output (source) impedances do my sources have? (Which is another way of asking, what input impedance does the preamp have to have?)
- How much gain is required?
I came up with:
1. 10k ohms (powered speakers)
2. 1k ohms or lower, so input impedance shoud be >10k ohms (I ended up using a 50k ohm pot for the volume control).
3. I needed very little gain, only 6 to 9 dB.
I ended up with an inverting amplifier with shunt NFB from out to grid.
If you need more gain and can work with a higher Zout, you could possibly use a single triode-wired 6V6GT per channel, like the Salas 6V6 preamp. Or a single 12B4A per channel.
There are quite a few ways to skin this cat.
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Does your current setup drive the speakers to full output?
The project at the link you provided has a minimum gain of 19.9.
Maybe you should explore a line stage with much lower gain or a tube buffer stage.
I have a version of the Blue Velvet Preamp using 12SN7 tubes (gain is 6 or less). I used zeners and a mosfet for the regulated supply instead of the vacuum tube regulators. I use a DAC for an input and drive amplifiers that need 2 volts or less for full power. I find that most of the time I adjust the volume control for unity gain. I have been using this setup everyday for 15 years. I bought several dozen 12SN7s so I would have a lifetime supply of tubes for the preamp. In 15 years none have failed!
Original
https://www.enjoythemusic.com/magazine/equipment/1103/midmonth/bluevelvet.htm
Updated version
https://www.enjoythemusic.com/diy/1110/blue_velvet_line_preamplifier.htm
Steve
The project at the link you provided has a minimum gain of 19.9.
Maybe you should explore a line stage with much lower gain or a tube buffer stage.
I have a version of the Blue Velvet Preamp using 12SN7 tubes (gain is 6 or less). I used zeners and a mosfet for the regulated supply instead of the vacuum tube regulators. I use a DAC for an input and drive amplifiers that need 2 volts or less for full power. I find that most of the time I adjust the volume control for unity gain. I have been using this setup everyday for 15 years. I bought several dozen 12SN7s so I would have a lifetime supply of tubes for the preamp. In 15 years none have failed!
Original
https://www.enjoythemusic.com/magazine/equipment/1103/midmonth/bluevelvet.htm
Updated version
https://www.enjoythemusic.com/diy/1110/blue_velvet_line_preamplifier.htm
Steve
That looks very much like the John Hogan SRPP 6SN7 preamp I use to have. I loved the sound of it. I agree Steve: As these speakers are, more or less, in my face I don't need that much gain, however, I have noticed all these years, that gain = dynamics and I fear I would not get that with just a buffer.
The way I see it, if you don't need much gain, why start with a higher gain tube and then dump most of it to ground. And if you need low output impedance, why not use a tube with relatively low plate resistance instead of adding a cathode follower / buffer stage.
After reading numerous comments by Andy Evans over the years about the sonic qualities of the 1626, I used it to build a very basic preamp. I call it the Boogie Factor, which is the term Andy often used in his descriptions.
https://www.audiokarma.org/forums/index.php?threads/1626-preamp-build.931276/
I tried about 10 or 12 different tube types while I had it breadboarded, all of which were inexpensive, low gain with relatively low plate resistance. The 1626 was my preference, although a few others were also excellent.
I mostly use it with tube amps but I recently picked up a little Class D Aiyima A-07 to power the bass in a bi-amped setup with an active crossover. This little amp has gotten a lot of praise so I decided to listen to it full range for a while. I was impressed by the sound but when I added the preamp it took it to another level. More lively, more swing. I assume the amps in a powered monitor are also Class D so it's likely that there would be a similar synergy.
Lots of other choices too, of course.
The blue velvet is a typical gain stage driving an anode follower with plate to grid feedback. It is not a buffer and the gain is approximately 12db in the configuration in the link.
The only tests I have were done with the volume pot at full volume. I used an HP analyzer and the distortion was 0.1% at 100mv rising to 0.2% at 1 volt and 0.4% at 2 volts output. At 5 Volts it was 1% and that was the limit of my tests since that was sufficient to drive my power amps into heavy clipping.
I mocked up another preamp to test a driver for a power stage. It a single stage 6JC6A in triode with a mosfet regulator feeding a CCS for the plate and an led resistor combination in the cathode. The results were shocking. The gain was approximately 10 times and the distortion was very low. The only test I recorded was 1 volt input and 10 volts output with 0.025% distortion.
I liked the sound of that 6JC6A but, not enough to swap out my blue velvet.
The blue velvet is driving a 300B SE Amp and I like the way it sounds. Maybe the small amount of 2nd harmonic distortion masks other distortions in the system.
I really don't know if the Blue Velvet would play well with your powered speakers.
Steve
The only tests I have were done with the volume pot at full volume. I used an HP analyzer and the distortion was 0.1% at 100mv rising to 0.2% at 1 volt and 0.4% at 2 volts output. At 5 Volts it was 1% and that was the limit of my tests since that was sufficient to drive my power amps into heavy clipping.
I mocked up another preamp to test a driver for a power stage. It a single stage 6JC6A in triode with a mosfet regulator feeding a CCS for the plate and an led resistor combination in the cathode. The results were shocking. The gain was approximately 10 times and the distortion was very low. The only test I recorded was 1 volt input and 10 volts output with 0.025% distortion.
I liked the sound of that 6JC6A but, not enough to swap out my blue velvet.
The blue velvet is driving a 300B SE Amp and I like the way it sounds. Maybe the small amount of 2nd harmonic distortion masks other distortions in the system.
I really don't know if the Blue Velvet would play well with your powered speakers.
Steve
The Bottlehead Moreplay is a fantastic preamp for very little money. https://bottlehead.com/product/moreplay-preamplifier-kit/ It does have a relatively high output impedance, my recollection is around 3.5K Ohms, so that might not pair that well if your powered speakers have low input impedance. Volume control in the Moreplay is on the output which really helps with lowering the noise floor of the 6V6 tubes which tend to be microphonic. Sonically, the Moreplay competes well with preamps costing much more money, especially if you upgrade the tube to a good NOS 6V6. Personally I prefer it to my B1 Korg or my Waynes BA2018 Linestage although the BA2018 has its charms. It is better than the Cary SLP-03 and Cary SLP-70 preamps I own but not quite as good as my PS Audio BHK preamp which costs 10x as much.