Maybe try a Schiit Saga+ preamp.
The functional purpose of an active buffer is to improve impedance mismatches by reducing higher impedance inputs to lower impedance outputs. This can be helpful when driving amplifiers with low input impedances, when using passive volume controls that do not actively buffer the signal, and/or when driving long interconnects. The effect can be significant, even in cases of unity gain (i.e., no voltage gain between input and output), and the change in sound is sometimes described as having more body, tonal color, and drive. The buffer can be either fully solid state or tubed.
I use the Hattor Audio Big preamp in passive mode to control the volume of my system and it sounds significantly better to me when followed by my SMc Audio buffer (solid state and unity gain) that is based on their VRE-1 preamp. I also have the Hattor Audio Tube Active Stage, which is a tube buffer that typically comes with 9dB gain (mine has 6dB). It is basically a tube buffer stage without a volume control. I have tried the Tortuga Tube Buffer on one of their tours, so I had it in my system for about a week, and I also tried the Purity Audio tubed buffer in my system.
IMO, and in my system, the Hattor Tube Active Stage sounds very good although it just doesn't provide quite the magic of my SMc Audio buffer, so it is currently sitting in a box. However, if I didn't have the SMc buffer, I would be perfectly happy to substitute the Hattor after my passive volume control.
The Hattor Big preamp also comes with an opamp active stage (mine has the NewClassD discrete opamp stage), which can be set to 3/6/9 dB gain. I bypass the active stage to run the Hattor as a passive into the SMc buffer. However, I have tried it through the discrete opamp stage and I also find that to be an improvement over running it passively. Therefore, in ranking buffers (some with low gain) in my system, I would put the solid state SMc Audio buffer first and the Hattor Tube Active Stage second, both of which I would be happy to use. Third would be the discrete NewClassD opamp stage in the Hattor Big preamp, which I would judge as just a step below the first two. Finally, I just did not like the sound of the Tortuga or the Purity Audio buffers in my system.
Since you have an active preamp, you probably don't need a buffer. If you want to change the sound of your system, adding a buffer may be an inefficient way to do that. I suggest looking into a different preamp, or some type of EQ to deliver the type of sound you want to hear.
I had the Zpre3 as my preamp in my main system for quite some time (a great little preamp). I also ran an iFi Micro iTube2 between the Zpre and my amp. The iFi iTube is highly recommended. It’s a bit pricey, but does so much more than most all ‘tube buffers’. It added quite a lot, and has a variety of settings you can use to dial in to taste, or even change on the fly. Check it out. Great piece of equipment.
The ZPre and iFi is now in my bedroom system, and still in use.
I have a ZPre3 and compared it to a Schitt Saga with a very good tube in it, volume matched AB comparison I couldn't tell the difference between the two. I was quite surprised actually, the ZPre3 punches way higher than expected. The matching Zamp is a little darling too! Great for starter or second systems.
That’s like “dabbling” in the tube world. I started that way. When I liked what I heard I invested in a tube preamp. Like @russ69 recommends. Think of it as the “gateway drug” to the tube audio experience.
You have to be careful using the inexpensive tube “buffer” preamps. Some are just straight wires input to output. The tubes only see filament voltage. I have one; only when I pulled off the covers, traced the circuit board, did I find that there was no “tube buffer”.
Another one I have uses a unity gain opamp with only filament voltage to the tubes.
Three times is the charm….The third one I bought actually uses the tubes for unity gain.
And….The whole idea is to add tube harmonics to the sound! So yeah, they are distortion machines!! LOL!!!!
The TFM-35 is an amazing sounding amp. I found one on eBay new in the box. Even today, its top end is astoundingly smooth even by today's standards.
I ran it through a Don Sachs preamp wih 6SN7s and it was heaven. Doing that and having a dedicated AC line put in helped bass output a good bit.
Bass output on these amps is extremely flat. But, in many ways, this is a good thing because speaker position and treatment can fix that without things getting boomy.
As mentioned, no need to get tube buffers. Get the best front end you can afford.
I tried a couple of those cheap Chinese tube buffers you find on eBay and they were no good. They were starved plate designs - only about 12 volts or so on the plates and op-amps in the circuit doing the work. Then I tried a Bellari PA555 tube preamp for only $300. The single 12AX7 is actually functioning with high plate voltage followed by op-amps for a very low output impedance. This is not a starved plate design. Let the trolling begin but I am happy with the tube sound it adds.
👍🏼 Folks shouldn’t ‘poo poo’ tube buffers until they actually hear the iFi Micro Tube2 and understand it’s capabilities. It’s an incredible little piece of equipment that can transform your rig, if that is what you are looking for. It’s also very well engineered and does not integrate distortion, it’s really quiet actually. But again, it isn’t cheap vs the crappy ones out there.
It did it’s job for me quite well until upgrading my preamp by a significant amount. Could I still have it in the chain? Sure, but isn’t really necessary now, for me.
I' purchased a new itube2 late March 2018 and it and system has been running 24/7 (fingers crossed) Many pieces (streamers, amps, couple of dacs, wiring, power supplies, TVs, speakers etc) many multiples of its cost have come and some gone but after I heard what it does I've not had a desire to run without it. Sources are Qobuz/Tidal/TV. Everything solid state except for the iTube2 in unity gain. I've enjoyed this amazing piece the last 4 years, hope I didn't just jinx the tube lol.
Wow, I had no idea that they discontinued the iTube2. What a shame, but it sure seems to be the case searching around. Incredible little piece of equipment. If you can snag one used, I would still recommend that.