I have enjoyed my short time with the Tortuga Audio Tube Preamp Buffer.
It arrived on Wednesday without any issues and I appreciated the solid, no-nonsense design.
Unfortunately, when I saw it was single-ended only, I knew I was going to have trouble integrating it and making the most of my audition since I run all balanced connections and my amps only accept balanced inputs.
My system consists of;
Antipodes DX Level 3
Metrum Pavane DAC Level 3 (Adagio without the volume control)
SMc Audio buffered unity-gain line stage with AN Tantalum resistors (essentially the VRE-1)
Clayton M300 Class A monoblocks
Aerial 9 speakers
Aerial SW12 subwoofers (2 each)
Although I have been interested in Tortuga Audio’s LDR passive preamps, I do not own one. In addition to my main preamplifier listed above, I have a Goldpoint balanced passive preamplifier, using their latest SMD resistors and also a pair of balanced Endler Attenuators using Yageo metal film resistors. I mainly used the Tube Preamp Buffer with the Goldpoint passive preamp.
I worked around the connection issue by first connecting the Tube Preamp Buffer inputs directly to the single-ended outputs of the Metrum DAC and then sending the buffer outputs to the inputs of a pair of Jensen transformers that convert single-ended signals to balanced signals. There is an impedance penalty associated with the conversion but since the input impedance of my Clayton amps is 100K ohms, using the transformers typically works just fine, and much better than rca/xlr adaptors. The balanced outputs from the transformers were sent to the Goldpoint passive preamp and the balanced outputs from the Goldpoint were sent to the amps, so the attenuation occurred after the buffer. All the ICs used were 1M or less in length but the set-up was still more complicated than I had hoped.
The good news is that there didn’t seem to be any penalty for the complications. The Tube Preamp Buffer sounded great. As others have pointed out, the buffer is absolutely quiet, and surprisingly so since it uses two tubes. I heard a clean, clear sound, with nice body, nice tone, and realistic dimensionality. If there were any trade-offs, I thought I noticed a slight softening of the bass, leaning toward roundness and fullness instead of detail. These effects were not to an extent that detracted from the overall enjoyment of listening to the buffer, which always sounded musical. Without trying a more direct set-up using the balanced version of the buffer, I will never know what impact the extra cables and transformers had on the sound.
To verify what I was hearing, I took the Tube Preamp Buffer out of the signal chain so the only thing between the DAC and the amps was the Goldpoint passive preamp. The sound became a touch more dynamic and detailed but also a bit harder, sharper, and overall a little less musical. In my experience, the clarity of a passive preamp is initially attractive but over time I typically begin to notice a slightly flatter image, less body and tonal color, and maybe a bit less dynamic impact, so I have always gone back to whatever good linestage I had in my system at the time. The effect seemed a little less pronounced when I had an autoformer unit in my system (the Acoustic Imagery Jay-Sho) but I still liked the sound of my SMc preamp better. I believe that using an active stage or buffer (which is basically a unity gain active stage) improves impedance matching and optimizes signal delivery to the amplifier.
In a comparison between the Goldpoint/ Tube Preamp Buffer combination and my SMc unity-gain buffered preamp, I preferred the SMc unit and believe it displayed a bit better clarity, definition, dynamics, and tone without giving up dimensionality and fullness, and without displaying any hardness or sharpness. I have owned close to 30 really good preamps over the past 10 to 15 years and the SMc Audio preamp is the best of the bunch, so for the Goldpoint/ Tube Preamp Buffer combination to be anywhere close sonically is quite an accomplishment IMO.
In summary, I found the Tortuga Audio Tube Preamp Buffer to be well-built, quiet and to do exactly what it was meant to do, which is to optimize the signal between a passive attenuator or preamp and the amplifier that is being driven. When used in the signal chain with my Goldpoint passive preamp, it improved the flavor of the Goldpoint by providing a richer sounding tone and adding fullness and a touch of roundness that made listening to music more enjoyable. While these differences were not like night and day, they were noticeable to the point where I believe I would be satisfied long-term with the sound of the Goldpoint preamplifier/ Tube Preamp Buffer combination, but not with the Goldpoint alone. However, the Goldpoint/ Tube Preamp Buffer combination was not good enough to displace my SMc preamp.
I believe the Tortuga Audio Tube Preamp Buffer is a really good product that may be almost essential for people using passive preamps or attenuators alone. At a minimum, folks using passives should at least try the tube buffer. I would like to try the balanced version someday. IMO, Tortuga Audio could turn a triple into a home run by combining the Tube Preamp Buffer with their LDR passive preamp for a unity-gain, buffered, one-box preamp solution. Offer balanced and single-ended options with a volume display and remote and the result would be likely to compete with some really good preamps.
Thank you for the opportunity to audition the Tube Preamp Buffer. I plan to ship it out to wirenut on Monday.