Sonic Farm: Tantra Bass Tube Preamp

A bass amp is not a typical product often seen on the review pages of Tape Op. Reviews usually center on mainstream recording equipment as opposed to performance amps, but I was really curious about Sonic Farm’s Tantra bass tube preamplifier, especially since Sonic Farm makes one of my favorite tube-based mic preamps: the Creamer [Tape Op #81]. However, I think I figured out a way to justify this review. The Tantra is designed not only as a performance tool but also as a seriously versatile front end for direct studio tracking. In fact, it can be ordered with either a 1000 watt class D power amp, a monstrous 2500 watt amp, or no amp at all. They even included separate power switches and fuses, so powering up just the preamp for DI tracking studio work is easy while leaving the amp off.

Features: I don’t know where to begin. Sonic Farm has put more thought into this thing than I put into my entire college career. Listing all the features in depth would take pages, so I’ll try to briefly hit the important points. The Tantra’s tube front end incorporates the same EF86 “no feedback” tube circuit used in their Creamer mic preamp. Like the mic preamp, there’s a switch that changes the tube between triode and pentode operation. This not only changes the tone character but also raises the gain. You get a cleaner sound with a little more sparkle in triode mode, whereas pentode mode increases the weight of the sound, and adds a small hint of saturation, while still being clean if you want it to be. Furthermore, they’ve added a second EF86 tube reserved for overdrive tones. So, you’ve got two parallel circuits – one clean and one drive. That means you can blend full clean with saturated. Pretty cool. The EQ is a bit more sophisticated than your average bass amp. You get five bands of EQ with fixed frequency high and low shelving plus three fully parametric mid bands. The parametric bands alone cover the entire sonic range, so it’s extremely flexible. If that’s not enough, they’ve included additional high and low frequency boost switches that add more thump or sparkle, with boost amounts that can be pre-set via trim pots. These boosts appear in the circuit after the clean tube, but before the overdrive tube, so engaging them won’t affect the clean tube drive.

So, that’s a good place to pause momentarily to make an observation. This amp requires a good long study of the manual. The included block diagram is very important because you have to understand the signal flow to effectively gain stage the amp and correctly use its controls. It’s not a “crank the volume and go” preamp. You have to learn the features and layout, but that’s the price you pay for amazing versatility.

Besides having a clean/drive blend control, there are many other amazing options for the drive tones. In addition to the tube drive, there’s a second FET overdrive. These drive modes can be combined to achieve monstrous tones. Therefore, it is insanely configurable and does much more than deliver only one stock drive tone. Also, it has a high-pass filter into the drive section, so that the low end remains clear and punchy while the mids and upper frequencies are being overdriven. This became apparent when listening to the DI output, as well as through a cabinet.

The built-in solid-state compressor has a fixed threshold, so turning up that knob pushes gain into the compression, much like a Universal Audio 1176 would. The XLR DI output can be fed from right after the tube stages, or after the compressor, EQ, and effects loop. The back panel also includes a line and tuner out in addition to the DI output.

Then there are a couple of unusual knobs that add second and fourth-order harmonics to create very interesting tonal options when blended in. These circuits are filtered out below 300 Hz so they only affect the mid and high frequencies, leaving the low end clean. I found these controls almost gave me that bridge pickup growl – even with the warmer tone from the neck pickup. This circuit is always routed through the compressor so that the effect stays even and controlled.

Also, the build quality is more than impressive. The knobs and switches are studio-grade, and I mean “spare no expense” studio-grade. The pots feel better than most high-end rack gear I’ve used. The metal case can be used either as a desktop unit or racked with optional rack ears.

Using only the DI out, my first impression was that this was a very nice tube preamp. It took a few more knob turns to appreciate how good the Tantra is. Once you wrap your head around the controls, it’s quite easy to get to the sound you are looking for. If I used EQ at all, it was only in very small amounts. I’m used to having to push EQ to get punch and snap out of a bass head, but with the Tantra, the integrity of the sound is already there. My bass is set up in a “P/J” (Fender Precision/Jazz) pickup configuration. I don’t remember being able to hear the character differences of each pickup with such detail before. I can get a deeper neck pickup sound that still had articulation and detail or a growl from the bridge pickup that still had weight. Switching into pentode mode added more weight to the sound while still retaining the original character. The Lo and Hi boost gave me different EQ characteristics, so having both options available was perfect.

Next, I got a few other bass players with vastly different playing styles to meet up at Tanglewood Studios in Fair Oaks, CA, to put the Tantra through its paces. First up, I got comments from Jon Talbot, who is much more familiar with overdrive tones than I am. After setting up his 8x10 cabinet, his first reaction was, “This is the greatest sounding amp I have ever plugged into this cabinet.” For this review, Sonic Farm supplied the 2500 watt version of the Tantra, so headroom was not a problem. Jon was impressed with the range of saturation and overdrive tones, spanning from subtle tube drive all the way to (his words) “gut-wrenching, blistering, bit-crushed fuzz that could end a marriage and everything in between.” He also noted that the low end was still round and punchy and thought this amp could easily replace several of his expensive pedals.

Next, Kevin Cain played some funk tones with his Modulus and Tobias basses. We started in Triode mode with no EQ. The transient response of the Tantra was insanely dynamic. We turned the compressor on and didn’t think about it again. It never got in the way and did an amazing job of getting parts to sit consistently without killing the transients. We also got hooked on the low frequency bump switch. I didn’t realize that you could get such a subby low punch without inducing any muddiness; the addictive bottom end never got out of balance. Again, Pentode mode beefed up the sound and was still very articulate. We then dialed in additional EQ, more out of curiosity than need. It didn’t matter what we did. Push the lower mids or the upper mids. Push more lows. It just shaped the tone without destroying the sonic integrity. The clarity and articulation never suffered. The last time I remember hearing that type of character in equalization was through a $7000 mastering EQ.

We began trying to seriously mess things up. What doesn’t usually work with funk playing? I know – OVERDRIVE. I cranked up the gain and dialed back the clean/drive blend knob. We sat in disbelief that it actually WORKED. Don’t get me wrong – full overdrive gain abuse was absolutely hideous for the style. But in moderation, it added tonal depth, even for slap playing. I have never experienced that before. Kevin has a large collection of basses and amps, but noted that the Tantra was the best sounding and most versatile head he had used.

We now wanted to go outside the usual application. Bassist Brett Cole often plays upright in surf bands, among other genres. After 20 seconds, he stopped and shook his head saying that was the best upright sound he had gotten. It was clean and articulate while sounding balanced and full. Adding some second-order harmonics naturally enhanced the articulation.

There’s a common thread here with the Tantra – as there was with Sonic Farm’s Creamer preamp: the “no-feedback” tube design allows the tone to happen with a clarity that other topologies don’t always produce. No matter what we asked this amp to do, musicality in the tone never suffered. It takes some deliberate time to understand the myriad of controls and options to get the most out of it, but it will deliver almost any tone with excellence. It’s an amazing studio DI front end that can also drive a cabinet with more power than you thought possible (if you choose the amp option). Not cheap, but in my opinion, it’s worth every penny, and will provide an amazing tone in the studio. Pricing based on configuration.