If you happen to browse Gearslutz or any other popular audio forum from time to time you’re bound to come across a thread asking for advice on what the best mic preamp to purchase is. In fact, you probably come by such threads often. Unfortunately there’s usually very little worthwhile information contained within. Among enthusiastic endorsements for any of the multitude of fancy mic pres that are popular that week, you’ll usually find the obligatory snide remarks about how the question is impossible to answer because choosing a mic pre is both a very personal choice and one where form fits function. That is, you can’t possibly get a useful answer because it is impossible for the people responding to know what is expected of the preamp or how the intended source, mics and pre will interact. For the most part it’s true. It’s simply a question that comes without a correct answer. Take the time to consider who would ask such a question, however and it would appear there may be a useful answer after all – a mic pre that can perform well at just about any task, by changing its personality to fit the situation. It just so happens that such a pre has found its way to my bench and for someone looking to step up to their first “real” mic preamp it’s both perfect, and way less expensive than it ought to be. Ironically, it might also be a must-have for commercial studios as well.
Earlier this year I happened upon a new and unassuming little single channel, half-rack preamp based on the venerable API 312 circuit called the Warm Audio WA12. After an in–depth review of the product I concluded that the WA12 was not just another clone, but a very new and welcome twist on the famous circuit. That is, it took the merits of the design and added some personality of its own to create a truly fantastic-sounding and professional box worthy of rack space in any studio. Of course, its unusually low price drew attention both good and bad, but in the end I think it’s a fantastic product that has obviously sold well and helped to make a name for Warm Audio. You can read my in-depth review here (http://gearautopsy.com/warm-audio-wa12-microphone-preamp-review/) to find out the finer details. Suffice to say, there was some “cost engineering” that creatively refined the design so that the sound wouldn’t be compromised, but the preamp could be made and sold for a price previously unheard of for its level of performance. At the WA12’s $450 list price, it wasn’t hard to give up some of the more luxurious features like metering, a high pass filter and an output attenuator. That being said, the important stuff like polarity inversion, a 20dB pad, and even an instrument input managed to make the final design. Personally, I couldn’t help but wonder if another $100 or so might have been worth having those other features, but understood that price was a very big design influence. Warm Audio must have also wondered just how much better the product could have been with these other features because while I was enjoying a new price/performance milestone in the WA12, they were creating an even better mic preamp. Enter the TB12, also known as the Tonebeast.
The TB12 takes the formula that made the WA12 such a great product and adds to it just about every feature you could have conceivably missed – plus some you probably haven’t even though of. First, let me re-iterate that both preamps make use of high quality components throughout, and while some parts like electrolytic capacitors are Chinese-branded parts they are still high spec, and do their job as expected. 1% metal film resistors are used throughout, as are capacitors rated for 105 C. Transistors are name brand (ON semi, Fairchild, BC) and possibly the most critical components, the input and output transformers, are courtesy of the American company Cinemag (one of the best transformer makers in the business, as any equipment designer will tell you). Even the voltage regulators are coupled to their heat sinks with thermal compound, a detail that is probably overkill but one that shows the WA12 and TB12 are built by a company with a passion for doing things right. The jacks, connectors, and knobs are some of the areas that may have helped to minimize cost, but not at the peril of audio quality. Most people will rack these boxes, hook them up to their interfaces and patch bays, and leave them connected anyway. In practical use, it’s not an area I’m all that concerned about. So both preamps use quality parts, are inspired by the same time-tested design and offer performance well outside their price point. How is it that the WA12 and TB12 differ? Prepare to be amazed, as I was.
The TB12 takes the wonderful WA12 and adds a bright 6 LED VU meter, a high-pass filter, a front-mounted XLR (in addition to the one on the rear of the unit), a line level input (in addition to the front mounted instrument input), inserts to add your favorite compressor or EQ (maybe an upcoming product from Warm?), and an output attenuator for dialing in extra saturated goodness. All of this comes in a new, full rack space chassis with the same robust construction and good looks. Thankfully, all of these additions come without losing a single feature of the original WA12, and for less than you’d expect to pay for the chassis alone. The difference in price is a mere $150, and for just these improvements the TB12 is already an amazing value. Of course, Warm decided not to stop there. Assuming there would be folks out there with an itch to mod the TB12 and see just how far the design could be taken (there are plenty out there), Warm thought better to do it for us. In addition to the Melcor 1731 op-amp from the WA12, they have added a second switchable op-amp based on the Jensen 918 (older brother of the popular modern 990), a pin compatible but much cleaner sounding gain block. Also, while the WA12 used a custom designed steel output transformer, the TB12 adds a second switchable nickel-steel hybrid transformer, which offers another cleaner output stage to the original. A third switchable option has also been added allowing the selection of either tantalum or standard electrolytic capacitors on the signal path. By manipulating these selectable features, you can take the TB12 from the original, musically-colored sound to a smooth, high definition clean sound with several steps in between. All these new features are switchable in real-time, and without annoying audio pops, so comparing them is both a breeze and a blast. Combined with the original tone feature, and the ability to drive the gain stages into distortion by attenuating the output, there are really so many different configurations that this may be the most versatile mic pre you can buy today at any price. And the TB12 sells for a mere $600!
Looking Inside The TB12
Popping the top on the TB12 revealed some nice surprises, the most exciting being that this time around Warm has decided to appeal to the experimenter in us by socketing the op-amps, making them interchangeable! That means any of the dozens of op-amps on the market that fit the standard 2520 footprint will work inside of the TB12, so long as they are comfortable running at the +/-18v rails the unit provides (and most are!). Swapping them is as simple as popping one out and inserting another for even MORE tonal variations (power off the unit first). I also noticed that there is an unoccupied space for a PCB-mounted input transformer that Warm tells me is for a possible future switch to a board-mounted part. It is wired in parallel with the existing Cinemag input transformer, but could serve as a means to easily try some other input options if you feel adventurous. The power supply is very familiar since it is the same design used in the WA12. There are local regulators for both the positive and negative voltage rails, as well as phantom power, and they are well filtered by 105 C rated electrolytics. Voltages measured at the supply output were steady and well within spec, and since clean power is essential for a well performing mic pre, I was happy to see this design re-used in the TB12. The wall-wart from the WA12 has been replaced with a more convenient line-lump type transformer this time, but both are the same specification and are interchangeable. Also, a single supply can power multiple units (at least 4) if you get one with enough amperage and a splitter cord (both available from Jameco or a similar vendor for very little money) so there are certainly advantages to using an external transformer. I was hoping for an internal supply this time, but understand the reasons it was left out. At least the new transformer won’t block three precious wall outlets like the original wall-wart did.
The preamp itself resides on four individual circuit boards that are very cleanly wired together. This may be for ease of serviceability as well as modularity for possible future updates and upgrades. Either way the boards are of high quality, contain no surface mount components, and all connections between them and the transformers are made by easily removable wires so servicing them should be a breeze should the need arise. All external jacks are PCB mounted parts, and the transformers are securely mounted to the bottom of the chassis. The overall internal design is very clean and well executed, just like it is in the WA12. The chassis appears to be a standard off-the-shelf part again here, and there is a fair amount of unused space inside. That means there’s plenty of room to stash the money you’ll save by choosing the TB12 Tonebeast.
On the Outside of the TB12
You’ll either be a fan of the TB12s looks or you won’t, but regardless, you’ll have to agree that Warm’s bright orange faceplate won’t be overlooked in the rack. The unit thoughtfully has a multitude of inputs and outputs for total flexibility. XLR mic inputs are available on both the front and back of the unit, making it easy to connect to the TB12 when the unit is racked. There is also an instrument input next to the front XLR jack for a guitar or bass, and a standard line level input beside the rear XLR. All of the inputs go through the input transformer and the entire signal path, so while the TB12 is a mic preamp it will also be perfect for warming up instruments, synths, and even as a tone-shaping tool for a passive or active summing mixer like the Dangerous D-Box. Outputs are available on both XLR and TRS jacks and since they are wired in parallel you should be able to use them both simultaneously. New for the TB12 is a pair of insert jacks (send/return) for use with your favorite EQ or Compressor. Something tells me Warm will be offering some options to make use of these in the near future. Finally, there is a single jack for connecting the 24VAC power supply. It would have been cool to see a pass-through for chaining multiple units (you will want at least two of these gems!) but clearly I have already been spoiled by all that the Tonebeast offers. The front panel is home to more controls than you ever expected to find on a mic pre, let alone one at this price. From left to right there are push buttons for selecting the hi-z input, rear line input, 48V phantom power, a 20dB pad, polarity inversion, and an 80Hz hi-pass filter. Warm has been kind enough to give us LED confirmation on each of these switches so there’s no need to toggle them to see which position is engaged – a nice touch. Next are the tone-shaping controls, where the Tonebeast’s magic happens. The first is a rotary toggle switch for selecting between the 1731 and 918 op-amps, or whichever other op-amps you have chosen to install. Next is the familiar tone button from the WA12, which changes input impedance while adding 6dB of additional step up gain, followed by the capacitor toggle, the output transformer bypass and then another rotary switch for selecting between the two Cinemag output transformers. After the tone controls come two stepped pots for controlling input gain and output attenuation followed by a convenient 6 LED VU meter, and the unit’s power switch. All of the functions are well labeled and very easily adjusted, most giving confirmation through bright red LEDs.
So How Does the TB12 Sound?
Considering I had the lid off of the TB12 already, and I am very familiar with the sound of the WA12, I decided to experiment a little. I had a 4 pack of genuine API 2520 op-amps on my bench so I decided to first test the unit with a 2520 installed beside the Melcor 1731 and compare the two. With the unit set to use the 1731, tantalum capacitors and all steel output transformer, the TB12 sounded exactly like my familiar WA12 mic pres, which is great news because they sound fantastic. It’s a rather colored sound with a gentle de-emphasis of the high frequencies (without sounding dark) and that lovely, milk chocolate harmonic smoothness that becomes most evident on transients, and “esss” sounds. It is my opinion that the design is a perfect match for some of the cheaper Chinese condensers because it helps to tame the spittiness and harshness that they often exhibit in the high end. The saturation just smooths it out and makes it less obtrusive. I used my recently-built, custom C12 microphone (vintage style) and was surprised to find that as colored as the preamp is, it still sounded sublime despite the fact that the mic has a lot of saturation of its own. Switching just the op-amp from the 1731 to my genuine API 2520 yielded a subtle, but noticeable, increase in mid and high frequency focus, while maybe de-emphasizing the fat low end the Warm pres render so well. Overall, I would characterize the sound as unexpectedly similar, but slightly cleaner, and with less tendency to break-up and saturate with the 2520 engaged. Switching from the steel to hybrid nickel/steel transformer has a similar effect, but it was more pronounced. While still having the smoothness of gentle saturation, there was a detectable reduction of low/mid heft and weight along with a sense of increased clarity. Switching the signal path capacitors from tantalum to electrolytic was much harder to quantify but it seemed that, in a similar way, the tantalum capacitors had more weight while the electrolytics felt cleaner. Quickly realizing that the TB12 is designed as a WA12 that can be coaxed into being a much cleaner pre, I removed my 2520 op-amp and replaced it with the intended 918. After switching from the 1731 to the 918 I was instantly aware of two things: the first is that switching between the two op-amps demonstrated the greatest differential in tone, and the second is that the 918 is a remarkably clean, high bandwidth op-amp (similar to my experiences with the 990 it inspired). Starting from the very fat and warm sound of the WA12, switching from the 1731 to the 918, the tantalums to the electrolytics and finally the steel to the hybrid transformer, will take you gradually through several intermediate steps to a much cleaner sounding configuration. Don’t get me wrong, the harmonics are still there when dialing in clean tone, but they are more subtle and graceful. The main difference is in the extension of the upper frequencies and less low end emphasis than the preamp exhibits on the other end. To get even an even cleaner sound, you can engage the output transformer bypass switch to drive the output straight from the gain stage. The disadvantage will be an 8dB gain drop, as well as the loss of the balanced output since there is no output buffer to take over balancing duties. You can use the tone feature to add 6dB of gain back, but remember the input impedance drops to 150ohm when this setting is used, so make sure your mic’s output impedance is low enough to cope. Since the loading is different, the mic’s sound will most likely be altered slightly – more so in the case of dynamics and ribbons. I was glad to find that auditioning all these variations while listening was seamless and none of the switches made any audible pops or artifacts to be concerned about. At no time did I find the TB12’s self noise to be objectionable either. I discovered that when set for its cleanest output, the Tonebeast is a perfect alternative to the excellent pres in my Apollo interface, which sound less exciting and slightly brighter overall, in comparison.
For fun, I decided to see how dirty of a sound I could dial in using all of these tone options. I engaged the tone button, selected the 1731 op-amp, tantalum capacitors and steel output transformer, and cranked the gain to the max. I then used the output attenuator to dial in a reasonable level to my AD. The result was full on fuzz-box distortion. Trent Reznor would love it! The resulting waveform was clearly clipped flat on both the top and the bottom even though I had plenty of headroom left in my converters. This is an extreme setting, but it makes it easy to see how the TB12 can also compress the source as well as distort. Extreme settings like this are best reserved for special effects, but I can see how dialing in a hair of distortion could really make a snare come alive, or help a bass line or lead guitar cut through the mix better. Plus, distortion is an effect not yet mastered by plugins yet, so it’s nice to have the option to do it in the analog domain when the project calls for it. The TB12 can go from dirty to clean and every stage in between. As stated above, the warmer settings are (in order of how drastic their influence is) 1731 op-amp, steel output transformer, tone button engaged, and tantalum capacitors. For clean sounds, use the 918 op-amp, nickel/steel output transformer (or no output transformer), and electrolytic capacitors. Either combination can be driven into audible distortion by increasing the gain above what’s needed and dialing down the output. Talk about multiple personalities!
Transformers, Impedance, and Tone Selection
One of the special things about the very simple design the WA12 and TB12 are based on is that they are not only very simple, but they derive gain from 3 stages – the input transformer, the actual gain block, and the output transformer. Since these three stages provide gain, they also provide the tonal characteristics that shape the amplified sound. Warm audio is using this fact to their advantage, not only to tailor the design to their own specific sound, but to allow manipulation of the tone throughout the signal path. The obvious way the TB12 can shape the sound is through actual switching of the components in the signal path. This is similar to what happens when people mod their gear. Changing certain components changes the sound, hopefully in a positive or useful way. The other way these components shape tone is by manipulating how they are used. For example, the input transformer can be switched from a series wired primary to parallel by engaging the tone button. This will increase the step-up gain derived from the input transformer by 6dB and will also increase the saturation and harmonic content that comes from it. The side effect of doing this is that the additional voltage gain has to come from somewhere. Transformers are used to isolate input and output stages from DC voltage while passing AC voltage (such as an audio signal), but they can also convert voltage gain to current (lower the impedance) or vice versa (raise the impedance). Since the additional 6dB of gain must come from the mic’s output, and we need current to convert to voltage gain, the mic gets “loaded” down more heavily and not all mics will like this. A rule of thumb is that the input impedance of the preamp should ideally be 5 times the output impedance of the mic to get a perfect loading match. Since the input impedance drops to 150ohm when the tone button is engaged, we would ideally need a mic with an output impedance of 30ohm to get a proper match. Most mics are in the 100-150ohm range, and some passive ribbon mics are much higher. The result is that the response of the mic will change. Some mics, especially condensers, can easily cope with this demand since their FET or tube preamps can supply the extra current needed. Dynamic mics and ribbon mics, however, usually have higher output impedance and therefore will be affected much more noticably. The effect may be just what you’re looking for, but when it isn’t, there is a simple solution. Using an impedance buffer such as a Cloudlifter or Cathedral Pipes Durham will provide a sufficiently high impedance load to the mic, and will handily create more current (lower output impedance) to feed the mic pre by using phantom power. You get 6dB of extra gain, increased harmonic content from the input transformer, and still get the expected response from the mic thanks to the proper loading.
Another way to manipulate the tone is to increase the amount of gain by the discrete gain stage itself. This wasn’t easily done on the WA12 since increasing gain always meant increasing output and eventually clipping the AD converter, but the TB12 introduces an output attenuator to prevent this. That means you can increase gain beyond what you actually require at the output, until you start to run out of headroom in the gain stage. Output levels that would normally toast your AD converters can then be reduced to a manageable level with the output attenuator. It should be noted that you will be increasing harmonic distortion not only in the gain stage, but also in the output stage as well since the transformer will be fed a much hotter signal. The TB12 is easily capable of sounds ranging from slightly saturated to full-on distortion. Keep in mind that distortion doesn’t have to be obvious to be useful, and dialing in a little bit can really add “balls” to some sources like drums and bass. It’s not to be overdone, but when used judiciously, this technique can be a secret weapon of sorts.
Finally, the TB12 allows for removing the output transformer from the equation altogether. This will cost you 8dB of gain since you are no longer getting the step-up gain from the transformer, and since the preamp is transformer balanced, and doesn’t have an output buffer you will also be stuck with an unbalanced signal. In most practical applications this won’t be a problem, but if you are driving long lines it can potentially cause issues. This does allow you to get remarkably clean tones from the TB12, really highlighting the unit’s ability to go from audible distortion, to warm and fat, all the way to clean and present without a single component swap or upgrade. In fact, I even question the need to swap op-amps since the two installed at the factory are designed to maximize the gamut of tones you can achieve with the Tonebeast. That’s not to say experimentation isn’t both fun and harmless.
So What’s The Final Verdict?
For a mere $150 more, the TB12 takes the successful formula of the Warm WA12 and literally triples its practical usefulness. If the price to performance ratio of the WA12 blew me away before, then I am simply beside myself trying to figure out how Warm can offer this new preamp for only $600. I’d love to see more robust Neutrik connectors throughout, sealed relays instead of contact switches and military spec switches and pots for gain attenuation, but none of these things would likely improve sound, nor do I think the components used are likely to prematurely fail in most usage scenarios. Part of me thinks that the unbelievable price of Warm Audio’s products might cause them to be unfairly judged by the self-proclaimed elite engineers, and confrontational members on Gearslutz, and unfortunately people do believe what they read. All the same, Warm audio is making it possible for musicians and engineers at every level of expertise to gain access to tools that will undoubtedly enhance creativity, teach and inspire them to make more music, and better sounding recordings along the way. Just as I suggested that the WA12 could easily sit beside pedigree mic amps in any studio, I feel the same about the TB12. In fact, at this price, everyone should have at least a pair. I think it would be cool if Warm introduced a Mk2 unit with more expensive jacks and knobs, and maybe a flashy aluminum faceplate so the big studios and “golden ears” would be more likely to seriously consider this product. Even at the $1500 mark, I’d consider the TB12 a great value. The amount of tonal variations possible with this box make it a candidate for the most versatile preamp ever, and from now on when I come across someone looking for advice on what their first “real” mic pre should be, I will recommend the TB12 every time. I can only hope Warm Audio is planning to give us some goodies to wire up to those insert jacks soon too, and that they follow in the tradition of the WA12 and TB12.