Arkham Oracle Tube Preamp Review
March 19, 2020
Arkham Sound is a small company operating out of Maine building just a small number of amplification devices by hand. The Oracle takes all that people love about the Zephyer rack mount preamp and puts it into a smaller, somewhat pedalboard friendly enclosure.
I suspect anybody reading this is doing so because of their interest in tube amplification, seeking tube tone in a small(ish) package. You'd be wise to consider the Arkham Sound Oracle preamp.
The Oracle is inspired by Ampeg's iconic Portaflex series. To start, the Oracle uses a 12AX7 preamp tube which is selected for low noise and good tone and is run at 300V B+. Note: this is not a starved plate design. It is a high voltage design. Yes, after some time as the unit heats up you can feel the warmth radiating through the vent on the top of the enclosure.
The Oracle lacks a XLR connection for DI use. Instead it offers dual Lo-Z outputs. Out 1 is for connecting to a power amp, some other interface and such. Out 2 may then be used for an additional feed to a DI box. You can use both simultaneously, but only Out 1 is active individually. There is plenty of output. The master volume controls the volume of both outputs.
The gain and EQ section is based on the James Tonestack of which there is plenty of documentation available online to pursue. It is not the point of this review so I'll just point you to Google or the Arkham website for more on that topic. I'm pleased with the EQ and find it to be quite versatile.
Unlike many circuits based on the James Tonestack the Oracle includes a Mid switch which provides a decent bump around 250Hz. I prefer this switch flipped up which is activated. Then you have a Range dial which is also featured on the Arkham Zephyr. It allows you to sweep a boost or scoop throughout the entire midrange. It is highly useful and highly interactive with the Mid switch and Bass and Treble dials. Cut all bass and treble and adjust the Range dial for a wide sweep. Dime the bass and treble for a different effect.
Flat response is with both bass and treble dials at noon. There is an excellent amount of bass and treble on hand. In fact, with treble boosted too much the sound becomes quite brittle and as to be expected, a bit noisy. I found my sweet spot with the bass knob between 2:00 and 3:30 and treble around 9:00 to 11:00 depending on the bass I was using. Dime both treble and bass for mid scoop.
The Lo switch adds another decent bump at 80Hz. Since it is sitting at 80Hz it isn't increasing the sub frequencies or what tends to be described as muddy. On the other hand, it doesn't necessarily add that low presence or rumble that you might have hoped for. That said, it will make your tone more robust in a mix for sure. Used in combination with the bass dial provides a lot of flexibility. I tend to prefer leaving the Lo switch in the down (off) position.
The Hi switch adds definite brightness to the circuit which does open up the high frequencies a bit. I like the Hi switch flipped up (on) as it seems to do something special to the overall upper mids and highs and makes the Range dial more useful. But in doing so, you really need to dial back the Treble dial, at least I must with the basses I tested with.
By the way, I used a Sadowsky Jazz (60's position), Sadowsky Modern, Xotic XB-2 (humbuckers), and Pedulla Pentabuzz fretless for my testing. This combination of basses allowed me to experience the Oracle with higher output basses with preamps, passive signals, and also fretless. You might wonder whether a device like the Oracle is overkill when used with a bass with on-board preamp. Well, at risk of my readers not reading any more of this review, I will say absolutely not.
If you're still with me it's worth noting the HPF switch. Arkham says flipping the HPF on (up) moves -3dB point from 30Hz to 100Hz. It's a gentle roll-off (-6dB/octave), used in conjunction with the Bass control and boost switches to shape your low-end tone. That it does. You definitely feel the reduction of boom and low end. But this might be exactly what you need in some situations such as boomy rooms or recording scenarios.
Use the gain dial to add some grit, but if you want overdrive flexibility look elsewhere. That is not what the Oracle is all about. It will deliver that "on the verge" of breakup feel we so often talk about but it doesn't deliver flat out distortion or overdrive. That's fine by me because that's not why I like the Oracle. I just want that spacial, lush sound that you associate with tube preamps.
Therein lies one of the primary differences between the Arkham Oracle and other preamp pedals on the market. Having used many bass preamps on the market including the Shift-Line Olympic MKIII and Shaw tube Injection I find the Oracle to be more like the Shaw Tube Injection than the Olympic. I do prefer the dimensions of the Oracle compared to the Shaw.
Though it isn't a small pedal, it fits better on a pedalboard and is not as heavy as the Shaw. Comparing the two, the Range dial of the Oracle gives it the edge over the Shaw in my opinion. That said, the Fat switch on the Shaw is killer. More useful than the Low switch on the Oracle. That Shaw Fat switch does exactly what it says; makes the tone fat (wide and huge). Other than that, the Oracle wins in the tone department.
Compared to the Shift-Line Olympic MKIII, the EQ section of the Oracle offers more flexibility and tonal variation. Again, that Range dial delivers the goods here. The Olympic easily delivers more in the gain driven breakup/OD department. In fact, it can become all out distorted in a non-pleasing way in my opinion. But the Olympic is far more pedalboard friendly than the Oracle (or Shaw) and still sounds fantastic. In a mix, many would never notice. But in a recording scenario I give the edge to the Oracle in the tone department. The Olympic includes an on-board XLR out (which is no small feat in engineering in something so small) and sounds fantastic as a DI. Oracle edges out the Olympic in the tone department but the Olympic is much smaller.
I'd describe the base tone of the Oracle as full bodied and lush. Arkham literature says the Oracle is designed to impart a "warm, thumpy, vintage tone." I don't find it to be overly wooly or thuddy unless you want it to be. It can certainly be punchy and relatively open sounding too. It is the opposite of solid state circuits which you might describe as "clinical" or "sterile". While there are certainly exceptions to that rule, the Oracle is a nice alternative or happy ground between solid state and overly dark tube devices. Compared to the Olympic, the Oracle is more round and wide. But the Olympic might be inherently brighter and open. Now with EQ adjustments you can make both sound a lot alike. The Shaw is the darkest of the three.
Enclosure size is 7.39" x 4.70" x 2.06" so it isn't small. You aren't going to run the Oracle with a typical pedalboard power supply. It requires 120 volts stock (230 volts or dual voltage available special order) and an IEC type cable. Now, a possible scenario to consider is purchasing an IEC splitter like the one pictured below which allows you to connect one end to the Oracle and the other to your pedalboard power supply and then use a single IEC cable connected to a wall outlet.
Please note: the Oracle operates at lethal voltages, 300VDC.
The jewel covered LED illuminates a purple hue and is nice break from all the red and blue LEDs out there on pedals these days.
After using the Oracle in many scenarios I am pleased. It is a fantastic preamp and edges out the Olympic and Shaw for me. I find the EQ section to be more pleasing than either of those devices and like that I can operate the Oracle at higher gain levels than I could with the Shaw or Olympic before breakup. If you really want lush and highly spacial tone put an Effectrode LA-1A tube compressor in front of the Oracle. Wow!
The Arkham Oracle seems very well made. The enclosure is glossy and will probably show scratches easily. It does show fingerprint smudges easily. It's a fantastic piece of kits and the size and hefty power requirements are worth it for me.
Tone (big and spacial and punchy)
Plenty of gain before distortion (positive for me anyway)
Possibly not "vintage" sounding enough for some
Retail price: $550 (2 - 3 week build time)