1979 Vintage
Sunn Beta Lead Amplifier Head

Punk to grunge, rock to metal, and country to blues - there is no better all around guitar amp! Groups and individuals that use the Sunn Beta Lead include: Nirvana (Kurt Cobain), The Melvins (Buzz and Kevin) and Tool (Adam Jones). Even Slash (of Guns n' Roses fame) in various interviews referred to the Sunn Beta Lead as "his first decent amp!" There are simply too many garage and bar bands out there using Beta series amps to count!!

There are three primary reasons for the popularity of Sunn Beta Series amps - first is the sound, second is the flexibility of the amp's controls to get that sound, and third is the huge sounding power these amps are capable of producing. At 27 pounds it isn't too difficult to move around, and being solid-state you could literally save hundreds not having to periodically purchase tubes.

Overview

• The Beta Lead head weighs in at 27 pounds.
• The size of the head enclosure is 24 1/2" wide, 10 3/4" deep, and 6 3/4" high. The height is total including the rubber feet and handle. The height of the case alone is 5 3/8".
• Power output is rated at 100 Watts RMS into a 4 ohm load, with less than 0.25% total harmonic distortion.
• The serial number of this unit is A56005.

Front Panel

The amp has two channels, designated "A" and "B". Each channel features an input jack, indicator LED (Red for channel A, Green for channel B.), Drive, Bass, Mid, Treble, Reverb, and Level controls. In addition, the front panel contains a "both inputs" jack to run the channels in parallel, a Master Volume control, and the power switch.

The Drive control will take the sound from country clean to a wall of distortion. The control operates smoothly and doesn't jump from clean to dirty. You can control the amp to be as "touch sensitive" as the best of tube amps, and the sound cleans up nicely with the guitar volume control. Even at a 10 setting, individual notes, like those as found in a arpeggiated chord will remain distict - the sound will never crap out into a synthesizer sounding mush of square waves. It remains very musical throughout the range.

And it should come as no surprise that the Master Volume adjusts the overall loudness of the amp.

Control Secrets!!

A classic mistake of first time Beta Lead users is to jump right in and use the remaining controls the same as every other amp they have owned. The controls do not work the same as any conventional amp and unless you know their secrets, you'll never experience the range of sounds that the Beta Lead can produce.

Tone control is not provided by a traditional tone stack, so forget all about your favorite settings from those other amps. The Beta Lead tone controls are not interactive and are best used by thinking of them as a 3-band equalizer.

The Bass and Treble are "shelving" controls and function more like individual volume controls for their frequency range. The Mid control, in addition to adjusting the level of middle frequencies, also changes the bandwidth - broad down low and sharp up high. The best approach to finding a suitable tone setting is to start with these controls on "5", and adjust from there based on what your ears are telling you.

The Reverb on the Beta Lead is different from most amps. The Reverb control does not adjust the level of reverb!! The Reverb control functions as a "DWELL" control (for those of you that have used a 3-knob reverb unit, you know what I mean). Dwell controls how hard (or soft) the reverb unit is driven. More drive means a longer overall decay time and more re-echoing of the signal through the springs. With more drive it sounds like the reverb is being created in a larger space. Dwell can be thought of as providing control over the illusion of "room size".

The volume level of the reverb is more or less PRESET and bypasses the channel Level controls. Yes, the Level control does adjust the volume of each channel. However, if you are using the Reverb effect, this adjustment also determines the "dry" signal level that gets mixed with the reverb signal. Yes, it will seem almost backward at first - turning down the Level control to get more reverb and turning it up to get less. But once you master this, you'll find those single knob reverb level controls too limiting!! The range of Beta Lead reverb effects can vary from an apparent size of an enclosed garage to wide open canyon - it is simply AMAZING!!

Back Panel

The back panel of the Beta Lead has the power cord, fuse holder, the connector for a footswitch and two parallel speaker output jacks. The Beta Lead is rated for a minimum of 4 ohms. If you are using both speaker jacks make sure your cabinets are 8 ohms or higher - each.

Next is the "Master Accessory" set of jacks where an external effects unit can be connected to work with both channels. The "To Accessory" jack can be used as a preamp out - to feed another power amp as an example. The "From Accessory" jack can be used as a power amp input, and it does disconnect the internal preamp.

Finally, we have separate accessory jacks for each of the channels. These open up the possibility of connecting different external effect units to each channel. Overall, lots of plug and play capability with this amplifier.

Keep in mind the discussion about Reverb when you're thinking about how to use the accessory jacks. The individual channel accessory out jack does not have the reverb mixed in yet. The individual channel accessory in jack will not loop back to feed the internal amp reverb. The master accessory output jack does include the reverb mix.

These two pictures show the serial number tag, and a shot of the power transformer. Notice that the transformer is dated "7850" meaning the 50th week of 1978.

The Beta series uses a 74C04 digital chip, sometimes called a hex inverter, in the circuitry around the drive control. The Beta Lead further uses a 74C04 chip for the reverb drive circuit. This chip is manufactured using "Metal Oxide Semiconductor" processes which gives us the MOS. The "C" in front of C-MOS stands for "Complementary" and means that each of those six inverter units inside the chip are made using both n-channel and p-channel FET (Field Effect Transistor) devices - in order to obtain the high gain and low power consumption required of digital devices.

Sunn was one of the earliest amplifier pioneers to use FETs in their solid-state amps to make them sound closer to a tube amp. While others used FETs, only Sunn used them in circuits meant to be intentionally overdriven, as in the Sunn Concert Series from the early 1970s. The Beta series continues this tradition using a digital component to get the FETs. By applying feedback through a resistor, the extremely high gain of the inverter is reduced and it becomes a very linear analog audio amplifier stage!!

If this sounds familiar, you might recall that Craig Anderton in his book "Electronic Projects for Musicians" presented his "Tube Sound Fuzz" built around a hex inverter chip. EH produced a distortion device called "Hot Tubes" which also used a hex inverter. However, both of these devices use a CD4049 chip. It may be subjective and personal preference, but to my ears, the CD4049 chip doesn't have the softer clipping characteristics of the 74C04.