AMP Lab – Peavey MiniMEGA

On a basic level, an amplifier only needs to faithfully make the signal larger. The Peavey® MiniMega™ does this quite well. Beyond the basics, Peavey has packed in an impressive list of features that can dramatically change the sound of this amp; from a plain reproduction of your signal, to something that adds character to your sound. Additionally, this amp looks like something you want to show off instead of a boring box to set somewhere out of the way. Looks like Peavey has all the ingredients for a great product. A run through its paces on the test bench will show how well those ingredients are mixed and how the result tastes.

Walk Around

Before getting close enough to walk around, the lights on this amp definitely stand out. Peavey has put a lot of effort into creating a LED lighting scheme that is not only functional, but very appealing. A range of colors can be selected, as well as visual effects. It is also functional, in that the color will change when the amp is muted. This amp definitely deserves to be out in the open while playing, not hidden back with the other gear.

Moving around to the back of the amp, shown in Fig. 2, it is also pretty straightforward. On the left are the typical power cord, switch and fuse. There is a source voltage selector switch under a protective plate that will need a screw driver to access. Two Speakon® connectors wired in parallel are the main outputs. The Aux In is a 1/8” jack. The DI has XLR or balanced TRS outputs, with the normal set of feature buttons, while the effects loop and Tuner out are both ¼”. There is also a dedicated footswitch input that can control a lot of the features of this amp.

1-5 (unacceptable to impeccable)

On-bench

EDM-1 SONIC PROFILE:

Low: Big and powerful, versatile through filtering

Mids: Present and defining, with plenty of adjustment

Highs: Clear and transparent, with plenty of control

Internals

It took just four minutes to get the top cover off of this case to access the internals of the amp. Inside, there are just three circuit boards: a pre-amp board, a power amp / power supply board and an output board. All of the potentiometers are board-mounted, micro-style.

Quality and assembly of the circuit boards is very good. Layout is very clean, and all solder joints are good. Wiring inside the case could be better. There is a piece of electrical tape securing the ribbon cable running down the right hand side of the amp. I am concerned about this tape coming loose. Wire routing could also be done better. Right in the middle of Fig. 3, the black-and-white AC power wires from the plug to the power supply cross and actually touch the output signal wires going to the Speakon connectors. This increases the possibility of noise on the output of the amp.

Cooling a 1,000-watt amp is always a concern for providing a long, reliable life for the amp. This usually requires a large, finned heatsink connected to the power amps and power supply. To get the picture shown in Fig. 3, there was no heat sink to remove. There are, however, four smaller, finned heat sinks lined up on the left side of the power amp board. The variable-speed fan mounted on the top of the case does blow down directly on these small heat sinks, but that still leaves no heat sink or direct air flow on the power supply tasked with supplying power to those large amps.

Input

The single ¼” input has an impedance of 991 kOhms with a 200Hz sine wave input at 200 mV. This feeds into the Crunch and optical compression circuitry, before heading to the tone stack.
The optical compression circuit will compress the higher voltage spikes of the input signal to avoid clipping and even-out the signal. It has an enable button and knob to vary the amount of this effect. More details of this effect are seen in the Gain section of this article.

The Crunch effect shapes many aspects of the signal. It is designed to give an entirely different tone to the amp, and effects can be seen in the tone stack section, as well as the harmonics and gain of the amp.

Tone Stack

The EQ is advertised as semi-parametric. With the variability that is built in, it is getting close to being a fully parametric EQ. It is 4-band EQ with Low, Lo Mid, Hi Mid, and High controls. The Low band also has a Punch button to increase the bass output even more. The two Mid bands are adjustable for frequency, as well as Q (width), and the High band also has a Bright button to increase the higher frequencies even more.

The sweep of the Low EQ control in Fig. 6 shows that it is a shelf-type with a maximum cut of 12 dB and gain of 17 dB at about a 40Hz. This continues to have some effect all the way up to 800Hz. Additionally, the Punch button adds approximately 10 dB of gain centered at 78Hz when the Low EQ control is set to maximum. Interestingly, the Punch button has less effect as the Low EQ knob is turned down. With the Low EQ knob all the way down, the Punch button has less than a 2dB effect on the frequency response.

Fig. 7 and Fig. 8 show the Lo Mid and Hi Mid responses, respectively, and also my ability to make something that looks a lot like a Spirograph® image on the test bench. Both of these EQ knobs have very similar responses, with the main difference being the frequency range they effect. Both give a +/- 25 dB cut or gain with the Q button off, and +/- 30 dB with the Q button on. Also, both have the same shape response curve. The frequency of the Lo Mid knob response is centered between 175Hz and 900Hz, and the Hi Mid knob is centered between 800Hz and 3,250Hz.

The High EQ sweep shown in Fig. 9 is another shelf-type response, similar to the Low sweep. The maximum effect is above about 5kHz, with a possible gain of 12 dB and cut of 14 dB. Also similar to the Low EQ, there is a Bright button that has an additional effect on the frequency response. The Bright button gives an additional 8 dB boost centered at about 8kHz. Unlike the Punch button on the LOW EQ, the Bright button effect is not dependent on the position of the High EQ knob.

The special effects on this amp also change the tone stack. Fig. 10 shows the effects of Kosmos® and Crunch on the tone stack. The Crunch effect has about a 7 dB gain at frequencies below 40Hz, which tapers to 0 effect at 200Hz. Above that, Crunch give a 3 dB cut at frequencies above 1kHz. The effects of Kosmos are where things get weird. Kosmos C gives a slight boost below 25Hz and a cut between 25Hz and 70Hz. Kosmos A is the very “spikey” zigzag line. Peavey is definitely after something very specific with their Kosmos feature. They have obviously spent a lot of time fine-tuning the low-end frequency response for this feature. With anything tuned this specifically, it will undoubtedly either sound awesome, or pointless, depending on the speaker cabinet and the rest of the setup.

Harmonics

As with the rest of the results, this amp has a very clean harmonics response with all the features turned off. Fig. 11 and Fig. 12 shows just how clean it is. Graphs in this section include both 1kHz and 100Hz results. Due to specific features of this amp being tuned to affect only lower frequency harmonics, it would not be possible to show the nature of these features without including more than one test frequency. Kosmos A has no effect on harmonics at 1kHz. But lowering the frequency to 100Hz provides a very noticeable difference, as shown in Fig. 13. All harmonics are noticeably higher, with a dramatic peak of the 2nd, 3rd and 5th harmonics.

Kosmos C has much more of an effect on harmonics. Even at 1kHz – shown in Fig. 14 – it produces an increase in the 2nd harmonic. Down at 100Hz – in Fig. 15 – things get very different. The odd and even harmonics are paired up and have a near linear decrease as the order number is increased.

Once again, the Crunch effect shows up in the harmonics of the amp. The dramatically different Fig. 16 shows the harmonics at 1kHz with Crunch enabled. All of the odd-order harmonics are increased dramatically, resulting in a much different sound with Crunch enabled. At 100Hz, shown in Fig. 17, the results are no less drastic. The odd-order harmonics are still enhanced, but with a little less effect in the higher orders.

Gain and THD+N

The blue trace in Fig. 18 is the Gain of the amp with all the features turned off. This is a very good example of a gain map for a clean class-D amplifier. The response is very flat, with a sharp knee where clipping occurs. In Fig. 19, the blue trace is the THD+N map with all features disabled. The sharp rise between 800 mV and 900 mV corresponds with the gain map where clipping is starting to occur. However, the rise between 125 mV and 500 mV is a little odd. Keep in mind, though, that this amp is very clean, and the scale here is very small. The total rise in this section goes from 0.07% to 0.16% THD+N. Hardly a major change.

The Comp feature of this amp is an optical compression circuit that cuts the higher input voltages and keeps the amp from clipping the signal. Interestingly, the Comp knob does not control the voltage level that the circuit kicks in. It only changes the level of the cut made at a given voltage. Fig. 18 clearly shows the amount that the compression circuit is cutting the higher voltage levels, and Fig. 19 shows that the THD+N values stay lower well into the higher-input voltage levels.

And again, Crunch is affecting the amp. It would appear that the Crunch feature touches just about every aspect of the amp. Fig. 18 shows that Crunch has more of an effect on the gain map than Comp does. The gain map is entirely changed by the Crunch feature, with much softer transitions and a lower overall gain. Crunch has the opposite effect on THD+N than Comp, as shown in Fig. 19. It is actually designed to increase distortion over a wide range of input voltages.

Power

As always, the selection of a target THD+N is a crucial part of power testing. Peavey lists their power specs using 1% THD+N. Observing the output of this amp, 2.5% THD+N was selected for measurement in this review. This is based on the point at which hard-clipping occurs on the output, which is consistent with other reviews on this test bench. This should produce power ratings even higher that what Peavey claims. It is also worth remembering that the test bench produces a continuous sine wave for all power testing. This type of input is far harder on an amp than an actual musical input. But, it is used here for two reasons. First, is that some standard is needed, and a sine wave is used for most audio testing. Second, since a sine wave makes the amp work harder, it gives insight into how the amp handles heat and overload conditions. In general, it indicates the robustness of a given amp design.

With an 8-ohm resistive load, using a cutoff of 2.5% THD+N, the continuous power was measured at 798 watts and the burst power was measured at 888 watts. With a 4-ohm resistive load and a cutoff of 2.5% THD+N, it was impossible to get a continuous power measurement from this amp. The thermal protection circuitry cut off the output of the amp before the test bench could determine an output power rating. However, burst mode was able to get a result of 1,435 watts.

All of these numbers meet expectations for a rated 1,000-watt amp, but the lack of results for a 4-ohm continuous load is worth noting. While our continuous power bench test is definitely more demanding than your standard musical signal input, many other amps are able to handle the thermal demands of our bench testing procedures without shutting down. A large internal heatsink (the lack of which was noted above) would almost certainly have helped greatly.

Conclusion

  From the light show, to the knobs, to the styling of the face, this amp looks very appealing. Because the Crunch feature affects almost every aspect of the amp, it is like getting two amps in one. Peavey has obviously put a lot of effort into tuning the Kosmos feature to solve very specific problems that may help you sound dramatically different. However, I am a bit concerned about the vent holes in the top of the case, and I would have liked to have seen more heat-sinking capabilities. Overall, though, Peavey has a nice design, here, with a great list of features.