C-7 TruTechnology Amplifier

TRU Technology is the new kid on the car audio block and is making amplifiers that cater to audiophiles and those individuals who simply have too much money in their bank accounts. Today we have an opportunity to look at its unique Copper Series, C-7 amplifier. Parts for the Copper Series are hand picked, matched and hand built by TRU engineers. TRU rates this amplifier 4 x 125 watts at 4 ohms. Along with the power comes a big price tag of $2500.00. Are you excited yet?

MSRP: $2500.00

The C-7 amplifier is just that, an amplifier. No crossovers, sub-sonic filters, or bass boost. I've always felt that a power amp should be simply a power amp, but those disappeared years ago. Basic power amps still remain in high-end home audio, and now one has cropped up again in car audio. I like that -- a true amplifier just as the name suggests.

Cosmetics
Obviously, TRU Technology did not design this amplifier for the Gen Y crowd. This amplifier has class! Its copper color and gold accents are striking, giving it a very high-end appeal. The C-7 also struck me as being a bit retro in look, with the simplistic design of the massive extruded aluminum heatsink. To the left and right of the chassis cover are two rectangular nameplates carrying the TRU Technology logo, flaked in gold. That's it; no model numbers, power ratings, or excess baggage detracting from its appeal. Beautiful.

Obviously, cost was no object to TRU Technology, as the build materials are second to none. The C-7 amplifier just feels as solid as it looks. There is no question that great care was taken in choosing or designing each of the components gracing the outside of the amp. Two fans are flushed into the long sides of the amp to assist with temperature control. The RCA connections are beautifully machined and complement the output binding posts on the opposite side, each plated in gold. The gain controls use a gold-plated metal knob rather than plastic for a more surreal feel. This could be the Bentley of amplifiers.

Layout
Internal layout of the C-7 is exceptionally clean. The power supply is at one end, far away from the sensitive analog input circuitry. The OP amps are top quality Burr-Brown OPA2604; they are low-noise and very fast slewing devices. TRU Technology put these in sockets so the user can customize the input stage with their own selection. This option, four Analog Device AD797 chips, will run you roughly $240.00. Quality film caps are used throughout. TRU Technology's engineer also used high quality 105-degree C filter capacitors on the 12-volt input to the power supply. Elsewhere, 85-degree C caps were used, but should be a non-issue because of their location. On the output: eight 20-ampere MOSFETS per channel. This is a lot of drive capability, which allows this amplifier any amount of output current required. The power connectors are heavy duty and accept 4-gauge cable. The speaker terminals are gold-plated binding posts (very similar to those used in pro audio) and are fastened to the side panel of the amplifier. They are not supported by the circuit board. These terminals accept an 8-gauge wire or eight individual banana plugs, which is a $25.00 option. The input uses very high quality machined and gold-plated RCA connectors, again mounted to the side panel instead of to the circuit board.

Input Gain Circuitry
This amplifier employs four input gain pots, one per each of the four channels. In the full clockwise rotation 700mV is required to drive the amp into clipping. In the center position, about 5.3 volts are required. We discovered a flaw: the amplifier cannot achieve full power at lower gain settings. For example, if the gain pot is set to full counter-clockwise, only about 10 watts per channel can be achieved before clipping. The workaround: set the gain pots to "12 noon" or higher. I contacted TRU Technology's chief engineer, John Fairchild, about the problem. He informed me that a running change was already in progress and this would not be an issue in all future C-7s. Unfortunately, I could not get my hands on one for this review.

Power Supply
The power supply in the C-7 is unregulated. Like all unregulated amplifiers, the internal power rails rise with the battery voltage. This is not a bad thing; however with battery voltages above 15-volts, the rail voltage exceeds the filter cap maximum rated voltage that could cause damage. While a normal vehicle's electrical system only makes up to 14.4 volts, SPL competitors often modify their electrical systems to achieve battery voltages as high as 18 volts. Of course, we don't foresee any SPL competitors using this otherwise fine piece of audio gear.

MEASURED SPECIFICATIONS
Output power @ 1% THD 1kHz 14.4 volts, Battery Current
4 ohms x 4 channels	4 x 152 watts, 76 amps
2 ohms x 4 channels	4 x 230 watts, 130 amps
1 ohm x 4 channels	4 x 293 watts, 204 amps
2 ohms x 2 channels	2 x 587 watts, 204 amps
Output power @ 1% THD 1kHz 12.5 volts
4 ohms x 4 channels	4 x 112 watts, 67 amps
2 ohms x 4 channels	4 x 171 watts, 112 amps
1 ohm x 4 channels	4 x 220 watts, 127 amps
2 ohms x 2 channels	2 x 440 watts, 127 amps
Distortion at 200 watts x 4, 1kHz, 14.4 volts	0.06% @ 2Ohm
Input sensitivity (with gain control)	700mV-5.3V (see text)
Frequency response (+/-1dB)	5Hz-55kHz
S/N (A-weighted, below clipping)	> 100 dB
Damping Factor @ 100Hz, 4Ohm	> 65
Idle current	2.2 amps
Slew rate	13 V/uS
Standby current	65 mA
Efficiency at 1/3 power, 2Ohm/Ch.	32%
Efficiency at full power, 2Ohm/Ch.	49%
Maximum current consumption, unclipped sine	204 amps @ 1174 watts

Protection
The amplifier passed its short circuit test perfectly. Once the protection circuitry has been engaged, the turn-on lead must be cycled to clear the short condition. Although the C-7 thermally cycled, it did so at 100 degrees C, a much higher temperature than most amplifiers. The two fans mounted on each side did not kick in until the amp reached 65 degrees C. I felt that they should start up at a lower temperature, so again I contacted John Fairchild at TRU. He informed me that this too is being addressed and that the fans will cycle at a much lower temperature in all future C-7's. To TRU's benefit, even though our test subject runs quite hot, it should be reliable due to the large number of output devices. If you do load this amplifier with 1-ohm loads, you may want to consider an external fan.

The amplifier easily passed our reactive load test, performing flawlessly into a 0.15uF capacitive load. Having a massive number of output devices, it didn't surprise me that it breezed through this ugly load test.

Our last test was over-voltage protection. Unfortunately, the amplifier never protected itself. I don't consider this to be a problem though, as most electrical systems are regulated below 14.4 volts.

Performance
The frequency response was exceptionally flat from 5Hz to well beyond 20kHz. Most amplifiers are frequency limited by design to decrease the chance of picking up high frequency oscillations. The C-7 runs without noticeable filtering and could be troublesome if you route the input wires near the speaker wires (Figure 4). Of course, you should never run input cables near power or speaker wires in any audio installation.

The C-7 met the factory power rating, producing over 125 watts into 4 ohms at less than 0.1% THD (Figure 2). Power into 1 ohm was 293 watts x 4 for a total power in excess of 1,000 watts. This equates to 587 x 2 into a 2-ohm bridged load (Figure 5). Bridging this amp is, well, not the easiest. Just like many amplifiers that do not use a bridging switch, you simply have to connect the speakers across the speaker's "hot" terminals. The problem is setting the gain controls. Most amplifiers use one dual gain pot per two channels to adjust the level, so setting the gain in bridge mode is easy. As mentioned earlier, the C-7 uses one gain pot per channel, and bridging the amplifier requires that both the left and right input (front or rear, whichever is being bridged) gains are set to exactly the same level. Although time consuming, this can be achieved by using a digital voltmeter on the outputs and adjusting both left and right until both channels are within 1/10th of a volt.

Speaking of the four channels, the C-7 has four individual "Status LED" indicators. The LEDs turn green when operation is normal and red when in protection, depending upon which channel is causing the problem.

Separation was measured to be 55dB (front) and 65dB (rear), a bit lower than TRU Technology's published specification of 70dB. While the amplifier met this spec unloaded, the separation fell to 55dB in the front at 1kHz with four 4-ohm loads connected. This indicates an internal layout problem. Although 55dB is not a great figure, it is unlikely to affect the sound quality of the amplifier.

A very unusual issue came to my attention as I turned off the amplifier. A miserably small amount of current, 65mA, was being drawn from my power supply. Although miniscule, this could drain a typical car battery if you leave your car for 30 days without starting or charging. We like to see a maximum of 1mA or less drain on any single piece of audio gear.

Total Harmonic Distortion (THD) was typically below 0.07 percent at 1kHz into 4 ohms at 125 watts. This was the same amongst all four channels as seen in Figure 2. I repeated the test in 2 ohms at 200 watts into four channels (Figure 3). At 2 ohms, the distortion was below 0.15 percent from 20Hz-20kHz. Good. Figure 4 shows the amplifier in bridged mode, driving 2 ohms. I ramped the amplifier up to 460 watts into each of two channels. The distortion remained considerably lower in bridged mode, typically below 0.05 percent. In the graph you can see that all of the curves show the distortion falling above 7kHz. This is because high frequency filters are turned on so that power supply switching noise does not cloud the distortion measurements.

Damping factor measured greater than 65, an average figure. The slew rate, however, was a bit slow at about 13 volts per microsecond. From Figure 6 you can see the fall time of the amp. This scope display shows the signal falling about 37 volts in 2.88uS. This gives us 12.8 volts per microsecond. Note that we severely overdrove the amp for this test. In doing so we also noted that the amplifier recovered from clipping very nicely.

Amplifiers run more efficient at full power than at a third of full power. So why do we test one-third power? Quite frankly, this is a level at which an amplifier is typically played, therefore an important factor when driving your system. Efficiency at full power for the C-7 measured in at a mediocre 49 percent into 2 ohms, which is below average for a class A/B amplifier. At one-third power the efficiency fell to 32 percent, just a tick below average.

I noted that the amplifier drew about 33mA from the remote turn on pin. Some decks in the past have had difficulty providing more than about 2mA. If using more than one amplifier, you will likely have to use a relay to turn the amplifiers on.

Listening Test
I conducted several listening tests both inside our test facility and in our test vehicle and was pleased with the results. As expected, this amplifier sounded very natural; I could not detect any coloration of the music. The C-7 was very detailed especially in the mid and high ranges, allowing me to hear subtle nuances other amplifiers we have tested did not reproduce. The bass was reproduced with accuracy, but did not overwhelm me.

The C-7 was absolutely quiet when turned on; no noticeable clicks or pops were detected. Turn off was just as quiet; however, we detected another issue. When the amplifier was turned off, it took about one second for the amp to mute. This is not a problem with the amplifier, but a possible issue when it is connected to certain decks or signal processors. Some of these units produce a thump when they are turned off that could play through the amplifier because of its delayed turn-off. If you experience a turn-off pop, your only solution may be to change the offending source.

Conclusion
The C-7 has a tremendous amount of drive capability. Because of its incredible output current capability, you know it will be unyielding to any load. While it slews a bit slower than most amps, it sounds totally transparent. It may not have any of the whistles or bells many other amplifiers do but it certainly makes up for it with power and sound. TRU Technology has crafted one stunning looking amplifier and it comes with a stunning price tag too. v