A good power amplifier design is a good power amplifier design whether it was created in 1950, 1960, 1970, or anytime thereafter. Given how long audio has been around, you can expect any list of all-time great amplifiers to have 100 entries and there would be still some worthy examples that would not make the roster. Depending on whom you ask, and who answers, the Goldmund job 225 power amplifier ($1499) could very well be one of the amps that would make it onto that list. Recently Optoma NuForce (along with Goldmund’s knowledge), introduced a new amplifier that is based on the Goldmund job 225 amplifier, called the STA200 ($1299).
How did collaboration between Goldmund and Optoma NuForce come about? According to Optoma NuForce, years ago Goldmund used to offer its customers Optoma projectors. When merger discussions between Optoma and NuForce began, the leaders of the emerging company-to-be considered how to move forward and how to expand or refresh the NuForce portfolio. At the same time Goldmund was curious to see whether younger audiophiles and audio enthusiasts would be interested in affordable high-performance equipment, and whether its own brand awareness could be expanded through NuForce. For Optoma NuForce, introducing a Class AB amplifier was a way to test the market and see whether this was a direction the company should pursue. So the STA200 power amplifier is an experiment for both firms.
While the STA200 has many similarities to the Goldmund job 225 power amplifier, it is not identical. The primary difference is the power output specification. The job 225 puts out 125 watts into 8 ohms while the STA200 has only 80 watts of output into 8 ohms. This difference in power output was instituted so that the STA200 would not be a direct competitor for the job 225 (it could even be argued that for the $200 difference the job 225’s additional power offers a better value). Another difference between the job 225 and the STA200 is the latter has a slightly lower gain (34.4dB) that’s closer to a more standard figure, as opposed to the job’s 36dB gain.
According to a review by Brent Butterworth of the job 225, that amp’s Class AB design “was taken from an amplification circuit originally used in a Tektronix oscilloscope in the late 1960s.” Michel Reverchon, Goldmund’s CEO, said that the circuit has since been refined by nine generations of Goldmund engineers, and variations on the circuit were used on all of that company’s amplifiers.
The STA200 has the same wide bandwidth as the job 225, spanning the range from 10Hz to 100kHz. The STA200 also extends its high-frequency response up to 900kHz (at 3dB down). The reasoning behind such a wide bandwidth design is to eliminate phase shifts caused by the high-frequency roll-off effects.
The STA200 has all the controls you normally find on a basic power amplifier, which are not many. The only input option is a pair of single-ended RCA connections. For output the STA200 has one pair of five-way binding posts. The only other features on the back panel are the IEC AC line connection, a heatsink that takes up three-quarters of the back panel, a 115/230V AC switch, and a power output connector that can deliver power to the Optoma NuForce WDC200 streamer. The STA200’s front panel is an unadorned expanse populated by a single power on/off button located on the right side next to a small red power indicator LED.
Dimensionally the STA200 ranks as a ¾-sized cabinet. It’s 14 inches wide, only 8 inches deep, and 3¼ inches high. Even when it’s left on 24/7 the chassis only gets warm to the touch—the heatsink on the back does a good job handling all the serious heat dissipation duties.
I used the STA200 extensively during a two-month period while I was listening to and reviewing the Mytek Brooklyn DAC/preamp. The STA200 was installed in both my nearfield desktop monitoring system where it was connected to the Audience 1+1, Dali Opticon 1, ATC SCM7 II, Role Audio Sampan FTL, and Role Kayak; and in my room-based system where it drove the Spatial M3 Turbo SE loudspeakers. I did not connect the STA200 to any especially difficult-to-drive loudspeakers since I do not currently have anything with a sensitivity of less than 87dB on hand. I did find with the high-sensitivity Spatial M3 loudspeakers that the STA200 did not generate any more hiss from the tweeters than the more standard 27dB gain specification of the Bel Canto REF M600 power amplifier.
Given STA200’s extremely wide bandwidth specification I was curious if there would be any noise issues. As mentioned, during the review period I had the amplifier in two systems, and neither displayed any noise issues that could be attributed to amplifier instability or to RFI/EMI issues affecting the amp’s performance.
Another potential sonic issue was the STA200’s higher than usual gain specification. With some preamplifiers, the STA200’s higher gain could mean that the preamplifier could be operating in a less than optimal gain range. With the Brooklyn DAC/pre I rarely got above -45 on the Brooklyn volume scale of -100 to -0). The last potential downside of an amplifier with higher gain is it can amplify the basic noise levels in an audio signal chain from inaudibility to unfortunate audibility. When the sound was muted, I had no issues with added noise from my loudspeakers in either of the systems where I used the STA200.