My engineer, Dan, and I set up a very useful experiment yesterday, allowing us to do some equipment evaluations using our ABX Comparator that we could not have done previously,
Dan modified two of our ABX Comparators to each have A and B Source in XLR balanced inputs and an A and B Amp out XLR balanced outputs. One ABX unit is used for the left channel, the other for the right channel. Both are controlled simultaneously with a single IR signal sender as both have identical receiving codes.
This allows us to test two pairs of amplifiers that have XLR balanced inputs using a balanced source.
However, this new capability can also test RCA single ended to XLR output converter boxes. These converter boxes are very useful for people with preamps that have single ended RCA outputs who want to drive power amps that have XLR balanced inputs.
We tested four different RCA to XLR converters using this modified pair of ABX switchers.
Each converter box had a different circuit. Some used a single op-amp to flip the phase of the incoming signal. This method sends XLR output jacks one signal as a simple pass through, and a second inverted signal after the op-amp did its job. Different op-amps were used in two of the converter boxes.
A third RCA to XLR converter box used two op-amps per channel so that the inverted and non-inverted signals each saw a closer to identical signal and had the same output impedance.
The fourth RCA to XLR converter used interesting chips that provided the same function as box #3 but requiring much less external circuitry to achieve this process.
The test setup takes the RCA stereo signal out of our DAC MK 5 and splits it, using the splitters on one of the ABX boxes. This creates two identical RCA stereo signals that drive the RCA inputs of two RCA to XLR converter boxes. The XLR outputs of these two converter boxes connect to Source A In and Source B in on the ABX box pair. Only two channels of amplifier are used in this test, a pair of AVA monoblocks with XLR inputs. These connect to the left and right Amp A Out of the ABX pair. By switching from Source A to Source B we now switch converter boxes and keep everything else the same.
Thus we could directly compare two different RCA to XLR circuits instantly.
There definitely was a sonic difference audible. Keeping the “winner” in the setup, we then substituted a different RCA to XLR box into the test set up and ran the tests again. Again, we keep the new winner in the setup and tested it against the final RCA to XLR box. Again we heard differences, but they were more subtle.
We need more testing with others of my crew here, but our preliminary results say we should be able to provide you people out there who only have RCA output connection on your preamp, a very transparent and inexpensive RCA to XLR conversion box.
Regarding the XLR input and output equipped ABX Comparator, the only catch is that you need two of them to do balanced line stereo comparisons. There is not enough real estate on the back panel for all the XLR jacks required and all the internal parts required to support these functions. It was a time consuming and difficult process to convert the two ABX Comparators to XLR in and out capability and thus is not something its designer wants to offer for sale. In house though we now have more objective testing capacity then ever before.
We never quit innovating here
Stay tuned.
Frank
