By Juan C. Ayllon The hum was driving me nuts. At normal listening volumes, it wasn’t apparent, however, when I played HD TV movies or music shows like “The Voice”, I had to turn up the volume on my PrimaLuna Prologue 3 preamplifier to at least the 10 o’clock position due to the lower gain on my cable TV feed -- and that’s when I’d notice it: a notable 60 Hz hum during quiet moments or when shows were paused. Now it wasn’t a ground loop between the AT&T cable hardwired to my system, as a router and wireless access point fed the signal to a wireless TV receiver, which then connected to the TV via HDMI cable and out to my Lampizator Lite 7 DAC (Digital to Analog Converter) via optical (Toslink) cable. Following the advice of Angus, a retired engineer who builds and repairs audio components, I tried using cheater plugs on various components one at a time. No change. Then, disconnecting all the components, I worked my way backward: I powered up the amp connected to the speakers -- no noise; the preamp turned on with volume at 10:00 o’clock, connected via RCA cables to the powered up amp -- no noise; then the DAC connected to the preamp (volume at 10:00 o’clock), connected to the amp -- and presto! I had that dreaded hum! I took my DAC to my technician, who opened it up and tested the various paths within. He noted that while there was a slight hum, it was not anything abnormal or excessive. He also found that one of the RCA Radiotron vacuum tubes I used in my DAC’s tube output stage was faulty and throwing out some aberrant signals, so he set that pair aside and tested it with another pair I’d left him. All was good. However, when it returned, I still heard that darned hum when the volume was turned to 10:00 o’clock on the preamp. I reached out to Lampizator North America’s Fred Ainsley, who recalled an incident at a recent audio show: when he connected his reference DAC to a certain make of preamplifier, there was a pronounced hum. “Normally, it’s dead quiet,” he said, but when it interacted with this specific piece of equipment, the noise resulted. “Maybe it’s an issue specific to your preamp,” he offered. Let's Not Go To Extremes Angus recommended a look at ground loop isolators, specifically the inexpensive ExtremPro Hi-End Ground Loop Noise Isolator/Filter for Car Audio/Home System that retailed for $26.99 at Amazon.com [Editor’s note: currently unavailable on Amazon]. It boasted HD< 0.001 percent, transmission ratio of one to one and a frequency range of 20 to 30,000Hz (“ExtremPro Hi-End Ground Loop Noise Isolator...”) As I researched my options, I discovered the Jensen CI-2RR that was used in professional recording studio applications and sells for $212.99 on Amazon. A survey of the internet revealed its great reputation; amongst other things, I discovered that some sound engineers swore by it. According to its literature, the Jensen CI-2RR eliminates hum and buzz caused by ground loops has extended frequency response from 10 Hz to 40 kHz with less than 2° phase deviation at 20 Hz (“CI-2RR Two Channel Isolator”) Curious, I requested a review sample from Jensen Transformers. I mentioned it to Angus, who was well aware of their reputation; he said that while the Jensen CI-2RR has much better specs, the ExtremPro should handle my 60Hz hum issue fine. “It would be interesting to compare the two,” he suggested. I went ahead and purchased the ExtremPro for $26.99 and fee shipping via Amazon Prime, figuring I’d return one of the two isolators after comparisons. No Hum Drum Experience Several days later, the ExtremPro arrived. Powering up my system, I turned the volume to 10:00 o’clock. The hum was ever present. Turning it off, I ran a pair of Straight Wire Virtuoso RCA cables out from the DAC into the ExtremPro and a second pair out from it to the PrimaLuna. Turning it up to 10 again, a hum remained, but was hardly noticeable; at 12:00 o’clock, it was there, but not so much, while playback remained unaffected. This was good! Several days later, the Jensen CI-2RR arrived. Similar in size to the ExtremPro at 4.32” W x2.6” D x 1.45” H, the dark grey powder-coated Jensen had the RCA inputs on one side. Putting it through the same paces, audio playback sounded identical. Then, pausing the music and comparing the noise on both units at 12:00 o’clock, I discovered they sounded the same. I was astonished. The ExtremPro was in place in these two reviews: Qobuz Review AV Room Services Anti-Vibration Pads Review I contacted David Hill, General Manager at Jensen Transformers, who acknowledged that lower cost isolators that use transformers are effective at removing 60 cycle hum resulting from a ground loop, but added that the CI-2RR outshines other products by also removing higher frequency "...buzz" noises, which occur as harmonics of the 60 cycle ground loop hum.” Elaborating further he wrote the following: The Jensen transformers inside the CI-2RR are built with electrostatic copper shields (known as "Faraday" shields) that are added in between the internal winding layers. Faraday shields are essential in eliminating several other types of noise interferences besides just 60 cycle hum. So along with higher frequency buzz, our CI-2RR will also eliminate clicks & pops from machinery motors (A/C systems & refrigerators), R/F interference (AM radio station pickup), and interference caused by light dimmers. Isolation transformers that contain internal Faraday shields have higher material costs due to the copper shields, and are much more labor intensive to build. So although our CI-2RR is more expensive, it can be the only solution to fixing the noise problems I listed above. Lower cost isolators use audio transformers that are simple bi-filar types that don't have Faraday shields inside, and therefore only work on applications where there is just 60 cycle hum. Higher frequency "buzz" noises will remain, as they get capacitively coupled through a bi-filar audio transformer from input to output. When the internal Faraday shield inside our Jensen is grounded to the signal reference ground of the transformer's secondary/output side, capacitive coupling between the transformer's primary and secondary windings is virtually eliminated. Instead, the high frequency noises "bleed" off out of the audio signal and into the audio reference ground. Thankfully, those higher frequency issues were not a problem at my home, hence, I returned the Jensen CI-2RR. However, in the event that we someday relocate, I may be calling them back up. Associated Software and Equipment
Work Cited “ExtremPro Hi-End Ground Loop Noise Isolator/Filter for Car Audio/Home System.” Porlo.123. Ebay.com. N.d. Web. 7 March 2019. “Jensen CI-2RR Two Channel Isolator.” Jensen-Transformers.com. Jensen Transformers. N.d. Web. 7 March 2019. (You can view it here) http://www.jensen-transformers.com/wp-content/uploads/2014/07/CI-2RR.pdf
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Juan C. AyllonA writer, artist, educator and owner of Prairie Audio Man Cave, he lives with his wife, Isabel (AKA Belle), and their Goldendoodle, Liam, enjoys listening to high fidelity music and all things hi-fi at their home in the greater Chicagoland area.. Archives
March 2024
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