Digital Processor Reviews

When she reviewed two iFi ZEN Signature combos for our January 2022 issue—the ZEN DAC Signature V2 with two versions of the ZEN CAN Signature headphone amplifier, which include a custom-EQ curve for particular headphones—Julie Mullins was impressed by their performance. She wrote, "the ZEN Signature sets delivered highly resolved, clean, pristine, dynamic sound. The amplifiers are powerful. Backgrounds black as a new-moon nighttime sky brought musical details to the foreground." But there was an issue with the volume—the gain—that I wanted to check on, hence this follow-up review.

One version of the set includes the ZEN CAN Signature 6XX, which includes a defeatable custom EQ intended to optimize the frequency response of the "Massdrop x Sennheiser" HD 6XX headphones, which several online sources indicate is the same (in sensitivity and frequency balance) as the HD 650 headphones, although the build is slightly different. (I was able to roughly corroborate that the sensitivities are close.) The other set includes the Zen CAN Signature HFM, which has defeatable custom EQ for the HiFiMan HE-4XX headphone—another "Massdrop" item—and a few other HiFiMan headphones. Both CANs are appropriate for other headphones, but without the custom-matched EQ.

Both sets include a Pentaconn 4.4mm balanced connector for joining DAC to amp in optimal fashion. Julie wrote that the two sets, priced at $595, "sounded more expensive than they are."

However, according to Julie, the Signature sets were too loud, even when used with the very headphones they're intended to drive. "I found the output levels to be on the high side for comfortable listening at the recommended volume-control settings," she wrote. (The iFi components use potentiometers in the volume control that achieve optimal channel matching above 10 or 11 o'clock on the volume knob.) This was surprising and mysterious, but it seemed to be corroborated by iFi's own headphone-matching calculator, which indicated that both versions of the CAN, in combination with the recommended headphone, would result in sound-pressure levels of 121dB. Is that a maximum volume? That isn't clear, but iFi's own calculator puts it in the red—just barely—indicating that it's "Too loud." Odd. Still, Julie had a review to write, so she asked iFi to send along an iEMatch—the company's $49 attenuator, made for situations just like this. With the attenuator in the circuit, Julie was happy with the listening levels. The matter seemed settled. Still, I wanted to hear it for myself. I had

Julie ship me all the stuff she'd used in the review: the two iFi sets, a pair of HiFiMan HE-4XX headphones I bought for the review, my Sennheiser HD 650 headphones, which I'd loaned Julie, and the iEMatch attenuator. I set them up on my laptop and opened the Qobuz app. After making sure that my laptop's volume control was disabled, I gave them a listen.

To my surprise, I had no problem at all with volume; I never needed to use the iEMatch attenuator. Starting with the HFM amp and the HE-4XX headphones, with the iFi ZEN DAC Signature's output set to Fixed, I put on "Ach neige, du Schmerzenreiche," the first track of Sandrine Piau's album Chimère (24/96, Alpha Classics/Qobuz), which Jason Victor Serinus mentioned favorably in this month's music feature.

The sound was lovely, but, with the amplifier's switchable gain set to 0dB and the potentiometer set at noon, I found the volume too quiet. Increasing the gain to 6dB—potentiometer still at noon—I achieved what for me would be a good level for background listening. Bumping up the gain again, to 12dB, put me in the ballpark for active listening. At 18dB, the system was too loud.

Seeking music that was recorded hotter, I put on what I think was the original version of Metallica's Black album—I'm not sure because metadata on Qobuz, and the other streaming services, seems at best an afterthought—and listened to "Enter Sandman" (24/48, Blackened/Qobuz). This music should be listened to loud, and the 0dB gain setting, with the volume control at noon, wasn't loud enough. Adding 6dB of gain, it still wasn't loud enough, but I was in the range: Rotating the potentiometer to about the 1:30 position did the trick. I'm not an expert on people's headphone listening levels, but I think most people wouldn't consider this especially loud. It was loud enough for me, however.

Next, I switched out the HFM version of the amp for the 6XX version and the HiFiMan 4XX headphones for my Sennheiser HD 650s. I found this pair to be hotter, but only a little. I didn't listen again to the Sandrine Piau track; rather, I skipped straight to "Enter Sandman." Setting the gain at 6dB and the potentiometer to about 1:00 got me where I wanted to be, volume-wise.

I repeated these experiments with Roon as the source, with my laptop as an end point and with the iFi DAC hard-wired to my Roon Nucleus+. As expected, it didn't matter. It's the same data. The volume didn't change.

What the heck? Why was my result so much different than Julie's? Why did she require significant attenuation while I was setting the gain at 6–12dB? Does Julie have especially sensitive ears and so listen to headphones very quietly? I doubt it. She listens to rowdier music than I do, and she goes to more rock concerts than I do; if anything, I'd expect her to listen louder than I do. These days, the loudest live music I routinely hear is at the Village Vanguard (which, with its natural horn amplification, can indeed be loud) or good seats for a symphony at Carnegie Hall. Julie and I have never traded headphones side by side, but we've sat in the room together at audio shows, neither complaining. I've got no reason to believe that Julie is an especially delicate headphone listener. I'm flummoxed.

In a perfect world, or in more optimal times, one of us would have traveled. We'd have stood side by side, here or at Julie's place in Ohio, and handed the headphones back and forth until we came to a consensus on optimal levels, or failed to. Then we'd know the answer. Regrettably, circumstances (including COVID, which was heating back up) didn't allow it, so we had to do it this way instead, with less-than-optimal results. I doubt we'll ever know why our experiences were so different.

I enjoyed my time with the iFi DAC and amplifiers, short as it was. The sound was clean and quiet. The ZEN Signature components showed off the (very different) sonic character of the two headphones I tried. The effect of the CANs' custom EQ wasn't dramatic, but it was positive, especially with the HiFiMan, which could sound a bit woolly without it.

In practical terms, I found the iFi's 6dB gain increments convenient; I could set the gain range easily to suit different recordings, which made it easy to fine-tune the volume with the potentiometer in its optimal range. If I were in the market for a desktop/portable headphone setup, I'd be quite happy with these.—Jim Austin