Bluetooth interference on Sprout 100

I just purchased a Sprout 100, and while I’m very happy overall, I’m having an issue with noise coming through the headphones. The problem seems to be connected to the Sprout’s bluetooth. There is a low but noticeable noise, probably in the range of 5000 to 10,000 Hz, intermittent, that comes through when the bluetooth is activated. The noise is not related to the Sprout’s volume—it is there when the volume is completely turned down and does not increase when I turn the volume knob up. Listening at moderate volume I can somewhat hear the noise somewhat during in passages of music that are moderately loud, and it becomes noticeable (and very annoying) during quiet passages.

I’ve tried to troubleshoot this, and it’s a strange problem. It doesn’t seem to be affecting the speaker signal, or the analogue RCA output signal. But when wearing headphones, once the noise starts, the interference is present on every channel (bluetooth, digital, analogue, and “vinyl”). Selecting different inputs does alter the sound slightly, but it gets no quieter—the noise just changes slightly. Usually. Occasionally switching the input shuts the noise off, but I haven’t been able to find a consistent pattern—perhaps it’s just the bluetooth shutting off.

I’ve noticed this with several headphones: Sennheiser HD579’s (50 ohm impedance), cheap earbuds (sound is louder), and Etymotic IEMs (16 ohm impedance, I believe—sound is loudest, and competes with low-to-moderate music coming through).

Getting the noise to start is odd. Once turning the Sprout off for a few seconds, then on, the noise begins if the knob is set to bluetooth. There is a repeating sound until I connect a bluetooth device such as my phone, after which the noise becomes more active and unpredictable. So it’s clearly the bluetooth module interfering somehow. If I turn the Sprout off and on while it is set to vinyl or analogue, the noise won’t start until I switch to either digital or bluetooth. Note that the bluetooth module begins to engage when I set the dial to digital—even if I don’t turn it all the way to bluetooth. And if I have my phone, say, connected to another bluetooth audio device, and then switch the Sprout to digital (but not all the way to bluetooth), the Sprout tries to kick off my other bluetooth connection and get my phone connected to the Sprout (and the noise coming through headphones connected to the Sprout gets more lively). Some of this is probably just general bluetooth nuttiness, but it’s odd that the bluetooth activity starts even when I only turn the Sprout’s knob to the digital input. Thus, when listening on headphones I have to avoid both the bluetooth and the digital settings if I don’t want the noise to begin.

The sound may also be related to whether the Sprout is warmed up—I didn’t notice the problem at first, but then it became obvious after listening with headphones for a while. The patterns above occurred when the unit was fully warmed up, but I just tried it again with the unit cold and got more inconsistent results.

Anyway, let me know what can be done. Perhaps it’s just a bad unit. It’s frustrating to not have a usable headphone amp—and I love the Sprout otherwise.

I’ve sent this to a few days ago, but haven’t heard back yet.

Shoot me an email and I can get you in the right hands. I’ve never heard anyone have an issue like this so I think it is likely specific to your unit. We’ll get it checked out.