I like to listen to music or recordings of tree frogs and crickets when I'm going to sleep so I've had a stereo system set up in the bedroom for years. The system consisted of an old (1983) Luxman RX-103 receiver, a SqueezeBox Touch to stream music from my server, and a pair of 20 YO Canton Ergo 22 DC speakers. The receiver was too big for the nightstands, so it sat on the dresser near the wall opposite the bed. Running speaker wires all over the bedroom wasn't an option, so the speakers were on the dresser, too. Unfortunately, that required turning the volume relatively high which might disturb my neighbors late at night because the walls/floors/ceilings are a little thin in this building.
An ideal system would fit on the nightstands near the bed so the volume could be kept to a reasonable, late-night level, but there was already too much junk on the nightstands, including table lamps. I started by getting rid of the lamps and replaced them with a couple PS 2014 hanging lamps from Ikea. It turns out that besides not taking up any space on the nightstands, they throw very nice patterns on the walls! They don't provide a whole lot of light, even when open, but that's OK for me.
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| The new system in place. You can just see the new amp in the left corner beside the speaker. |
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| This is what it looks like with the lamps open. |
A lot of the other stuff was disposed of or put in drawers and the result is that one nightstand has a speaker and my phone charger, and an alarm clock, and the other has a speaker, the new amplifier, and a CPAP machine. It looks a lot nicer, and is easier to keep dusted.
WAP!
When I was looking for amplifiers, I initially thought I'd continue using the SB Touch streamer. So I looked at the small class D amps by Fosi, Wiim, Marantz, Eversolo, and a few others. It occurred to me that the Wiim Pro Plus streamer in my living room system plays music from my Lyrion Music Server just fine, so maybe I could buy an amp with a built in streamer that would replace both the Luxman receiver and the SB Touch. Some of the amps I looked at had built in streaming with touchscreens on the front panel, but I decided I didn't need that as I'd be using my phone to control it anyway. I almost never used the touchscreen on the SB Touch.
After much digging through reviews and specs, I settled on the Wiim Amp Pro (WAP). It's small, has more than enough power for my purpose, and has a built in streamer that works with my server and Tidal Connect, just like the WPP in the living room. Both players can be synchronized so they play the same music at the same time (nice when I'm cleaning the condo).
The WAP has toslink, USB, HDMI, and line inputs. It also has BlueTooth in and out but doesn't support high quality codecs (yet). There is no phono preamp. It has built-in graphic and parametric EQ with room correction(!) called RoomFit, and real bass management that can apply high pass to the audio in the WAP, and low pass to the subwoofer output. The Wi-Fi antenna is built into the case so there's no ugly antenna sticking up from it.
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| Front panel- just a few LEDs and the volume knob with play/pause button. |
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| Back side of the WAP. Yes, power supply is built in! |
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| The side holes easily allow 12 gauge wire, if you feel you must. |
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| Bottom of the WAP. The holes along the sides and bottom are all they need to ventilate this thing thanks to the efficient class D amplifiers. |
When I got the amp, I connected it to my Wi-Fi network via the Wiim Home app on my phone (already there for the WPP in the living room system), and it immediately started updating its firmware. After a few minutes it was ready to go. Lyrion Music Server saw it as a player without any messing around. Everything just worked exactly as it should, unlike so many other things these days. It's been in the system for about two weeks and I haven't had even the slightest trouble with it.
The amp can be controlled via Wi-Fi (phone or tablet) or its own Bluetooth remote control, so I don't need to access the front panel of the amp at all, and it may end up under the bed, out of sight, if it can get a decent Wi-Fi signal down there.
Technical stuff
The WAP uses TI TPA3255 class D amplifiers to drive the speakers. They are very efficient compared to class A or AB amplifiers. That efficiency is achieved by switching the output transistors on (very low resistance) and off (very high resistance) at hundreds of kHz, so they spend very little time between those states generating heat. That efficiency means they don't need large heatsinks which minimizes the size and cost of the amplifier. The PWM output from the transistors is run through a low pass filter to create a smooth analog output waveform that drives the speaker.
Unlike class A and AB amplifiers, class D amps don't normally provide a lot of dynamic headroom. This amp is rated for 60W at 8 Ohms (and 100W into 4), and that's all you'll get from it. That means if you're driving inefficient speakers and/or your room is large, it may not play as loudly as you'd like before it distorts audibly. Neither of these are problems in my situation.
I was curious about the switching frequency used so I connected the amp to an 8 Ohm dummy load and my Siglent digital oscilloscope to see what the output looked like when there was no music playing. Here's what I found:
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| This is the output of the amp with no music playing- about 600 mVpp at about 595 kHz. It's far beyond audible frequency range, even if you have golden ears, but could pose a problem if you're trying to listen to MW or SW radio anywhere near this amp. This signal could be the output switching clock leaking through, or it could be from the power supply that is also a switching circuit. |
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| I used the scopes FFT to look at the spectrum of the output and found plenty of harmonics of the 595 kHz output. |
That output looks ugly, but there's no audible component of it coming from my speakers, even with my ear close to the tweeter.
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| Here's noise in the audio band from 10 Hz to 20 kHz. It looks very quiet except for a little 60 Hz from the power line. |
My scope's FFT is OK, but it's not an audio analyzer. I suggest that if you want to see a real detailed technical review, you check out Audio Science Review.
I have read online that some people complain of a whining sound coming from the amplifier. If I press my ear against the top cover of the amp I can hear a very faint whine, but there's nothing audible (to my 67 YO ears) otherwise.
Using it
It seems to pick up 5 GHz Wi-Fi very well (plays 24 bit, 48 ksps music via Tidal without buffering), so I haven't had to use the ethernet port to connect to my network like I did with the SB Touch. The front panel has only a status LED that changes colors to indicate different things, a few more LEDs to indicate the relative volume level, and a single encoder knob with a built in push button to control volume and play/pause music.
The volume control has an odd feel to it, almost like turning the knob in a soft piece of rubber. There are no detents. I have noticed that changing volume by any of the available means seems to react a little slowly- it takes a fraction of a second for the volume to change when I start turning the knob, so I tend to turn it a little further than needed for the change I want to make.
The unit has a BT remote control with a mic built in for doing the "hey Google" or "Alexa" thing. I don't use either, so I can't comment on the performance. You can put the amp out of sight - under the bed, in my case- or in a cabinet or drawer because it doesn't use IR for the remote control. The remote control's mic can't be used for RoomFit equalization tests.
The RoomFit function is a nice extra that you may or may not want to use depending on how picky you are about the sound. What it does is send a swept tone through the speakers, measuring the response in your listening position with a mic (usually in your phone or tablet running the Wiim Home app), and then it generates an equalization curve that alters the frequency response of the amp to achieve optimal sound quality. An uncalibrated mic's frequency response or directivity patterns are unknown so results of RoomFit using the mic in your phone or tablet will be questionable at best. For better results, you can get a calibrated mic (like my UMIK-1 that I used to check resonance when I was rebuilding the Quads) that plugs into a phone or tablet, and RoomFit can use the mic's calibration file when it does its magic.
The amp sounds great with the Cantons, as expected. I haven't tried driving the Quads with it yet to see if it sounds any different from the A12 amp that's in the living room system, but soon. I expect it will sound the same/fine until it starts to distort (if I can run it that loud without freaking out the neighbors).
The Quads can't play very loudly compared to "normal" speakers, mostly because the narrow spacing between the stators in the drivers limits the diaphragm excursion when playing low frequencies. The WAP's bass management could be used to set up a biamped system in which the low frequencies are sent to a subwoofer (keeping them out of the Quads) which would allow the Quads to play much louder than they could otherwise. More experiments to follow.
