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Reviews (3)
Dec 01, 2017
Excellent power supply, solved my problems
I had been using an RPi with a Hifiberry audio interface to play media from USB hard drives for the last year or more. The playback would often halt, or play unevenly, and the hard drive would sometimes fail to power up when plugged in. I was using a 2.5A rated power supply specifically sold for the RPi, so I had thought the power supply was not the cause. But I have now switched to this NorthPada power unit and all those problems have completely disappeared. I've been using it for a month now. I'm totally thrilled.
Oct 16, 2019
Excellent design, high power amp
This is an excellent high power, low distortion amp, built entirely using LM3886 chips. The six chips are in two sets of 3 each. The 3 chips in each set are in parallel, and the two sets are then configured as a BTL pair to deliver high power. Because each BTL half is configured with 3 chips there is enough current drive to handle even 4 Ohm or 3 Ohm loads, something which smaller BTL amps struggle with.
There are seven opamps used for auxiliary duty. Each power amp chip uses one opamp to work as a DC servo to bring the DC offset down to negligible levels, plus one opamp is used for converting a single ended signal input to balanced, to drive the two BTL half-amps. There are therefore 4 dual-opamp chips. You can replace these opamps with others more to your liking, but then note that out of the seven opamps used, six are just used as DC servo opamps.
The power output tracks are super thick copper rods as shown in the photos. This is necessary since the overall current rating is pretty high.
Each amp board is best driven with a 24-0-24V or 25-0-25V transformer with at least a 400VA power rating, if you want very good transient response at high SPL levels. You may like to use 30,000uF filter caps per rail, or higher. (Opinions vary.)
The amp does not have any DC detect or turn-on delay speaker protect circuit. You may trust the internal protection circuits of the individual LM3886 chips, or you may add an external module. One needs to be careful to select an appropriate module, because few speaker protection modules work with BTL amps. So, you either need to use a stereo speaker protect module for each amp channel, or you need to use a speaker protect module designed specifically to work with a BTL amp. There are one or two such modules available on eBay.
Fixing six LM3886 correctly to the heatsink is a pain when they are already soldered to the board. I prefer to fix my OPS devices or chipamp chips to the heatsink first, then fix the power amp PCB to the heatsink, then solder the devices to the power amp PCB. This ensures that there is no mechanical stress on the device pins. In order to do this with this amp, I had requested the seller to supply me the assembled boards but with the LM3886 ICs separate, not soldered. They readily agreed. I also asked for the TF (isolated-back) version of the ICs, so that I don't need to worry about electrical insulation of the ICs from the heatsink. They supplied those too. It's been a very good experience in that sense.
Feb 24, 2017
Compares with good full-size decks
4 of 4 found this helpful When people say that this little thing compares with most high-end full size decks, they are not joking. It performs as well as any good 2-head full size deck, including some of the Nak, Aiwa Sony and other brands. It has only a single-capstan transport, but the transport seems to be super-smooth because of its quartz-PLL controlled servo for the capstan drive. Its headphone output can drive large, moderately high impedance headphones without trouble: something almost no other Walkman can. Luckily for us, rubber parts, etc can be replaced -- there are reliable sellers who make these parts. Get the azimuth aligned correctly if you're keen to get the best performance. And if maintained well, these things can give 2 more decades of service.
I still remember the jaw-dropping feeling I had, listening to a good metal cassette recorded with Dolby B on a Nak BX-300 on this Walkman. I've had similar feelings many times after that.