So, I’ve been playing with the Topping TP30 USB DAC and integrated T amp. You can find them at a number of ebay sites for under $100 shipped.
What do you get? You get an integrated low power T amp based on the tripath 2024 chip, along with a usb DAC based on the ubiquitous TI2704 and a single 12meg crystal. The specs as best as I can tell are 16/48 and the usb uses standard windows audio class 1 drivers. The Tripaths are well regarded as an efficient, but generally low power solution and the TI27xx series is considered a pretty solid usb DAC solution in the midrange for 16/48. Below you’ll find a higher resolution image if you’re so inclined. Just click on it…
Question is, how good is it? Is it relegated to the office, streaming background classical, or can it really play?
Well, a couple tests first.
Let’s look at FR using praxis and running 96k through the m audiophile card.
Well, not bad except for the rising high end. The output is measured into a high impedance load, with the input adjusted to give Vp of 2.85v. Yes, somewhat arbitrary, but repeat measurements at different gains show the same behavior.
(UPDATE-Note that the FR into a high impedance load doesn’t change based on level, but it does change based on load. See the FR measurements into multiple loads for a number of T amps at Michael Mardis’ site. Under load the FR flattens. You don’t have to worry about oscillation. However, into a 4 ohm load there is actually extra roll off in some of the T amps. So, I’ll repeat the FR into a 4 ohm load and into a couple of speakers to see what the real world FR would be.)
What about distortion? Below you’ll see two graphs. One is a measurement with the volume set all the way down, as the control, and the other with the gain adjusted to 5.6 Vp.
Is this good? Well, notice that the spikes are multiples of 60 Hz. The spikes turn out to be multiples of 60 Hz line frequency. It’s a problem with the power supply and filtering. The switching PS is very noisy. The distortion is improved by locating the unit as far away as the power supply as possible, but I suspect the distortion would be improved with a better PS. I’ll retest it with a car battery-I suspect the numbers will look much better.
How about peak V and distortion? Well, let’s look at it a different way, with a wavelet. This is a nice way of doing it because it’s not likely to destroy the unit, since the level can be gradually increased such that only a single cycle will clip.
Praxis allows you to window a sine wave. The stimulus is a blackman windowed 7 cycle sine wave of 1k. You can see the center peak wave clips at 12 volts, the power supply rail when driving a high load. The red curve is with a 5.6 ohm dummy load. You can see the rail/clipping sag to 11 volts. The moral of the story is that you have about 11 volts and 1.5-2 amps of usable voltage and current.
Physically it’s a good looking, well built unit. The volume control is quite smooth and linear, and it is very quiet unit in operation. It does have a bit of turn on thud though. Did I mention it’s only $94 shipped… Windows recognizes it instantly as a usb audio device and it becomes the primary sound output device. When unplugged, windows drops back to the prior sound device, so there don’t appear to be any software glitches. As an alternative to on board sound, with the right speakers (i.e. relatively high sensitivity, low impedance-I think a 4 ohm mtm, 90 dB sensitive, would be perfect) it’s an attractive budget solution. It definitely needs a better power supply. Or, just run it off a battery.
Feel free to post comments on what other tests you might like, what you think of these so far.