JohnSwenson;693112 Wrote: > As many of you know by now the SB Touch includes inexpensive > electrolytic caps on its outputs. These caps are polarized, which means > they are supposed to be run with a bias voltage across the cap, this > bias actually makes the cap work properly. But in the case of the touch > there is NO bias voltage, I've been trying to find out what this lack of > bias voltage does to the sound. > > I finally tracked down some articles on the web where people have been > looking into this. It turns out that without bias a polarized capacitor > still behaves as a capacitor for small AC voltages, BUT the distortion > through the capacitor goes up exponentially as the AC voltage > increases. The upshot is that at the full output of the Touch (2V RMS) > the unbiased cap has 22 times as much distortion as a film capacitor > does. At lower output voltages this distortion goes down significantly, > but even at its best it's still about 5-6 times as much as a film cap. > > This has some interesting ramifications for connections to a system. > The conventional wisdom says that you shoulkd run the Touch at 100% > volume all the time and use an analog domain volume control, thus > maximizing the bits used and the signal to noise ratio. But that > doesn't take into account this exponential distortion. A number of > people have reported that they get much better sound running the Touch > directly into a power amp and using the digital volume to bring the > level down. This is usually attributed to preamps not being very > "transparent", but in this case it might be the significantly lower > distortion when you run the Touch at a lower output level. > > Of course all the above is JUST for the analog outs, it has nothing to > do with running the digital signal into an external DAC. > > So what to do about it? You can use an external DAC, that has been > talked about a LOT. You can open up the Touch and bypass the output > caps. Opening the Touch and performing surgery and getiing it back > together is not an easy task, so don't attempt this unless you know > what you are doing and are willing to risk destroying it. There are > threads on this over in the DIY forum. > > You can also build an external bias circuit that biases the capacitors > without having to open up the Touch. I'll try and get a thread on this > started over in the DIY forum in a day or two. I'm kind of surprised > that none of the companies that supply "tweaks" haven't marketed one of > these yet. It very simple, a 6V source (AC supply or battery) and 2 > resistors. You can put it in a box with connectors, but then you need > an extra set of interconnects. You can have pictails sticking out of a > box, you can take an interconnect and cut it in half and insert this > etc. There are several ways you can do it. > > Its still not as good as getting rid of the capacitors all together, > but its much lower distortion than what you get out of the box, and you > don't have to do anything to the Touch itself. > > John S.
22 times ! as measured separately or -in this actual application- ? Touch has 0.0014% thd acording to stereophile so will it be 0.0014%/22 after for example removing the caps ? If I used the analog out I would remove them , so I'm fairly confident in your original assessment on how they work (or rather don't work ) plausible enough for me for an almost free mod and btw great initiative to actually have solution that can make people keep the warranty on the unit . -- Mnyb -------------------------------------------------------------------- Main hifi: Touch + CIA PS +MeridianG68J MeridianHD621 MeridianG98DH 2 x MeridianDSP5200 MeridianDSP5200HC 2 xMeridianDSP3100 +Rel Stadium 3 sub. Bedroom/Office: Boom Kitchen: Touch + powered Fostex PM0.4 Misc use: Radio (with battery) iPad 64gB wifi +3g with iPengHD & SqueezePad (in storage SB3, reciever ,controller ) ------------------------------------------------------------------------ Mnyb's Profile: http://forums.slimdevices.com/member.php?userid=4143 View this thread: http://forums.slimdevices.com/showthread.php?t=93875 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
