Many months ago I bought a DAC to use with my computer in the bedroom to connect to my Musical Fidelity X-Can V2 for some headphone listening. I have used it, but not been impressed by it at all. But when surfing around, I got into this crazy page about installing a tube amp output on CD players and DACs. And he listed the cheap one I have as one of the best DACs he ever heard. The guy bypasses the output stage and replaces it with a simple tube buffer/amp. That got me interested.
I was in the middle of modding my Tianyun Zero DAC and wished that I had done some measurement on it before starting the mod, to be able to compare and see if it’s an improvement. But I forgot.
So I took out the CS4397 DAC and measured it.
Here’s the frequency response, and as you can see it’s horrible! -3db down at around 12.000 Hz. No good.
I knew that oversampling Digital to Analog converters usually has a lot of noise in the higher frequencies, but the applied low pass filter is apparently wrong. So I started to search the net and found this forum. So I tried all the classical mods first, like beefing up the power supply. Changed the surface mounted capacitors to low ESR (Panasonic FM) and removed the output caps etc.
All these changes made for better sound quality, but did not fix the big dip in the upper frequency. So out came the soldering iron again and I changed the C32, C33, C34, C35 to 150pF surface mounted caps. And as always when dealing with surface mount parts, you realize that you’re getting old. Shaky and with lousy vision. But I managed to get them mounted. The DC output offset on it used to be 0.300V but is now 0.006V on both the RCA connectors.
Did it improve? Well, let the measurement do the talking.
I say! That obviously worked!
And here’s the annoying part. My wife thinks that this cheap DAC sounds better and more open than my extensively modified Zero DAC, that I’ve been working on for weeks. And she’s right.
So now, I have to rebuild and improve the power supply to try to lower the noise level to the same I have on my ZERO DAC.
After that, I’m going to rebuild the SPDIF input with a transformer. And then modify it so that it will work with 24/192khz input.