Mod and compare
Mod time.
I went over to my buddy Walter's house today. Walter is a no BS highend audio engineer. Most of his gear is home brewed, in fact he used to perform custom services for people designing and building various components.
His main system has 3 Bryston amps triamped with home brew speakers. The preamp is also of his own design.
After hearing my Sony HD tuner he was intrigued so he bought one for himself. Then he proceeded to perform some of the mods described at:
http://www.ham-radio.com/k6sti/xdr-f1hd.htm.
Today's mission was to compare his modded Sony to my stock one.
His had two major mods - tweaking the bias on the output transistors so they operated at a slightly higher voltage and the removal of 4 capacitors (C11, C12, C21, C22) whose function is described here from the original article:
Each D/A drives a ferrite bead and shunt capacitor within the tuner module. The module drives cascaded RC filters on the motherboard. The filters remove low-level (−47 dB) ultrasonic noise that extends to a few MHz, but they also cause the frequency response to droop within the audio passband. Disabling the filters by removing their capacitors flattens the response as shown above and causes no interference to AM or FM reception. The preceding photo identifies filter capacitors C11, C12, C21, and C22.
First thing we noticed was that the modded unit had a slightly lower output level so we had to compensate our comparison tests by adjust the level when we switched back and forth.
Right away we could detect a difference. Not night and day but a noticeable difference. It sounded like the stock unit was duller, like a veil was over the speakers. He described it like looking out of a slightly dirty window; I thought it sounded like after drinking a beer (out of a slighty dirty glass). No surprise since the capacitor removal mod as describe results in a restoration of the treble frequencies as shown in the graph below:
Into the shop we went with my stock unit to remove the 4 caps. These are quite small but not a problem to remove with a small tipped iron (we left the 100 watt gun on the shelf) and a solder sucker. The locations (and labels) are shown in the picture below:
After that mod we went back to the listening room to compare. At this point we noticed that my unit sounded essentially the equal of his unit. Also my unit now had a similar output level. Not quite identical, but very close. I still thought that his sounded a little better but wasn't sure if it was a result of the other mods or because the levels were slightly different. Generally the louder unit will sound better and I'm guessing that his mods resulted in the slight difference.
Bottom line is that if you have the skills, tools and inclination I heartily recommend the removal of the 4 caps.
JimB