Hi all,
I've been following this thread for a few days, and wanted to reply but haven't had time til this morning. First of all, thanks for all the kind words Laura. I really appreciate it. I'd like to make a few comments about the work I did on your 4 boards, the two output driver boards and the two quad boards.
Your problem with the crackling and popping is a fairly normal problem that occurs with amps. If it can be isolated to just the amplifier stage, it practically always is the first two transistors in that stage, called the "differential pair". It is so hard to troubleshoot an amp stage, that whenever I get that problem, I just change out the diff pair. It's worked every time so far. And then of course, I change all the other diff pairs for the other channels, it's just good practice. Whatever stress caused the problem on the bad channel, likely occurred to the ones that are still good, and they could give future problems. Usually the noise is not too loud. I can imagine, though, with your 98db per watt Klipsch speakers that the noise practically pinned you to the wall. I also changed out a few of the fusible resistors on those boards that had not been changed by QB.
Your quad boards already had the HG alignment. The blend resistors had been removed and the alignment was there. That is done with the 4 trimpots on the 8087 board. The alignment was off a little, I just tweeked it back in. Maybe QB wasn't calling it the HG alignment yet, when you had your 9001 done by him.
And now to the modifications to your output driver boards. The first thing I do is reduce the gain of the entire stage. Most gear from the 70's has too much gain. This can be identified by the fact that most people are at full volume at 10:30-11:00 oclock on the vol control. There are several benefits to this. First, like you said, the noise floor is reduced, allowing the music to play over a silent background, which in your case, with your hyper efficient Klipsch's, is a real benefit. Second, this causes the preceding stages to run at higher output voltages, effectively increasing the current flow there by 4-6 times. Low level audio circuitry always sounds better when run louder. Third, the vol control tracking L to R and the rears also is at its worst at the low end of its range (balance and tracking). By running the vol control higher, these issues are lessened.
The modern SS amplifier in it's current topology was first put on the market by Crown in 1967, with the Crown DC300. The Crown was an implementation of a circuit called the "laboratory amplifier" that had been around forever with tubes, and was mainly used in lab test equipment, because of its accuracy, such as the input to an oscilloscope, or VTVM. All the other manufactures, including Sansui, followed suit and began using this circuit in their higher powered amps. Only problem was, they left part of the circuit out.
I don't know if you remember, but during this time a new measurement, called TIM, or transient intermodulation distortion, appeared on the scene. It was an attempt to codify why amps sounded different. The manufactures didn't like this measurement and did everything they could to discredit it, because it showed up the real problems with their amplifiers. They also responded by adding back the circuitry of the missing parts of the lab amp. I don't agree with how they did this. They did it with, what I call, trick circuitry. They used a couple more transistors to balance the very small currents flowing in the input part of the amplifier. It's my opinion that this "trick" is what brings about the cold and sterile but accurate, sound of the later Sansuis, the AU919 and all the others from about '79 on.
What I do is add back the missing parts of the lab amp, using circuitry of my own design, and painstakingly balance the currents by hand, instead of using the trick. My opinion, is that this opens up the inner detail of the amp without removing the warm and tube like quality of the Sansuis that we love so much. Practically everyone who I have done this mod for, says something like you did Laura, "I mean there was even imaging in front on Aqualung, though I also had all the discreteness in rears and all around -don't even know how to explain it!"
In music that you know and love, with this mod, you will hear things that you haven't heard before. The first time I figured this out and did this mod, on my first restored 9001, I was dumbstruck to listen to the Beatles White Album and hear things that I had never heard before, after almost 40 years of listening. The front imaging was so good, all kinds of little vocal licks and sounds were just popping up. I had a hard time believing the mod was that good at first, just because I had put a tremendous amount of work into it, and you know how psychology works, especially in audio. I've noticed in the past that just dusting off and cleaning my audio gear, putting the CD's away, that kind of stuff, always makes my stereo sound better. LOL Lots of listening since, and the opinions of many other people have led me to believe that the "diff mod" that I do, really opens up the sound.
So, I'm really glad that worked so well for you.--Jim
