4 channel newbie

[jaybird100]

Actually you can decode QS with the Composer. You use the Stereo Enhance mode and set the stereo enhance control midway. Everything with the exception of full centre (which skews to the right back) decodes properly. Only in recent times (20 years maybe) did I own a real QS decoder. Prior to that everything went through the Composer!

I owned a S&IC. I tried that method, but it's far from accurate. I used the channel identification tests on the "Quadrafile" QS side, and no matter what I did with the stereo enhance control, it didn't decode the rears as intended. Of course, the SQ side, in that mode, was spot on.

 

[SPXER]

Interesting direction this discussion is taking. But I think it will do nothing to help out @SPXER .

Actually, Sonic, I am learning that there are lots of contention with the various surround methods. EXCEPT, no one is complaining about Sansui Vario-matrix.

 

[gvl_guy]

Aside from the QRX ?001 series receivers, do any Sansui quad amps or processors etc. have the Vario-matrix decoders?

I believe the previous set of Sansui receivers had them in later models. For example, there was the QRX-7500 and then the 7500A. I believe the A models had a more advanced QS decoder, but not quite as good as the x001 series. I vaguely remember reading the A's has two of the three ICs that ultimately ended up in the x001s.

 

[par4ken]

Actually, Sonic, I am learning that there are lots of contention with the various surround methods. EXCEPT, no one is complaining about Sansui Vario-matrix.

Yes Vario-matrix works well and seldom produces any artifacts.

If you go the vintage route remember that QR receivers are not Vario-matrix but use a more basic decoder with "phase modulation" on the rear outputs. That produces a nice effect in a smaller room but IMHO does almost nothing in a larger room. The QS-1 decoder is a fantastic looking device but uses phase modulation rather than Vario-matrix. Some sellers are offering them for over $1000, so don't get stung. I think I paid $100 for mine years ago.

Sansui made type A and type B Vario-matrix decoders. As I recall the cheaper simpler version only enhanced front to rear separation, while the other does left to right as well. Sonic wrote an article years ago about it "A Vario-Matrix Survival Guide". Early units like the one in my QA-7000 doesn't use all the chips that are used in latter models. I don't know if that is a reflection of type A vs type B or just that all the chips were not yet available at time of manufacture, so a board with discrete components was used instead.

Tri-banding as used in the QSD-1 is touted as a way to reduce artifacts. Rather unnecessary in my view as there really are no artifacts with Vario-matrix decoding. The other (more obvious) advantage of tri-banding is that separation is increased based on frequency, as lows mid and high can all be steered in different directions. The QSD-1 still sells for very high prices and is built like a battleship. The tri-banding in that unit uses a lot of analogue circuitry. All that extra circuitry IMHO gives the unit a bit of a coloured or darker sound. I modified my unit by replacing the numerous coupling capacitors with film types and increasing the value of the output capacitors. The unit now sounds much better.

When I first got my QSD-1 it seemed to smear the sound, instruments could be heard from more than one location but still with good separation. At first I blamed the whole concept of tri-banding. When I finally got to check it out I found that the midband decoder wasn't working right, it could not be adjusted. Replacing some of the chips fixed it. The QSD-1 contains three separate Vario-matrix decoders each which has to be properly adjusted for the unit to work properly. Each separate decoder board is optimised for the frequency band for which it covers.

 

[par4ken]

I owned a S&IC. I tried that method, but it's far from accurate. I used the channel identification tests on the "Quadrafile" QS side, and no matter what I did with the stereo enhance control, it didn't decode the rears as intended. Of course, the SQ side, in that mode, was spot on.

Funny that you say that because a while ago I was making a digital copy of "Quadrafile" while monitoring it through the S&IC and everything including the sides decoded nicely (exception full center). Stereo Enhance was set at 12 o'clock. I know that is not the right decoder for QS but it can be used in a pinch.

Sorry Sonic if you think that we are straying away off topic but as I say to the moderators, please don't disrupt our natural flow of conversation! I'll try to stay more on topic but SPXER seems to be entertained and enlightened by our banter!

 

[MidiMagic]

Pumping was caused mainly by gain riding. Variable blending is much better.

 

[SPXER]

I am back with news. I have acquired a QRX7001. After a bit if dusting and vacuuming the insides look quite good. The front is stained with what looks like years of cigarette smoke. I will start another post for some help in getting it up and running.

 

[SPXER]

Finished product. Many thanks to all that helped me along the way.

 

[SPXER]

An addendum to the fake transistor part of this dialog. I opened up the fake or mislabeled power transistor to have a look inside. I don't have any experience at what to expect, but it doesn't look massively undersized. (in pic on right)
So for comparison, I opened the bad original transistor. Some quantity of tan colored powder came out. Some is attached to the internal semi. What is that? (in pic on left)

 

[DuncanS]

An addendum to the fake transistor part of this dialog. I opened up the fake or mislabeled power transistor to have a look inside. I don't have any experience at what to expect, but it doesn't look massively undersized. (in pic on right)
So for comparison, I opened the bad original transistor. Some quantity of tan colored powder came out. Some is attached to the internal semi. What is that? (in pic on left)

View attachment 100090

I suspect that the powder is some form of hermetic sealant as the transistor packages won't have been. The one on the right looks OK, and the wires look machine bonded (eutectic bonds), as the modern transistors have better passivation layers I don't think anything is wrong with it so no hermetic sealant (at a guess the wire connected to the outer section of the die is the Base, and the wire in the middle is the Emitter, Collector looks like it is via the bottom of the die.