Sansui QRX7001 repair

[MidiMagic]

Picture of connections. Left AUX to phone at 1KHertz. Tape REC center connections to each meter lead.

View attachment 99490

Why are there speaker cords (not shielded cables) plugged int6opp the record jacks?

 

[SPXER]

I brought pins 2-5 on 2088 out on some small wires soldered on to measure with the meter. They are colored resistor color code to keep track of.

red=pin2=rear left
orange=pin3=right rear
yellow=pin4=front right
green=pin5=front left

Going through the alignment again, they never perfectly matched, so I set them as low as they would go. This pic shows a typical reading. Using two meters speeds thing up. The settings were not much different than the setting by ear.

 

[mandrix]

Yeah doesn't seem all that far off. But I have no idea what is kosher for that unit like these other guys.
I mean one of the meters could account for the small difference. 4mv Vs 16.
Ah geez forgot he was talking about ouput voltage. My bad.

 

[Sonik Wiz]

I brought pins 2-5 on 2088 out on some small wires soldered on to measure with the meter. They are colored resistor color code to keep track of.

View attachment 99525

red=pin2=rear left
orange=pin3=right rear
yellow=pin4=front right
green=pin5=front left

Going through the alignment again, they never perfectly matched, so I set them as low as they would go. This pic shows a typical reading. Using two meters speeds thing up. The settings were not much different than the setting by ear.

View attachment 99526

Smart move using 2 meters.
However the goal is to get matching lowest separation figures. These show a great deal of difference. I don't know what configuration this is but using your example of left input only, and if the left meter shows right front, and right meter shows right back, that is over a 15 dB difference. In other words I don't know what true dB separation right front would have from the left side, but right back would be 15dB louder than right front. Wow! That ain't gonna work!

Clever making the extension wires from the board. But from the pics it looks like you are using unshielded test leads. My experience is test leads & other wiring must be shielded to keep from picking up hum & noise from the wiring. Take a shielded coaxial audio cable, put banana plugs at one end & little gator clips at the other.

Edit: And also suggest using shielded cable from phone to receiver input.

The last thing I notice is that you should be showing higher V's than in the low mV range. You said the phone app read 173mV output & 158mV on the receiver. That is probably too low for the Sansui chips to latch on to. Do what you can to get a higher level input signal ~.5V & try testing again with shielded test cables.

 

[par4ken]

The last thing I notice is that you should be showing higher V's than in the low mV range. You said the phone app read 173mV output & 158mV on the receiver. That is probably too low for the Sansui chips to latch on to. Do what you can to get a higher level input signal ~.5V & try testing again with shielded test cables.

I think that he is showing the outputs from the opposite side; ie Left in reading Right front and Right back out. So 150mv in and 15mv out is ten times less so about 20dB separation, even higher on the other output. I wouldn't worry much about the imbalanced crosstalk front to back. It might be possible to tweak a bit to make them more even at the expense of a bit of separation, but I wouldn't bother.

 

[SPXER]

Smart move using 2 meters.
However the goal is to get matching lowest separation figures. These show a great deal of difference. I don't know what configuration this is but using your example of left input only, and if the left meter shows right front, and right meter shows right back, that is over a 15 dB difference. In other words I don't know what true dB separation right front would have from the left side, but right back would be 15dB louder than right front. Wow! That ain't gonna work!

Clever making the extension wires from the board. But from the pics it looks like you are using unshielded test leads. My experience is test leads & other wiring must be shielded to keep from picking up hum & noise from the wiring. Take a shielded coaxial audio cable, put banana plugs at one end & little gator clips at the other.

Looks like I need to make out another Mouser order.

Edit: And also suggest using shielded cable from phone to receiver input.

The last thing I notice is that you should be showing higher V's than in the low mV range. You said the phone app read 173mV output & 158mV on the receiver. That is probably too low for the Sansui chips to latch on to. Do what you can to get a higher level input signal ~.5V & try testing again with shielded test cables.

Mt phone will put out only 1/4 volt at full volume with the tone generator app.

 

[Sonik Wiz]

Looks like I need to make out another Mouser order.

Mt phone will put out only 1/4 volt at full volume with the tone generator app.

Yes Sir, there's always another Mouser waiting to be made.

In regard to Ken's comments above what was the input location (left only?) and what was the left/right meter measuring?

 

[SPXER]

Yes Sir, there's always another Mouser waiting to be made.

In regard to Ken's comments above what was the input location (left only?) and what was the left/right meter measuring?

Sorry, I don't recall which combination that photo was of. I should have written it all down, but I didn't think it was important. Since I couldn't achieve parity, I went for the lowest numbers I could adjust to.
I did switch the meter leads and the readings followed the leads, not the meters.
The unit sounds pretty good to me, but I don't know what perfect sounds like.

 

[SPXER]

I would be glad to share test signals I made for QS if you want. Each one is 2 mins long allowing for a decent amount of time to adjust. Created in AA 3 these are white noise and usually sine waves would be used but I've used them in preference with good success. Just let me know if you want them.

Yes, I will try your test signals. I assume a laptop will provide the necessary output voltage? Thanks, Mr. Wiz

 

[Sonik Wiz]

Yes, I will try your test signals. I assume a laptop will provide the necessary output voltage? Thanks, Mr. Wiz

Done. See PM.

 

[SPXER]

Here is the QRX up and running. Many thanks to all that helped me get to this point. I still have the get the quad boards properly aligned. A handsome unit, I think.

 

[SPXER]

I have been using the QRX exclusively since the rebuild. I find that in my room, I prefer the Hall setting over the Surround setting. The issue, and it's not a killer, is that the "rear" output in Hall is much reduced. I think this is on purpose as Hall is for ambience. I prefer it turned up about equal with the front speakers. The question I have is, are there resistors somewhere I can short to get the rear output up? I do turn the balance to the back to achieve the same, at the expense of running the front lower and thus the general volume higher. I have reviewed the schematic and I don't see any such resistors outside of the quad boards. I can't follow the Hall path through the quad boards to find how Sansui is reducing the volume.

 

[Sonik Wiz]

I have been using the QRX exclusively since the rebuild. I find that in my room, I prefer the Hall setting over the Surround setting. The issue, and it's not a killer, is that the "rear" output in Hall is much reduced. I think this is on purpose as Hall is for ambience. I prefer it turned up about equal with the front speakers. The question I have is, are there resistors somewhere I can short to get the rear output up? I do turn the balance to the back to achieve the same, at the expense of running the front lower and thus the general volume higher. I have reviewed the schematic and I don't see any such resistors outside of the quad boards. I can't follow the Hall path through the quad boards to find how Sansui is reducing the volume.

Glad to hear the good news that the 7001 is up & running & behaving itself.

Let's say you are playing stereo & using basic QS on the unit as a reference. Any left only (right only) signal wil reproduce equally from the left (right) side speakers. Switching to the surround synth mode involves some out of phase blend to the input signal that changes the decoding. For a left only (right only) input it now shroud decode strongly to left back (right back). The rear probably sounds louder now & it should because more direct sounds are moved to the rear speakers. It would be fair to (users choice) move the balance a bit forward.

Switching to the Hall mode does almost not quite the opposite. The front chs are now unaltered, undecoded replica of the stereo input. Meanwhile some in phase blending is done to the input signal to the decoding circuitry. That means no direct sounds will be coming from the rears, only ambience. This of course means the rear chs have dropped in volume referenced to basic QS decoding. It is users choice to raise the volume in the rears to get satisfactory balance.

There are a few blending resistors both at the input to the decoding circuitry and at the last front/back output stages that are typically clipped by modders in an effort to improve performance. I've done it & I recommend it. But it won't affect this level change your asking about when using the Hall mode.

 

[SPXER]

Yes, Sonik, I have switched from Hall to Stereo (front speakers only) and I do not hear any difference. When I switch from Surround to Stereo (front only), I do hear some difference.

In rear speakers only, I cannot tell any difference between Hall or Surround except for the volume difference, which I quickly adjust for. Of course, I am positioned at the receiver and not in the best place to hear both rear speakers.
With that test, I assumed that the Hall effect was a reduced level of Surround.

I think it is the removal of sounds from the front in Surround that causes me some dissonance.

I have lifted the three resistors you mentioned from the quad boards. I have no information as to what each of them do independently, or what effect they may have in Hall mode.