Sansui QRX7001 repair

[Owen Smith]

They have lower dielectric absorption, they sound better. Impotent if there are a lot of them in the signal path. They do not age like electrolytics do (so should never need replacement). They are bipolar. They have very low leakage.

In short, film type capacitors are better than electrolytics in every way. Low value electrolytics can usually be replaced by film type.

 

[Owen Smith]

My first job straight from Uni in '79 as a junior Electronics Engineer, we had to draw rectangular resistors - yep, draw! on Melinex sheets with a Rotoring ink pen. The PCB layout guy used different coloured tapes to do the layout as well, on vastly oversized Melinex sheets which were then photographed - and even though everything is on a computer, the term tape-out is still used today, though mainly in the semiconductor industry.

I work for a semiconductor company and we still do tapeouts. However it refers to sending the data on magnetic tape which is how it used to be done. Obviously it's done electronically now, but given export and intellectual property hoops we have to jump through it often takes longer in total than sending the tape by courier used to.

 

[MidiMagic]

This diagram is wrong.

If the capacitor has a "+" on it (some have a "-" ), it is polarized. If there is no sign, it is not polarized. This is always true on the diagram and on the capacitor.

Some electrolytics have NP on the case. They have two positive electrodes, one at each end, with no negative connection lead. They are for AC circuits (such as the crossover of a tweeter in a speaker cabinet). This capacitor symbol has three lines instead of two.

The symbols in the diagram above, going across, should be:

Top row: standard new, air capacitor (old), Leyden jar (or cap with a ground can)
Middle row: polarized new, standard old, variable old, polarized japan
Bottom row: variable new, trimmer new

The old symbol for capacitor has one curved plate because the "new" symbol was (and still is) used for industrial relay contacts (normally open). The curved line lets you know it is a capacitor when both symbols are on the same diagram.

Some capacitors have a ground symbol on one lead. This is not polarization, but for grounding for noise reduction. It is connected to the metal outside can of the package.

 

[mandrix]

My reason for posting that chart was to illustrate the Japanese symbol for polarized cap, as shown on his schematic.

 

[mandrix]

unmucking. lol.

 

[SPXER]

They have lower dielectric absorption, they sound better. Impotent if there are a lot of them in the signal path. They do not age like electrolytics do (so should never need replacement). They are bipolar. They have very low leakage.

So how would one identify "in the signal path"? Looking at the tone control again, would it be those that feed into the trans bases? Such as C12, C24, C40, and C52 (going to next stage)? What about C28 and C44 or others? Or just for replacing electrolytics? I looked them up. They are expensive!

 

[DuncanS]

So how would one identify "in the signal path"? Looking at the tone control again, would it be those that feed into the trans bases? Such as C12, C24, C40, and C52 (going to next stage)? What about C28 and C44 or others? Or just for replacing electrolytics? I looked them up. They are expensive!

View attachment 98721

Yes C12, C24, C40 & C52 are in the signal path, they tend to be a high value capacitance to block the DC but let through the Low Frequencies, so 10's of uF.
What values are they? I'm not sure its worth swapping them again.

I wouldn't touch C20, C28, C32, C36, C44 etc.

 

[SPXER]

Yes C12, C24, C40 & C52 are in the signal path, they tend to be a high value capacitance to block the DC but let through the Low Frequencies, so 10's of uF.
What values are they? I'm not sure its worth swapping them again.

I wouldn't touch C20, C28, C32, C36, C44 etc.

C12= 1uf 50v (BRN), C24= 3.3uf 50v (BRN), C40= 3.3uf 50v (BRN), C52= 3.3uf 50v (BRN)
Not 10's of uf. What does the (BRN) indicate?

 

[mandrix]

electrolytic?

 

[mandrix]

Might read this thread:
https://audiokarma.org/forums/index.php?threads/real-meaning-of-brn-in-caps.475010/

 

[SPXER]

Might read this thread:
https://audiokarma.org/forums/index.php?threads/real-meaning-of-brn-in-caps.475010/

Some are labeled E.C. Some are labeled E.C. (BRN)

 

[mandrix]

I would think, though I'm not the expert here, a modern high quality EC would be fine. Caps have improved a lot over the decades.
Don't think I would let the BRN designation slow me up. JMHO.

 

[SPXER]

Too late anyway. The caps are in. Not doing well though. One channel out. One weak. I should have left it alone.

 

[DuncanS]

C12= 1uf 50v (BRN), C24= 3.3uf 50v (BRN), C40= 3.3uf 50v (BRN), C52= 3.3uf 50v (BRN)
Not 10's of uf. What does the (BRN) indicate?

The low frequency response is set by the capacitance & impedance seen, so its a Low Pass filter, probably -3dB at 5Hz-10Hz, so the impedances seen by the capacitor are lower than I guessed.

I wonder if BRN indicates the construction & electrolyte used in the capacitor. Either way I'd ignore it.

 

[par4ken]

C12= 1uf 50v (BRN), C24= 3.3uf 50v (BRN), C40= 3.3uf 50v (BRN), C52= 3.3uf 50v (BRN)
Not 10's of uf. What does the (BRN) indicate?

I would swap out the low values 1µF and 3.3µF with small WIMA capacitors which are readily available. Search eBay for the best deals. As others' have stated Sansui often uses special electrolytics in the signal path. Why is open for speculation. They might be bipolar. I would like to think that they recognised the sound of capacitors choosing their coupling capacitors accordingly but I doubt it.

Might it be possible that an electrolytic that you replaced is in the circuit backwards?

 

[DuncanS]

I would swap out the low values 1µF and 3.3µF with small WIMA capacitors which are readily available. Search eBay for the best deals. As others' have stated Sansui often uses special electrolytics in the signal path. Why is open for speculation. They might be bipolar. I would like to think that they recognised the sound of capacitors choosing their coupling capacitors accordingly but I doubt it.

Might it be possible that an electrolytic that you replaced is in the circuit backwards?

WIMA capacitors are a good choice, I have used them a lot in filter designs.

 

[SPXER]

Might it be possible that an electrolytic that you replaced is in the circuit backwards?

Surely you jest! Anything is possible, or probable even. Those four tone circuits are illegally gerrymandered. Not nicely laid out like the driver boards at all.

 

[mandrix]

If you find a electrolytic cap is backwards, and the circuit has been powered up, the cap is likely toast, or soon will be and should be replaced.

 

[MidiMagic]

Yes C12, C24, C40 & C52 are in the signal path, they tend to be a high value capacitance to block the DC but let through the Low Frequencies, so 10's of uF.
What values are they? I'm not sure its worth swapping them again.

I wouldn't touch C20, C28, C32, C36, C44 etc.

C12, C24, C40, and C52 are coupling capacitors between stages. They are intended to pass all audio frequencies. Their values depend on the resistances in the circuit so they pass all audio signals.

C20 and C44 are feedback connections for the amplifiers. Very small values here prevent RF amplification.

C28, C32, and C36 are parts of the tuned circuits in the tone controls. Their exact values are critical.

C16 and C48 are AC bypass capacitors around resistors that set the DC bias of the transistor. They keep those resistors from reducing the AC signal.

C16 and C48 are typically electrolytic capacitors.
C12, C24, C40, and C52 are usually not electrolytics unless their values are large enough to preclude other types.

 

[SPXER]

Why Wima brand film caps? Why not Kemet films, or any other brand?
What does automotive grade mean vs general use?