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Sansui QRX-8001 filter caps?

KeithD

KeithD

AK Subscriber
Subscriber
Thinking about replacing the filter caps on my QRX-8001. I'm not having any issues with the caps or the receiver. Just heading toward finishing restoring this great receiver. So I suppose the first question is, if one is having no issues, should the filter caps be replaced? I guess I've seen opinions on both sides of this question.

There are two filter caps: 15,000µF/50V, 2 inches (51mm) diameter by 3 inches (76.2mm) tall. Looking at replacements, I am leaning toward Nichicon LKG. The only values that are near that and would fit inside the case are the Type II Gold Tune. Choices are 15,000µF/50V (40x80mm) or 22,000µF/50V (50x80mm). Any issues with going with the 22,000µF caps here? I'm wondering if the inrush current can have an affect on the power switch/premature ageing?
 
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KeithD said:
Thinking about replacing the filter caps on my QRX-8001. I'm not having any issues with the caps or the receiver. Just heading toward finishing restoring this great receiver. So I suppose the first question is, if one is having no issues, should the filter caps be replaced? I guess I've seen opinions on both sides of this question.

There are two filter caps: 15,000µF/50V, 2 inches (51mm) diameter by 3 inches (76.2mm) tall. Looking at replacements, I am leaning toward Nichicon LKG. The only values that are near that and would fit inside the case are the Type II Gold Tune. Choices are 15,000µF/50V (40x80mm) or 22,000µF/50V (50x80mm). Any issues with going with the 22,000µF caps here? I'm wondering if the inrush current can have an affect on the power switch/premature ageing?
Click to expand...
I can't remember, does the 8001/9001 have a soft start circuit? 22KµF is getting big, the inrush will shorten the life of the power switch......But then again 15KµF is not exactly small either so maybe the switch is good to go?
 
I think I'll go with the 15,000µF ones to be on the safe side. They are 40 mm vs. the 51 mm originals, but that's easy to accommodate.

Don't know if there is a soft start circuit. I know they have several relays inside, but I think the two on the quad board are just to isolate it.

Will look at getting a new safety capacitor. Should do that for every referb, but it's easy to forget.
 
KeithD said:
Assume this is to replace C708, which is listed as 0.0047µF on the schematic. The replacement you suggest is 0.1µF. Is that a good value to replace the 0.0047µF original?
Click to expand...
I don’t have the schematics but the safety cap , should be installed across the power switch. The exact value is not critical, a value between 0.022uF-0.1uf should be fine .
The one I suggested is a bit more expensive but it’s the best you can use to protect the switch if you don’t want to install triac or soft start , any XY-rated type, should be fine too.
 
KeithD said:
Assume this is to replace C708, which is listed as 0.0047µF on the schematic. The replacement you suggest is 0.1µF. Is that a good value to replace the 0.0047µF original?
Click to expand...
My schematic shows it as 0.033 across the switch. A 0.047 will do just fine as a spark quencher.
 
Skywatcher said:
My schematic shows it as 0.033 across the switch. A 0.047 will do just fine as a spark quencher.
Click to expand...
That is C707, and is indeed across the switch on the "UL" diagram shown as an inset on the schematic:

Screen Shot 2025-03-31 at 7.58.23 AM.png

The "regular" part of the schematic only shows C708 with nothing across the switch:

Screen Shot 2025-03-31 at 7.58.57 AM.png

Since mine is a North American model, I assume the "UL" schematic is correct? Is the other schematic drawing for JDM?
 
KeithD said:
That is C707, and is indeed across the switch on the "UL" diagram shown as an inset on the schematic:

View attachment 3469096

The "regular" part of the schematic only shows C708 with nothing across the switch:

View attachment 3469097

Since mine is a North American model, I assume the "UL" schematic is correct? Is the other schematic drawing for JDM?
Click to expand...
UL is the correct schematic. :thumbsup: C708 is 0.0047 and is likely fine, but you could change it if you like for peace of mind. It seems to only (really) come into play when something is plugged into the outlets.
 
Sui-Yogi said:
I don’t have the schematics but the safety cap , should be installed across the power switch. The exact value is not critical, a value between 0.022uF-0.1uf should be fine .
The one I suggested is a bit more expensive but it’s the best you can use to protect the switch if you don’t want to install triac or soft start , any XY-rated type, should be fine too.
Click to expand...
Not as familiar with installing a "soft start", though I remember them being mentioned in other threads. Is there a good thread that describes this/what parts you need/how to install one?

I am a bit paranoid about the power switch on these larger units since the one on my AU-9900 stopped working about a year ago. Not a huge issue since it is a double sided switch and I was able to just move the connections to the other side, but would prefer to no have to do that again.
 
KeithD said:
Not as familiar with installing a "soft start", though I remember them being mentioned in other threads. Is there a good thread that describes this/what parts you need/how to install one?

I am a bit paranoid about the power switch on these larger units since the one on my AU-9900 stopped working about a year ago. Not a huge issue since it is a double sided switch and I was able to just move the connections to the other side, but would prefer to no have to do that again.
Click to expand...
The power switch on my QRX-9001 had the 2 sets of points jumped over from the factory. They handle twice the load that way and last for decades. I always jump the points when available so a switch lasts much longer. If your 80001 has dual points, and is not jumped over, I suggest you do it. But likely it already is for the size of the main filter caps.
 
KeithD said:
Not as familiar with installing a "soft start", though I remember them being mentioned in other threads. Is there a good thread that describes this/what parts you need/how to install one?
Click to expand...
The Triac is the only installation that will eliminate the inrush current completely but the problem is that if the Triac fails and as a device potentially can , the amp will tern on “permanently” until you fix it … not good if you are on vacations ;)
The soft start will reduce the inrush current but it will not eliminate it . The engineer suggestion for soft start instillation has to do with the size (VA) of the transformer and its suggested to be installed if the unit carry’s 500VA trofo and above , so it’s not the size of the capacitors that draw the current at the start up that can damage the switch……….
At least this is how I understand it.
I don’t have the schematics but Do you know the size of the trofo in the
QRX-9001 ? It might be ladled on the transformer ? I doubt with the power that outputs that it’s more than 300VA…

I have installed one , made by Hipocrates on my AU-D907Limited as the original transformer was 330VA and I installed a 500VA due to available space .
I can forwarded you the gerbers if you like and BOM , it’s not a big deal , other than you need to calculate the dropping resistor for the relay to engage, somewhere between 18V to 22V drop voltage will be fine.

I cannot find the thread that Hipocrates shows it , mind that the suggested relay in that thread is a wrong part , you will need a non-latching .
Here is a video from Tony too:

And here is where I found a little space to install one in the AU-D907limited (AU-919) , do you think you have that amount of space in the QRX?

IMG_5427.jpeg

Edit : Video is not available, search on YouTube: “Adding a soft start to a power supply “
 
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Thanks for all those insights @Sui-Yogi . Makes me wonder if plugging the receiver/audio equipment into a power strip with a switch is a much simpler and cheaper alternative for powering a high watt receiver on/off? Then, the switch in the power strip takes stress rather than the switch on the unit. :dunno:
 
KeithD said:
Thanks for all those insights @Sui-Yogi . Makes me wonder if plugging the receiver/audio equipment into a power strip with a switch is a much simpler and cheaper alternative for powering a high watt receiver on/off? Then, the switch in the power strip takes stress rather than the switch on the unit. :dunno:
Click to expand...
So you will control the on/off from the socket and the switch on the receiver will be permanently “on” ?
That’s a solution but you can do that if eventually the switch die ? and my only concern would have been if the switch is permanently “on” maybe the contacts stick to each other? Then maybe every now and then switch on/off the switch with no power ?…..:dunno:
 
By the way @KeithD i don’t think that your switch will die any time soon (at least in our life time ) nor if you increase the capacitance of the big filter cap (reasonably) . You are overstressed and it’s understood.
Do your thing and enjoy the best quadraphonic ever made !!!!
 
Sui-Yogi said:
The Triac is the only installation that will eliminate the inrush current completely but the problem is that if the Triac fails and as a device potentially can , the amp will tern on “permanently” until you fix it … not good if you are on vacations ;)
The soft start will reduce the inrush current but it will not eliminate it . The engineer suggestion for soft start instillation has to do with the size (VA) of the transformer and its suggested to be installed if the unit carry’s 500VA trofo and above , so it’s not the size of the capacitors that draw the current at the start up that can damage the switch……….
At least this is how I understand it.
I don’t have the schematics but Do you know the size of the trofo in the
QRX-9001 ? It might be ladled on the transformer ? I doubt with the power that outputs that it’s more than 300VA…

I have installed one , made by Hipocrates on my AU-D907Limited as the original transformer was 330VA and I installed a 500VA due to available space .
I can forwarded you the gerbers if you like and BOM , it’s not a big deal , other than you need to calculate the dropping resistor for the relay to engage, somewhere between 18V to 22V drop voltage will be fine.

I cannot find the thread that Hipocrates shows it , mind that the suggested relay in that thread is a wrong part , you will need a non-latching .
Here is a video from Tony too:

And here is where I found a little space to install one in the AU-D907limited (AU-919) , do you think you have that amount of space in the QRX?

View attachment 3469237

Edit : Video is not available, search on YouTube: “Adding a soft start to a power supply “
Click to expand...
The inrush current comes from the main filter caps charging up no matter what transformer you have. That charging many times actually exceeds the fuse rating, but only for a split second. Once the caps charge to a certain level, the current drops off dramatically. Time is on your side when talking fractions of a second. Soft start circuits route the AC through a resistor to lessen the blow, then the relay takes the resistor out of circuit in about a second or so. Using a triac is fine if you cannot find a replacement power switch. And as you say, if the triac shorts, you're stuck on.
These switches in the 8001/9001 rock the points when you flip the lever. It would be extremely rare for the points to stick on.
With the power off you can check the resistance in the power switch points to be sure. Little to no resistance and the switch is fine.
 
Skywatcher said:
The inrush current comes from the main filter caps charging up no matter what transformer you have.
Click to expand...
Dear Skywatcher with all do respect the inrush current at the switch is related to the size of the transformer core for a split of the second when it’s energised .
This current is caused by the sudden change in magnetic flux in the transformer's core.
Yes , if increase the capacitance of the filter caps by 100% that might add up to the problem but it’s minimal versus the proportional current flowing through the primary winding of the transformer.
I’m not an expert , by far …. but I have build quite a few transformers and the particular issue was always my concern and it seems that has nothing to do with the size of the capacitors rather the charge of the transformer at start up .
Again , no argument here , just maybe something worth investigating….i might as well be wrong here…..
 
I think skywatcher is correct. I burned out the power switch on my AU-999 after upgrading the filter caps to 2x 12,000 uF, it was the increased inrush current at poweron

the amp works great otherwise
 
KeithD said:
Thanks for all those insights @Sui-Yogi . Makes me wonder if plugging the receiver/audio equipment into a power strip with a switch is a much simpler and cheaper alternative for powering a high watt receiver on/off? Then, the switch in the power strip takes stress rather than the switch on the unit. :dunno:
Click to expand...

I have been wondering about this too. What are the advantages to using the amp's power switch? Other than a soft start circuit, if it exists in the amp.

Most old amps don't have that...so what's wrong with bypassing the amp power switch & just using an external powerbar?

With the above mentioned 999 & tuner I've just been running on a powerbar until I get time to install the new higher rated omron switch.

A powerbar has the advantage of killing power to all your devices, so if you go away or aren't at home nothing is "live" into the wall in case of surges or triac failure etc

( I first started doing this with my Fisher 400 to prolong it's internal power switch, those often fail )
 
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