What are my options for this restored SX-880?

[hillaryj]

Greeting all. I haven't been on this forum for ages.

I had my SX-880 fully restored in June of 2017. Now I find out it cuts out at half volume. I took a video:

What should I do? Any help is greatly appreciated. THANK YOU IN ADVANCE!

Full story below:

Not sure if I should name the shop or not, but I think of them as high quality. I was on quite a waiting list and paid good money to have this thing fully reworked. Not trying to throw any blame at them - I want folks here to know that it was a quality job (I think).

After restoration, I played it at home for several months at low volumes in my home. My main speakers were not ready yet and I just played everything through some old bookshelf Jensen speakers that I had. Honestly, I never even had this thing up to half volume on those speakers. I don't think they could handle it. Mostly vinyl and a little FM play. All sounded fine. No cutting out.

Then I moved all the components to an office that I was planning on using. The receiver sat there unused for about 5 or 6 months.

This past weekend, I finally finished refoaming my main speakers (AR58bs) and got motivated to hook everything up in my garage. Put on some vinyl and got things cranking. All sounded good, but then the receiver clicked off at just under half volume. It clicked back on in a few seconds and I figured it was some kind of protection circuit or something. The more I thought about it, the more it bothered me. I paid for this full restoration and I want a receiver that can crank to its full potential! Am I doing something wrong?

I called the shop today to ask about it and they said that I have to "bring it in". Not really much help. The one person I talked to (not a tech) did mention that if it sits unused for a while it will "not charge the capacitors". Well... I don't really know about that, but I'd be surprised if the issue is that these things can't go more than a few months without being played. I live an hour away from this shop, so if I can get a head start on things here on AK, I will. Maybe even a full solution because I'm doing something dumb?!

 

[Watthour]

What is the rated impedance of the speakers? What is the measure DC resistance of the speakers?

 

[Skylab]

The AR58bs are 4-ohm nominal speakers whose impedance curve dips below 4 ohms quite a bit. The SX-880 at 60 wpc into 8 ohms probably just isn’t up to the task of playing it as loudly as you were there. The protection circuit is doing what it is supposed to do - keep the amp from blowing up and taking the speakers out with it.

 

[petehall347]

you could try 8 ohm speakers if you have any . or wire the 4 ohm ones in series and test one channel at a time .

 

[hillaryj]

Extremely helpful - thank you all very much. Will I damage anything by playing these speakers at lower volumes, so as to avoid the cutout?

 

[petehall347]

should be fine so long as its not something else . even so how long is this piece of string ?

 

[Skylab]

I would still measure the resistance across each of the speakers’ terminals just to see that they measure 4 ohms or so, as suggested above, assuming you have a multimeter. But since it doesn’t cut out until you crank it, it’s likely fine to play them at lower levels.

 

[petehall347]

I would still measure the resistance across each of the speakers’ terminals just to see that they measure 4 ohms or so, as suggested above.

good idea .

 

[hillaryj]

just curious... why should I measure the resistance? What will that reveal / help me avoid?

 

[petehall347]

Not being stubborn, just curious... why?

if you are referring to the speaker ohms it is because 4 ohm speakers present more like a dead short than 8 ohm speakers do . the amplifier doesn't like this and works accordingly .

 

[petehall347]

being technical q33 q34 in the protect circuit appear to detect over-current caused by too low ohms speakers or other problems . .. this in my opinion is a nice feature to have . it looks like nothing was harmed . and all is working as expected .

 

[hillaryj]

if you are referring to the speaker ohms it is because 4 ohm speakers present more like a dead short than 8 ohm speakers do . the amplifier doesn't like this and works accordingly .

Sorry, I revised my comment. I was asking why I should measure the resistance.

 

[quiet]

I had a SX880 do this with ar3a speakers a very long time ago. If I remember correctly this is how it went down.
The protection circuit used a relay. The relay sensitivity was adjusted with a resister next to the relay. I selected a resister to show the relay circuit what it wanted to work with according to the book.

 

[Skylab]

Forgive me if you already know this, but using a multimeter to measure the resistance will be a basic measure of the impedance of the speaker, in ohms.

Of course the impedance of a speaker is more complicated than you can measure in that way because it’s a curve that varies by frequency. But it’s a something.

Then again, the published spec of the AR58 is 4 ohms, so unless the speaker has an internal problem, that’s likely what you will find. So just playing the less loudly, assuming this doesn’t still trip the protection, should be totally fine.

 

[hillaryj]

Forgive me if you already know this, but using a multimeter to measure the resistance will be a basic measure of the impedance of the speaker, in ohms.

Of course the impedance of a speaker is more complicated than you can measure in that way because it’s a curve that varies by frequency. But it’s a something.

Then again, the published spec of the AR58 is 4 ohms, so unless the speaker has an internal problem, that’s likely what you will find. So just playing the less loudly, assuming this doesn’t still trip the protection, should be totally fine.

Just want to acknowledge how helpful this has all been. I will measure them and hope to find 4ohms (indicating nothing wrong). I would rather be running some nice 8ohm speakers but these are the best I have for now, so I'll stick with these.

 

[LesE]

I noticed in your vid that the Loudness is engaged. While the loudness compensation is reduced as volume is turned up, there may still be a little bass boost present so you may want to try turning it off when listening at higher levels. Also when listening to phono, try engaging the Low Filter to prevent any subsonic content from reaching the amp.

Les.

 

[EastPoint]

This is a known issue. There’s a thread about it on this forum. You have to replace a cap in the protect circuit. You may want to change the value of the big cement resistor attached to the heat sink, but I had bad luck with that part.

 

[hillaryj]

I noticed in your vid that the Loudness is engaged. While the loudness compensation is reduced as volume is turned up, there may still be a little bass boost present so you may want to try turning it off when listening at higher levels. Also when listening to phono, try engaging the Low Filter to prevent any subsonic content from reaching the amp.

Les.

Les,

Thanks for your comment. I did play around with the "loudness" a bit before taking the video. With the loudness turned off and the bass and treble set at halfway, I can definitely go higher before things cut out. I didn't like the sound much, though. Seemed much too bright.

As far as turning on the "low filter" during Phono listening - I will give that a try, thank you!

 

[hillaryj]

This is a known issue. There’s a thread about it on this forum. You have to replace a cap in the protect circuit. You may want to change the value of the big cement resistor attached to the heat sink, but I had bad luck with that part.

Thanks EastPoint,

Not sure I want to do that if everything is working as it should to protect my receiver. If I manually override these safety settings, wouldn't I be asking for trouble?

 

[quiet]

No it doesn't work that way. The caps and or resistors are used to adjust the protection circuit to spec. The values can change over time, as mine did, and the circuit can become to reactive.