Help DC offset on Yamaha rs202d normal or not

[Stuart83]

I decided to meter the terminals on the Yamaha after blowing a pair of mission mx3s on all four drivers.
The law of averages has me suspicious as for all four to go at the same time is abnormal although I suppose not impossible.

The usual paranoia ensued as usual and the late night OCD head scratching commenced.
I decided to measure the DC offset expecting around 20mv as usual but found a uniform 40mv across all the speaker terminals.
(I've heard more DC offset is found with class a/b amps)

It's late and I've just popped the lid back on after finding it's a non adjustable amp whilst fishing the speaker terminal spring out from inside the amp that I'd pushed in with the multi meter probe 🤬

I know that up to 50mv is usually deemed acceptable and that the higher quality amps are much lower.
I tested my 30 plus yr old pioneer a400 and got only 4.2mv left channel and 2.5mv right.

That caused me to track down the service manual for the Yamaha RS202d and from what I can make out 27-136mv is normal but it's not exactly clear.

I find it on the high side which has me questioning things.

I have attached a picture of the service manual and would really appreciate your insight.
Am I reading it correctly?
It's late and it's possible I'm reading it wrong.

Is 40mv considered ok on such an amp.

As some of you know the Yamaha is within my second set up with the pioneer a400 via an amp/speaker switching box but after purchasing the new speakers (fayne audio) for my primary hifi as mentioned on another post I'm planning on moving the QA 3050i they've replaced into this system thus replacing the blown mission mx3s.

I'm now pondering even though my common sense dictates otherwise that 40mv DC offset could of contributed to the earlier failure of the said mission mx3s.

Anyway please see the attached screenshot, any advice would be helpful.

Attachments​

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[nopiano]

Relative to the power handling of the speakers, even a slightly high DC offset shouldn’t make them expire. And the crossover will offer some protection.

However, if this measurement points to other anomalies then those might be the cause.

I recall you’re a fan of very high volumes? Many modern digital recordings can carry very low and high frequency content at significant levels, and these will potentially cause clipping which is surely a more likely cause?

 

[Stuart83]

I realise that the high pass filter will eliminate some of the DC offset but 40mv is higher than I'm used to seeing.

I know it can be a cause if early failure due to overheating of the voice coils but usually only over 100mv offset is pointed to for this to happen.

The missions 150w were twinned with a 100w Yamaha to avoid clipping yet as I showed on another thread they indeed had bubbling of the inner throat of the voice coil and scratching due to heat malformation thus causing an ill fitted throw of the speaker.

The speakers were second hand and a 2016 build but I checked them and they ran perfect with the pioneer a400 at higher volumes and in turn the Yamaha.

I realise they could of been nearing their end being 8yrs old and I turn may of been sold because the seller knew something I didn't but it seems suspect to me.
I've had mission speakers before although before China got hold of them as the missions in question were indeed stamped china inside the cabinet and on the drivers.

The 760i I had as a youngster only failed after 26yrs around the rubber ring which is what I usually see with a speaker failure and the 763i were going for even longer and didn't exactly fail.
They simply wore out and were outright abused at times.

I do indeed like the higher volumes that decent hifi brings but also know the limits of the gear at hand.

I back off of anything sounds suspect, but that's just it everything sounded great.
I often admired the little Yamaha for its musical sound for relative peanuts.

I quoted "the clash" as being the speakers failure point but maybe it's been an excessive DC offset (or Maybe not).

My experience dictates that im not certain on what the threshold really is with DC offset.
The amps I've tested through the years have always been around 4-20mv so I haven't had to pursue a problem this needing to learn more about it.

I've found various quotes saying a general rule is that 0-20mv is good, 20-40mv is the upper limit anything over needs addressing.

There's plenty on YouTube of course stating that anything over 40mv terminal and 100mv will destroy your house and kill the cat.

I never pretend to know anything I do not hence I though of asking you guys again 😀

Im not sure if the attached photo of the data sheet is indicating what's the usual DC offset specs or if it's indicating a formula for an existing DC error code calculation.

I only carry out rudimentary repairs on appliances myself in what I'm comfortable with so any help in finding out if this 40mv is normal with the Yamaha ra202d will help me avoid much research and further head scratching.

I've often course emailed Yamaha etc and await reply.

Until then I'm playing safe and not letting it near my QA's.
I will use the pioneer until I have answers.

 

[nopiano]

I agree with your thoughts. I can’t see how that offset in isolation can cause speaker failure.

 

[Stuart83]

Well I've had time to ring Yamaha and although they agree 40mv is high they won't give out the data.
They say it's Technician only information and I would have to pay despite the unit being under guarantee to find out wether it's within spec.

Of course the unit will be replaced if it's not it's a billed to me.
I've indicated clearly that a process of elimination can't be carried out without knowing if a fault exists and withholding such rudimentary information means I'm stuck in-between a rock and a hard place.

Not to know this spec means I can't rule out a fault in view of returning it or accepting its within spec therefore not faulty.

He rather cheekily commented that it's a cheap amp and basically what the masses purchase.
I'm not sure that qualifies as an excuse even to me.
He may as well of said "hey it's cheap crap don't worry"

After a long conversation he let go the revelation they don't have the information which negated the whole conversation on it being protected info" for Yamaha technicians only"

I have expensive kit and to me price shouldn't matter after a point and at 279 it's not exactly cheap crap.
The kicker is it sounds better than some amps I've had at over twice the price.

I'm somewhat dissillutioned with Yamaha now.

I realise something they didn't and that's there's a protection relay but it doesn't click in until way to high and way to late apparently.

All I do know is 40 plus mv is high and the 4 amps I have are all below 20mv one very old.

There's so much more to it after researching it of course but I dont care to mention.

I'm back to using one of my favourites instead the pioneer a400 which I'm replacing the selector dial on, which is within my knowledge to carry out fortunately.

I have thought of leaving it because the channel drift is only on the cd selection but once I know something isn't right my OCD makes it impossible to live with of course.
It's a horrid desiese people undermine by claiming they have it with personal preference being the chief reason the deem so.

It would of been nice to have the specs to find out as it's usually general information, why this secrecy I'm not sure it's daft to me.

Usually manafacturer s click in when a somewhat negative post is left on a forum it would be nice if they did on this one and plainly told me what the reading should be in view of 40mv being high.

 

[Gray]

I'm somewhat dissillutioned with Yamaha now.

Rightly so, I think.
You shouldn't have to pay to find out whether or not it meets their spec.

Maybe you just picked the wrong advisor, but I wouldn't settle for the response you've had so far.

 

[Stuart83]

Rightly so, I think.
You shouldn't have to pay to find out whether or not it meets their spec.

Maybe you just picked the wrong advisor, but I wouldn't settle for the response you've had so far.

Thanks "grey"
I did try live chat and got pretty much the same response.

After that I decided to chase down with much trouble the schematics and find out that way.

A very helpful gentleman on another forum also sent me the same schematic which was nice.
I'm using his in the attachment as his has the DC offset highlighted.
(I felt a little unfaithful going on another forum 😲🥺) as I only generally frequent here.

It seems the amp is actually lower than spec at 40mv offset so I may of caused clipping somehow despite a good partnering of speakers and amp power output.

I do use a smartphone (Google 6 pixel pro) on 100% volume then about 80 out of the 100 on the Yamaha on occasion which tbh isn't all that loud but maybe as "nopiano" mentioned I've put it into clipping.

The Yamaha rs202d is known for being underpowered despite being rated 100w per channel it needs it's neck rang to get anything respectable out of the thing.

It sounds good for relative peanuts that's why I had a bit of a love affair with it (we all love a bargain)

Maybe I will never get to the bottom of it as the speakers were second hand and although I checked them for damage maybe I missed something the seller knew I did not, or maybe I just toasted them.
(I've never completely toasted speakers before) even at louder volumes hence my suspicion.

As for Yamaha I'm very dissatisfied.
I know manufacturers seemingly chime in sometimes as if by magic on these posts in defense and thought (hoped) I'd of been given the specs that way.

Im astute enough to of recorded my conversation with Yamaha to avoid such blunders as I've seen on forums before with mistruths being told.

Anyway I'm not trusting enough to put my Q acoustics the fayne audio f502 mentioned on another thread are replacing within my main hifi with this Yamaha rs202d in my second setup.

I've decided to use my trusted pioneer a-400 at 25 plus yrs old instead with its just 4mv offset 🙂
and use an ifizen blue to bring it up to spec with Bluetooth.