CV 1460 dead right channel

Hi E.N.S

We do call us by the name, usually....

The schematic does only show the left channel. F2 relates to F1 . R96-R94 should be R95-R93 in schematic I guess. You have to "transcribe".

Grüße Klaus

Hi Elim !

Essentially: even numbers are right channel, odd numbers left.

Diagram only shows odd numbers ...

But the F1 / F2 are "only" speaker fuses. So if it hits *them* you have a low resistance / over-current condition on the speaker end rather than on the amp itself. Unfortunately the 1460 neither has a speaker relais nor any security circuit that shuts off the speakers at least in the case of an amplifier malfunction. And the "speaker switches" are after my taste ridiculously under-rated. They use to cause a lot trouble contact wise.

First of all I would check the speaker wiring for shorts or "bits sticking out" and -maybe- switch speakers left to right.

If the F1 fuse blows after that your speaker connected to the left channel is toasted and causes overcurrent to the amp.

Hi Elim !

Zitat von E.N.S.

Could it be one of the components located on ETC 3 or 7 before F1 or F2 ?

Weeeell ...

... there is a vage chance that the problem *might* be amplifier-induced. Given it is in a DC-imbalance and a DC-current runs over one of the final transistors through the speaker. And given the imbalance has a pretty high value - that *might* trigger the fuse on short and strong impulses.

But a) that would most likely cause audible "error" on the low frequences, because it pulls (or pushes) the speaker membrane of the woofer and b) it should be visible on the speaker itself. By turning the amp on the woofer membrane moves inwards or outwards *and stays there*. It does not re-center - as usual.

You might test the DC-offset with a digital multimeter in DCV. Just turn volume to Zero, switch the amp to an unused input (or one currently not driven), turn on Pair SP-1 and connect the black meter lead with "-" and the red one with "+" on the right channel. With decreasing the meter range to -say- 200mV you should read almost Zero (+ / - a few millivolts) from it. That would be a normal condition.

Everything over that is a DC-offset and if it reaches 1V or more it is critical already. Unfortunately the 1460 has no preset to trim the DC-balance. It relies on a group of zener-diodes and constant current sources within the front-end of the final amplifier.

There is a set of trimmers VR5 and 6 to set the quiescent current and another one VR7 and 8 to set the VU-Meter reading ... but none for the DC-balance.

On the other hand:

What speakers are you using ?

On generic multiways speakers there is often a pretty large bypass capacitor across the woofer. Some in the range of 60µF or even larger. They reside behind the Low Filter coil and parallel to the woofer voice coil. If *that* capacitor is going to die it may develope an internally short. In that case the woofer coil is bypassed and a direct connection over the Low Filter coil occures, which surely exceeds the normal current flow from the amplifier due to a way lower electrical resistance.

Depending on what you use for your home theater amp that might be a bit more tolerant -or- simply deliver a higher output current without blowing a fuse or triggering a safety circuit. Particularly Class D or T digital amplifiers can deliver quite a bit of current in excess of 10 to 15 Amps for short bursts without damage.

Finally: due to the somewhat weird wiring of the speaker switches which connect the speaker pairs in series rather than in parallel to avoid total impedances below 4 Ohm (to which the amp is not stable and capable to drive) there are both - Speaker Minus and Speaker Plus - represented in the switches. If there is some conductive crud in them from the very fragile and less-rugged contacts that might lead to a local occasional short in the speaker switch as well. Something to test very awfully and complicated.

Hi Elim !

I'm Peter ("The Black Peter") - but if you are using the mobile version of the forum you might not see the footer under my answers:

Peter aus dem Lipperland

Solo mio, vendro unscrupuloso, custombres sansaclu.

Zitat von E.N.S.

To get it right, have I to measure at the RCA's input on the amp, or at the speakers' connections on the amp ?

For measuring the amplifiers DC-Balance you need to test at the speaker outputs. Black lead into "-", red lead into "+" on the right channel.

Volume to Zero, appropriate Speaker-Pair selected (SP-1 most likely, SP-2 set to Off), starting meter in DCV (Dc-Volts) at highest range and successively switching it to lower ranges down to 200mV. Some offer even 20mV. In either case the displayed value should not exceed a few millivolts. That's normal and within specs.

Zitat von E.N.S.

My speakers are Focal-Jmlab Chorus 726S, 8ohms and 150 W max power.

Well ... not the worst choice I'd say. I think they came out in ... 2003 ? 2004 ? Around that.

A potential malfunction depends on the age of the speakers. If they are newer than 10 years they are lesser suspectible.

Older ones ... who knows.

Hi Elim !

Zitat von E.N.S.

(Indeed I couldn't see your footer with my phone)

I'd guessed it.

Many people look at the pages with mobile devices and are surprised "where did they get to know their names from ..."

Zitat von E.N.S.

So for SP1 I'm reading on the

Right Channel :

@2000mV : 000

@200mV : starts at 00,3, not stable, it then slowly grew to 01,9 (I doubled checked after doing the left channel, then the number was 04,9)

Left Channel :

@2000mV : 031

@200mV : 32,5

I'm surprised by this HUGE difference (eventhough it's millivoltmeters)

Alles anzeigen

Well. I think the over-all difference isn't that important.

The confusing fact is the instability on the right channel. The minor DC-offset should settle after a while when components warmed up and generally stay there. The absolute value depends on the parts used: resistors, z-diodes, diodes, transistors and stabilizing capacitors. And as long as it is in the low millivolt range it does not harm at all.

This "rising from almost zero" to a few millivolts lefts me a bit suspicious.

Not that it *needs* to mean something, but that's the channel that blew a fuse for no obvious reason, so a wake mind and open eyes may help.

Zitat von E.N.S.

For the speakers, yes this production serie is kinda old, but mine was a bit more recent, I think the last owner bought it around 2012, the same age as the home theater amp I have.
I'm quite happy so far they fit both needs music and home theater use so far. I've switch to listening music to my AV receiver not the same music, not the same joy

Sure not.

AV-receivers use digital class-D or -T final amplifiers in most cases for room constraints, lower power losses and denser packing and higher efficiency. They have a lot of filtering and "sound effects" to make stupid TV programs at least sound after something if the content is lousy already. I have no TV. Don't need that sort of stuff.

And they are designed as multichannel amplifiers with lots and lots of computer gear inside. Programming them to an un-effected stereo two-channels only scheme might help a bit, but generally they tend to sound flat and uninspiring.

My old master said "Son - you only got two ears. What do you need more than two speakers for ?"

The main reason Quadrophony failed. Apart from costs, complications, different standards ... and because it was an analog method to store the signals. And for musical purposes: the distraction-factor was higher than the audiophile gain on it. Been though that. Ack !

The only thing left is, that you swap left and right speaker.

The one currently on the right was attached when the fuse blew on the right channel.

If you swap them and the fuse blows next time on the *left* channel you know that the error must reside *outside* the amplifier.

If it blows the right channel fuse again then something is wrong with the amp.

Hi Elim !

Zitat von E.N.S.

I agree with you, no need for a lousy TV.

Rumours say that the next generation Smart-TVs runs on Bio-Gas.

Gained from the stinking crap they'll have to show ...

Zitat von E.N.S.

Now that I'm done recapping my TT I'll plug everything back and switch the speakers channels, I'll let you know !

So I hope it was maybe just a faulty fuse and some sort of non-repeating coincidence and everything works with no further problems.

Time will tell.

And the fuse ...

Hi Elim !

Zitat von E.N.S.

Do you believe in "bad fuses" and all ?

Just a short while ago I'd equipped a Dual CV120 with new fuses ... and one new out of the package was defective.

Sometimes it is not only the fuse - but the holder as well. Particularly those stupid sheetmetal holders tend to corrode and break.

Contact problems in between may cause trouble. Okay - the chance is low and on a speaker fuse even lower, since you should have noted "a drop out" in the signal due to bad contacts. But fuses with the "F" (Fast) release characteristics are a bit quirky anyway. And while the 1460 has no speaker relais and only a muting switch that works *on the input* of the final amplifier stage, a power-on "Blob" could have killed that fuse already. Been there - seen that.

We will see.

Hi Elim !

I'm glad I'd sharpened your sensitivity to "the case" so that error didn't come away unrecognized ...

Zitat von E.N.S.

So I guess I'm down to check the Filter, there's 3 capacitors in it : one 15UF, one 75 uF, and one 170uF. Should I try those ?

Well ... here we are skating on thin ice.

Given the speaker chassis themselves are undamaged and don't have internal faults like burned / deformed / partially loose voice-coils I would suspect the caps for the mishaviour. Testing the chassis is a bit difficult to do. But if you a) measure the speakers DC resistance and b) move the woofer membranes slowly and carefully by hand and *do not* feel any unusual scraping or scratching they should be okay. Testing mids and tweeters without a soundgenerator and a scope is practically impossible.

(You need to curve in the dynamic resistance of the coil towards a load resistor against the soundgenerator signal. A defective coil does not respond accordingly and does not create a counter-current while moving. That for the protocol.)

Some points: these filter capacitors are usually bipolar. Means because they are built for AC-operation they don't have plus and minus like polarized capacitors in power supplies etc. Secondly they are *a tad* more expensive. And - yes - for a unique structure and identical sound on both speakers you will have to replace them on both speakers.

And the need may occur to parallel wire in two capacitors for one since the matching values might be unavailable. And at least the 170µF is one fat piece of a capacitor in that position.

You could waste a lot money on them if you buy "handpicked, made by virgins at a full moon night" and made from "stuff outside our physical understanding" (= HiFi-Voodoo-Caps). Don't use them. Look at the voltage ratings first. I would guess since the speakers are rated for 150W peak they might be 50V types. "Modern" ones are rated 63 or 75 or even 100V - you are not using these *unless* they are not much more expensive than the 50V-types and if 50V's are available. Since at least the smaller two are likely to be the mid- and treble-filter caps you should get caps values as close as possible, because the capacity affects the crossover frequencies.

I don't know where you would buy that sort of stuff in Paris. I would bet there are shops that sell DJ- and Musicians stuff for selfmade speakers. A shop like that would be the proper adress.

Need more input ?

Hi Elim !

Zitat von E.N.S.

How can I measure this ?

Zitat von E.N.S.

Update : I took some measures this afternoon I've found : 6,9 ohms for the upper speaker, 8,8 ohms for both the middle and lower one. I haven't measure the tweeter as it appears to be working...

The assumption on the tweeter should be okay.

However: I forgot to note the fact that the chassis need to be disconnected from the crossover for measuring.

The values nontheless are plausible, since the upper is midrange and the lower ones lowrange. Wonder how the whole system is wired on the crossover to gain 8 Ohms nominal impedance with two 8 Ohms woofer chassis. The data sheet mentiones that the lowest impedance is 2.9 Ohms. Which points in the direction that the woofers are coupled in parallel with a large filter coil and appropriate resistance.

https://www.focal.com/sites/ww…6-specification_sheet.pdf

Zitat von E.N.S.

I do not hear any of those noises, *fingers crossed*

Good sign.

Zitat von E.N.S.

I do have those, but no dummy load 8ohms if that's what you meant in the following sentence by "the load resistor".

No, not of that kind.

The usual way is to wire the "chassis to test" in series with a large ceramic resistor (no wire-wound !) of same or larger resistance.

You feed a sound generator signal to both and use the scope over the resistor. The resistor has a low impedance and largely only ohms-resistance. The resonating coil has a ohms-resistance (the length of wire) but also an inductive resistance (the coil form). When moving it creates a counter-electromotoric power, particularly around the chassis mechanical resonance point. You can read the resulting peaks of a proper moving coil along the resistor then. With only measuring the chassis the low output impedance of the signal generator surpresses the inductive countering peaks most likely so you need a "ballast resistor" or load resistor for that purpose.

By touching the membrane you could also test whether this value changes along with the mechanical swing (or with dampening it respectively). A defective coil creates peaks through induction as well, but that a) does not result much in sound output or b) are pretty much unaffected if you mechanically dampen the membrane.

Zitat von E.N.S.

Yes there's one shop which sells only speakers and related items

You should talk with them first before ordering "something" on the internet.

A) it is a local business, which needs support and B) they might have the stuff right from off the shelve.