Amplifier - wiring help required

[panovice]

Any pointers based on why the amp switches between being "loud" and then "dimmed" (without actually being completely off)?

When it drops out, it's not that you lose sound completely. It will be working well (i.e. sounding nice and loud and then the sound feels like it's dimmed. This can work in cycles, and sometimes it could be loud or quite for a while.

We've had the amp/mixer for about 5 years. I was looking at a 2 step process.

1 - split the cables and stop using bridged mode. If that fixes the issues, great.
2 - if that does not work, get a new mixer/amp (Yamaha EMX5 seems like a reasonable replacement?)

Thanks again all!

Currently the amp/mixer is dropping out occasionally and before we purchase a new one wanted to try this (as we wouldn't want to use bridge mode with any new amp purchased).

Are you sure that it's the mixer amp dropping out? It could be other kit. How frequent are the dropouts? Are they triggered by high signal levels? Can you, for example, pass low level audio consistently without problem, but turn the level up and it will drop out?

I'm not sure on the speaker specs (no labels on the casing).

That's a shame, as basic information like this is obviously helpful for diagnosis. How old are the speakers and the mixer amp?

In the absense of any other info, all this helps give a sense of where root causes could be.

[ef37a]

And, have you obtained a test meter yet?

Dave.

[panovice]

Not yet. Recommend a cheap one, and guidance on how I use it ?

And, have you obtained a test meter yet?

Dave.

[ef37a]

Not yet. Recommend a cheap one, and guidance on how I use it ?

And, have you obtained a test meter yet?

Dave.

https://www.amazon.co.uk/Mercury-600-10 ... 2796&psc=1

The above will I am sure be easily good enough for your immediate purposes. in fact it looked so good for the money I have ordered on as a spare!

As for instruction, they are one of those things it is almost impossible to guide you about without one. Hopefully it will come with a decent manual but testing speaker resistances is pretty simple.

Dave.

[Hugh Robjohns]

Not yet. Recommend a cheap one, and guidance on how I use it ?

For guidance, just type "How to use a multimeter" into your favourite search engine and you'll find lots of tutorial videos and articles. Much easier to do that than for us to try and give a fill general tutorial here — but if you have any specific application questions then please do ask.

With no details on the speaker specs we're all floundering in the dark, so if you can at least measure the speaker resistances that would be of some help in providing more appropriate guidance.

[Wonks]

You may find an auto-ranging multimeter easier to use if you aren't familiar with them. Something like this.

https://www.amazon.co.uk/gp/product/B075L7PQ3Y

Saves having to guess what range voltages and resistances are in.

For what you'll use it for, you don't need to spend anything more.

The sound dimming behaviour, rather than full cut-out could be down to the way any amp overload protection works. Hard to say as there's no mention of it in the manual.

One other possibility is if both the EQ IN and FBQ buttons are both activated. The first brings in the built-in 7-band graphic EQ, the second the automatic feedback detection and limiting circuit. The FBQ circuit can only be active if the graphic EQ is enabled. Again, the manual is less than clear about how this circuit operates, but if the LIM LED is illuminated on the main meter display, then there is something going on with the internal amp protection circuit to reduce the output and prevent feedback.

You may not be experiencing actual feedback, but the circuit might think it is, and so reduces the output. More sophisticated feedback prevention systems will notch out the offending frequency, but that requires a digital EQ system, whilst the PMP has an analogue one.

But it may be that an amplifier over-current situation triggers a similar process, and reduces, rather than cuts out the output if the over-current isn't too great. Maybe you could try and test the system and see if you can get the LIM LEDs to light up with a corresponding drop in output when lit?

Having read more of the manual, you definitely will want the amp mode switch set to 'MAIN L/MAIN R'. The 'MON 1/MONO ' selection uses amp output A to feed any monitors connected to it, with signals from the Mon 1 aux sends on the input channels, and output B from the main mix. So to get both outputs feeding the speakers with the left and right signals from the main mix (one speaker per output), you'll definitely need the 'MAIN L/MAIN R' setting.

[James Perrett]

https://www.amazon.co.uk/Mercury-600-10 ... 2796&psc=1

The above will I am sure be easily good enough for your immediate purposes. in fact it looked so good for the money I have ordered on as a spare!

That looks remarkably like one that I bought from CPC a couple of years ago. Good clear display and a nice loud buzzer for testing continuity. The CPC version has temperature measurement too.

https://cpc.farnell.com/duratool/d03144 ... dp/IN07522

However there are actually very few bad multimeters around. Even the cheap £3 meters from CPC work well and are surprisingly accurate. Their display is smaller and they don't always have a beeper to tell you if you have any continuity but they're still very usable.

The one area where you need to be careful is with high voltages. I probably wouldn't go prodding around valve amps or check the mains with these cheap meters.

[ef37a]

I have to sound a note of caution Wonks about auto-ranging DMMs they tend to get confused by inductive devices. Even my quite expensive Fluke just goes nuts if I try to measure mains transformer primaries and I have to short a couple of secondaries to stabilize it.

I don't know how that basic meter I suggested will fare but at least the OP might be spared that confusion. Soon as it comes I shall check it out for him.

Dave.

[Wonks]

I have to sound a note of caution Wonks about auto-ranging DMMs they tend to get confused by inductive devices. Even my quite expensive Fluke just goes nuts if I try to measure mains transformer primaries and I have to short a couple of secondaries to stabilize it.

I don't know how that basic meter I suggested will fare but at least the OP might be spared that confusion. Soon as it comes I shall check it out for him.

Dave.

I have that very auto-ranging multimeter. Just worked fine measuring the DCR on an old 10" Fane POP 15W.

..and a meatier 80W Laney 12" speaker.

[ef37a]

I have to sound a note of caution Wonks about auto-ranging DMMs they tend to get confused by inductive devices. Even my quite expensive Fluke just goes nuts if I try to measure mains transformer primaries and I have to short a couple of secondaries to stabilize it.

I don't know how that basic meter I suggested will fare but at least the OP might be spared that confusion. Soon as it comes I shall check it out for him.

Dave.

I have that very auto-ranging multimeter. Just worked fine measuring the DCR on an old 10" Fane POP 15W.

..and a meatier 80W Laney 12" speaker.

Ah, SHOULD have said HIGH inductance devices. If the OP's speakers are indeed 100V jobs that could be a problem.

Dave.

[Wonks]

Keep up, Dave. The OP’s already said the speaker cables run direct to the speakers from the back of the mixer, no interposing transformer. So no 100v/70v line system.

[ef37a]

Keep up, Dave. The OP’s already said the speaker cables run direct to the speakers from the back of the mixer, no interposing transformer. So no 100v/70v line system.

I have installed SHEDS of speakers in factories where the transformers were INSIDE the cabinets. Have you not worked on many 100V line systems?

Think INSIDE the box a bit Wonks!

Dave.

[Wonks]

It’s a standard powered mixer with speakon outputs. Yes, at the speakers you often have transformers inside 100v line speakers, but you need something at the amp to get your standard power amp output up to 100v. There is nothing, ergo it’s not a 100v system.

[Hugh Robjohns]

This is getting silly now because the OP is probably drowning in all the tangents and suppositions, when all he wanted was confirmation that it wouldn't be disastrous to rewire his speakers....

As was pointed out earlier, it is possible to drive nominal 100V speaker systems directly from a bridged amp since the full voltage swing is likely to be 70V or more. Not ideal, certainly, but possible.

I would suggest, though, that the OP tries to gather more information about his speakers if possible, and measuring the DC resistance would be a big step forward.

Failing that, rewiring as proposed and setting the amp to normal stereo main L/R output (not mono or Bridge modes) is unlikely to break anything and may solve the dropout issues very simply.

[ef37a]

The Mercury DMM turned up an hour ago. It is a bit of a rip of my Fluke 83 but of course nowhere near its performance.

OK though, the display is twice the height of my Fluke at 25mm and nice and clear and bright. It comes with a decent instruction booklet and a quick check showed it to be within a digit of the Fluke measuring a few random Rs and transformers.

I personally find the Blue on Black legends for R and C very hard to read but younger eyes will no doubt cope. I simply could not hear the cont'y buzzer with naked ears and barely with my aid in!

But, I am sure it will do.

Dave.

[panovice]

Sorry not checked in for a while - don't get an email on replies, although notifications turned on?

Anyway, managed to get hold of the original installers!

They tell me the speakers are 8 ohm and High Bandwidth Module. Won't tell me the wattage ("does not apply to HBM speakers"?). He tells me they are Bose branded but not sure if he's being truthful tbh

Anyway, the speakers are connected to one output and NOT in bridge mode. I was wrong here, sorry. I think it's because they wanted to reduce the power to the speakers as they might blow (amp too powerful 800w per channel)?

But based on 2 speakers connected in parrel, will the amp only be delivering 4 ohms?

[Wonks]

Yes 4 ohms. More power as a result but shared across two speakers, so they get pretty much the same power as if powered from a channel each. But the sound quality would probably be very slightly better with each channel feeding 8 ohms.

[Wonks]

A search for ‘high bandwidth module’ with or without ‘Bose’ turns up nothing, so I’m mystified.

[Hugh Robjohns]

They tell me the speakers are 8 ohm and High Bandwidth Module. Won't tell me the wattage ("does not apply to HBM speakers"?).

That sounds like first class BS to me.

[panovice]

According to ChatGPT

HBM (High-Bandwidth Module) speakers are a type of compact, high-performance speaker technology that uses a specialized driver design to produce exceptionally clear and accurate sound. These speakers typically feature a compact, lightweight design that allows them to be easily mounted in a variety of settings, including cars, boats, and home theater systems.

The HBM driver design uses a unique magnetic structure and voice coil to produce a powerful, high-quality sound with minimal distortion, even at high volumes. HBM speakers are also known for their high efficiency, which allows them to deliver a lot of sound with relatively little power.

HBM speakers are often used in high-end audio systems and are valued for their exceptional clarity and accuracy, as well as their ability to reproduce a wide range of frequencies. They are a popular choice among audiophiles, home theater enthusiasts, and anyone who wants to enjoy high-quality sound in a compact, convenient package.

A search for ‘high bandwidth module’ with or without ‘Bose’ turns up nothing, so I’m mystified.

[Wonks]

The Bose speakers that best match the description do have a transformer module inside with various wattage tappings, but can also be used with that bypassed, giving 8 ohms.

This is the 8" driver version

https://pro.bose.com/en_us/products/lou ... dm8s_black

As the PMP6000 is rated at 600W per channel into 4 ohms and 300W per channel into 8 ohms, there is no power handling benefit from going to one speaker per channel, though I'm sure the PMP6000 will drive an 8 ohm load a bit more comfortably without risk of the impedance dropping below 4 ohms at certain frequencies.

The 8" Bose DM8S listed above has a 150W power handling capacity. The 6" DM6SE version has a 125W power handling capacity.

So the 8" version is on the upper edge of typical power amp matching recommendations, whilst if the 6", then the speaker is a bit underrated if pushed hard.

The 5" speaker DM5SE model is only rated at 60W, so easy to overload with the PMP6000.

The speakers do have inbuilt overload protection- a "Resistor-network power reduction with automatic reset", whatever that is!

But the drop in output could be down to one speaker going into overload protection mode. I don't know if this will take the speaker connection out of circuit, or adds in a resistor to reduce the speaker load. If adding in a resistance, this could up the overall input impedance seen by the amp, and so it outputs less power, and hence the drop in volume.

Given the estimated speaker size of 8" wide by 12" high, if they are this model of speaker, then the DM5SE, at 7.5" x 11.2" would seem to be the closest match.
https://pro.bose.com/en_us/products/lou ... m5se_black

The DM6SE is 9.75" x 13.4", so a bit bigger but a possibility.

The DM8S is 9.8" x 15.5", so probably too large for it to be that.

Checking the speaker appearance against the data sheets should give you an idea if these are the installed speakers.

If they are the DM5SE model and the speakers are set for the transformer bypass 8 ohm setting, then for reliability, you either could:
1) Get speakers with better power handling capability
2) Replace the powered mixing desk with an unpowered mixing desk and a separate power amp with a rating more in keeping with the speaker's rating
3) Keep the powered desk but get a separate power amp fed from the mixers main mix line outputs to feed the power amp.

Given that at full output the PMS6000 peak voltage is over 110v, I don't know if it may be possible to look at using say the 12W/25W transformer tapping setting (you'll need to move the wiring connections and internal power selector in accordance with the installation guide) which will provide a lot more impedance for the amp to drive into and will seriously drop its power output.

But not knowing the rating of the internal transformer, it might be that the transformer itself tries to pass too much current and gets damaged. It would require careful testing and measurement. Given a lack of in-house expertise here, this may be best forgotten about.

[Wonks]

According to ChatGPT

HBM (High-Bandwidth Module) speakers are a type of compact, high-performance speaker technology that uses a specialized driver design to produce exceptionally clear and accurate sound. These speakers typically feature a compact, lightweight design that allows them to be easily mounted in a variety of settings, including cars, boats, and home theater systems.

The HBM driver design uses a unique magnetic structure and voice coil to produce a powerful, high-quality sound with minimal distortion, even at high volumes. HBM speakers are also known for their high efficiency, which allows them to deliver a lot of sound with relatively little power.

HBM speakers are often used in high-end audio systems and are valued for their exceptional clarity and accuracy, as well as their ability to reproduce a wide range of frequencies. They are a popular choice among audiophiles, home theater enthusiasts, and anyone who wants to enjoy high-quality sound in a compact, convenient package.

Thanks.

So, basically, a speaker system with decent bandwidth and power handling and nothing to do with overload protection.