Answered Two brand new Marantz Amplifiers faulty?

gibbsy

Moderator
Sorry if you thought I was being rude but I tried to make a simplified analogy that you were blaming the Marantz for it's failures when you were simply asking too much from it. Which in fairness several others had pointed out and had given excellent replies and reasons for such failures. Such premises and the work it is expected to do requires specialist equipment.

Me being a moderator has absolutely nothing to do with my opinions.
 

BlueWizard

Distinguished Member
Assuming your correct the wiring, you can reduce the strain on the amp with additional cooling.

I had my amp in a very tight space where it clearly would not get enough air circulation, so I added two computer fans to the top drawing air out.

yamamp-fan1-jpg.514879


In my case, the Amp had a Switched Electrical Outlet on the back, so when I turned the amp on the Fans came on automatically. There are 12v computer fans which I ran at between 7.5v and 9v. This was still enough cooling but the fans ran quieter, which mattered in my living room.

While you are investigating the integrity of the wiring (no stray strands) also investigate the correctness of it. All wire as a mark on one of the wires, sometime a ridge, sometimes embossed printing, sometimes actual printing, other times a stripe, but one wire is absolutely marked. That Marked Wire should be consistent through out the system. If the Marked Wire in on the Red+ at the amp, then it should be on the Red+ of each speaker.

You previously said -

> However the teacher when it was last used had it 3 quarters of the way she said - I didn't see it, but I would imagine that would be around 1 o clock.

Quibbling but 3/4 volume is closer to 2 o'clock or 3 o'clock which is likely in excess of 100dB or to put it another way - WAY TOO LOUD!

The speaker impedance is something of a problem but at normal volumes under 12 o'clock, is perhaps less of a problem. This is about CURRENT. The lower the Impedance, the higher the Current, and the higher the Current, the more Heat is generated. More heat equals more strain and more danger to the equipment, both speakers and amp.

So among other things, you might want to inform the teachers that there is a limit to how loud they should set the volume control. Make sure they understand that about 12 o'clock is the Maximum, NOT the ideal.

Again, in my experience, when you get up to 1 o'clock or more you are at or in excess of 100dB which is VERY loud, especially for children with tender ears. Likely if Health&Safety came around, you would be in trouble for reaching those volume for more than a couple of minutes.

Here is a test I ran for other unrelated purposes -

Next using my turntable and the Hendrix LP, I tested the volume from 9 o'clock up to 1 o'clock

Hendrix - Stone Free

9 o'clock = 75dB
10 o'clock = 85db
11 o'clock = 90db
12 o'clock = 94db
1 o'clock = 98db


Though I had somewhat larger speakers, this somewhat confirms that there is really no need to be over 12 o'clock on the volume dial.

Hope that's helpful.

Steve/bluewizard
 

Timmy C

Distinguished Member
Quibbling but 3/4 volume is closer to 2 o'clock or 3 o'clock which is likely in excess of 100dB or to put it another way - WAY TOO LOUD!

It crossed my mind when reading this thread earlier that if this is a school with different teachers plugging in various devices, they may well be using headphone sockets from phones or mp3 players with variable outputs. 3/4 volume would surely be obviously deafening otherwise.

Out of interest, would using an phone/mp3 players headphone out at low volume, then cranking the volume on the amp to compensate, put the same strain on the amp as if you you were using a fixed/full output from the phone with the amps volume in the same position? If so then perhaps this might have been part of the problem
 

BlueWizard

Distinguished Member
It crossed my mind when reading this thread earlier that if this is a school with different teachers plugging in various devices, they may well be using headphone sockets from phones or mp3 players with variable outputs. 3/4 volume would surely be obviously deafening otherwise.

What you are getting at if I can paraphrase, is the using a MP3 player introduced another Volume Control. The MP3 output could be cranked to the max, which would not make the position of the Amp's Volume Control Reliable.

The correct way to use a device like this that has its own Volume Control is to FIRST set the amp volume to a known, consistent, and common level. Then bring the MP3 volume up until what you hear is consistent with the position of the Amp's Volume Control.

Out of interest, would using an phone/mp3 players headphone out at low volume, then cranking the volume on the amp to compensate, put the same strain on the amp as if you you were using a fixed/full output from the phone with the amps volume in the same position? If so then perhaps this might have been part of the problem

Realistically you want a balanced approach, turning the MP3 down and the Amp up, makes no more sense than turning the MP3 up and the Amp down.

Set the Amp at a known, consistent, and common level, then bring the MP3 up until what you hear is consistent with the position of the Amp's Volume Control.

If the MP3 (or other device) is too loud, you will over drive the input stages of the amp causing distortion and clipping. If the MP3 (or similar) is too quiet, then the Amp has to be too loud, and noise levels, if any, will be higher. Plus with the amp cranked up so high, there is a danger that some transient could over drive the Amp. Say you pull the Headphone Input out with the amp cranked up, that could cause a transient POP that could in theory damage either the Amp and/or the speakers.

The only reasonable way to do this, it to set the amp to say 10 o'clock or 11 o'clock and bring the input levels up until what you hear is consistent with that amp volume setting.

Steve/bluewizard
 
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BlueWizard

Distinguished Member
Just as a nice reference for OHM's LAW, here is a chart -

ohmslawcolor2-jpg.72038


As you can see the Letter designation are not what you might expect -

V or E are Voltage
I is Current in Amps
P obviously Power
R obviously Resistance

If you know any two parameters, you can figure out the other one.

For exmaple, let's say I have a 8 ohm speaker with 40 volts applied to it, what is the Power? Using the chart -

P = V²/R = 40²/8 = 1600/8 = 200 Watts.


Working backwards if we have a 200w amp feeding an 8 ohm speaker, how much Voltage is applied -

V = SqRt(PxR) = SqRt(200 x 8) = SqRt(1600) = 40 volts

Another factor is that because there is a Square and Square Root factor, Voltage and Power are not linear.

If 200w = 40v what does 100w equal?

V = SqRt(PxR) =SqRt(100 x 8) = SqRt(800) = 28.28 volts

Let's take TWO 8 ohms speakers for a total of 4 ohms, and see what the power is for the same input voltage. We will assume a 30 volts because it is a nice even number.

P = V²/R = 30²/8 = 900/8 = 112.5 watts

Now to 4 ohms -

P = V²/R = 30²/4 = 900/4 = 225 watts


It was previously determined that the combined impedance could drop as low as 2.67 ohms -

P = V²/R = (900/2.67) = 337 watts


Perhaps think of this in terms of light bulbs, a 25w light bulb still gets hot but not remotely as hot as a 300w light bulb.

Those greater Powers, equal greater Currents, and greater Currents equal substantially greater HEAT. Greater HEAT means more stress on the system.

If you do an Google Image search for Ohm's Law Chart, you will find many of these charts. On the wall above my computer, I have a Black and White Chart that I refer to all the time.

Ohm's law chart - Google Search

This is the one that I use -

OhmsPie-1.jpg


Very handy reference.

Steve/bluewizard
 

Paul7777x

Distinguished Member
As an aside here, if you’re testing the sound and find the volume loud enough at a given dial position that is very unlikely to be loud enough in a room full of children making noise. The volume will have to be higher just to compensate for the background noise.

And it’s not unlikely that the teachers/adults are understating the volume position to you. No one wants the blame.

And if kids are allowed to mess with it too, then...

And the Marantz is a small room, domestic amp.

Way out of its league in its current setting.
 

BlueWizard

Distinguished Member
As long as we are on the subject of Ohm's Law, here is how Speaker Impedance works.

Information taken from one of my previous threads -

On the Nature of Impedance?

As a public service to those who don't know, here are the formulas for calculating combine impedance of multiple speakers.

1.) When you are combining two speaker of equal size, they simply divide in parallel and add in series.

- two 8 ohm speakers per channel, wired normally

Rt = R/n

Where "n" is the number of speakers on a given amp channel.

Rt = 8/2 = 4 ohms

- wired in Series or in a chain, they add

Rt = R1 + R2 + R3 + .....

Rt = 8 + 8 = 16 ohms

Any combination of speakers in Series is merely the total of those speakers -

Rt = 4 + 6 + 8 = 18 ohms


2.) Two speakers of unequal impedance in parallel.

Rt = (R1 X R2) / (R1 + R2)

Example: 6 ohm with 8 ohm

Rt = (6 X 8) / (6 + 8) = (48) / (14) = 3.43 Ohms


3.) Multiple speakers of unequal value in parallel.

Rt = 1 / [(1/R1) + (1/R2) + (1/R3) + ...]

If you have a common calculator this is easy. Most cheap calculators have a reciprocal key [1/x] meaning ONE divided by 'X' where 'X' is the number.

So, using a calculator with the key strokes shown in square brackets [] and numbers in round () brackets, here is the sequence for 6 ohm with 8 ohms with 16 ohms -

(6) [1/x] [+] (8) [1/x] [+] (16) [1/x] [=] [1/x]

Here is what you should see

6 [1/x] = 0.166666666
[+]
8 [1/x] = 0.125
[+]
16 [1/x] = 0.0625
[=]
= 0.3541666666
[1/x]
= 2.824 ohms

Sorry if that last bit was boring for you.

That should give you a general overview.

Steve/bluewizard
 

BlueWizard

Distinguished Member
One additional point that has been hinted at is COOLING. If the Amp is covered, either permanently or temporarily, or if the amp is in a very tight closed space, that will effect the cooling and therefore the reliability of the Amp.

By covering the amp temporarily I mean, if the amp is in the open and someone set some papers or a book or a book-bag, or by some other means blocks the cooling vents, that can potentially be a problem.

Steve/bluewizard
 

Lawrence001

Active Member
There is no need to be rude especially if you are a moderator. I find your reply very unhelpful given that I have already said I don't know a lot about amplifiers and I have already said that I am going to address the amplifier speaker mismatch by replacing the speakers and presumably the amplifier, so what more do you want?

I have acknowledged that the speakers and the amplifier won't work together because of the ohm impedance issue. I didn't know why the amp was blowing which is why I came here and asked and I have now got an answer as to what the problem is and I can start with a resolution process!

So I will sort it by matching amps to speakers taking into account size of room obviously. I just ask a lot of questions because it's not an area that I understand very well as I don't normally deal with worrying about voltages, ohms etc in my line of work, but I do have an interest in hi fi equipment, so i am just wanting to understand how it all works that's all!

Anyway I will go to the supplier and explain the situation and he can advise the best solution for our situation, my preference would be to replace speakers and amp together to ensure that we get a match! Thank you for you help as you made it clear replace the amplifier! I will mention that to them.

I don't want to be accused of also being rude, but if you are supplying several schools with audio equipment as a business it's your responsibility to understand the products you are supplying. If heat and smoke is coming out of the electrical equipment you are supplying because you don't understand the specification and wiring then you are endangering the school, pupils and staff. In my opinion you should either stick with the products and services you do understand or, if you want to supply audio equipment as well, do some training on it so that you can specify and supply the correct equipment.

If on the other hand you are doing it as a favour then that is a bit harsh, but the point about the risks still stands.
 

Heavenlysounds

Standard Member
Dear all,

Sorry to take so long to get back to you. I have been occupied with other work lately. I have given Blue Wizard best answer because he gave me the clue as to what the problem was!

It would seem that the four speakers were wired to some point on the wall, where two speakers (4 wires) were wired into this connector and ultimately ended up with two wires. Same for the other two speakers. So ultimately I ended up with four wires instead of 8 wires. So effectively two speakers were being wired to one speaker terminal!

When I connected up the new amplifier I wasn't thinking about number of wires because the speakers and cabling were already installed and you know how you just plug the cables in on auto pilot - so it never clicked that I was four wires short until Blue Wizard mentioned it. Also it doesn't help that I probably put in an amplifier once every three years as its not a commonly replaced item.

While I work in IT, there is a huge difference in knowledge about laptops, servers and computers as opposed to knowing about amplifiers and in my defence I never had a problem before. I am not a hi-fi expert, merely someone who has an interest in audio equipment so I know a bit about - in any case more than my clients do!

I spoke to the guys at the shop and explained the wiring situation and what speakers we had and showed him pictures of the hall and we have agreed on the following.

The more powerful and original amplifier obviously could handle having two speakers on one speaker terminal, but this Marantz can't. However, I don't regard that as a fault of the Marantz amplifier, but rather the wiring should never have been done like that in the first place. It is not a recommended wiring design and regardless of what amplifier goes in there, I would rewire the cabling in any event.

So we are going to replace the wiring completely. We have also decided to replace all four speakers so we get matching speakers running at 8ohms. This means that we don't have the problem the next time the amplifier is replaced and we have long since forgotten about this wiring and ohm mismatch problem ! I don't see any value in 4ohm speakers which then requires a more powerful amp given the budget of most primary schools. They just use it for assembly music - hardly audiophile requirement!

I have asked the client whether they want to go with a more powerful Cambridge amp (as the more powerful Marantz amp is four times the price), however both myself and the store agree that the current marantz while having less power than the Cambridge, the Cambridge amp does not have the same build quality as the Marantz. So I would personally would prefer to stick with the Marantz amplfier over the cambridge!

In addition to listening to your points, I have also done some research and I have decided that in future I will opt for the more expensive Marantz amplifer which I think is 700 watts, because I agree that this Marantz is a little bit low on power. However, given the fact that I have put a similar Marantz amp in at several schools with no issues whatsoever and the volume is something everyone was happy with, I don't feel that the amp is underpowered for the use it's put to. The only reason there was a problem was actually down to the strange wiring system at this school. Even the store guy said, while he would personally prefer a more powerful amp, he did not feel that the Marantz was underpowered for the size of the hall - he has seen pictures!

In short, I agree that the amp is a bit low on power and I will in future recommend to schools that they go for the 700 watt option and if they can't afford that, this option will still be adequate. But I want to highlight that problem is not that the amp is underpowered - it is the wiring that was the cause! Thank you Blue Wizard for picking up on that! But I agree that it would be ideal to go for a more powerful amp in future bcause then you don't have to have the volume at three quarters! So everyone is right!

Thank you everyone for your advice. I was really baffled by this problem, so I am pleased to have found the cause. I really like Marantz and would like to stick with them - I think they are a well made product and reviews seem to bear me out on this. But if schools can afford it, I will go for the 700 watt option.

Thank you everyone for your support. Much appreciated.
 

Lawrence001

Active Member
I really can't stress enough that given schools' limited budgets they don't need high power expensive audiophile Marantz amps.You can get PA amps for a fraction of the price that are more than up to the job and 99.9% won't notice a difference, or find this even better given it's designed for the job. Your love of sound quality, though commendable, should not be a factor in their purchasing policy and I hope you have at least given them the option to save money.

If I found out my daughter's school supplier was selling them high quality beefy audiophile amps and they had a shortage of books as a result or something then I would be rather unhappy.
 

Heavenlysounds

Standard Member
I really can't stress enough that given schools' limited budgets they don't need high power expensive audiophile Marantz amps.You can get PA amps for a fraction of the price that are more than up to the job and 99.9% won't notice a difference, or find this even better given it's designed for the job. Your love of sound quality, though commendable, should not be a factor in their purchasing policy and I hope you have at least given them the option to save money.

If I found out my daughter's school supplier was selling them high quality beefy audiophile amps and they had a shortage of books as a result or something then I would be rather unhappy.

That's why I sell the Marantz PM 6006 as it's a well made inexpensive amp so achieves best value for money! It is only £30 more than the Cambridge amplifier that I suggested to the school as an alternative. My intention is to suggest the Marantz Pm6006, offer the more powerful, but lower build quality Cambridge Audio Topaz SR20 amplifier and also offer the more expensive Marantz that is over a thousand as the premium product. That way they have three choices. You are missing the point - the issue I am concerned with is not sound quality difference, the issue is reliability and longevity! That's why I like Marantz. The thing is the Marantz Pm 6006 is suitable - it's just the wiring that was the issue.

But thank you for highlighting your view.
 

Ugg10

Distinguished Member
I still have a feeling that for this application something like this -

SubZero 500W 12" PA Speaker System with Digital Media Player & Stands at Gear4music

would be more than adequate, designed for the job and easy to use - just Bluetooth an ipad/phone to it or plug in a CD player and off they go. Buy a cheap mic and they have a full music/PA system for £100 less then the PM6006 alone (excl. speakers). OK, quality may not be as good but as you say that is not a high priority.
 

gibbsy

Moderator
There's no getting away from it though, a hifi amp is not the right tool for the job. PA systems are much more effective and like others have pointed out the kids are not going to sit back and discuss the merits of the quality of the audio.
 

abmscopes

Active Member
Must agree with the two posts above. As a fully paid up and subscribed audiophile myself, I totally get that the OP maybe wants to hear hi-fi sound wherever he goes, including at work, but the point the OP seems to be missing, that many are making on here is that Marantz hifi amps are NOT, repeat NOT designed for PA duties. A cheaper PA amp will outlast the Marantz by many years, if not decades. So the claim that sound quality isn't the issue; longevity is, doesn't quite add up to me. The OP seems to have unrealistic concept of how long hifi amps should last, stating that he expects to replace the ones at the school every 6 or 7 years:eek:. There are thousands upon thousands of hifi amplifiers from the 1970's and even older, still doing sterling service in people's homes. That's because they are being used correctly within their design paramaters; just playing music at domestic levels for a few hours per day or maybe per week in rooms with dimensions in single figure meterage.
Honestly, please take the advice above and stop throwing money at hifi amps for your school. No matter how well wired up they are or how low you claim the volume is being set at, they reeally are the wrong tool for the job. Buy PA amp and speakers and you'll never have to replace them again in your working life.
*edited to remove mention of mic. use; I see that the OP is using it for music only. But my point still stands.
 
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abmscopes

Active Member
I would also add that amplifier power is the wrong metric to be looking at in larger rooms. Or if not the wrong metric, a far lower priority than speaker sensitivity. It's been ages since I studied electrical engineering so I'm sure I'll be corrected here, but doubling the power of an amplfier only increases loudness by a few dB 10 dB maybe? But by increasing the sensitivity of the speakers by a few dB, say from 89 to 92dB will result in a very significant increase in loudness. So the other thing you could do to releive strain on your amplifier, is to buy more efficient sensitive speakers. Cerwin Vega's should do the job ...;)
 

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