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Old 2nd September 2010, 11:29 AM   #11
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Well, now that i found official information about the speaker
from it's original brochure, i guess i was wrong as it says:
Nominal impedance: suitable for 15 Ohm output

PS, i don't have a multimeter.
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Old 2nd September 2010, 11:32 AM   #12
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by rg12 View Post
.... I don't have a multimeter.
then I would suggest you are in the wrong Forum.
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Old 2nd September 2010, 12:06 PM   #13
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Originally Posted by AndrewT View Post
then I would suggest you are in the wrong Forum.
I am not, i don't need to own a multimeter if i don't know how to explain
what it reads.

im not dealing with electronics much, i came to this forum at first for
asking about a replacement cap brand for my amp, i didn't know i needed
a multimeter to ask a few questions.
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Old 2nd September 2010, 01:31 PM   #14
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You don't need a multimeter to ask a few questions.
The meter would make it easier to provide you with some answers.
As a pure guess, I'd say that the amplifier is putting out as much power as it can.
Turn the amp on with the volume all the way down. Let it run that way for 10 minutes or so and see if the heat sink is getting hot. If the heat sink is hot, the transistors are probably drawing too much idling current. The bias is set too high.
If the heat sinks remain cool, that would indicate that you've been pushing the amp pretty hard ... perhaps to full power or beyond.
Hope this helps.
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Old 2nd September 2010, 03:30 PM   #15
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by rg12 View Post
im not dealing with electronics much, i came to this forum at first for
asking about a replacement cap brand for my amp, i didn't know i needed
a multimeter to ask a few questions.
A new Member that appears to have almost no access to resources for DIYaudio projects raises alarm bells for me.

A multimeter is probably the most basic instrument a DIYer needs to start his hobby. Without it you will always be asking yourself questions and have no resource that is capable of giving you the answers.

If you have a problem and ask the Forum a question, you usually need to give us information to work with.
Voltages are a very indicative bit of that data.

Ask all the questions you like, both of yourself and of the Forum. But, without an interchange of information, do not expect useful answers.


edit
I have decided to go further:
If you are not prepared to invest time in learning which resources you need and learn how to use them and buy/borrow them, then I consider you are definitely in the wrong Forum.
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Last edited by AndrewT; 2nd September 2010 at 03:33 PM.
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Old 2nd September 2010, 04:11 PM   #16
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OK. Lets lose the teeth into this guy.

The SA 7300 was specified as 35W into 8 Ohms which in general terms will give you about 17W into 15 Ohms.

Although not a huge amount of power this will, with efficient speakers, produce a modicom of volume.

Class A, Class A/B and Class B amplifiers are the norm. in the Hi-Fi world with Class D and onwards creeping into the specialist market.

How can I explain this to a non-technobrat. ????

Think of a common garden tap, of the water variety.

In Class A, the tap will always be ON, always dripping water. It must drip sufficient water to provide the amount of water required at full output (volume). This could be quite a significant flow of water, most of which will be wasted.

In amplifier terms, a Class A amplifier is always ON and drawing power, most of which is wasted, in this case as HEAT.

In real terms, this is unacceptable as the costs of getting rid of the heat far outweigh the commercial benefits of Class A.

Class B is the more common solution. Here we use two taps, one to provide the +ve side of the signal and the other to provide the -ve side. CONFUSED. If there is NO input oe output signal the taps are both, to all intents and purposes OFF so no water is wasted. In the amplifier world, no electricty or HEAT is wasted so it runs much cooler.

Class A/B is a mixture of the two and is the generally accepted "best of both worlds".

When commercial amplifiers are built they are constructed using the most economical components available which are generally less than perfect. This results in afinal design that needs some factory adjustment to work as designed.

The manufacturer will adjust the amplifier to work within certain design criteria, one of which will be heat dissipation.

Within limits there are sonic advantages to altering the "bias" of the amplifier from Class B towards Class A but care must be taken to ensure that all the components stay within their Safe Operating Area (SOA).

Many forums will give advice on how to play with this biassing. It is possible that someone has tried to adjust your amplifier or it may simply be a case that one or more components is failing and the amplifier requires attention.

As EVERYONE is saying. TAKE IT TO A COMPETENT ENGINEER. At this moment in time it appears that there is no REALLY EXPENSIVE damage, but operating the amplifier in this condition could cause it to fail catastrophically and could even take out your speakers at the same time.
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Old 2nd September 2010, 04:27 PM   #17
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Quote:
Originally Posted by AndrewT View Post
A new Member that appears to have almost no access to resources for DIYaudio projects raises alarm bells for me.

A multimeter is probably the most basic instrument a DIYer needs to start his hobby. Without it you will always be asking yourself questions and have no resource that is capable of giving you the answers.

If you have a problem and ask the Forum a question, you usually need to give us information to work with.
Voltages are a very indicative bit of that data.

Ask all the questions you like, both of yourself and of the Forum. But, without an interchange of information, do not expect useful answers.


edit
I have decided to go further:
If you are not prepared to invest time in learning which resources you need and learn how to use them and buy/borrow them, then I consider you are definitely in the wrong Forum.
The things you say are true, but i don't think your attitude is right.

You could have just recommend me getting or borrowing a multimeter
and thats it.
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Old 2nd September 2010, 05:28 PM   #18
Mooly is online now Mooly  United Kingdom
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Hmmm... let's try to keep it friendly... the original question was "is it too hot" so let's see what we can determine.

rg12 Did you try as in post #6... does the amp cool back down naturally when you turn the volume back down ?

Check these,

1. With no speakers connected the amp should run cool.
2. With speakers connected the amp should still remain cool as long as no music playing.
3. When the amp plays music and is hot when the music is stopped then the amp should cool off... may take longer than you think.
4. It's unlikely if it were faulty, that both channels would be duff, so try it using just one channel and see as well.

And how hot is it... if you can hold a finger on the metal or the transistors for 5 seconds or so then it's OK. If it sizzles then it's too hot.
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Old 2nd September 2010, 05:41 PM   #19
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Thank you Mooly.
There have been some very rude responses to rg12's questions.
Your response is a sensible one.
Without measuring the static currents on the individual output transistors, a multimeter would be of little use. Rg12 appears to be a novice and need guidance.
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Old 4th September 2010, 09:23 PM   #20
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I just did a check and i guess i was just overloading the amp with high volume (even though it was only at 3 in the dial numbers), because when
i turned down the volume, it cooled down.

Thanks for the help guys.
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