Work out the maximum volume of your Amp

[admin_exported]

This post will tell you how to easily, quickly and reliably work out when your amplifier's volume reaches maximum and when you will introduce distortion.

To work it out, you need to know the input sensitivity of your amplifier's line level inputs and the output level from your line-level source. This should be measure in millivolts (mV).

Let us assume we have an amplifier with the input sensitivity of 150mV at the aux. input. The output level of the CD player we are using is 2000mV (which is 2V). Then use the formula:

20 * log(V1 / V2) When V1 is the input voltage and V2 is the input sensitivity
Substituting in,
20 * log(2000/150) = +22

This answer is in dB, so on the given amplifier at the given output voltage of the line-level source and the given input sensitivity on that amplifier, the maximum power of the amplifier will be at -22db (when referenced to maximum = 0db).

Therefore the true formula to working out this is:

dB = 20 * log(V1/V2).

If your amplifier gives its volume level in -db (such as Arcam and Cambridge Audio) you should be able to work out when the amplifier is at full power before distortion kicks in. Obviously, the speaker load plays a small part in this (as does how clean the mains power is) but on the whole, this is true.

If you have any questions, do not hesitate to ask!

J Hughes.

 

[John Duncan]

"Too loud".

 

[plastic penguin]

I'm overwhelmed with deja vu.

 

[Anonymous]

plastic penguin:I'm overwhelmed with deja vu.

In what way?

 

[chebby]

Maximum volume is when people have to start raising their voice to be heard over the music. At this point I back it off a bit.

I like to hear the music, not be relieved I can still hear after the music.

 

[Anonymous]

Log base 10 it seems -- got confused because Python's math module seems to default to natural log.

So, if my Audiolab 8000a says "MM 2.0 mV/47k/85pF" and my Audio Technica cartridge says "Output voltage at 1000 Hz, 5cm/sec.: 3.5 mV" then is it:

20 * log (3.5/2) = 4.86?

So that means it will distort at 4.86 db below the amplifier's maximum output? Or have I misunderstood? Do the turntable specs matter at all, or is it only the cartridge?

Also, isn't 3 db doubling the volume? So will it distort at below half volume?

The other inputs on the Audiolab says "100mV/20 kOhm; Power amp: 707
mV/50kOhm". Using the 2V CD player that you use in your example, I get:

20 * log (2000/100) = 26.02?

Or have I done my maths wrong? Doesn't seem right, isn't 20 decibels two orders of magnitude??

 

[the record spot]

I think "too loud" was good enough for me.

 

[Anonymous]

Lydgate, let us just concentrate on line-level inputs at the moment. Phono stages introduce new problems, of which i'll discuss later regarding the RIAA equilisation and cartridge impedence.

On the Audiolab's line-level input calculations, you have done the the calculation exactly right. The calculation,

20 * log(2000/100) = 26.0205991 to 7 d.p

Therefore, at -26db on the volume of your Audiolab (I can't remember whether it has the -db numbers on it or not) it will be outputting at full power.

If I use my Arcam A32 and CD73 as an example, I'll prove that my Arcam has a less sensitive volume control, so that if we assumed they outputted the same power my Arcam would be quieter at -26db than your amplifier. Although the input sensitivity can be changed on the Arcam A32, let us assume it was at 250mV. Then looking at the output of my CD73, it is 2.2V, so substituting that into the forumula:

20 * log(2200/250) = 18db

Therefore, at -18db my amplifier is at full power. If we use my 8ohm Wharfedales as an example, the Arcam will be outputting 100watts of continuous power at -18db when using the CD73. However, the A32 has a feature which allows the user to change the sensitivity of the input. It can be changed to 2V (or 2000mV), so putting that back into the equation:

20 * log(2200/2000) = 0.83db

Therefore only when I turn the amplifier up over -1db will full power be reached. This is a useful feature as it stops overloading on different inputs and brings each source to a similar volume. Take my Rotel RT-02 tuner for example, it outputs at 1V (or 1000mV) so I would want to increase the sensitivity compared to my CD73's input so that I don't have to change the volume when I switch sources.

Hughes.

 

[chebby]

Hughes123:This post will tell you how to easily, quickly and reliably work out when your amplifier's volume reaches maximum and when you will introduce distortion.
If you have any questions, do not hesitate to ask!

J Hughes.

OK.

So what went wrong with your equations when this happened?...

http://whathifi.com/forums/p/119266/119266.aspx

 

[Anonymous]

chebby:Hughes123:This post will tell you how to easily, quickly and reliably work out when your amplifier's volume reaches maximum and when you will introduce distortion.
If you have any questions, do not hesitate to ask!

J Hughes.

OK.

So what went wrong with your equations when this happened?...

http://whathifi.com/forums/p/119266/119266.aspx

Dunno - I wasn't overdriving it. That was my old JVC, not the one I have now. I sold that one a couple of months ago. I think it may have been a problem with the speakers that were on it and it didn't have enough heat dissapation and eventually it overheated.

Did this come in handy to anybody, by the way?

 

[Andrew Everard]

Hughes123:chebby:Hughes123:This post will tell you how to easily, quickly and reliably work out when your amplifier's volume reaches maximum and when you will introduce distortion.

If you have any questions, do not hesitate to ask!

J Hughes.

OK.

So what went wrong with your equations when this happened?...

http://whathifi.com/forums/p/119266/119266.aspx

Dunno - I wasn't overdriving it. That was my old JVC, not the one I have now. I sold that one a couple of months ago. I think it may have been a problem with the speakers that were on it and it didn't have enough heat dissapation and eventually it overheated.

Did this come in handy to anybody, by the way?

Hmmmm, off the wall audio ideas. J Hughes. Sound familiar to anyone?

 

[chebby]

Andrew Everard:Hmmmm, off the wall audio ideas. J Hughes. Sound familiar to anyone?

Och that's a Belter Jimmy!

 

[Andrew Everard]

chebby:Och that's a Belter Jimmy!

Come to think of it, isn't JMH's day-job something to do with working with cameras?

I think we may be on to something here...

 

[chebby]

Andrew Everard:
chebby:Och that's a Belter Jimmy!

Come to think of it, isn't JMH's day-job something to do with working with cameras?

I think we may be on to something here...

I thought JMH passed away one day back in the 1980s when a shaft of sunlight (coming through the window of his Barbican listening room) reflected from a thousand foil triangles, caught young Jimmy in the focal point and incinerated him instantly.

Friends rushed to telephone the ambulance but he had removed the telephone to another room and they could not find it under the acoustic wadding.

 

[Thaiman]

I don't think I can get maximum volume on my rig without badly damage my ears (and other near by)

Good hifi rig, at reasonable volume, should let you have a good old conversations with your mates or family without feeling wanted to turn amp down a tad all the time.

 

[Anonymous]

chebby:Andrew Everard:
chebby:Och that's a Belter Jimmy!

Come to think of it, isn't JMH's day-job something to do with working with cameras?

I think we may be on to something here...

I thought JMH passed away one day back in the 1980s when a shaft of sunlight (coming through the window of his Barbican listening room) reflected from a thousand foil triangles, caught young Jimmy in the focal point and incinerated him instantly.

Friends rushed to telephone the ambulance but he had removed the telephone to another room and they could not find it under the acoustic wadding.

Yep. Havn't got a clue what your on about. The only person I can think of with J Hughes that is related to audio is Jimmy Hughes, the hi-fi reviewer, but that's it...where does the humour lie?