AP20 vinyl trouble

[MK1LN4E:)]

"Sorry mate you don't understand, you are not running the amp harder"


All I mean is running that amp for let's say 4hrs at three quarters it would be close to overheating if not already gone, but at hardly any volume it would be quite comfortable. It got quite hot at just over an hr. I did the same with my old amp it's safety cut out prevented me from blowing it up, thankfully, as I didn't think it was that loud.

[Dr Bunsen Honeydew]

I am sorry you don't understand and I don't have time to teach you electronics.

[_D_S_J_R_]

Like I said - please try to understand me - the POSITION of the volume control is MEANINGLESS, as it depends on the 'log law' of the control itself in addition to the other things discussed above.

In days gone by, volume controls were designed to give you good volume levels around 2/3rds the way up and micrometer-fine control of low volume settings below half way. Naim amps used to be like this on the phono setting, together with when you connected a tuner and/or tape deck from the period. CD players offer nearly three times the nominal output of a typical 70's tuner and Naim owners, in addition to the other issues early CD players caused with Naim preamps' filters, found that a comfortable playback level for CD was around 9 o'clock on the volume control as against around half way to 2 o'clock for vinyl at roughly the same volume as heard through the speakers. The pro-ject phono stage you have may well have a low output in comparison with, say, a CD player, so the volume control will be set higher to compensate. Doesn't mean you're using more power at all as the volume LEVEL as heard through the speakers will be the same as a CD player with the control turned down lower.

Does the above now help you understand what a volume control actually does?

An AP20 is a 20 Watts per channel device. The clarity of sound and lack of 'smear' means you don't need to whack it up to high sound levels to get the musical vibe in the recording/production like you have to do with many others, but twenty Watts is twenty Watts at the end of the day, so long term high power usage will cause the thing to run hot. The one I'm using runs barely warm after a day of (gentle) use. Higher power requirements will mean a bigger, more expensive transformer and power supply and bigger heatsinks to cope with the extra power. More again would eventually need bigger and/or more output devices adding to complexity and cost, which goes against the whole NVA philosophy I believe.

Hell, even Naim's stupidly insanely priced 555 power amp is basically two pairs of amp cards bridged per channel, and it seems low impedance drive suffered as a result on the early ones (cutting out when driving big B&W 800 nautilus series IIRC).

[jimbob]

Just to clarify, as the amp Mark is using is my amp, the volume control is simply a means of matching the gain/output voltage of different sources and it is music volume/SPL which would make an amp clip or cause damage to amp and not the position of the volume control??? Does this mean that if with a CD player the volume control is at 9 o'clock and to get the same volume from another source the control is at 12 o'clock there is no more demand on the amp simply because of the volume controls position and extra demand on the amp would only come from increased SPL/music volume???

Sorry but I am genuinely cluless about electronics.

[_D_S_J_R_]

That's right The volume control simply matches levels and comes BEFORE the amp itself.

[jimbob]

okay. In that case what would have caused his Cyrus to go into protection mode under the same circumstances? Mark said to me that when his Cyrus shut of it was extremely hot even though the music wasn't any louder (just volume control higher to get same SPL).

[SteveTheShadow]

okay. In that case what would have caused his Cyrus to go into protection mode under the same circumstances? Mark said to me that when his Cyrus shut of it was extremely hot even though the music wasn't any louder (just volume control higher to get same SPL).

It didn't like the speaker load it was driving into.
The output stage was oscillating due to some fancy expensive speaker cable it wasn't happy with.

Those are about the only reasons an amp will shut itself off bar it being faulty in the first place.

[Dr Bunsen Honeydew]

Heat is from current not voltage. It means the amp doesn't like the load or you are using too much volume (voltage gain) and the amp is going into clip. The input and driver stages of an amplifier are voltage amplifiers where as the output stage is a current amplifier (not absolute but mostly). Which is why the output transistors are mounted on a heatsink to dissipate heat generated by them. If the amp has a thermal trip on the heatsink then that is a switch that cuts the amp when it gets too hot from too much current passing through the output deveices for too long. It is a VA thing which is time v amps v temp rise.

[jimbob]

I know I might be sounding a bit stupid but does this mean that the amp has to work harder to amplify the vinyl source to the same spl as the cd player? I think this is what Mark wanted to know. Sometimes on forums it is hard to word things right and I think the original question has been misinterpreted a bit with the mention of the volume control position.

[Dr Bunsen Honeydew]

Obviously not. An amplifier is not a human being, it doesn't give a ferk what is giving it the voltage and amps (signal) it is only reacting to said voltage and amps from where ever it comes.

UNLESS that signal is unstable, but that is a different fettle of kish. An unstable signal contains masses of very high frequency harmonic distortion mostly beyond human hearing range that makes the amplifier draw current to try and amplify it, and then it will get hot from what seems like a relatively low volume signal. BUT you will mostly know this is the case as there will be distortion in your hearing range as well. Instability is caused by a circuit ringing or taking off, in other words becoming a signal generator. This is caused by fault condition or the circuit involved not likng the load it is being asked to drive which causes the circuit to latch up / oscillate (for example because of very high capacitance interconnect or speaker cable).