Film-Tech Forum ARCHIVE: Amplifier "Clip" and "Protect" lights... what do they mean?

This is topic Amplifier "Clip" and "Protect" lights... what do they mean? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=006914

Posted by Mark J. Marshall (Member # 1409) on 01-29-2005, 01:04 PM:

We have EV Amps, models AP2600 and AP3200. They have two lights on each channel. "Protect" and "Clip". What is the difference? What do they mean exactly?

When one of those lights comes on, we send the amp out for repair. What happens when they're repaired? Is there something inside that needs to be replaced, or reset, or what? Also, will either of these lights on one channel impact the other channel in any way?

Thanks.

Posted by Gordon McLeod (Member # 33) on 01-29-2005, 02:02 PM:

Simplisticaly Clip indicates that the peak of the waveform has exceeded the rail voltage and the top of the wave form is squared off or clipped
Protect means that the amp has usually disconnected the load from the amp due to a temperature or DC voltage fault
that is a very simple explanation as each manufacturer has there own method

Posted by David Stambaugh (Member # 1102) on 01-29-2005, 02:04 PM:

"Clip" probably means the amp is being pushed so hard that it can't reproduce the output waveform without "clipping" the peaks, which causes audible distortion. The amp is being overdriven. Occasional brief clipping is probably OK and not necessarily noticeable, but frequent or constant clipping is bad and will be audible.

"Protect" may mean the amp's output is detecting a very low-impedence load, so low that the amp thinks it's as a dead short, which is very bad. So it's shutting itself down to protect the possible frying of the power driver transistors.

I'm sure someone else will have more to add.

Posted by Monte L Fullmer (Member # 2797) on 01-29-2005, 03:14 PM:

..the comments by Dave and Gord pretty well seals this topic on the "Clip" and "Protect".

For I had QSC amps with both lights as we just kept the preamp input at a level to prevent clipping. Clip light stays on, meaning an amplifier repair, as per what Dave said.

-Monte

Posted by Michael Schaffer (Member # 1204) on 01-29-2005, 04:30 PM:

Newer EV amps don't have a clip indicator anymore, but a "limit" because when clipping is detected, an internal limiter is switched on briefly. I am not familiar with those older models, I wonder if they didn't have the limiter and simply let you know that clipping was going on. Apart from shorts and thermal problems, many amps also go into protect mode when HF oscillation is detected at the output. I do not know if this can cause or is caused by internal amp damage, but HF oscillation can take out HF drivers almost immediately, so that is a good protective strategy.
When the protect light comes on, you should wait for a while and then check again because the output can be temporarily thermically overloaded. You don't have to send them out for repair immediately. Check if the fan(s) operate properly and blow the amp out with air. I have rarely seen amps go into protect because the ambient temperature was too high, but in a really hot booth this can be a contributing fator.
If it stays on, disconnect the speaker cables to see if there was maybe a short there.
If it stays on all the time, it's now time to send it to the amp doctor!
I don't think the other channel is affected when the prot light comes on only on one.
Frequent clipping may be an indication of improperly set levels or the amp may simply be underdimensioned for what it is asked to do.
I have found that many amps here are set up with the output level trim (gain) all the way up and the levels are controlled only in the processor output level settings to avoid that people play with the levels. While this may be a good security strategy, it also can lead easier to clipping and distortion if the levels are not set properly and headroom taken into account carefully.
In Germany, we usually set the amp output to about 2/3 of it's range and then adjust the channel levels in the processor accordingly. When we find that sombody has played with the gain knob, we simply cut his hand off.

Posted by Jonathan M. Crist (Member # 413) on 01-29-2005, 04:41 PM:

Anytime the clip light comes on, there is a good chance you may also have blown a speaker or a diaphram somewhere. Speakers don't like clipped signal anymore than amps do.

Posted by John Hawkinson (Member # 1135) on 01-29-2005, 08:22 PM:

Rane Technical Note #128 (PDF format; Power Amp Clipping and It's Effects on Loudspeakers) is worth reading.

Also, Rane's recommendation in the Setting Power Amplifiers section of Rane Technical Note #135 (Setting Sound System Level Controls) is also worth a glance (i.e. setting your amps so they never clip).

--jhawk

Posted by Antonio Marcheselli (Member # 373) on 01-30-2005, 12:14 PM:

Rane's note is very correct but it supposes that you can achieve the maximum level in the auditorium with your equipment! If you have poor amp or poor speakers following the Rane's note will cause to have a lower SPL setting in your theater!

If your equipment is correctly dimensioned following the Rane's note will cause to optimize the S/N ratio and have a better sound. If your system is not well dimensioned followinf the Rane's note will cause you to have a lower setting for the "7" fader setting on your CP.

Bye
A

Posted by David Graham Rose (Member # 1450) on 01-30-2005, 01:29 PM:

Greetings All from Cambridge

I write firstly to agree completely with all that has been said on this toipc. Secondly, and rather less importantly, I write to inform you all of my retirement. As from tomorrow, I will no longer be Professor Sir David Graham Rose B.Sc., M.Phil, F.B.K.S, but merely Sir David Graham Rose B.Sc., M.Phil. I should also like to let all the projectionists who seek my advice in the UK that I will no longer reside at 12 The Railway Cuttings, Gamlingay, Cambs., since this is a University residence to which I am no longer entitled. I am afraid that my retirement means that tea and scones at 4pm daily will not be held at this address!

I would like to thank all the denizens of Film-Tech who contributed to my rather embarrasingly large retirement fund and who have enabled me to purchase my camper van. This means that from tomorrow onwards, I shall be pursuing the cause of fine cinema presentation, and engineering excellence in Europe - a whole new world awaits!

I would particularly like to thank Brad Miller, who had put up with my (almost!) insane ramblings for the past three years, but more so my research team who have endured many issues including the project to convert an Kinoton FP30ES to that of an FP30ECII via the gift of octally based relays. I know you could do it!!! I realise that you should not have had to be examined in A-Level German to understand the Service Manual, but I imagine the qualification may be useful later in life.

I leave you, albeit temporarily, until I manage to restore my internet access in my van with the image of my successor, the Emeritus Professor Ian Archer, B.Sc.,PhD, M.Phil, MBKSTS, presenting me with me retirement gifts.

From Cambridge for the final time I bid you all Goodnight

David

p.s I trust the new Chair in Cinema technology will not be too dissapointed that he was edited out of the above image to preserve valuable bytes!!