clip indicators - how do they work ?

Normally its when the limiters are kicking in above a certain dB threshold on the input gain isn't it? Stops the input waveform from flattening, therefore preventing the amplification of a distorted input signal to a distorted output signal, just the knowledge I have

odc04r wrote: There are loads of different ways to do it, ranging from the very simple and not much use to the much more sophisticated limiting methods of modern amplifiers. If you really want to see what is happening then there is unfortunately no substitute for an oscilloscope and some dummy loads.

OK. Was just musing on whether there's any sense in trying to "retrofit" a meaningful gain and/or clip indicator to an amp that doesn't have any ..... in my case car amplifiers for use with battery-powered systems. Car amps usually have screwdriver PCB-mounted pre-set type gain controls on the bottom panel ....

I was thinking of mounting a car ampflifier (not one of the things with huge lumps of ally heatsink) in a kind of outer chassis - with sensible connectors for DC in, spkr out (mebbe speakon), but also some proper POT type gain controls, prob a DC voltage indicator, power-on switch etc.

Would be useful to have a degree of control over gain e.g. somehow calibrate the pre-set gains so that "front panel" gain is useful - and know (roughly) where you are wrt the amps o/p capability. (Hope that makes sense)

Slaz
another '3 minute circuit sketch'

this time for a simple peak signal indicator:


The value of *R1 can be roughly calculated from needing a little over 0.7 Volts peak on the base of the BC182 so as to indicate a peak positive half cycle of signal at the required level
Mik

Nearly, the BC212 will saturate, Vbe at 0.7V, and the collector will give Vs-Vcesat across the series R and LED, whilst the BC182 is 'on'.
'Slow recovery' is from the time constant provided by the 2 4k7 Resistors and the 2µ2 Capacitor; so 'fast on' and 'slow off' for the LED.

Same circuit with different values to allow for a different supply rail can be used for Amplifier outputs.

This Circuit dates back to the late 1960's when it used a low current filament lamp instead of the LED
Mik

Aw thanks guys. Really didn't mean anyone to go drawing circuits or writing essays about this.

Dunno about this .... so many variables involved - and no test gear or dummy loads available here (other than an OK analogue test-meter - since my mate's scope died) .... plus I wouldn't dare put continuous sine waves through the amp .... well mebbe at 16R load ....

Kind of thinking I may just stick to using a combination of ears and putting back of hand on amp chassis to gauge temperature, as o/p trannies bolt directly to it.

Its just the kind of music we play (Jamaican reggae/ska - some from the 60s, some more modern etc. ) is so variable wrt level, media quality, crest factor, recording quality, frequency spectrum etc. .... its quite hard to know "where you are" and set good levels - and even more so when there's someone on the mic having a yack over the tunes ..... but decided (on the mic front) that its better to just train the guy doing the yacking to dip the music level a bit manually when he's about to cut in - or for me to hover over the channel fader when this is going on ......

Just made a folder called "audiomik_sketches" to grab em

P.S. guess it would also make sense to assume old DJ mixer with LED meters on o/p (post master fader) is part of the rig (which in fact it isn't always) - and assume that the car graphic EQ after the mixer is unity gain at "full" o/p ..... then take the amp manufacturer's power rating (with current Vibe amp = 80W or so/ channel -> 4R) - work out voltage ( = about 18V) .... set 50Hz sine wave input to mixer to read 0dB on meters, then tweak pre-set gain to get 18V of 50Hz at spkr o/p.
50Hz is all I can measure. Dunno how much lower the voltage would be on load - might be able to try 16R or 24R with speakers in series at this power level.


Edited by slaz - 06 November 2012 at 2:19pm

There are still to many variations to take into account for the above to be correct. This is a good general rule only.

Edited by Muckerbarnes1 - 09 November 2012 at 1:43am