Clipping indicator for high powered audio amplifier? - Page 1
Forum section: electronics / projects

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: October 03, 2014, 10:34:34 pm
content: I have an amplifier than runs somewhere in the range of +-180volt rails...I'm wanting to add a clipping indicator to it, as different media is recorded at different levels, so I'd like an instant, visual indication of when I'm reaching the amplifiers limits.I've seen this circuit here, but it only lists upto +-80volt rails:http://sound.westhost.com/project23.htmIs it possible to take this circuit to +-180volt rails, or is this just getting unrealistic due to the resistors needing to be too big?Thanks!

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 03, 2014, 10:52:43 pm
content: Tap off the logic level drive signal and then watch for the duty cycle hitting the extremes for more than a few cycles.

author: dannyf
author_rank: Super Contributor
timestamp: October 04, 2014, 12:13:20 am
content: QuoteWhy do you need to take it to 180v rails? Put it on the input (if the amp is of a fixed gain), or with a divider if you want to use it on the output.

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: October 04, 2014, 10:39:24 am
content: I came up with a similar thing (before I'd seen Rod's). Rod's is probably slightly better (albeit rather more complex), but my scheme does work pretty well.To make it work with 180V rails, you'd need to find transistors that can take the entire supply voltage (nearly 400V). Or you could lose some of the volts in zener diodes. And of course, you'd need to scale some of the resistor values. Depending on how close your amp gets to the supply rail, at clipping, you might need to add one or two more diodes in the emitters of the transistors (or use zener diodes). As shown, mine is working at 12V or so, from a TDA2030 power amp IC.http://www.markhennessy.co.uk/activespeaker/electronics.htm- details of this circuit about 2/3 down...The opto-coupler arrangement is quite nice, and of course can be powered from any rail you like (alter the transistor and LED resistors accordingly). The transistor in the opto-coupler only sees 0.6V.You might like to think about adding pulse-stretching to make HF clipping more obvious. I didn't bother because my application was driving a full-range loudspeaker, plus most music has the bulk of its energy at LF anyway. YMMV.But do bear in mind that this circuit only detectsvoltageclipping. Current clipping will be missed, but sounds equally bad. For that reason, you might prefer the SIM project:http://www.sound.westhost.com/project57.htmI've also done this (different version, again before I'd seen Rod's), and in most applications it's a better bet. Generally no need to get involve with high supply rails...

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 04, 2014, 01:25:57 pm
content: To detect current clipping, just monitor the current limit circuit. But with proper design, hitting current limit will only happen under a gross overload.

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: October 04, 2014, 06:28:15 pm
content: Not impossible, but generally easier said that done. The SIM circuit is by far the easiest approach, and kills both birds with the one stone. Been there, got the t-shirtLooking forward to hearing how this pans out. Things get very complicated with such high supply rails - in the commercial world, most amplifiers that need to achieve these sorts of output powers (circa 2kW into 8 ohms) use bridged output stages. In pro audio, it's rare to come across such big amplifiers, as it's a bit of an "all eggs in the basket" situation - far safer to use multiple saner amplifiers driving multiple loudspeakers so that a failure doesn't end the gig. Wonder what the OP's application is?

author: wiss
author_rank: Frequent Contributor
timestamp: October 04, 2014, 06:50:19 pm
content: Yea, we need pictures!

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 04, 2014, 07:06:19 pm
content: My guess is a particularly big subwoofer amp. The 360V total rail voltage works nicely with commonly available 600V IGBTs and also happens to be just above rectified mains, meaning a common PFC stage works nicely.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: October 04, 2014, 09:50:31 pm
content: Its a car amplifier... actually more like 10kw into 1ohmI feel that I really need to monitor the output with reference to the rail voltages, as the rails are going to sag...Another large amplifier I have actually clips the preamp stage, and measures that, I'll post a schematic of that, as I thought it was a strange way to do things.