Carvin B1500 clipping/protect circuit

[groovaholic]

The other night at rehearsal, my B1500 went into protect mode on several occasions.

Typically, I've used the amp thru a 4 ohm cab (Peavey 412TVX) and not had any problems, but I was using an 8-ohm cab that night -- so I suspected wiring problems, but the cab and my cables are all solid.

Got the amp home and tested it without a speaker connected, and I was able to trigger the protect mode without a speaker connected, which sugests that the amp is "sensing" the input signal and initiating protect mode based on the signal leaving the preamp.

So, it seems like the amp is working as-designed, but my feeling is that the protect circuit is a bit overzealous and doesn't allow the amp to deliver full power.

My question is; is there a way to mod the amp to decrease the sensitivity of the protect circuit?

Most of my circuit tracing experience is on tube amps so this schematic (www.carvinguitars.com/manuals/B1500.pdf) looked a little alien to me.

I'll do some testing with my dummy load later to see what kind of voltage/wattage it's putting out at the threshold of shutdown, but it sure didn't seem like the advertised 700w @ 8 ohms...

[groovaholic]

http://www.carvinguitars.com/cartech...tics/B1500.pdf

[seamonkey]

Nice Amp
Optical Limiter - people pay big bucks for these on outboard gear.

There's a lot of protection there, short circuit, over current, thermal, ..
It could anything but I don't think it's simple overdriving the input.

To check the thermal, get a can of air. turn it on until it goes thermal and measure the temp at the sensor. Shoot some air on it and see if it comes out.

The other protection is measured off random output transistors. I doubt it but it could be one of them acting up. Here too you could blow air on them to see if they're thermal sensitive.

If it's still under warranty - or even a little out, get hold of Carvin, they are usually great about fixing stuff, especially if there is some design flaw in a protection circuit.

[BassmanPaul]

Are your cables speakon or 1/4" phone???

[Passinwind]

Originally Posted by seamonkey

Nice Amp
Optical Limiter - people pay big bucks for these on outboard gear.

Just a black box, no magic there. Really cheap to implement too.

[seamonkey]

Originally Posted by Passinwind

Just a black box, no magic there. Really cheap to implement too.

Careful ... we don't want to get into huge discussions on if LED or incandescent lights are better

I just glad to see Carvin adding all these features in for their price point. They still are a bunch of great (US) engineers.

[groovaholic]

My cables are Speakon, man!
Short as possible too...<3 ft.

1/4" scares me for anything above 50 Watts...

I use 12ga Carol cable, tinned at the ends, and Loc-Tite on the screws.

I'm a little OCD about speaker cables...

[groovaholic]

Follow up to this thread; I didn't have any audible clipping, but as part of my experiments, I engaged the active input pad.
With it engaged, was able to get even more usable volume out of this amp.

It really is a big beast...