ICEPOWER Bass Amplifier

[Robin28]

Hi,
I'm on a new project,
I try to build a bass amp with an Icepower 700AS1.
=> https://icepoweraudio.com/buy/as-series/700as1/
I built before it a Baja Orange preamp and a mixer to add more fonctionnality to the amp (liked below)

=> https://pcbguitarmania.com/product/lemon-bass/


Everything is working find and sounds really good but if i turn the volume up the amp goes to safety mod and cut the sound (the volume isn't really loud when cutting, lower that my 500w aguilar).
If I limit the input to more or less +/-0.7 V it isn't cutting, but the volume is really low. (the datasheet says +/-12v)

I check all the safety point and evrything looks fine.
The overcurrent Monitor pin:
It gave me 5V
The Termal shutdown Pin:
3.8 V
and the temperature monitor pun
5V

I tried to plug my preamp in the return of the FX loop of my aguilar tonehammer 500W (who as a Icepower 250ASX2 inside) and it works fine (so no issue with the preamp)
I pluged  FX send of the tonehammer (so the output of the aguilar preamp) into my Icepower 700AS1, and the sound cuts .

i tried a High pass at the output of my preamp at 10khz, didn't change anything.
I tried Different speakers, 4 and 8 ohms.

I'm kind of stucked, i don't know what else to try and Icepower doesn't answer to my emails :/

[ElectricDruid]

I had a read-through of the datasheet and I don't see anything that yells at me.

As you say, the input level is way off what's required to shut the board down, so that seems unlikely. But then you say that turning the volume down fixes the problem, which makes it sound like that's *exactly* what's going on!

So could there be some other complication here? What are you running it *into*? Maybe it's that that it doesn't like?

The good news is that it sounds like they've done pretty comprehensive protection on their circuit board, so once you get it sorted, it'll be fine.

One other minor thing: From your numbers, it looks like the you got the temp monitor and thermal shutdown voltages the wrong way around. That's clearly a simple mix-up.

[Rob Strand]

If I limit the input to more or less +/-0.7 V it isn't cutting, but the volume is really low. (the datasheet says +/-12v)

I can only look at it quickly today.   

You sound like you know what you are doing but I will mention it anyway:  Are your speaker outputs floating from ground?  If the socket is ground at the speaker output it will cause a short and the amp will shut down due to over current.

Your description of the symptoms seems like the amplifier is cutting out due to the "loop saturation protection".  When you crank a bass amp it's inevitable the output clips at times and that will trigger the "loop saturation protection".   The document says the amp will handle loop saturation for 100ms to 500ms before tripping in order not the trip with clipped music -which is fair enough.   What's not clear is how the loop saturation detection resets after a short overload.   What happens if you get a whole stream of clipped peaks in a short space of time?

While the maximum analog input is +/-12V, the amp output is 76Vpk and the gain is 27.4dB.  So the nominal sensitivity of the audio input is 3.2Vpk or 2.3V rms for full output.

It would be helpful if you had a 4 ohm or 8 ohm dummy load and a sine-wave generator.  Then you can see exactly what conditions of clipping cause it to trip.    You mentioned 0.7V, which I'm assuming is peak, but I'm not 100% sure how you are generating that input.   It does seem very low.

As an experiment you could place an LED clipper between the preamp and the power amp:

Preamp out (ac couple o/p) --> 2k2 resistor --> two parallel back to back RED LEDs --> Power amp input (ac coupled).

That won't give you full power but it might help identify the problem.   You can play with different clip levels.  For example try just silicon diodes to start - if that doesn't work there's something seriously wrong.

Just an idea: I'm not exactly sure what the HF protection looks at.  I suspect it might be there in case the output inductors fail and short.   It's not clear if the HF protection can trigger when clipping.     Even the clipper will produce higher order harmonics so maybe a 20kHz low-pass filter is required after the clipper.

The fact the manufacturer doesn't respond is odd.  Maybe they have a build problem and wrong/small cap values in the fault detection circuits and that's causing the amp to trip with very short fault times.

[Robin28]

Thanks a lot for the answer ..
I feel really dumb cause I've been on this project for 3 weeks without finding the issue. I you found it right away.
It was the output jack. I stupidly used a regular one the the -  of the amp was connected to the ground.

Thanks a lot for the help.
I could finish it today. And sounds amazing. And really loud

Thanks again

[Rob Strand]

I could finish it today. And sounds amazing. And really loud

Yes, the last generation of Class-D amplifiers are good quality and get crazy amounts of power in a small footprint.   I look at my old 300W BJT amps with massive transformers and heatsinks and wonder why I bother with them.  (Mind you, I doubt the class-D amp will last as long.)

[Robin28]

Hahaha I agree with you on that point.
I still use my trusty bassman 100 from the 70's.
But the class d is convenient and light weight.
And truth is with a good preamp. It doesn't sound bad at all.
By the way here is the finished amp

[Rob Strand]

By the way here is the finished amp

Awesome - it's like wolf in sheep's clothing.