Crest CA9 power amp questions

[coolhandjjl]

Can I ask Crest CA9 questions here?

[JoshM]

Can I ask Crest CA9 questions here?

You can ask whatever you like.

The answer you will depend on a lot of factors.

So yeah, ask away.

[coolhandjjl]

The internal jumpers are set for input sensitivity of .775v. I would like to change it to the next step of 1.66v, but there is no information I can find to show me what position to move them to. I was hoping someone who knows the CA9 inside and out could help me out rather than having to send it in.

[Enzo]

So you want to reduce its sensitivity so you have to feed it more signal for full output?

Talk to customer service at Crest and ask for advice. I am embarrassed to say I don;t know if the number is the same for Peavey itself or not, but I am sure the Crest web site has contact information.

Here is the support page that includes Crest, phone and email addresses there.:

http://www.peaveycommercialaudio.com/support.cfm

[JoshM]

I just spoke with the fantastic guys over in Crest Audio Support.

Apparently this is very easy to do by simply moving a jumper on the preamp board on each channel of the amplifier on amplifiers that have been manufactured in the last 12 or so years. Prior to that you needed to bust out your soldering iron and use a little piece of wire to do what the jumpers do in the newer versions.

If you want to change the input sensitivity to the 1.66V setting, you will need to move the jumper to the middle two pins.

Please see the attached document for more specific instructions.

If you have questions about this, please take a moment to call and speak with Crest Audio support. They would be glad to help you.

[coolhandjjl]

Thanks Josh. I emailed tech support and Roger just replied with the PDF as well.

Right now, they are at the factory position of .775v.

If I have a preamp that is outputting closer to 1.5v or so, am I damaging the CA9 in the .775v setting, or possibly distorting my input signal? Should I move the jumpers to the 1.66v setting?

[JoshM]

You will not damage the amplifier by doing this. However, you may cause it to clip if you actually drive it that hard. There are clip indicators on the front of the amplifier to tell you that you are driving the input too hard. When these flash, you should turn it down.

Changing the input sensitivity will not change how much output you get from the amplifier. You will always be able to drive it to full output. You are just changing the amount of input signal that is required to do that.

When the clip lights flash, you are getting all the amp can give.

Because you are curious about it, I would say go ahead and move the jumpers and see how the behavior changes. Then you will know which way will work better for you. You will not hurt the amplifier either way, but you may like how your preamp control works better one way or the other way.

[Marty McCann]

I would not recommend for the reason that you would be throwing away headroom in the device driving the power amp. If the device has a max output of 1.5 Volts and you set the amp for a 1.66 Volt sensitivity, then the device will clip beofre the amp reaches full power and goes into soft limiting.
You are best to leave it alone.

If you do not understand this, then you definitely need to leave it alone.

[coolhandjjl]

Yeah, I'll leave 'er alone. I can use the CA9 clip lights to monitor my input level and adjust at the preamp master as necessary.

[Enzo]

And remember to use your ears. It is OK for the clip lights to blink now and then. If you don;t hear a problem then there probably isn't a problem. I don't know the CA9 myself, but Marty mentions soft limiting, which if it is like the Peavey DDT system means you can send it a lot of peaks that will never clip audibly.

[coolhandjjl]

Thanks for all the helpful information, and especially to Peavey for their great support!

[JoshM]

And remember to use your ears. It is OK for the clip lights to blink now and then. If you don;t hear a problem then there probably isn't a problem. I don't know the CA9 myself, but Marty mentions soft limiting, which if it is like the Peavey DDT system means you can send it a lot of peaks that will never clip audibly.

Hey Enzo,

Yes, the Crest amplifers generally have had an anti-clip limiter built in that is similar in operation to Peavey's DDT. This was present at least as far back as when the old Professional series was developed and I believe (but I am not certain) that it was in the CA series as well. So, it was built into the amplifiers long before Peavey bought Crest Audio. Consequently, I expect that the design and implementation is different, but functionally I would say that it performs in a similar fashion. It engages to limit the input to the amplifier section when the incoming level is high enough to drive the output into clipping.

One neat thing about the Crest implementation is that it is actually two stage in operation.
First you have the softer limiting just to keep it from driving it straight into clipping.
But, if you drive it hard enough for long enough...
Second you will get gain modulation. This is where the input level is actually reduced to keep the output stages of the amplifier from clipping.
This is why you will see on some amplifiers "Clip/Limit/ACL" on one LED and "IGM" on another LED. This is to inform the user that they are activating the clip limiting firstly, then that the gain is being modulated.

It is a good system, and it seems to work really well.

[sla-ms]

hello,

I have just applied the changes you have said, and have just cleared a power stage of this change!

help me ...