NHT Surplus plate amps- Foster

[bobhowell]

I have two of the Foster amps from NHT. I have read over the instruction for adjusting the filters many times but can't make sense of them. I think I have figured out the spectral tilt adjustment, but not the highpass filter part. It uses terms that I know nothing about.

I understand it has a high pass filter set to roll off the sub at 29hz and I can live with that but what about the talk about Q and .707. Where does this fit in?

I want to know if it has a cross over function built in that will allow me to use it to roll off the mains as the sub comes up. I dont think so but what is all the electronics for? I will run the speaker level inputs into the plate amp and on into the mains. Is there way it will roll off the input to the mains?

I'm hoping someone has these and figured out the answer.

Thanks

Bob Howell

[ThomasW]

Not having access to the instructions makes it a little difficult to comment.

Brandon (augerpro) is making a design with these amps. If he doesn't post in your thread PM him.

[augerpro]

The Q just tells you about the slope of the roll off. A Q=.707 is simply saying this a 3rd order Butterworth filter. Don't worry about any of that, the important point is that if you want to change the boost frequency you have to first switch it to a 2nd order filter than tweak the values to adjust the boost.

It appears that the speaker outputs are not high passed. Looks like the speaker in/out is simply passed through, it's just tapped into for a signal to the sub amp. It also doesn't appear that the sub low pass can be turned off (bypassed) with a switch.

Are you using a regular HT receiver? You'll use the reciever to HP the mains, and then either use it's sub LP in addition to the sub's own LP, or if possible you may be able to send a full range signal to the sub amp and just use it's LP. Some receivers allow you to do this and some don't. For example on my Rotel I can turn on/off the crossover and adjust it's frequency for every channel independently of the others. On my Yamaha it's a global setting, i.e. if it is on you pick one crossover frequency and it is used to HP all the speaker channels and LP the sub output.

[bobhowell]

Thanks,

That's just what I wanted to know. I want to initially use this as the B speakers set with my A/V receiver, which has no sub pre out for that set and no crossover. I guess I will have to get a Rechorn or some such to make this work. Or cross over at f3.

Bob