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Old 30th June 2005, 12:11 PM   #1
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Default Gain adjust? Where?

I will be building some filtering and buffers into the same case as my chip amps, and I will configure and use them for various things eg stereo power amp, active bi-amp system, tri-amp system.

Anyway, there seems to be options of adjusting gain at the input buffer, or the output buffer, or in the power amp.

Note, I am interested here in fine adjustment to the different (channels?) that I have split the signal into. The overall volume and levels between the 5.1 channels will be set with an AV pre-amp.

I've not seen any mention of adjusting the gain of the chipamp section. Can I put a variable pot in here?

What are the pro's and cons of where you put the trim pot?

I can make gross changes as well by changing fixed RC values, so maybe +/- 3db could be all I want for this fine adjust.

Any comments?
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Old 30th June 2005, 02:20 PM   #2
diyAudio Member
Join Date: Dec 2001
Location: SIUE, Illinois, USA
there was a thread on this a while back. dealing with various ways to handel the gain. not sure where it is now thoguh. maybe someone else remebers?
if only it could be used for good, not evil...
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Old 30th June 2005, 03:42 PM   #3
Mr Evil is offline Mr Evil  United Kingdom
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I would favour putting the level adjustment as late as possible for the best signal-to-noise ratio. Immediately before the power amp if possible.

You can do it even later by adjusting the gain of the power amp itself, but there are reliability issues with using a pot in the feedback loop.
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Old 30th June 2005, 04:24 PM   #4
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Join Date: Jun 2005
Location: Seal Beach, CA
If you are going

AV/Reciever -> Buffer -> Chipamp

And your AV Reciever has a per channel control, just leave the chipamp with nothing but a power button on the face. Build in a 12V ON switch so that it will automatically turn on with the amplifier, and just be done with it.

No reason to have too many volume controls. Plus having an adjustable feedback resistor (pot) is pretty iffy. I only put very high quality resistors in my feedback. Usually you control the volume via preset gain and just attenuating the signal using a standard pot.
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Old 30th June 2005, 04:38 PM   #5
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Location: UK, bristol
I need gain adjustment when bi or tri amping.

I think I now favour adding it to the input buffer because I don't think I willl have an output buffer between the filters and the amplifier chip. So that is one less op-amp (unless I use passive attenuation).

PS. what do you call the separate signals that result from splitting a channel into eg Hi/Mid/Lo, are they channels?
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Old 30th June 2005, 04:56 PM   #6
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Join Date: Jun 2005
Location: Seal Beach, CA
Well if you insist on it then I would get either a high quality pot or use a digital pot. There are some easily controlled linear taper digital pots out there that would suit you nicely.
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