Re: Need ideas for 8-channel output
- From: "Doug B." <c.difficile@xxxxxxxxx>
- Date: Wed, 1 Jul 2009 19:06:36 -0700 (PDT)
On Jul 1, 1:36 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@xxxxxxxxxxx> wrote:
Doug B. wrote:
Hello all,
I am getting started in electronics and would like some design advice
for a circuit that I have built, but am trying to improve.
This project involves a simple, 8-channel power amplifier. The input
will be a 1-10 Hz, audio-level control signal that will be either a
pure sine wave or something very close to it. The output stage will
drive a mainly resistive load (NOT audio at all, just driving lamps,
solenoids or similar). My current design and prototype uses IRF-511
power MOSFETs, driven in switching mode from a 13.2 V regulated power
supply.
The client is a artist friend of mine who uses sub-audio range signals
to control a bunch of different gadgets he has built. Currently he
amplifies these with a stack of car stereo amps that are hard to
transport and only provide four mono channels each. I believe we can
get all eight channels of amplification into a small box, as long as
the output stage is driven PWM-like. I am basically looking for a way
to provide reasonable dynamic range on the output, given the audio-
level inputs.
My current prototype uses an LM124 op amp with > 100db gain to
transform the input into a square wave, directly into the gate of the
IRF-511. This "on or off" amplification is not flexible enough.
My current thinking is that PWM is the way to go on the output, but
how to do that for 8 channels? I have looked into Class D amps, but
workable designs seem over my head in complexity and would require
absurdly large output filters for the low frequencies involved.
I have thought of using an analog Mux and microcontroller with ADC to
sample the levels on the 8 input channels. Given the low frequencies
this should be fairly straightforward.
I'm not sure how to handle the output, however. I could create a PWM
signal in the uController and analog Mux it out to an op amp buffer/
gate driver, but I would only get 1/8 of the PWM cycle on each
channel.
Ideas, anyone?
Thanks,
doug beeson
Maybe that'll help you out.http://focus.ti.com/lit/an/sloa031/sloa031.pdf
you could make a board that holds a single Class D IC and power driving
section, out source the boards to be etched and drill and simply make a
form of card rack to support the number of channels desired.
This rack would have one main power supply for it.
Just and idea..
Jamie,
Thanks for the idea and document. I'll have a look, but full out Class
D seems overkill for this (and frankly too hard for me to tackle at
this point).
For my prototype board, I did the design in Eagle and had a couple of
boards etched by Batch PCB (http://www.batchpcb.com). Double-side and
through-hole (so a lot of soldering pins for me), but they did a nice
job. I eventually want to move up to SMD parts using some of the tiny
soldering techniques that have been discussed here.
doug
.
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- Need ideas for 8-channel output
- From: Doug B.
- Re: Need ideas for 8-channel output
- From: Jamie
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