Curious how this design with op amps functions?
https://ibb.co/S4ryQJcF
Apparently the voltage divider network resistors are precision values,
so I suppose the op amps are comparing the incoming signal with the
input side of the op amp tied down to certain voltage levels and the higher >that signal is, it just turns on the op amp?
Would that input signal have to be DC? Its for an audio processor
so it cant merely be the audio signal?
Curious how this design with op amps functions?
https://ibb.co/S4ryQJcF
Apparently the voltage divider network resistors are precision values,
so I suppose the op amps are comparing the incoming signal with the
input side of the op amp tied down to certain voltage levels and the higher that signal is, it just turns on the op amp?
Would that input signal have to be DC?
Its for an audio processor
so it cant merely be the audio signal?
On Tue, 30 Jun 2026 15:40:43 -0400, "UFO" <techforce@nospam.gmx.com>
wrote:
Curious how this design with op amps functions?
https://ibb.co/S4ryQJcF
Apparently the voltage divider network resistors are precision values,
so I suppose the op amps are comparing the incoming signal with the
input side of the op amp tied down to certain voltage levels and the higher >> that signal is, it just turns on the op amp?
Would that input signal have to be DC? Its for an audio processor
so it cant merely be the audio signal?
The IC power connections aren't shown, but I assume the low sides are grounded. And LM339's do not like negative inputs.
Maybe the audio was processed into DC elsewhere.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
On Tue, 30 Jun 2026 15:40:43 -0400, "UFO" <techforce@nospam.gmx.com>
wrote:
Curious how this design with op amps functions?
https://ibb.co/S4ryQJcF
Apparently the voltage divider network resistors are precision values,
so I suppose the op amps are comparing the incoming signal with the
input side of the op amp tied down to certain voltage levels and the higher >> that signal is, it just turns on the op amp?
Would that input signal have to be DC? Its for an audio processor
so it cant merely be the audio signal?
The IC power connections aren't shown, but I assume the low sides are grounded. And LM339's do not like negative inputs.
Maybe the audio was processed into DC elsewhere.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
On 6/30/2026 3:40 PM, UFO wrote:
Curious how this design with op amps functions?
https://ibb.co/S4ryQJcF
Apparently the voltage divider network resistors are precision values,
so I suppose the op amps are comparing the incoming signal with the
input side of the op amp tied down to certain voltage levels and the
higher
that signal is, it just turns on the op amp?
Essentially yes.
The 339 is a comparator. You could think of it as a digital
switch - either on or off - depending on the comparison between
two levels. All of the even numbered pins on the input side in
your schematic have a reference voltage established by the
resistor chain. When the input signal on the odd numbered pins
varies above and below the reference voltage, the op amp comparator
turns on or off.
Would that input signal have to be DC?
No.
Its for an audio processor
so it cant merely be the audio signal?
It can.
Ed
On 30/06/2026 21:19, ehsjr wrote:
On 6/30/2026 3:40 PM, UFO wrote:There is a problem with that.-a The comparators could have a
Curious how this design with op amps functions?
https://ibb.co/S4ryQJcF
Apparently the voltage divider network resistors are precision values,
so I suppose the op amps are comparing the incoming signal with the
input side of the op amp tied down to certain voltage levels and the
higher
that signal is, it just turns on the op amp?
Essentially yes.
The 339 is a comparator. You could think of it as a digital
switch - either on or off - depending on the comparison between
two levels. All of the even numbered pins on the input side in
your schematic have a reference voltage established by the
resistor chain. When the input signal on the odd numbered pins
varies above and below the reference voltage, the op amp comparator
turns on or off.
Would that input signal have to be DC?
No.
Its for an audio processor
so it cant merely be the audio signal?
It can.
Ed
-15V negative supply as they tolerate up to 36V in total.
However, if that were done, the leds could be reverse biased
by up to 15V which would be likely to destroy them.
So I think there is a rectifier and filter circuit first,
especially as the VU standard requires a relatively
slow time constant.
John
On 6/30/2026 4:17 PM, john larkin wrote:
On Tue, 30 Jun 2026 15:40:43 -0400, "UFO" <techforce@nospam.gmx.com>
wrote:
Curious how this design with op amps functions?
https://ibb.co/S4ryQJcF
Apparently the voltage divider network resistors are precision values,
so I suppose the op amps are comparing the incoming signal with the
input side of the op amp tied down to certain voltage levels and the higher >>> that signal is, it just turns on the op amp?
Would that input signal have to be DC? Its for an audio processor
so it cant merely be the audio signal?
The IC power connections aren't shown, but I assume the low sides are
grounded. And LM339's do not like negative inputs.
Maybe the audio was processed into DC elsewhere.
Or the supply is +15 and -15 .
Ed
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
On 30/06/2026 21:17, john larkin wrote:
On Tue, 30 Jun 2026 15:40:43 -0400, "UFO" <techforce@nospam.gmx.com>
wrote:
Curious how this design with op amps functions?
https://ibb.co/S4ryQJcF
Apparently the voltage divider network resistors are precision values,
so I suppose the op amps are comparing the incoming signal with the
input side of the op amp tied down to certain voltage levels and the higher >>> that signal is, it just turns on the op amp?
Would that input signal have to be DC? Its for an audio processor
so it cant merely be the audio signal?
The IC power connections aren't shown, but I assume the low sides are
grounded. And LM339's do not like negative inputs.
Also, the circuit relies on the fact that these are open collector >comparators. Unlike many op-amps they tolerate a large differential
voltage input without the inputs conducting. The output is either
open circuit or pulled down to ground to extinguish all the leds
below that point.
ground.
"UFO" <techforce@nospam.gmx.com>wrote:
Curious how this design with op amps functions?
https://ibb.co/S4ryQJcF
Apparently the voltage divider network resistors are precision values,
so I suppose the op amps are comparing the incoming signal with the
input side of the op amp tied down to certain voltage levels and the higher >that signal is, it just turns on the op amp?
Would that input signal have to be DC? Its for an audio processor
so it cant merely be the audio signal?
"UFO" <techforce@nospam.gmx.com>wrote:
Curious how this design with op amps functions?
https://ibb.co/S4ryQJcF
Apparently the voltage divider network resistors are precision values,
so I suppose the op amps are comparing the incoming signal with the
input side of the op amp tied down to certain voltage levels and the higher >>that signal is, it just turns on the op amp?
Would that input signal have to be DC? Its for an audio processor
so it cant merely be the audio signal?
Much simpler to use a Microchip PIC 18F14K22 (for example),
and its analog input (ADC)
and its outputs driving LEDs via resitors.
Singe chip solution.
And more external control options possible.
I traced back the input signal seems to be this area
https://ibb.co/HpbN7pDm
R196 seems to be taking raw audio and feeding it into the op amp.
D71 is the output to the other circuit I posted.
The NP cap is prone to fail, not sure if that is critical?
I replaced it, but maybe need to recheck it.
Neither circuit shows power supplies.
The 4.7 farad cap might be expensive.
John Larkin--- Synchronet 3.22a-Linux NewsLink 1.2
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
"UFO" <techforce@nospam.gmx.com>wrote:
Curious how this design with op amps functions?
https://ibb.co/S4ryQJcF
Apparently the voltage divider network resistors are precision values,
so I suppose the op amps are comparing the incoming signal with the
input side of the op amp tied down to certain voltage levels and the higher >> that signal is, it just turns on the op amp?
Would that input signal have to be DC? Its for an audio processor
so it cant merely be the audio signal?
Much simpler to use a Microchip PIC 18F14K22 (for example),
and its analog input (ADC)
and its outputs driving LEDs via resitors.
Singe chip solution.
And more external control options possible.
Pin8 is +15
Pin4 is -15
Its a 4.7uF non polarized
Neither circuit shows power supplies.
The 4.7 farad cap might be expensive.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
Martin Brown <'''newspam'''@nonad.co.uk>wrote:
On 01/07/2026 06:27, Jan Panteltje wrote:
"UFO" <techforce@nospam.gmx.com>wrote:
Curious how this design with op amps functions?
https://ibb.co/S4ryQJcF
Apparently the voltage divider network resistors are precision values,
so I suppose the op amps are comparing the incoming signal with the
input side of the op amp tied down to certain voltage levels and the higher >>> that signal is, it just turns on the op amp?
Would that input signal have to be DC? Its for an audio processor
so it cant merely be the audio signal?
Much simpler to use a Microchip PIC 18F14K22 (for example),
and its analog input (ADC)
and its outputs driving LEDs via resitors.
Singe chip solution.
And more external control options possible.
The venerable LM3915 is probably a cheaper and better single chip
solution. You can still get kits using it even today.
https://quasarelectronics.co.uk/Item/3089-stereo-vu-meter-2-x-10-led-kit
john larkin <jl@glen--canyon.com>wrote:
On Wed, 01 Jul 2026 05:27:23 GMT, Jan Panteltje <alien@comet.invalid>wrote:
"UFO" <techforce@nospam.gmx.com>wrote:
Curious how this design with op amps functions?
https://ibb.co/S4ryQJcF
Apparently the voltage divider network resistors are precision values,
so I suppose the op amps are comparing the incoming signal with the
input side of the op amp tied down to certain voltage levels and the higher >>>that signal is, it just turns on the op amp?
Would that input signal have to be DC? Its for an audio processor
so it cant merely be the audio signal?
Much simpler to use a Microchip PIC 18F14K22 (for example),
and its analog input (ADC)
and its outputs driving LEDs via resitors.
Singe chip solution.
And more external control options possible.
Would you digitize the raw audio?
You'd have to offset and clip into a
unipolar uP ADC. That pic only has a 10-bit ADC.
And then there's the code.
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