You messed up the input opamp so it is inoperative.
Vf5 is an extremely low signal voltage mixing node. Vf4 has the mixed output signal.
Can you turn off the dots that are all over the place?
Uncle $crooge
I redid TINA using your mixer
I found an interesting artical talking about mixers
Simple Mixer Schematics
Just for the learning process I inserted drawing # 3
The outputs look exactly the same??
hard to read with the gray background. printed it out = readable
any comments on schematics?
I thought you knew that an active mixer uses an inverting opamp and every input has its own input resistor.
But you do not show a mixer because yours has only one input. It is just an inverting opamp.
The second opamp is just an inverter and does nothing.
Can you turn off the dots that are all over the place?
Uncle $crooge
only simulating one channel
I can't simulate more than one input.
the schematic is of one channel with one input.
I added some extra inputs in attached.
I show some screen shots of both inputs and one has 10db gain while the other shows -70 db loss
why I don;t know.
I printed out the explaniation of the circuit on
Simple Mixer Schematics
It's hard to read but down towards the bottom it says something about the circuit is a virtual ground and the summing of all the inputs.
interesting reading. weather its right??
like what do I know--not much in this field
VF5 is a virtual ground without a signal voltage. It has some low and high frequencies because of the phase shifts of the filters and because C7 has some reactance that blocks some of the virtual ground effect.
The output is VF4 which shows two peaks at +10db.
Try simulating it with C7 replaced by a piece of wire.
OP3, OP6 and OP7 can be removed with no change in how the circuit works.
Last edited by audioguru; 8th March 2009 at 12:14 AM.
Uncle $crooge
removed c7
inserted piece of wire = only VF5 changed
I want to keep op3 & 6 to act as a way to isolate the outputs of the filters instead of one output to the displays I have 5 per channel
I simulated without OP3 & 6 and all the peaks are then on the one output.
remember I have 5 peak detectors/displays per channel
As for op7- After reading the artical about summing all the different inputs (a total of 4 per channel)
not really sure if the following is gospel??
op7 as I understand from the artical, it reverses the phase/.
Because the summing node (The inverting input of the op-amp) is at virtually earth potential, there is little chance that this signal will bleed it's way out to any of the other inputs. Essentially speaking all the audio sources are isolated from each other.
However we're still left with the problem of the phase being wrong. If the output of the first op-amp were recombined with one of the other signals at a later stage it would cancel out rather than mix. So we have to re-invert the phase with yet another op-amp. This is a unity gain amplifier just like the first except that there is no summing node as such. (Except for the feedback resistor of course) The output of these two stages will now be the summ of all the inputs with the correct phase. Because of the inherent compensation of the feedback/op-amp/summing node, there is virtually no limit to the number of inputs you can put on this. Most modern op-amps have enough drive capability that 128 inputs would be just peanuts.
However it must be remembered that you are summing the inputs so if you had a powersupply of say +/- 15 volts, and 4 inputs of +5 volts each, The result would be 20 volts mathematically speaking. But the op-amp can only produce +15 volts so you would be clipping by 25%. Distortion occurs. Most op-amps can't swing exactly to the supply rails so clipping and distortion would be even worse. In practice however most audio signal wouldn't exceed a few hundred milivolts. A 2 volt peak to peak signal is considered to be a very high level.
Yes only VF5 but were most frequencies at -75dB?Originally Posted by MrDEB
The filter's opamp drives only its own peak detector. Adding the tiny loading of the output mixer makes no difference. OP3 and OP6 do nothing.I want to keep op3 & 6 to act as a way to isolate the outputs of the filters instead of one output to the displays I have 5 per channel
I simulated without OP3 & 6 and all the peaks are then on the one output.
remember I have 5 peak detectors/displays per channel
The output mixer is supposed to mix the frequencies together.
You cannot hear if the phase is reversed or not. Many opamps in your circuit reverse the phase and you cannot hear it. You are not mixing a non-inverted signal with an inverted signal like the article warns about.As for op7- After reading the artical about summing all the different inputs (a total of 4 per channel)
not really sure if the following is gospel??
op7 as I understand from the artical, it reverses the phase.
Uncle $crooge
leave the wire or capacitor??
it looks like it dosn't affect to output with or with out. just at vf5 point which I put there just to see what it has. not to be included in design
I want the displays to show what each filter seperatly is doing. without op3 & 6 all the signals are mixed together so all the displays will show the same.
as for the op7, I will take it out as it really isn't needed. I just inserted it as the artical showed it in the circuit.
took out op3 and 6
left the 100k resistors and I still get seperate waves for each filter.
Vf4 has all and vf2 & 3 have their own wave.dosn't look like I lost any Db gain. still at 10db
now to get back to the mixer input.
going to go back to your design = 1 op am, 1 pot and 1 resistor per input per channel
See how the VF5 now has a frequency response now that is the inverse of the open loop frequency response of the last opamp?
True, the design does not use VF5 as an output.
The output of a filter feeds its own LM3915 display. It also feeds an input on the output mixer so that the audio of all frequencies are mixed together. Each display is separate from the other displays with or without OP3 and OP6. So remove OP3 and OP6.I want the displays to show what each filter seperatly is doing. without op3 & 6 all the signals are mixed together so all the displays will show the same.
Good.as for the op7, I will take it out as it really isn't needed. I just inserted it as the artical showed it in the circuit.
EDIT:
It is very confusing talking about the opamps since their numbering is different on the schematic and on the simulation.
Last edited by audioguru; 8th March 2009 at 05:23 PM.
Uncle $crooge
I will correct that later
I am going to etch a small pc board but trying out using fuji photo paper on a laserjet printer.
different project = the motorcycle flasher project that someone was talking about.
On the subject of etching I like using the acid/hydrogen peroxide mixture
not as messy. may take a little longer but works great and is lots cheaper.
will make revisions on schematic and post later today.
TINA looks good??
redrew simulation and it is back up to 10+Db
seperate output waves per filter
input mixer (only one showing is still under design
Tina & schematic are the same
changed the schematic to match TINA on the op amp #'s
turned off grid as well
I guess OP4 is the output mixer. Please label it as a mixer.
The input level control is only 10k ohms and the input opamp has an input impedance of only 47k ohms (is it a mixer too?). Thebn the small value of the 220nf input capacitor cause 89Hz to be reduced -3db and frequencies below 445Hz to be reduced (no deep bass). if the volume control is 100k and the resistors on the first opamp are also 100k then the cutoof frequency will be 14.5Hz when the capacitor is 220nF and will be 9.7Hz when the capacitor is 330nF. Flat down to 48Hz.
Uncle $crooge
input mixer circuit
is based on this link
6 Input Mixer
need to reconfigure input.
the output "mixer has 5 filter inputs (never really thought of it as a mixer??)
will make suggested changes
as for etching the pc boards -- don't even try using photo paper.
ended up using the PULSAR paper. works great.
when I get this design down pat I plan on using said etching system.
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