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virtual earth mixer NE5534 problem
virtual earth mixer NE5534 problem
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Old 9th February 2017, 11:58 AM   #1
b0red2tears is offline b0red2tears  Australia
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Default virtual earth mixer NE5534 problem

I'm building a 6 channel mixer with mute switches but its not working correctly.

Hopefully someone can help me…

For the audio switches I've used cd4016 ic's. For signal mixing I've used info from

Audio Signal Mixing
Active Mixing Circuit ('Virtual Earth')

The audio switching and the analogue portion of the signal mixing seems to work fine. The OP amp (referred to as Recovery Amplifier) works also but when it is operating the MUTE switches, they seem to "leak" when they are activated. You can hear, very quietly, the heavily distorted audio signal. Its the same symptom when the level pots are turned to just above minimum.

Without power supplied to the OP amps the mute's operate cleanly even if I turn my speaker gain right up.

Click the image to open in full size.

OP amp part only so its less confusing.
sorry, hope you can decipher the circuit from pcb layout. I could hand draw as schematic otherwise.

I noticed i've not included capacitors on the power inputs, could this be the problem? also no blocking caps on the inputs.
Its powered by the first dual supply i've ever constructed so the problem could relate to power supply also.
Click the image to open in full size.
I suppose I don't need to mention I'm a newbie to electronics and especially circuit design, my knowledge is limited to what I have been able to learn from the web and trial and error during the last 18 months.

Any help would be much appreciated
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Old 9th February 2017, 12:36 PM   #2
sgrossklass is offline sgrossklass  Germany
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Quote:
Originally Posted by b0red2tears View Post
For the audio switches I've used cd4016 ic's.
Wow, 4016s, who uses those any more? Any reason not to go with 4066s instead? They're basically the same but better, and have been available since some time in the early '80s.
Quote:
Originally Posted by b0red2tears View Post
sorry, hope you can decipher the circuit from pcb layout. I could hand draw as schematic otherwise.
Please do so. It's always a good idea not to require too many mental contortions from those trying to help you.
Quote:
Originally Posted by b0red2tears View Post
I noticed i've not included capacitors on the power inputs, could this be the problem?
Not good but seems unlikely. Looks like it should be easy to add some if you add a ground return to the power supply for each pair of +/-12 V.

Your grounding looks a bit suspect. The signal ground traces seem quite thin in parts, and apparently needlessly so. Since you haven't shown the entire layout it's hard to tell whether there's a general problem there, but it sure sounds like you're inserting signal into your ground prior to muting (pots?), and return impedance is not low enough to drain that effectively. Then the opamps pick that up via the ground.
Or does it all sound very thin? Might also be capacitive coupling then, your layout would be a bit on the sensitive side.
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Old 9th February 2017, 08:57 PM   #3
Zero D is offline Zero D  United Kingdom
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@ b0red2tears

If you upload a circuit diagram of the whole thing, we will have a better chance of assisting you

With 40 type switches it's better to use two as in my screenie. When A is on B is off & vice versa. So when A is off B gets shunted to common & no leakage gets through

As you're using CMOS switches then use a CMOS inverter, for eg 4009 series
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Old 10th February 2017, 12:14 AM   #4
b0red2tears is offline b0red2tears  Australia
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I'm sure now it is grounding problem. I've added 0.1uf caps on the power inputs and 1uf caps following the pots. But no help. Tried putting signal ground closer to OP amp - seems i had it in the worst place: everywhere else was an improvement.
But I think I need to start again at the beginning
this is the first part.
Click the image to open in full size.

@Zero D I'm using a complementary push pull circuit (with 2 555 timers) this takes the input from a momentary sw and outputs latched +/- red led for mute or -/+ green led for on. Another reason I used that was because I can
1. always start in Mute position on power up
2. accept an external trigger to mute (in my case a signal from clip limit)

Currently use this to control 4016 through a couple of diodes but couldn't it be used to perform function of the inverter also?
Or am I completely missing the point - I hadn't heard of a CMOS inverter

Thanks for the help so far
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Old 10th February 2017, 01:09 AM   #5
b0red2tears is offline b0red2tears  Australia
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better?
Click the image to open in full size.
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Old 10th February 2017, 02:25 AM   #6
b0red2tears is offline b0red2tears  Australia
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Quote:
Originally Posted by b0red2tears View Post
better?
Click the image to open in full size.
suppose the 1k resistor to earth is no longer required
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Old 10th February 2017, 05:22 AM   #7
PRR is offline PRR  United States
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The '4066 part will work better many ways.

The 1K loading makes HUGE distortion. Even 10K will be audible.

That "signal sense" is a heavy distorter. The '4066 part will work better many ways.

The 1K loading makes HUGE distortion. Even 10K will be audible.

That "signal sense" is a heavy distorter.

The one-side CMOS switches *must* have their audio ports biased-up halfway between their power pins, else they clip.

The '4051.. types can be connected audio on +/- supply and logic on 0/+ supply.

In general, pot-down before the switch to reduce level in the switch and point-one % order switch distortion (but fix the big distortions first).

If possible, buffer the switch into a 1Meg load so THD drops to oh-oh levels.

Really-really-- PLAGIARIZE!! This is not a new problem. Why drive through the swamp if there is a highway? And understand what you steal. Just call it "research". ((C)Tom Leher)
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Old 10th February 2017, 05:57 PM   #8
AuroraB is offline AuroraB  Norway
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I built some mixer additions and signal routing for a Soundcraft B400 many years ago using 4066 switches, but I put the switches in the virtual earth point, after the mix resistors. That worked very well, as I recall....... back in -84.....
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Old 10th February 2017, 06:01 PM   #9
Zero D is offline Zero D  United Kingdom
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As other members have noted, there are better IC's than 4016's. Search for them on the www & compare data etc. It's been a Looooong time since i used 4016's, but i'll offer what i can.

Quote:
I'm sure now it is grounding problem .....
Keep your LED & 555's & CMOS commons/grounds connected together to one point. Keep your OpAmps & audio commons/grounds connected together to one point. Then connect both points together. This should help keep noise etc away.

Quote:
I'm using a complementary push pull circuit .....
OK

Quote:
Currently use this to control 4016 through a couple of diodes ...
You don't show the diodes connected. What's the thinking behind using them ?

Quote:
better
No. First off, the CD4016 is Only rated @ 15V MAX ! You show it on a +- 12V supply ? That would blow them ! So, +12 to pin 14 & common/ground to pin 7.

Also, your better circuit is "trying" to do what i suggested with an Inverter, which "might" work, but i'm not sure if the resistor to pin 13 from +12V will cause problems ! I think you may need a resistor from each signal CMOS input & output to common, say 100k for eg. Then you could connect say 1uf non polar caps to each input & output.

Quote:
suppose the 1k resistor to earth is no longer required
Correct, due to the above.

If you havn't got the datasheet, then http://www.ti.com/lit/gpn/cd4016b
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Old 12th February 2017, 03:14 AM   #10
b0red2tears is offline b0red2tears  Australia
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@ Zero D
I tried the circuit on breadboard with the changes you suggested along with biasing the in out ports at half vcc without any success. Kept seeing close to the the control voltage at the in/out ports which can't be right? Also got heavy distortion (constant) and a clicking when grounding control for off state.
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