virtual earth mixer NE5534 problem

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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.

U4uSSZ4.png


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.
KQ2lEv5.png

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
 
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.
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.
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.
 
@ 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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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.
x57kb2D.png


@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
 

PRR

Member
Joined 2003
Paid Member
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)
 
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.

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.

I'm using a complementary push pull circuit .....

OK

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 ?


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.

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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@ 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.
 
the CD4016 is Only rated @ 15V MAX ! You show it on a +- 12V supply ?

Yes they're probably damaged now. I was aware of the rateing but didn't know if that meant +/- 15v Tried to find the answer on google but obviously wasn't entering the correct search terms. A typical newbie problem the answer should be so obvious that no one explains - happens to me all the time
eventually I just tried one and it seemed fine so I continued…

At least 1 (I have 3) is almost certainly damaged, its acting different.
 
The one-side CMOS switches *must* have their audio ports biased-up halfway between their power pins, else they clip.

Is the 4066 a "single side switch" also?

I found and tested this circuit. Drawn in red how I connected - Have I implemented it correctly?
ei3jBJ2.jpg

Seems to work well, clean on/off and I didn't notice any distortion.

The designs on this website seem ancient but he seems to know what he's talking about.

Audio Switch Notes
 

PRR

Member
Joined 2003
Paid Member
> Have I implemented it correctly?

Why a 1K load at the input?

Why a 20K/22K after that?

You only need one Vcc/2 bias source for a whole 96-in console's CMOS. But you should bypass it for cleanliness.

The Vcc/2 bias resistors should be high value. 300K, 470K, even 1Meg. They should put minimum load on the CMOS. They should be selected in conjunction with the blocking caps. 10uFd electrolytic is likely to leak a lot relative to 470K, and you do not need 0.03Hz response (until you grow to far larger systems). 0.5uFd will be a film-cap (low leakage).

The output blocking cap needs a to-ground bleed resistor, unless the next stage can serve that function.

The CD40xx series CMOS will BLOW UP if fed over 18V *total*. It is far safer to stay to 15V or 12V, as you show. At 12V they can pass not-quite 4V rms signal without clipping. This is very limiting in systems which run 10V (+20dBV) levels. However as an introduction, the CMOS do work OK in voltage-switching. (As mentioned, current-mode switching is more versatile but you need to integrate an amplifier into the switching.)

The control pull-up must go to the CMOS positive supply. Strictly it must go "way over half" of the supply, and worst-case it may need 2/3rd of supply to ensure switching with a bad chip in a hot room. 5V is not enough if the CMOS is eating 12V.

Are you sure you need the control inverter? CMOS control is zero-power, you sure do not need a buffer. Generally you can re-think your switching so you don't need added inverters.
 

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>

Why a 1K load at the input?

Why a 20K/22K after that?

I thought the 1k load might be to reduce presence of control voltage bleeding into the input? But thats a wild guess, I included it because this (and most of his other schematics included it. As for the 22k load I can't see any purpose other than reducing input level so was hoping it could be avoided.

>
You only need one Vcc/2 bias source for a whole 96-in console's CMOS. But you should bypass it for cleanliness.
I assumed only 1 source would be required but wasn't sure
>
Are you sure you need the control inverter? CMOS control is zero-power, you sure do not need a buffer. Generally you can re-think your switching so you don't need added inverters.

Not sure at this stage, but probably not.

Any you used on an over voltage supply, i would dump them, even if they appear to work. Even they didn't blow, they will be weakened/damaged in some way & not reliable.

Yes I was thinking that. I have some 4066's coming, the reason I started with the 4016 was because it was in my local retailers parts catalogue.

Thanks for the wealth of useful information and the time you took in providing it! It may take some time but I will do some further testing and post a schematic of my proposed circuit before putting it onto pcb. Hopefully at that time you would be able to suggest improvements and / or offer some tips on designing the layout
 
Hello, after playing around a bit I have my device working! But there are some issues and a lot that I think can be improved on. This is the schematic for the audio switch i've assembled:
9AXbLIe.png

Switching is clean and i've not noticed any degradation of sound quality, except a slight hum. Its very slight and was barely audible on my small test speakers, but on my larger sound rig its at an unacceptable level. I've tried moving circuit further away from PSU and tested with a different high quality PSU. The later greatly lowered the noise but it was still present.
I'm fairly sure this noise could be prevented with a better PCB layout and more attention to routing of ground traces but wanted to ask:
Would it be better to use a dual supply e.g. +/- 5v to power the 4066?
And if so, am I correct in assuming that the inputs/outputs would then no longer need to be biased up to 1/2vcc?
I also have some questions about routing unselected outputs to gnd and doing the switching at the virtual earth stage but one thing at a time..
 
@ 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

I've tested this to try to eliminate leakage. Experienced a sharp clicking whilst switching. Managed to stop the clicking by inserting a small (47pf) cap in between switch B output and ground. I feel this is not the correct solution though and instead switch times need to be staggered i.e. Switch A must be off before B is shunted to gnd for OFF state. But then, for ON state B would need to open the connection to gnd BEFORE switch A turns on. How would I achieve this?
 
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