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virtual earth mixer NE5534 problem
virtual earth mixer NE5534 problem
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Old 12th February 2017, 02:23 AM   #11
b0red2tears is offline b0red2tears  Australia
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[QUOTE=Zero D;4983368]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.
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Old 12th February 2017, 02:42 AM   #12
b0red2tears is offline b0red2tears  Australia
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Quote:
Originally Posted by PRR View Post

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?
Click the image to open in full size.
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
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Old 12th February 2017, 06:04 AM   #13
PRR is online now PRR  United States
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> 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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Old 12th February 2017, 08:53 AM   #14
Zero D is offline Zero D  United Kingdom
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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.

Glad you found a www with useful info.

PRR offers good advice above.
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Old 13th February 2017, 02:39 AM   #15
b0red2tears is offline b0red2tears  Australia
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Quote:
Originally Posted by PRR View Post
>

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.

Quote:
Originally Posted by PRR View Post
>
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
Quote:
Originally Posted by PRR View Post
>
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.

Quote:
Originally Posted by Zero D View Post
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
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Old 13th February 2017, 08:47 PM   #16
Zero D is offline Zero D  United Kingdom
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OK If i miss your new post, then PM me & let me know you have
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Old 16th April 2017, 12:07 PM   #17
b0red2tears is offline b0red2tears  Australia
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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:
Click the image to open in full size.
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..
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Old 16th April 2017, 12:47 PM   #18
b0red2tears is offline b0red2tears  Australia
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Quote:
Originally Posted by Zero D View Post
@ 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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Old 16th April 2017, 09:25 PM   #19
diyralf is offline diyralf
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The main problem is the low voltage supply. 15V -> -+7V -> no head room, low level, high THD. CMOS logic is not sufficient for quality audio.

Last edited by diyralf; 16th April 2017 at 09:27 PM.
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Old 17th April 2017, 08:58 AM   #20
AndrewT is offline AndrewT  Scotland
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Read John Roberts:
cmos 4066 as an audioswitch?
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