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Best electronic switch for audio signals-logic drive
Best electronic switch for audio signals-logic drive
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Old 20th August 2018, 02:54 AM   #31
davidsrsb is offline davidsrsb  Malaysia
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Quote:
Originally Posted by zenelectro View Post
Looking a bit closer I think

a/ simulating 10kHz would be worthwhile and
b/ the harmonic spectrum looks pretty nasty ie; you have dominant H5 / H7 / H9
.....
If you look at the datasheet of something like a 74HC4066, you will see some abrupt discontinuities in the resistance curve at just over one volt from either rail. To use one of these devices, you need to avoid these points at low signal levels. It doesn't matter so much at musical peaks.
Does the simulation impedance curve look anything like the data sheet?
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Old 20th August 2018, 07:16 AM   #32
voltwide is offline voltwide  Ireland
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Originally Posted by mictester View Post
Just for my amusement, I constructed the switch as presented a couple of posts ago, using Real Components™. Testing on the Audio Precision test set suggested that the worst distortion in the entire audio band happens at (roughly) 20kHz. I used 2N7000 FETs (as they were all I had today. Testing at several spot frequencies showed that there was essentially no measurable distortion - this could be a winning approach!
well done!
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Old 20th August 2018, 09:14 AM   #33
mictester is offline mictester  United Kingdom
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Originally Posted by stocktrader200 View Post
I used CD4052 in a car stereo unit that was excellent. I see no reason that 2 x cd4052 at 18v both channels paralleled for left and right would not be outstanding.
1 chip for each channel.

Unfortunately, I find that the basic 4000-series CMOS switches add noticeable distortion. I've used them for switching Pre Fade Listen in disco mixers, but I wouldn't consider using them in a critical programme path.
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Old 20th August 2018, 09:50 AM   #34
diyralf is offline diyralf
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Quote:
Originally Posted by mictester View Post
Just for my amusement, I constructed the switch as presented a couple of posts ago, using Real Components™. Testing on the Audio Precision test set suggested that the worst distortion in the entire audio band happens at (roughly) 20kHz. I used 2N7000 FETs (as they were all I had today. Testing at several spot frequencies showed that there was essentially no measurable distortion - this could be a winning approach!

Would you provide some measurement plots of the circuit?
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Old 20th August 2018, 10:55 AM   #35
voltwide is offline voltwide  Ireland
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Quote:
Originally Posted by mictester View Post
Unfortunately, I find that the basic 4000-series CMOS switches add noticeable distortion. I've used them for switching Pre Fade Listen in disco mixers, but I wouldn't consider using them in a critical programme path.
The results depend on the circuitry around. For lowest THD keep voltage excursions related to ground as small as possible.
For that reason switching into a virtual ground summing node is superior to simple hi-impedance voltage switching.
I do not use 4000er gates specially because of their charge injection that causes audible glitches. And as you cannot slow down switching speed there is nothing you can do about it.
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Old 20th August 2018, 04:40 PM   #36
stocktrader200 is offline stocktrader200  Canada
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I used cd4066 in a 10 bit volume controller for tape recording mid 80's. I used a 15 volt supply split at 7.5v for the 2 op amps and 4066's. It does a wonderful job as I could not hear any audible difference now or then, when my hearing was much better.
47k drive resistors removed switch noise to op amp noise levels.
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Old 18th January 2019, 03:56 AM   #37
dreamth is offline dreamth  United Kingdom
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A bit late now , but thank you all for your valuable insights! It's just now that i had the time to read the whole topic.
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Old 18th January 2019, 10:51 AM   #38
Kay Pirinha is offline Kay Pirinha  Germany
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Quote:
Originally Posted by diyralf View Post
Don't use reed releays. They have thermal voltage on their contacts.
Who says that? Are the contacts in a pair made of different materials?
Best regards!
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Old 18th January 2019, 11:33 AM   #39
dreamth is offline dreamth  United Kingdom
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Originally Posted by Kay Pirinha View Post
Who says that? Are the contacts in a pair made of different materials?
Best regards!
Unfortunately it's not Facebook to give a big LIKE for this question There are lots of overstated remarks in the audio world...The first Phillips cd players and some of the very good ones , had reed relays in the signal path, many of the best amplifiers out there used reed relays too...
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Old 18th January 2019, 12:30 PM   #40
jan.didden is online now jan.didden  Europe
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It is possible to slow down the switching of CD4006 - type switches to pretty must cure any switching noise.
But because those switches have on resistance which rises with voltage you must chose the topology and impedance levels carefully for best results.
(It is not the absolute R that is the problem, but the variation. A 100 ohms switch is fine as long as the 100 ohm is constant).

I have done quite a lot of investigations there and an article published at the time in Wireless World, see attached page 1. The full article is 5Mb so cannot attach it, but send me a PM and I will send you the article.

Edit: I made a quick page on my website so it can be downloaded directly A solid state switched attenuator | Linear Audio NL

Jan
Attached Images
File Type: png paa.PNG (490.3 KB, 43 views)
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Last edited by jan.didden; 18th January 2019 at 12:46 PM.
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