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Solid state switching
Solid state switching
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Old 28th March 2020, 01:31 PM   #21
MarcelvdG is offline MarcelvdG  Netherlands
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Quote:
Originally Posted by R1234 View Post
I would like to build a push-button solid state input selector with lots of inputs. Never done this before after having terrible experience with a Quad pre-amp about 25 years ago. I think it used 4066 c-mos switches and was quite un-reliable.
What was wrong with it? Did the 4066 get driven into latch-up by large input signals and self-destruct, or was it some other issue?

You can much reduce the risk of self-destruction after latch-up by using a power supply that can only deliver little current, for example something with resistors, Zener diodes and the bare minimum decoupling.
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Old 28th March 2020, 08:26 PM   #22
Mark Tillotson is offline Mark Tillotson
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Oh god yes, 4000 series latch-up, a nightmare, its all coming back! I think Horovitz and Hill had a few war stories about that.
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Old 28th March 2020, 09:43 PM   #23
MarcelvdG is offline MarcelvdG  Netherlands
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Even with much more modern chips it is a problem sometimes. The local broadcasting station here used to have a computer with a video digitizing card that was connected to a surveillance camera, the card had a Conexant Fusion chip. The supplies of the computer and camera and the video cable had to be connected in a very specific order, otherwise the video digitizing card would not survive. I've seen a blown-up card where the Conexant Fusion IC had a burst in its package, so I think it must have been latch-up.

Last edited by MarcelvdG; 28th March 2020 at 09:48 PM.
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Old 29th March 2020, 03:21 AM   #24
R1234 is offline R1234  Australia
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Thanks all, again. I have never played with arduino and don't really want to at present. However, the lo temp solder paste looks worth investigating.

My experience with the Quad control unit years ago was a "simple" repair job where the customer could not select inputs correctly. - I was staggered that a situation could arise where an otherwise excellent product would be totally screwed up by input selection. - Tape on phono, different channels swapped, like a brain hemmorrhage. But, to repair the thing I found it depended on the actual "brand" of IC that it would work on. I think it was RCA, but whatever, it certainly was enough for me to steer well clear of S-S switching in any of my own designs & has been so ever since.

Switched Relays, (thanks OlegSh & synonymous), may be worth investigating, but the added wiring complexity warrants PCB design, which for me, time-wise is a negative, but, does anyone know of, - or have a template for an edge connector where the PCB edge itself forms half of the connector. I have plenty of gold-plated multi-pin edge connector parts spaced at .1" (& .15"). - It would be nice just to be able to select a block of connections say up to 30 odd & just delete what is not needed when designing a PCB. - Express PCB which I have, does not have ready template for this.
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Old 29th March 2020, 03:29 AM   #25
jackinnj is offline jackinnj  United States
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Solid state switching
For low level signals, I found the Analog Devices switches virtually noiseless and contributed nothing to THD%. If you need help with code I have some routines for their switches and rotary encoders, displays etc, if you are going to use one of the Arduino platforms.
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Old 29th March 2020, 03:34 AM   #26
sgrossklass is offline sgrossklass  Germany
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Electronic input switches certainly enjoy a reputation for needing good input protection if you do not want them to fail. When used without input buffers, it is not uncommon to see 2k2 input series resistors. But as said, you really do want buffers. Even if it's just a bunch of (NJM)4558s. Minimal output loading, slew rate still adequate, minimal bypassing requrements.
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Old 29th March 2020, 10:58 AM   #27
OlegSh is offline OlegSh
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Solid state switching
Quote:
Originally Posted by R1234 View Post
...

Switched Relays, (thanks OlegSh & synonymous), may be worth investigating, but the added wiring complexity warrants PCB design, which for me, time-wise is a negative, but, does anyone know of, - or have a template for an edge connector where the PCB edge itself forms half of the connector. I have plenty of gold-plated multi-pin edge connector parts spaced at .1" (& .15"). - It would be nice just to be able to select a block of connections say up to 30 odd & just delete what is not needed when designing a PCB. - Express PCB which I have, does not have ready template for this.
I would not recommend using board edge connector with printed pins for a DIY project. It will make your PCBs too expensive because you will need gold finish for wear resistance and reliable contact and an edge chamfer to ensure easy insertion. To wire my boards I use ribbon cable with 2-row pin header (see examples below). I place the selector PCB right next to the inputs and control circuitry somewhere else. This is cheap, simple, reliable and takes no more space than a board edge connector with printed pins.

Regards,
Oleg
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File Type: jpg PinHeader.jpg (252.2 KB, 82 views)
File Type: jpg RibbonCable.jpg (37.9 KB, 85 views)
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Old 29th March 2020, 11:12 AM   #28
MarcelvdG is offline MarcelvdG  Netherlands
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Attached are the schematics of a simple eight-to-one audio multiplexing circuit I built in 2011. It is controlled from a switching output of a mixing desk that works as a momentary switch; every time a button is pushed on the desk, the multiplexer switches to the next input. As it is a balanced stereo circuit, the part with the HEF4051 and 1/2 OPA2134 was built four times.

The OPA2134 buffer ensures that the on resistance variations of the electronic switches don't generate much distortion. The 15 pF capacitor spoils this a bit, I included it to remember the old voltage while the 4051 is being switched (break before make, using the enable input).

The 470 ohm-220 pF filters suppress any picked-up RF signals, but also limit the current that could flow into the inputs in case a signal goes beyond +7.5 V or -7.5 V. The 4000-series ICs are supplied from a Zener-stabilized supply with little decoupling to minimize the risk of anything getting damaged in case the input current should still be enough to trigger latch-up.

By the way, the 33 V Zeners were needed because the supply transformer has an unusually large ratio between the output voltages without and with load. Under worst-case conditions, the voltage could get a bit higher than the 35 V that the voltage regulators can handle.
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File Type: jpg mr29$002.jpg (362.7 KB, 83 views)
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Old 29th March 2020, 12:57 PM   #29
Bonsai is offline Bonsai  Europe
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I think Muses do a solid state audio selector that runs off +-15V.

There’s also another crowd that does them and they were/are used in some of the Cambridge Audio stuff - so Doug Self would hav3 presumably approved.

I tried to find the data sheets on my iPad library but must have deleted them.
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Old 29th March 2020, 12:58 PM   #30
nigelwright7557 is offline nigelwright7557  United Kingdom
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To stop latch up a series resistor would limit the current.
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