Solid state switching

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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.

Just wondered what the latest thinking is for about 6 Hi-Z 10K line inputs with low THD. feeding straight into a volume control.

I don't want to go over complicated with arduino etc preferring simplicity with no pulse artefacts. - Any suggestions, - latest IC's etc would be welcome.

Thanks.
 
40 years ago (can't believe I'm typing that) I worked with a number of different analog switches in audio applications. The results were routing switchers for pro audio, intercom systems, etc. What we had back then were the 4066 (which we summarily rejected as trash very early on), and a line of much nicer switches from a company called Siliconix, who produced the very first analog switch in the 1960s. Time has marched forward and Siliconix is now part of Vishay, but a brief look around for current product also landed me on Analog Devices. Both seem to have quite a range of very nice analog switches. Start with the Siliconix DG1408, then have a look around. The AD stuff seemed to have very flat V/R curves.

The application rules are not much different today than 40 years ago, though the switch specs have improved. Drive them with a low Z buffer, load them with a termination resistance high enough that the voltage vs resistance curve doesn't introduce distortion, low enough to realize near perfect off leakage (10K worked then, and works now too). And watch their maximum voltage swing vs supply voltage figures. Today's chips have better headroom, lower on resistance, and better off isolation that we had, but what we had worked really quite well and would have been good enough for any audio today, so today's stuff is more than adequate. Both AD and Siliconix have several 8X1 multiplexers that can be controlled with 4-bit word presented in parallel. We used an 8-bit priority encoder to develop that word from discrete switches (like a CD4532B, still current), and the encoders could be chained for more switches. Add a 4-bit latch, perhaps a decoder/driver to light up individual switch indicators, audio buffers on the output and a pair could drive your volume control just fine. Of course, back in those days, real tracking stereo controls were a bit hard to get (you had to buy like 10K pieces, or use some really expensive P&G units) so ours ended up being a 1.5dB step digitally controlled attenuator chip, which also worked quite well, driven from an up/down counter. Even built in a reset reference level button. I saw some by TI, pretty nice and much better today. So yeah, no Arduino, no PC, no programming, it can all be done with logic chips.

We had one big advantage: DIP chips. You're probably going to have to deal with SMDs now. Have fun!

edit: Ha! One of our old favorites, the DG308 (one of the few chip numbers I still remember), is now in a B version, and still made! Wrong style for what you're doing, it's 4 switches individually controlled the 8x1 would be simpler to use as an input selector.
 
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Relays? Yuk. Some things get simpler, some more complex. They aren't a free ride either.

SMD's are not impossible, just a task. Need a tiny iron and a good magnifier. But if you look around you may actually find some DIP product from Siliconix. They've been at it SO long, they certainly have retrofit parts for the old product. I'd look for you, just not now. The logic chips are certainly still available as DIP. You're doing a PC board anyway, right?
 
I was trying not to bother with a PCB but it looks like I might have to, as this looks like being a lot more involved than I was hoping.

Thanks for the link Nigel, I have express PCB but have not used it, is the MP one better ?
Does the 7HC4051 arrangement have good THD/overload specs ?
 
I was trying not to bother with a PCB but it looks like I might have to, as this looks like being a lot more involved than I was hoping.

Thanks for the link Nigel, I have express PCB but have not used it, is the MP one better ?
Does the 7HC4051 arrangement have good THD/overload specs ?

I use the 4051 on a USB scope I designed and it works well.

Demo video of software at: YouTube
 
R_on looks lower than for a CD4066 at least. In return, it's only good for +11 V ab max instead of +20 V, but either should do for 2 Vrms and change. R_on nonlinearity looks similar between 74HC4051 at 9 V and CD4066 at 15 V, with probably an edge to the latter when give about a +1 V offset (or correspondingly asymmetrical supplies).

As previously stated, drive with a buffer for each input (and give that some minimal input protection, too) and load with as high an impedance as you possibly can... a 15 ohm R_on nonlinearity into 100 kOhms is still good for 0.015% p-p when it comes to distortion, so you want at least 100k, preferably 1 Meg.

When it comes to +/-15 V capable options, NJR has the NJU7301 that may be worth looking at, as well as the Siliconix-compatible NJU201A and 211. Unfortunately, their datasheets are quite useless and look like they haven't been updated for over 30 years. Toshiba's TC9163AN used to be quite popular, I don't think this one has been made in quite a while though.
 
Whenever this question pops up, I recommend to study schematic for Hafler 915 JFET preamp. You can find the relevant bits even searching on this site. The circuit there does what you want, performs well and is not terribly expensive.

Also, I agree with the recommendation to look at DG413 analog switch.

good luck!
mlloyd1
 
Thanks mlloyd1. This looks promising.

However, I tried to get the 915 cct., - but from 3 sites it appears to be from the same source as the pages are not quite complete although it does show the switching, and there are only 3 inputs.

I've no experience with these, can you double up the 4051 for 6 inputs ?
also, the 2SK163's appear to be obsolete.
 
If I had a need for this I would firstly look in purely mechanical switching.
There are plenty of rotary selectors.
Alternatively, the old push button was widely used, push one, it latches, while the others pop up thanks to a common bar.
If going CMOS analog switching I would mostly care about low R_on and flat R_on over the voltage of the audio signal. Then whatever the details, a 22V10 would do to glue things together.
 
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I've no experience with these, can you double up the 4051 for 6 inputs ?
also, the 2SK163's appear to be obsolete.
You need an inverter to drive one IC strobe so one 4051 is enabled for 0,1,2,3 and the other 4051 is enabled for 4,5
I tend to use cd4025 for inverters, as they are useful for other things too.
2sj 2sk anything are mostly unavailable in US, except a few fairchild numbers and ubiquitous counterfeits. I find the obsession of diyaudio with toshiba/sanyo/sanken semiconductors to be frustrating. And not even farnell can get a package through customs unpilfered. It took 3 1/2 weeks to get some CD4093 from UK to US SC warehouse.
 
hafler 915 has 4 audio inputs into the CMOS 4051: TUNER, VIDEO, CD, & AUX. See attached Hafler 915 snap below.

You can use other JFETs besides 2SK163; it's just a buffer. Take a look in the Pass B1 Buffer thread for comments about lots of parts that others have tried.

You can use a quad CMOS switch other than the CD4051 (such as the DG413), for lower and flatter Ron (leading to less distortion) if you want. You can also then chose a part that has higher rails for higher signal handling capability (and maybe lower distortion) if needed, but the 915 design already has the diodes to facilitate easy switching for input selection. CD4xxx logic DOES NOT handle +/-15V rails!!!

Maxim-IC makes an improved 4051 device with lower and flatter Ron, but you still are limited with the power supply. Years ago, I threw together a cheap quickie version just to use whenever I was working on my main preamps. Worked quite well.

I'm sure you can add more switches to get more inputs, just check the logic for selecting them.

have fun,
mlloyd1

Thanks mlloyd1. This looks promising.

However, I tried to get the 915 cct., - but from 3 sites it appears to be from the same source as the pages are not quite complete although it does show the switching, and there are only 3 inputs.

I've no experience with these, can you double up the 4051 for 6 inputs ?
also, the 2SK163's appear to be obsolete.
 

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Thanks everyone for your excellent replies.
Firstly, yes, mlloyd1 you are correct, I missed the aux 2 in my quick count !

edbarx, yes, - hear, hear, for the same reason and I suffer from "Essential Tremor" which my mother had and she only lived to 105 ! - I now really enjoy improving old technology.

Yes, edchambin, I really prefer mechanical switching & have used it for over 50 years, but, now I find I have lots of good old panels for 20mm spaced 6 gang, interlocking push-button switches, lots of other hardware, but no switches ! - I want to retain the existing metalwork to match with existing amps & tuners and I tried going on-line but I guess times have changed & no one makes these switches now or only at prohibitive prices. Hence now, my interest in alternatives. - Obviously, I need to select 6 stereo inputs. - I don't mind relays generally but they do add considerable space & complexity. (Now I see that S-S switching can do too !)

However, it is now looking like the input switching is becoming bigger than the whole pre-amp project & I may need to modify my metalwork.
 
Some time ago I designed this 6 way input selector PCB. The PCB size is 3x8cm and uses standard 2.5mm pin spacing connectors. The selector can be controlled by a simple rotary switch or interlocking push-buttons. The only drawback for you is that relays are SMD. I should have probably added a through hole footprints too but I did not think of it back then. Anyway, the pin spacing of these relays is not too tight (2.5 mm) so they should be doable.

Regards,
Oleg
 
On the SMD topic....

But 2 years ago I was not an SMD fan, then came in low temp solder paste to the rescue...
Put a small line of low temp paste (find it online) across all the pins and use your wifes hairdryer to heat the PCB. Within a minute or two, it will wick into a perfect soldering job all by itself. If you get too much paste on it and show a bridge here or there, just use your solder wick and iron to clean em up. Usually it's pretty rare to get too much on there, and you don't need as much as you think either. All the old parts that I used to use through-hole are junk compared to the SMD equivalent. The consistency and quality is muuuch better.
 
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