I was wondering about using solid state relays to switch between multiple inputs for passive preamps. Curious about distortion, bandwidth, and signal loss problems. Would ssr's work to keep the path short between in and out connectors. I am not up on these other than replacement for standard mechanical relays in motor control.
The sort of solid state relay used in motor control is unlikely to be suitable for audio signals.
You can use JFETs (discrete, or package on a chip) to switch audio. Done properly I would expect them to be not much worse than a good mechanical switch.
Why do you want to keep the path short between in and out? This encourages stray capacitance coupling between them. Better to ensure that the distance is sufficiently long.
You can use JFETs (discrete, or package on a chip) to switch audio. Done properly I would expect them to be not much worse than a good mechanical switch.
Why do you want to keep the path short between in and out? This encourages stray capacitance coupling between them. Better to ensure that the distance is sufficiently long.
I wasn't suggesting that motor control ssrs would work, just that that is the kind I am familiar with. I have seen on Digikey that there are some designed for telecom use and was curious if anyone has experience with these types. Such as Vishay LH1518AAB. Very small and operate on low power. Just thought that keeping the wiring closer to the inputs would be better than running back and forth between the rear and front of an enclosure. I am a little new at this. That is why I am asking.
I suspect that a motor control SSR and a telecom SSR use quite different devices (e.g. triac, JFET respectively) so the only thing they have in common (apart from the name) is that they both implement an electronically controlled switch.
Running wires back and forth inside an enclosure should not be a problem, provided that you use the right wire and get the grounding right. If the enclosure is metal and contains no power supply then you might not need to use screened/shielded cable for the internal wiring.
Running wires back and forth inside an enclosure should not be a problem, provided that you use the right wire and get the grounding right. If the enclosure is metal and contains no power supply then you might not need to use screened/shielded cable for the internal wiring.
inserting a T pad of resistances can be used to tun on, or turn off an input.
Signal to top of upper jFET.
Series connect second jFET.
Connect a third jFET from junction to Signal Ground/Return.
Input tapped off the last jFET.
Turn top two jFETs to near zero ohms and bottom to near infinite ohms using control signals to the gates and the input passes to the output.
Swap the control signals, near infinite to top two and near zero to bottom and the input is blocked.
As many inputs as you want/need with groups of three jFETs. One set of control signal High/Low so that one set of jFETs passes signal and all other block signal.
You can probably buy those 3 jFETs in an IC package. It might be called a signal SSR.
The package might even include the conversion to the opposite phase control signal. One control signal generates the two turn ON and Turn OFF gate drive. and maybe an anti bounce circuit to prevent chattering.
Signal to top of upper jFET.
Series connect second jFET.
Connect a third jFET from junction to Signal Ground/Return.
Input tapped off the last jFET.
Turn top two jFETs to near zero ohms and bottom to near infinite ohms using control signals to the gates and the input passes to the output.
Swap the control signals, near infinite to top two and near zero to bottom and the input is blocked.
As many inputs as you want/need with groups of three jFETs. One set of control signal High/Low so that one set of jFETs passes signal and all other block signal.
You can probably buy those 3 jFETs in an IC package. It might be called a signal SSR.
The package might even include the conversion to the opposite phase control signal. One control signal generates the two turn ON and Turn OFF gate drive. and maybe an anti bounce circuit to prevent chattering.
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Still kicking this can around. Thinking on momentary contact pushbutton on front panel with LEDs to show input. This SSR : Vishay VO1400AEF. with a logic stepping circuit to turn on/off SSRs. Maybe not a big advantage to mechanical switch, but it would be on the unique side. After all, it's just grownups playing with their toys
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Came up with a circuit to control the ssr switching with a single push button. Had help from someone that I came across on line. Didn't take him much longer than a blink to come up with this. He understands these IC's pretty darn good. I am going to build the board up and give it a try by itself and see how it works.
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That Vishay chip is an interesting device...
Your 4017 can be elaborated upon to use a momentary button for each data line (meaning you can have a row of buttons on the front panel to select the required input). To do that needs another IC though such as a 4011.
If you buffer the outputs (so no current draw from the 4017) then you can add a simple capacitor backup supply (one cap, one diode) so that the last input selected is remembered. Actually, for your circuit that could be possible without buffering.
Here is another simple CMOS one... can't remember where this came from.
Your 4017 can be elaborated upon to use a momentary button for each data line (meaning you can have a row of buttons on the front panel to select the required input). To do that needs another IC though such as a 4011.
If you buffer the outputs (so no current draw from the 4017) then you can add a simple capacitor backup supply (one cap, one diode) so that the last input selected is remembered. Actually, for your circuit that could be possible without buffering.
Here is another simple CMOS one... can't remember where this came from.
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Was just thinking that this could be used to control relays also if that is what someone wanted to use. I plan on running an indicator LED to the front panel to show the active source input. I think this shows promise to eliminate one more place where audio signal goes through physical contacts.
Yes it could drive relays. The 2N7000 FET is a great choice to interface CMOS logic to higher current loads.
At this point, I have no idea how well the Vishay chip will work as far as noise is concerned. I haven't found much information as far as it's audio capability is concerned. Moody, as you have shown, there are several possibilities here.
I don't think noise will be a problem, however although this is an interesting chip, I suspect it will have a few issues used for signal level switching. The main concern is high junction capacitance which will both load the signal source and also cause signal breakthough... how much breakthrough depends on how its configured. In all honesty I think the old CMOS 4066 bilateral switches would perform (infinitely) better for line switching.
This is how I do it using two JFET's per line to be switched but the downside to my approach is that the antiphase drive signals complicate things. The upside is truly excellent performance and extremely high attenuation of non selected lines, far in excess of any mechanical arrangement. Using 4066's in a similar arrangement would work very well too.
Post #2 here,
http://www.diyaudio.com/forums/soli...fet-amplifier-designed-music.html#post1452488
This is how I do it using two JFET's per line to be switched but the downside to my approach is that the antiphase drive signals complicate things. The upside is truly excellent performance and extremely high attenuation of non selected lines, far in excess of any mechanical arrangement. Using 4066's in a similar arrangement would work very well too.
Post #2 here,
http://www.diyaudio.com/forums/soli...fet-amplifier-designed-music.html#post1452488
I have a lot to learn here. Most all of you folks are way past my level. I have no formal education in electronics, just some I picked up from my Dad back in the 1960's and 70's. I have retired now and have had a resurgence of interest in audio. I built a four channel 100x4 watt power amplifier in 1973 from schematics and pc boards my Dad got from some of his engineer buddies. I didn't know any theory behind it, but It did work well. Hanging out on this forum is like going to school for me. And I love it. This looks like what I used in the '73 amp build. Now I am going to study!!
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Opamps from the 70's quite likely came in that sort of metal package, back then the uA741 was all the rage 😱 And its still current production and going strong.
Wish I still had that amplifier I built way back when. My ex made it disappear when I went to AF Basic Training.
Concerning high junction capacitance on the Vishay chip, is that a figure shown on the spec sheet?
I have been looking at the 4066. Seems it has been around a long time. I came across the 74HC4316 and the MAX4536 in a couple of articles I read. Man, I have a lot of studying to do. Sounds like all of these chips are used commonly in audio and some video applications. I guess I jumped too soon buying the Vishay chips. Oh well, they didn't cost much and I can practice and learn using them while I learn enough to decide what I really need to use. I also will learn about using JFETS. Looks like I have plenty to do during my retirement years-Haha
Concerning high junction capacitance on the Vishay chip, is that a figure shown on the spec sheet?
I have been looking at the 4066. Seems it has been around a long time. I came across the 74HC4316 and the MAX4536 in a couple of articles I read. Man, I have a lot of studying to do. Sounds like all of these chips are used commonly in audio and some video applications. I guess I jumped too soon buying the Vishay chips. Oh well, they didn't cost much and I can practice and learn using them while I learn enough to decide what I really need to use. I also will learn about using JFETS. Looks like I have plenty to do during my retirement years-Haha
Junction capacitance doesn't seem to be shown but generally, the bigger the device (power handling) and the higher the junction capacitance will be. That figure can also vary depending on the voltage difference between the junctions.
The Vishay parts will certainly work, and if fed from a low source impedance could well be satisfactory for your requirements.
The Vishay parts will certainly work, and if fed from a low source impedance could well be satisfactory for your requirements.
As far as signal breakthrough, are you referring to cross-talk between channels? Is this something I could check by listening with a headphone amp while feeding only one channel from a source?
Yes, you could check it like that. So much depends on the actual configuration used and the impedances of the various parts of the circuit as to just how good or bad it will be.
Surprisingly, this actually simulates quite nicely although you have to bear in mind that the FET's in the switch are not as big as the ones used here and so should be better... but it will give you an idea of what to expect.
The left part of the diagram is the switch and its two FET's. There is a voltage source at the left with the output taken across the 10k load resistor. The switch is in the 'off' state with no drive voltage present.
The graph shows the output rising as the input frequency rises. That is Vout_1 on the graph. So at DC and very low frequencies the switch is near perfect. As frequency rises the capacitance comes into play and couples the signal into the load. The higher the frequency, the more signal gets through.
The right hand part of the circuit shows what would be an 'equivalent' to the supposedly open switch, a 1000pf cap. The scale on the left shows the attenuation. So by 30kHz or so the attention is 0db and everything gets past. This is Vout_2
This type of switch using FET's is very good as a replacement for speaker relays because the low impedance of a speaker means the attenuation is very much higher as can be seen in the third graph (load is now 8 ohms). The attenuation is now still around -60db even at 20kHz.
Surprisingly, this actually simulates quite nicely although you have to bear in mind that the FET's in the switch are not as big as the ones used here and so should be better... but it will give you an idea of what to expect.
The left part of the diagram is the switch and its two FET's. There is a voltage source at the left with the output taken across the 10k load resistor. The switch is in the 'off' state with no drive voltage present.
The graph shows the output rising as the input frequency rises. That is Vout_1 on the graph. So at DC and very low frequencies the switch is near perfect. As frequency rises the capacitance comes into play and couples the signal into the load. The higher the frequency, the more signal gets through.
The right hand part of the circuit shows what would be an 'equivalent' to the supposedly open switch, a 1000pf cap. The scale on the left shows the attenuation. So by 30kHz or so the attention is 0db and everything gets past. This is Vout_2
This type of switch using FET's is very good as a replacement for speaker relays because the low impedance of a speaker means the attenuation is very much higher as can be seen in the third graph (load is now 8 ohms). The attenuation is now still around -60db even at 20kHz.
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Thanks for the simulation information. I will build up a test board and see what happens. Probably won't get much done till after the holidays. Curious if there is a version of LTspice that you used for Linux. I am currently using Ubuntu 14.04 64bit.
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