6
\$\begingroup\$

I'm thinking about controlling an audio signal (turning it ON/OFF) using a solid state relay switch? Is that even possible? If not, is there a different or easier way to do this?

I'm a noob in the field, so would greatly appreciate a simplified answer (i don't mind over simplification).

\$\endgroup\$

2 Answers 2

Reset to default
4
\$\begingroup\$

There are solid state relays designed primarily for audio, which is what you'll want to use. There are in general some things you'll want to be aware of when using a solid-state relay.

First, you'll want to make sure the on resistance is compatible with your load. For example, if you are trying to drive a low impedance like a speaker, you cannot use a SSR which has high on-impedance (for example, 300 Ohms), as most of your power will end up being wasted by the SSR.

Second, you'll want to make sure the SSR actually has fairly flat frequency response up to the audio range (20 - 20k Hz). This will typically also depend on your load (that is, what you are driving), and generally looks better the higher impedance your load is (for example, if you are going into an amplifier versus a speaker). The datasheet will have all this information.

The third thing you must be aware of is that some SSRs are only designed to drive DC loads, which will not work for you (AC coupled audio signals go both positive and negative). A related issue is crossover distortion, which may distort your signal when the voltage amplitude gets close to the zero point. Again, characterizations of all this is available in the datasheet.

Your best bet is to find SSRs which are specifically specced for audio for example, this one: Vishay LH1518AAB

\$\endgroup\$
5
  • 2
    \$\begingroup\$ The LH1518AAb is a remarkably high spec device. One problem with less capable devices with high input signal levels can be 'leakage' of signal though the device - ie dB of isolation loss not as high as desirable. A usually effective fix is to short the output with a second switch /gate / ... when turned off. This of course makes it that much harder to maintain impedances but can provide very substantial levels of isolation. \$\endgroup\$
    – Russell McMahon ♦
    May 18, 2014 at 4:23
  • \$\begingroup\$ Awesome. Thanks for the responses guys. I'm going to check out those options. \$\endgroup\$
    – chobbes
    May 19, 2014 at 20:33
  • \$\begingroup\$ I looked into this a little more. Would it be better to use a IC switch like CBT3244AD instead of an SSR? \$\endgroup\$
    – chobbes
    Jun 4, 2014 at 18:26
  • \$\begingroup\$ Sort of, the difference between a SSR and a IC switch is that: 1) The SSR has isolation, that is, there is no current path between the control side and the signal side, so presumably the signal side shouldn't 'care' what the control side is doing. This is not true with a switch, for example, a large signal might feed back into the control side. and 2) The power rails to your switch need to be compatible with your signal - that is, you need to have +/- power which is higher than your signal swing, otherwise the signal will clip. The IC switch is more like an amplifier in that sense. \$\endgroup\$
    – Zuofu
    Jun 5, 2014 at 1:12
  • \$\begingroup\$ You could probably engineer your circuit around a switch, but you need to think carefully about what ground is, and how to generate both positive and negative power rails. Also, I can't tell whether the CBT2344AD really works for analog signals, though this part definitely would: ti.com.cn/cn/lit/ds/symlink/cd4066bc.pdf \$\endgroup\$
    – Zuofu
    Jun 5, 2014 at 1:15
0
\$\begingroup\$

I made contact with Vishay engineering concerning a similar application.

I want to switch between three different electret condenser microphones for a ham transceiver. They came back (after testing) and reported the VO1400AEFTR as a perfect SSR for my application.

The output freq response is incredible and has on 5 ohm RON. I haven't built the circuits yet, but I am convinced this devise will be perfect. (very cheap too. I paid $1.10 ea)

(edit: I have fixed the part number above)

\$\endgroup\$
2
  • \$\begingroup\$ I have now bread boarded the circuit mentioned above using the Vishay VO1400AEFTR and the audio reports I received on the air indicated that no one could tell the difference between the mic direct or through the SSR. Marc \$\endgroup\$
    – user79066
    Jun 18, 2015 at 17:17
  • \$\begingroup\$ Marc, Could you provide a schematic of the circuit you got working with the Vishay VO1400aeftr? Thanks \$\endgroup\$
    – Kevin Rowse
    Aug 22, 2017 at 2:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.