Contactless switches for audio

[stereo coffee]

There are good reasons for audio signal paths to be switched with contactless methods. Conventional switches are subject to progressive wear

from contact metal to metal wear, and mechanism wear.

 

The all too common relay is one such traditional method that demonstrates ability to isolate the switching function from the load

but it is progressively now being replaced with mosfet base contactless relays.  The mosfet relay has almost unlimited switching capability.  

 

Here is one such device https://www.infineon.com/dgdl/pvg612.pdf?fileId=5546d462533600a401535683c1892937

 

 

Features
Bounce-free operation
High load current capacity
High off-state resistance
Linear AC/DC operation
4,000 VRMS I/O Isolation
Solid-State reliability

 

General Description
The PVG612 Series Photovoltaic Relay is a single-
pole, normally open solid-state relay that can
replace electromechanical relays in many
applications. It utilizes International Rectifier’s
proprietary HEXFET power MOSFET as the output
switch, driven by an integrated circuit photovoltaic
generator of novel construction. The output switch
is controlled by radiation from a GaAlAs light
emitting diode (LED) which is optically isolated
from the photovoltaic generator.
These units exceed the performance capabilities of
electromechanical relays in operating life, sensitivity,
stability of on-resistance, miniaturization, insensitivity
to magnetic fields and ruggedess. The compact
PVG612 is particularly suited for isolated switching
of high currents from 12 to 48 Volt AC or DC power
sources.

 

 

If your design can accept resistance ON of 60 ohms,  then other contactless methods become quite attractive too. 

 

 

 

[PicoWattson]

Thanks for bringing these wonderful little critters to our attention Chris. Apart from mechanical wear, conventional physical contacts may impart their own characteristics to the final audio output. Might have to look at using them for input switching function on the SC.

[stereo coffee]

23 hours ago, PicoWattson said:

Thanks for bringing these wonderful little critters to our attention Chris. Apart from mechanical wear, conventional physical contacts may impart their own characteristics to the final audio output. Might have to look at using them for input switching function on the SC.

Hi Hank

Yes the PVG612 are a nice device. they are really easy to implement. I built a board to try them using 12ma as bias to their internal led, and observed nice reliable switching on their mosfet output. From what I observed using a 12v DC supply  the led to trigger them to switch, just likes to see plain resistance, which keeps such designs, super simple.

 

SC already uses contactless input switching, so all catered for.  The anodes of the 3 series pairs being switched in turn from the main board, then causing audio to appear at each input , at the signal side. In use each are doing both attenuation and contactless switching.   I am though using a pair of the PVG612 in a SC build, to have a second boards input and output running separately to the existing board, causing the anodes for the shunt pair and series pair to switch. I can let you know how it goes.

[MLXXX]

Just a general comment.

 

I recall it used to be considered that using a MOSFET as a switch was suitable for the switching on and off of power to a device, but would introduce too much non-linearity to be used in the audio signal path. However switching MOSFETS have improved in their performance as regards their linearity, to the point where some of them can be used in the audio signal path with very little degradation to the audio waveform..

 

I think you'd need to take care how you used something like the PVG612, in terms of the circuit impedance and the signal voltages.  I'd expect there to be measurable THD introduced (depending on the sensitivity of the test equipment), but in practice the THD would hopefully be well below audibility, with appropriate component values and signal levels.

Edited September 28, 2021 by MLXXX

[stereo coffee]

The way these are being used by me never will be in the audio signal path, rather are planned as two levels back opto contactless switch.

 

The device though does have good linearity regardless, so is very promising as a second layer opto device to switch a LDR anode on. 

thus avoiding the non linearity of a conventional switch to switch an existing opto contactless path. Such care is extraordinary in audio

engineering, but is what is needed.

 

[stereo coffee]

I have designed and implemented a double layer contactless switching board, it see's the optocoupler internal to a PVG612 being switched at its cathode end via a 10k resistor to each contact , then to a lower potential. The mosfet switching is really good its fast reliable and effortless . 

 

First contactless layer is the mosfet activated by the PVG612 optocoupler. the second contactless layer is the anode and cathode of a light dependent resistor then enabling the resistance to appear across the signal side.

 

A very nice result, with extremely fast, and  reliable switching.

 

 

 

[bob_m_54]

15 minutes ago, stereo coffee said:

I have designed and implemented a double layer contactless switching board, it see's the optocoupler internal to a PVG612 being switched at its cathode end via a 10k resistor to each contact , then to a lower potential. The mosfet switching is really good its fast reliable and effortless . 

 

First contactless layer is the mosfet activated by the PVG612 optocoupler. the second contactless layer is the anode and cathode of a light dependent resistor then enabling the resistance to appear across the signal side.

 

A very nice result, with extremely fast, and  reliable switching.

 

 

 

A Light Dependent Resistor isn't polarity conscious, and doesn't have an anode or a cathode.

[stereo coffee]

21 minutes ago, bob_m_54 said:

A Light Dependent Resistor isn't polarity conscious, and doesn't have an anode or a cathode.

You may be referring to a different type, but if its a NSL32 SR3   https://media.digikey.com/pdf/Data Sheets/Photonic Detetectors Inc PDFs/NSL-32SR3.pdf  it features a LEd with a anode and cathode on one side  then opto coupling via photons emitted  to a formed variable resistor. Both the LED and variable resistor are in an encapsulated package.   

[bob_m_54]

Just now, stereo coffee said:

You may be referring to a different type, but if its a NSL32 SR3   https://media.digikey.com/pdf/Data Sheets/Photonic Detetectors Inc PDFs/NSL-32SR3.pdf  it features a LEd with a anode and cathode on one side  then opto coupling via photons emitted  to a formed variable resistor. Both the LED and variable resistor are in an encapsulated package.   

That device (an optocoupler) contains both a LDR and a LED.. the LED has an anode and cathode, the LDR doesn't. Note the cct diagram of the device shows both the LED and the LDR, which is also known as a photocell.

 

[stereo coffee]

6 minutes ago, bob_m_54 said:

That device (an optocoupler) contains both a LDR and a LED.. the LED has an anode and cathode, the LDR doesn't. Note the cct diagram of the device shows both the LED and the LDR, which is also known as a photocell.

 

and contains a anode and a cathode

[bob_m_54]

1 minute ago, stereo coffee said:

and contains a anode and a cathode

Sorry, I thought this was meant to be a technical thread. This may make it clearer:

 

The LED has an anode and a cathode, the LDR doesn't.. So the opto coupler (opto isolator) has four leads.. anode cathode (LED) and two non polarised leads (LDR)

[stereo coffee]

2 minutes ago, bob_m_54 said:

Sorry, I thought this was meant to be a technical thread. This may make it clearer:

 

The LED has an anode and a cathode, the LDR doesn't.. So the opto coupler (opto isolator) has four leads.. anode cathode (LED) and two non polarised leads (LDR)

Even clearer still:   Audio coupling LDR's, with four leads are the only type suitable for audio circuits, 

 

So its PVG612 contactless switching,  then enabling LDR contactless switching. it works very well.

[bob_m_54]

12 minutes ago, stereo coffee said:

Even clearer still:   Audio coupling LDR's, with four leads are the only type suitable for audio circuits, 

 

So its PVG612 contactless switching,  then enabling LDR contactless switching. it works very well.

Sorry, but you are still wrong.. LDRs don't couple, isolate or switch they are merely resistors who's resistance is affected by light ... Now if you mount that LDR in a situation, where it is illuminated by a light source (LED or Globe), you can vary the resistance of the LDR by applying a signal to the LED or Globe, to produce more or less light, thus varying the resistance of the LDR.

 

But back to my original post on the subject where I tried to enlighten you on your comment:

1 hour ago, stereo coffee said:

the anode and cathode of a light dependent resistor

 

a Light Dependent Resistor doesn't have an anode or a cathode.. simple fact..

Edited October 21, 2021 by bob_m_54

[stereo coffee]

24 minutes ago, bob_m_54 said:

Sorry, but you are still wrong.. LDRs don't couple, isolate or switch they are merely resistors who's resistance is affected by light ... Now if you mount that LDR in a situation, where it is illuminated by a light source (LED or Globe), you can vary the resistance of the LDR by applying a signal to the LED or Globe, to produce more or less light, thus varying the resistance of the LDR.

 

But back to my original post on the subject where I tried to enlighten you on your comment:

 

a Light Dependent Resistor doesn't have an anode or a cathode.. simple fact..

But if we can just take the next obvious step  and realise that LDR's for audio coupling always have four leads which include an anode and cathode 

and a variable resistor, there is then ease of describing them as LDR's,  In the same manner  I could also argue that Light Dependent Resistors on their own as a photocell,  are incapable in proper audio signal  circuits, as there is no proper aligned or specified power source.  But rather going down that pedantic path ... lets accept  that, LDR means a 4 lead device ... certainly in this thread.   

[bob_m_54]

7 minutes ago, stereo coffee said:

But if we can just take the next obvious step  and realise that LDR's for audio coupling always have four leads which include an anode and cathode 

and a variable resistor, there is then ease of describing them as LDR's,  In the same manner  I could also argue that Light Dependent Resistors on their own as a photocell,  are incapable in proper audio signal  circuits, as there is no proper aligned or specified power source.  But rather going down that pedantic path ... lets accept  that, LDR means a 4 lead device ... certainly in this thread.   

There is no "next obvious step" an LDR like any other resistor only has two leads. The device that contains both an LDR and a LED (or globe) is an Optocoupler, or Optoisolator..

 

I don't know why you are so insistent on mis-naming the device. It's not a LDR, and even your linked Datasheet calls it an Optocoupler. And your statement

Quote

the anode and cathode of a light dependent resistor

 is simply wrong

 

If you are trying to post technical threads, it helps if you are accurate when naming devices, or you may as well call it a doohickey....

 

An LDR is NOT a four lead device...

Edited October 21, 2021 by bob_m_54
accuracy

[stereo coffee]

Sticking to the topic, this plus this

 

 

 

[bob_m_54]

6 hours ago, stereo coffee said:

Sticking to the topic, this plus this

 

 

 

Are optocouplers, .. not LDRs

[Addicted to music]

6 hours ago, stereo coffee said:

Sticking to the topic, this plus this

 

 

 

2 totally different devices. 
 

the PVG612 are designed to operated as a power relay,  as  another member @MLXXX  has indicated there are MOSFET in series that is only designated for power delivery.   I wouldn’t be using it to switch audio signal paths, it’s not designed for that.

[stereo coffee]

2 hours ago, Addicted to music said:

2 totally different devices. 
 

the PVG612 are designed to operated as a power relay,  as  another member @MLXXX  has indicated there are MOSFET in series that is only designated for power delivery.   I wouldn’t be using it to switch audio signal paths, it’s not designed for that.

I thought it was plainly obvious... but ...  the PVG612 device switches anode current for the NSL32SR3, arranged with its cathode already with lower potential    Then having received said current, the NSL32SR3  switches audio signal path. In effect this is double layer contactless switching.  The actuation being via the PVG612 Pin 1 and 2 anode and cathode.  ..see it now ? 

[stereo coffee]

8 hours ago, bob_m_54 said:

Are optocouplers, .. not LDRs

If you are happy with that, and if you have done so already  I am really glad you are now discovering their uses. Of course there are many types of optocoupler. The thread here, ( respecting your worded choice )  examples two, but there are more still that can benefit contactless switching for audio. 

 

If we look at the primitive state the audio sector is in with switching audio paths, we find most are wiring audio path inputs from from the rear panel to the front panel, into a metal to metal contact switch  and  back again, or onward to other input stages. 

 

Some use a electromechanical  relay, which are subject to mechanical and contact to contact progressive wear. The thread here encourages we explore contactless methods, to switch audio paths. Actuation is then placed uninvolved with the direct audio path - but of course still entirely necessary to switch the optocoupler . In a month or so I will be able to example a pcb design image,  which will help show what is involved. 

[bob_m_54]

1 hour ago, stereo coffee said:

If you are happy with that, and if you have done so already  I am really glad you are now discovering their uses. Of course there are many types of optocoupler. The thread here, ( respecting your worded choice )  examples two, but there are more still that can benefit contactless switching for audio. 

 

If we look at the primitive state the audio sector is in with switching audio paths, we find most are wiring audio path inputs from from the rear panel to the front panel, into a metal to metal contact switch  and  back again, or onward to other input stages. 

 

Some use a electromechanical  relay, which are subject to mechanical and contact to contact progressive wear. The thread here encourages we explore contactless methods, to switch audio paths. Actuation is then placed uninvolved with the direct audio path - but of course still entirely necessary to switch the optocoupler . In a month or so I will be able to example a pcb design image,  which will help show what is involved. 

LDRs are old technology from the late 1800s, according Wikipedia. But later, in the late '20's / early '30s they were used in a primitive Optocoupler fashion, using a light globe, or even daylight as the light source. Even some of the early B&W TVs used them to adjust picture brightness and contrast for the difference between day and night viewing.

 

But it wasn't until the early 50's that Resistive Optocouplers (the device you are talking about), manufactured with the LED and the LDR in one package, were commonly being used. Due to their inherent slow switching times, Resistive Optocouplers are very rarely used these days, except in audio equipment or other less demanding applications.

 

 

[stereo coffee]

The same of course applies to many classes of electronic components, where the better the power supply used,  then delivers the better audio result.

 

[bob_m_54]

I give up...

 

 

 

[stereo coffee]

10 minutes ago, bob_m_54 said:

I give up...

 

 

 

Good, lots to learn then, unlike the statue

[bob_m_54]

Just now, stereo coffee said:

Good, lots to learn then, unlike the statue

Yes, you should start with electronic components 101, I think that covers all types of resistors..