Hi guys.
I'm looking for a solution/help with one thing.
As you might know most amplifiers with variable gain are using simple dip switches for those operation (and few resistors connected to each switch).
But I'm looking for something better because dip switches are rather fragile and must be placed near opamp for shorter as possible NFB path.
And OFC there must be two diffrent switches for each channel.
So what I want to do? I just want to use one switch for gain manipulation (for both channel in the same time) which can be placed anywhere I want because main circuit will be placed where it supose to be.
I'm looking for rather simple and stable solution without digital domain if possible.
I'm looking for a solution/help with one thing.
As you might know most amplifiers with variable gain are using simple dip switches for those operation (and few resistors connected to each switch).
But I'm looking for something better because dip switches are rather fragile and must be placed near opamp for shorter as possible NFB path.
And OFC there must be two diffrent switches for each channel.
So what I want to do? I just want to use one switch for gain manipulation (for both channel in the same time) which can be placed anywhere I want because main circuit will be placed where it supose to be.
I'm looking for rather simple and stable solution without digital domain if possible.
> two diffrent switches for each channel ... one switch ...which can be placed anywhere
"Relay".
You can use an electromechanical relay. You can use CMOS, FET, and other semiconductor switches. You can place a mini double-pole switch at the opamp and run a "relay rod" to the front panel; I remember a slew of Japanese receivers which did this.
"Relay".
You can use an electromechanical relay. You can use CMOS, FET, and other semiconductor switches. You can place a mini double-pole switch at the opamp and run a "relay rod" to the front panel; I remember a slew of Japanese receivers which did this.
Relays can be very small. Coto makes the 9117 series which is 0.270" x 0.150" x 0.385" - quite tiny. Here's a link to the product page: 9011, 9012 & 9117 Miniature SIP Relays | Coto Technology
Not sure where you are and whether you can buy Coto but Pickering in the UK also sells a wide range of high performance reed relays, and probably also has some tiny ones too.
Not sure where you are and whether you can buy Coto but Pickering in the UK also sells a wide range of high performance reed relays, and probably also has some tiny ones too.
Hi,
I use relays like Panasonic TX-S even for switching gains in a linear MC-Prepre stage.
Nothing I´d worry about.
If You use an instrumentation amp You can simply parallel the gain setting resistors and relays.
As the original gain setting resistor is of the largest value the gain of the INA is then lowest.
This means that when transiting from one gain to another the gain/volume is momentarily reduced -->safety
If Your using plain OPAmps see that it behaves similar ... hence reduces volume over the period of transition time .. or implement a full muting at the output.
Due to input bias currents of OPAmps You can´t really get rid of pops (wo dedicated output muting) but You may be able to reduce them to irrelevant levels.
Apart from relays You might use 2-pole switches in proximity to the circuit and elongate their axes to the front or backside of the casing.
There are switches that make-before-break and those that break-before-make (relay-like).
Think about which characteristic fits the bill better.
b-b-m typically suits paralling gain resistors better, m-b-b rather suits shorting series connected gain resistors.
jauu
Calvin
I use relays like Panasonic TX-S even for switching gains in a linear MC-Prepre stage.
Nothing I´d worry about.
If You use an instrumentation amp You can simply parallel the gain setting resistors and relays.
As the original gain setting resistor is of the largest value the gain of the INA is then lowest.
This means that when transiting from one gain to another the gain/volume is momentarily reduced -->safety
If Your using plain OPAmps see that it behaves similar ... hence reduces volume over the period of transition time .. or implement a full muting at the output.
Due to input bias currents of OPAmps You can´t really get rid of pops (wo dedicated output muting) but You may be able to reduce them to irrelevant levels.
Apart from relays You might use 2-pole switches in proximity to the circuit and elongate their axes to the front or backside of the casing.
There are switches that make-before-break and those that break-before-make (relay-like).
Think about which characteristic fits the bill better.
b-b-m typically suits paralling gain resistors better, m-b-b rather suits shorting series connected gain resistors.
jauu
Calvin
CMOS switches can work well, but you have to use the switches to either switch voltage, and load them into a high impedance (no current) load, or use the switches to switch current, and load them into a virtual earth (no voltage) load.
Essentially, you do not want any voltage to be developed across the semiconductor switches, since changing voltages across the switching transistors will alter the conductivity of the switches, and thus induce distortion. So, again, switching voltage while preventing current from traveling through the switch will do that, as will switching current while preventing signal voltage from developing across the switches.
Essentially, you do not want any voltage to be developed across the semiconductor switches, since changing voltages across the switching transistors will alter the conductivity of the switches, and thus induce distortion. So, again, switching voltage while preventing current from traveling through the switch will do that, as will switching current while preventing signal voltage from developing across the switches.
I used 2 12V latching relays at the feedback to connect/disconnect paralel resistors.
For control I used a 3x3 momentary switches 1 leg to to turn on a simple 12V regulator, then drive back the 12V to the switches other 2 legs and give the 12V to the relay "forward or backwards" depending on switching up or down. Mounted the relay sideways on the panel to take the least space and ptp wired it to the needed places.
For control I used a 3x3 momentary switches 1 leg to to turn on a simple 12V regulator, then drive back the 12V to the switches other 2 legs and give the 12V to the relay "forward or backwards" depending on switching up or down. Mounted the relay sideways on the panel to take the least space and ptp wired it to the needed places.
Thatcorp
THAT IC Selection Guide
THAT 2181-series trimmable Blackmer voltage-controlled amplifier (VCA) ICs are very high-performance current-in/current-out devices with two opposing-polarity, voltage-sensitive control ports. They offer wide-range exponential control of gain and attenuation with low signal distortion.
THAT IC Selection Guide
THAT 2181-series trimmable Blackmer voltage-controlled amplifier (VCA) ICs are very high-performance current-in/current-out devices with two opposing-polarity, voltage-sensitive control ports. They offer wide-range exponential control of gain and attenuation with low signal distortion.
I think this alternative switching was discussed in a few posts many months ago.
I tried recently googling but could not find any information on this.
What do we call these alternative methods so that I can try again to find more information?
Relays will always cause clicks. You cannot make them do a soft changeover, and their actuation time is too random to attempt 'zero cross switching', which only partially solves the clicking problem anyway. Even if you match the switching level (say at zero volts), you also need to match the slope and higher derivatives to eliminate the click, and that's not possible. You essentially need a crossfade to eliminate all clicks, and relays can never do that.
However, having clicks might not be an issue, as long as they are not extremely large. If you want two gain settings, then you can use one normally open SPST relay to parallel another resistor across a hard wired gain resistor. The hardwired resistor sets one gain resistor value and the parallel combination of the switched and hardwired resistor sets the other gain resistor value.
Don't use a pair of SPSTs since you'll then have to synchronize two contacts, which will never happen. Using a SPDT, you'll have a third state, the state with both contacts open, and that gives you a third unwanted gain. With a single SPST, it's either attached or not, and no other states are possible, so it's your simplest (and cheapest) option.
However, having clicks might not be an issue, as long as they are not extremely large. If you want two gain settings, then you can use one normally open SPST relay to parallel another resistor across a hard wired gain resistor. The hardwired resistor sets one gain resistor value and the parallel combination of the switched and hardwired resistor sets the other gain resistor value.
Don't use a pair of SPSTs since you'll then have to synchronize two contacts, which will never happen. Using a SPDT, you'll have a third state, the state with both contacts open, and that gives you a third unwanted gain. With a single SPST, it's either attached or not, and no other states are possible, so it's your simplest (and cheapest) option.
I don't think there are any specialized terms. I searched for "CMOS analog switch design" and found a good example of voltage switching into a high Z load:
http://www.ti.com/lit/an/slyt612/slyt612.pdf
This discusses the problem of current traveling through the switch. On page 3 of the above PDF, it shows a way to use a pair of switches to drive a load, and how to linearize it. However, a far simpler configuration would be to allow the op amp to drive the load as a follower, and use a single switch to switch the signal, and load it into the + input of the follower. You have the same high Z load, and only one switch.
For the current switching configuration, you can insert the switch between the input resistor and the - input of an inverting op amp. In this way, voltage is dropped across the input resistor, and the CMOS switch only switches current.
The biggest hassles of either configuration are in the details, like driving the gates of the FETs or handling voltage swing if you're using a complete CMOS switch IC. If you're using discrete transistors, maintaining a correct on or off gate source voltage over the full source voltage swing can be tricky to do. For current switching, making sure that there's no voltage swing across the switching FET can be very important, as junction isolation or body diodes might start to conduct given input voltages sufficiently below ground.
Thanks for that and for the JohnCaldwell .pdf.
I think he is a Member, but I don't know his alias.
I think TI has a tiny course on multiplexers, I don't know if that's what you're looking for. https://training.ti.com/ti-precision-labs-op-amps-basics-analog-multiplexers-1-0?cu=14685
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