switching question

[crutschow]

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Which of these relays (https://en.wikipedia.org/wiki/Relay#Latching_relay) should I use for PB switching?

Here's an example of some small relays you could use. Either the 1A or 2A versions would work.

 

[Vuki_Cro]

Edit: A few questions:-
1) do the paths highlighted in yellow in your circuit indicate the preset #1 combination of signals?
2) are the outputs from switches numbered 1,2,3 hard-wired together (as appears to be shown) before going into the effects units (reverb etc)?
3) do you intend the relays/multiplexers to replace all the switches 1,2,3, or will those switches remain?
4) which part of your circuit is the 'high chorus', 'high reverb'?

1)yes they do
2)yes because my effects units have only one input, so one effect can be selected on or off for each preset if needed
3)I don't know which ones are better to use with audio signals
4)high output chorus and high output reverb could be used only for preset 1 (highlighted in yellow)

 

[Vuki_Cro]

Here's an example of some small relays you could use. Either the 1A or 2A versions would work.

Which ones would be better: SPDT, DPDT or 4PDT?

Oh, I came up with another idea...the first design was based like a huge pedalboard (http://www.effectsbay.com/wp-content/uploads/2010/04/BenHoward_PedalLineClose-opt.jpg), so how would circuit look like if the switching unit is rack mounted and remote controlled (http://www.voodoolab.com/images/p_gcxbg.gif)? I thought that audio circuit could remain the same and be controlled by relays, but relays could be operated remotely or via cable connected controller.

 

[alec_t]

I bow to Carl's greater knowledge on this. Relays it is then. The complication is that relays don't have more than two Throws. Ideally we'd like nP3T relays to handle 3 presets .

Edit: According to their spec the relays Carl linked to have a turn-on current of ~40mA and a minimum hold current of ~ 5mA. By my reckoning there could be up to 4 relays 'on' simultaneously for prolonged periods, hence a drain of 20mA (with a complex driver circuit) or 160mA (with a simple driver circuit). Will you be relying on mains power for the control circuit or battery power?

 

[Vuki_Cro]

I'm going to use 9V transformer.

 

[alec_t]

I assume that means a regulated 9VDC supply?
OK, assuming too that logic used to obtain control signals Pr1, Pr2 and Pr3 for the preset channels also runs from 9V, here's a suggested circuit which I think does what you want. Please check the truth table shown. Preset1 etc are the audio inputs.
The relays are the types Carl linked to (or equivalents), rated for a nominal 9V coil voltage. Three are DPDT, the fourth can be also (to simplify ordering and wiring) or can be SPDT. Each relay needs a driver circuit controlled by a signal Pr1, Pr13 or Pr23 as appropriate for the truth table. Pr13 and Pr23 are derived from Pr1, Pr2 and Pr3 using OR gates (CD4071). I have shown two types of driver circuit. The first ('constant') simply drives a relay at constant voltage and current when 'on'. The second is more energy-efficient and applies a ~10mS pulse to pull in the relay then drops the coil voltage to ~1.7V to hold the relay on (conservatively above the specified 0.9V minimum holding voltage). Take your pick.
The waveform shows the coil current profile for the second type of driver.
I've attached the asc file in case you want to simulate the setup.

 

[Vuki_Cro]

Great, thank you very much! D
Which software did you use?

The first ('constant') simply drives a relay at constant voltage and current when 'on'. The second is more energy-efficient and applies a ~10mS pulse to pull in the relay then drops the coil voltage to ~1.7V to hold the relay on (conservatively above the specified 0.9V minimum holding voltage). Take your pick.

I don't know which one is better for audio signals, the first or the second type of driver?

 

[alec_t]

Which software did you use?

LTSpice. A free download from Linear Technology. Recommended.

I don't know which one is better for audio signals, the first or the second type of driver?

Makes no difference; the audio doesn't go through this part of the circuit. The driver just energises the relay coil. All audio goes through the relay contacts.

BTW, can you confirm the truth table sets out what you want?

 

[Vuki_Cro]

BTW, can you confirm the truth table sets out what you want?

Yes, the truth table is correct

 

[alec_t]

Just noticed an error in my schematic. Pr2 and Pr3 should be swapped over at top left corner.

 

[Vuki_Cro]

So it should be: pr1, pr3, pr2 because next to them are pr1, pr13 and pr23, am I right?

 

[alec_t]

Yes: Pr1,Pr3,Pr2.
However, the circuit I suggested works on the assumption that there is some external means for muting/switching preamps 1, 2 and 3 in response to the preset enabling signals, so that only one preamp at a time is active. It would, I think, be quicker/easier to leave all three preamps active simultaneously and just use the Pr1, Pr2, Pr3 signals to route their outputs as appropriate. This will involve two extra relays (and hence two extra driver circuits) but does away with the OR gates (CD4051). I attach a 'Mark 2' revised suggested circuit. As a maximum of 3 relays will be energised simultaneously, I think 'constant' driver circuits will suffice. It is simpler and cheaper than the 'pull_in_and_hold' alternative. Each 9V relay (as per spec) needs only ~16mA to pull in, so the maximum continuous load would be ~ 48mA (~450mW). The revised circuit includes 5 x SPDT relays and one DPDT relay, each with its own 'constant' driver.

 

[Vuki_Cro]

Wow, thanks. So it means-> I need a splitter that separates my guitar signal to 3 inputs of preamps. Then I'd switch their outputs on or off. Am I right?

 

[alec_t]

Yes, use a splitter (passive resistor one?) to feed the guitar signal to the 3 (clean, crunch etc) preamps, then feed the 3 preamp outputs ('Preset1' etc) to my suggested circuit, which will route them to the dry and wet channels according to the Pr1, Pr2 and Pr3 control signals obtained from Crutschow's suggested circuit in post #4 (logic 1 level signifies channel 'on').
When Pr1 etc are all logic zero the preamps will still be on, but the relay contacts don't connect anything to the wet and dry channels, so it might be advisable (depending on the input characteristics of the channels) to ground each channel input through a weak pull-down resistor (10k?) to reduce noise pick-up on otherwise-floating inputs.

 

[Vuki_Cro]

But how can I ground it if I use a 9VDC transformer? And another question, where do I wire drivers for relays (I learned only basics of electrotechnics in high school)?

 

[alec_t]

I think that to answer those questions I'd need to draw out a full schematic for you. I'll get back to you, but it may be a day or two before I can do so.

 

[Vuki_Cro]

OK if you'll have some extra time. Please, take your time...I'm not in hurry.
Thanks for helping out, I appreciate it very much.

 

[alec_t]

Hi, here's the full circuit for handling signals from your Preamps 1-3.
It uses:-
1 x CD40106,
6 x NPN transistors (2N3904 or similar),
16 x diodes (1N4148 or similar),
1 x DPDT 9V relay,
5 x SPDT 9V relays,
1 x 10uF 25V electrolytic capacitor,
4 x 100nF plastic film capacitors,
2 x 10nF plastic film capacitors,
16 x 27k resistors,
6 x 10k resistors,
3 x 1k resistors,
1 x 100k resistor,
4 x momentary-action switches,
1 x 9V regulated power supply,
Various plugs and sockets,
1 circuit board (Veroboard or custom pcb),
1 metal enclosure.

All resistors are 1/4 W rating.

 

[Vuki_Cro]

Wooow, cool! Thanks man!

 

[Vuki_Cro]

Hi! I made a sketch and I'd like to know if it would work...Thanks!
View attachment 63493