I implemented a basic switch for a temporary solution to the following problem:
selecting between the XLR outputs from my audiolab-mdac or the outputs from a cyrus preamp to feed my XLR inputs of my hypex ucd400 amps. This is a temporary (and hopefully cheap) solution waiting for the audiolab MPAX HTbypass to becoming available. Unfortunately, when switching there is then a not very reassuring popping noise from my speakers (which I would not like to blow up ...)
Reading through some of the threads here I think the problem comes from the fact that I use two simple 3P2T switches (one for each channel to switch the three XLR wires from one input to the other). These are "brake before make" I think . Solutions I identified are
a) get hands on a 6 pole 2 throw switch for low voltage applications, possibly "make before break". Disadvantage: need to rebuild and not easy to find rapidly the switch ?
b) put a high resistance (around 1Mohm) on each of the input xlr connectors, one between pins 2-1 and another between 3-1 (one is ground) to discharge capacitances on preamp sides. Advantage: relatively easy to do; disadvantage: not sure if damage can result somewhere.
c) turn off amplifiers before switching and turn them on (easiest solution but very low WAF)
Can someone tell me if I analysed correctly the problem and if the solutions are valid ?
Thanks in advance and sorry if I missed a thread presenting the solution.
selecting between the XLR outputs from my audiolab-mdac or the outputs from a cyrus preamp to feed my XLR inputs of my hypex ucd400 amps. This is a temporary (and hopefully cheap) solution waiting for the audiolab MPAX HTbypass to becoming available. Unfortunately, when switching there is then a not very reassuring popping noise from my speakers (which I would not like to blow up ...)
Reading through some of the threads here I think the problem comes from the fact that I use two simple 3P2T switches (one for each channel to switch the three XLR wires from one input to the other). These are "brake before make" I think . Solutions I identified are
a) get hands on a 6 pole 2 throw switch for low voltage applications, possibly "make before break". Disadvantage: need to rebuild and not easy to find rapidly the switch ?
b) put a high resistance (around 1Mohm) on each of the input xlr connectors, one between pins 2-1 and another between 3-1 (one is ground) to discharge capacitances on preamp sides. Advantage: relatively easy to do; disadvantage: not sure if damage can result somewhere.
c) turn off amplifiers before switching and turn them on (easiest solution but very low WAF)
Can someone tell me if I analysed correctly the problem and if the solutions are valid ?
Thanks in advance and sorry if I missed a thread presenting the solution.
Option (b), perhaps combined with checking that there are DC isolating capacitors at the appropriate places.
Thanks; not sure how I can do this. As I use commercial preamps, I suppose they use DC isolating capacitors, otherwise I guess they would tell use to be carefull when connecting to amps ?
The problem is:
You are switching "three" wires in an XLR circuit.
Each XLR pin #1 wire should be connected permanently to the chassis at it's connector.
You are switching "three" wires in an XLR circuit.
Each XLR pin #1 wire should be connected permanently to the chassis at it's connector.
Commercial stuff, except perhaps some 'high end', will almost certainly include DC blockers; many will also already have ground ref resistors too. Try adding the resistors; they will probably be sufficient. Do the switch output side first, as ground ref resistors are more likely to be omitted from amp inputs than outputs.
You mean I should permanently connect all pin 1 within my switching box to solve the problem as option d) ?
Yes, the XLR pin #1 connection is not part of the audio circuit. It should only be connected to the chassis near the connector.
Have put 1M ohm resistors between all pin1-pin2 and pin1-pin3 and connected all pin1 together.
Works perfecly now, no popping noise and reasonable WAF ;-)
Thanks for the help.
Jean-Marie
Works perfecly now, no popping noise and reasonable WAF ;-)
Thanks for the help.
Jean-Marie
Sorry to bring an old thread back to life, but I'm in the same situation as jmbulg - I intend to use relays with a 12V trigger to switch between 2 XLR inputs.
However I'm using Ncore instead of UCD400. Ncore has no DC isolating caps afaik.
* Is using 1M ohm resistors still safe in this situation?
* Potential audio quality impact?
Thanks for your feedback!
However I'm using Ncore instead of UCD400. Ncore has no DC isolating caps afaik.
* Is using 1M ohm resistors still safe in this situation?
* Potential audio quality impact?
Thanks for your feedback!
The switch is now working safely on my ncores which replaced the UCD400 in my setup.
I have no idea on the possible audio quality impact, the few times I directly connected the amp without the switch I was not detecting changes but did not make extensive comparisons neither.
Thanks Jean-Marie!
I'll order some 1M ohm resistors and continue with my project. I'm using this Two DPDT Signal Relays Module Board 12V for 8051 Pic | eBay to automatically switch between receiver & DAC, by using the 12 trigger on the receiver.
If it still pops, I'll try adding circuitry to mute the ncores (nAmpon) during switching inputs.
I'll order some 1M ohm resistors and continue with my project. I'm using this Two DPDT Signal Relays Module Board 12V for 8051 Pic | eBay to automatically switch between receiver & DAC, by using the 12 trigger on the receiver.
If it still pops, I'll try adding circuitry to mute the ncores (nAmpon) during switching inputs.
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