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Technical Review of the NJ&FX AUDIO PW-6 “HiFi Audio Power Switcher” (A/B switch)
- Thread starter KEFCarver
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KEFCarver
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I respectfully beg to differ in regards to the frequency response- I measured it from 20hz-20khz, and I have tested 2 or 3 different units, all with the same problem. I contacted Douk and they were aware of the problem, but thought it had been solved. Here is a typical frequency response that I measured, in this case the path from AMPA to Speaker 2. I believe that there are transformers used in the VU ckt that are causing this based on the email from Douk.
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KEFCarver
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Most of the switching I have down is with power levels that are <50w into 4ohms or <15w/8ohms (depends on which speakers I am using). Probably not much chance of arcing... until the contacts wear out which begs the reliability question. My unit has probably seen 3000 switches I am guessing so far- might be interested to remeasure it at some point to see if there are any measurable changes. Enough for tonight....
solderdude
Grand Contributor
As said, technically utterly impossible for relay contacts to do this. Certainly with speakers. The reason all units seemed to do this is because none of them really did and you are looking at the measurement system and a measurement error showing up consistently.
Relay contacts are flat from DC to well over 1MHz. Period.
When you measure the frequency response using an incorrect load (such as the very high input impedance of the QA) you could see weird things in the response caused by parallel circuits. But .... with speakers this is absolutely impossible.
Relays like the ones used in the device are designed to switch mains or DC voltages and are designed to operate optimally for that.
@pma is correct about the contact material being important and am sure, just like @restorer-john (and me) having to replace similar output relays in older amps that started to make intermittent contact (specifically at lower levels, once it 'arced' by shortly increasing the volume) it would work again till the next time the relay had to make contact.
Your device(s) will very likely work well for many years though so nothing to worry about ... yet.
After many years of usage you may have to replace the relays.
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KEFCarver
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At a cost of ~$80, I would probably just replace the NJ&FX switcher 
The response I posted was from the Douk device and not related to my QA analyzer and measurement techniques. If you were measuring just a relay you would expect pretty much a "loop thru" response like you get with just the measurement cables/adapters connected. In fact, I was surprised when I got the response I did, and pulled a NOS 12vdc relay out of a parts bin (it was at least 30years old), soldered some connectors onto it, hooked it up to a power supply and measured it- and got would you would expect from having a relay inserted- not much of a difference. If I am able to find the corresponce I had with Douk I will post it. Here is where I uploaded my review of the Douk if you are interested:
www.audiosciencereview.com
The response I posted was from the Douk device and not related to my QA analyzer and measurement techniques. If you were measuring just a relay you would expect pretty much a "loop thru" response like you get with just the measurement cables/adapters connected. In fact, I was surprised when I got the response I did, and pulled a NOS 12vdc relay out of a parts bin (it was at least 30years old), soldered some connectors onto it, hooked it up to a power supply and measured it- and got would you would expect from having a relay inserted- not much of a difference. If I am able to find the corresponce I had with Douk I will post it. Here is where I uploaded my review of the Douk if you are interested:
Any interest in measuring a loudspeaker/amplifier A-B switcher?
Is there a switch that anyone recommends that is set up correctly so as not to damage anything nor impact SQ adversely? I don't care about meters, I want to switch 2 amps, a SS and a tube, with 2-4 sets of speakers. OSD has some stuff but I don't think they have any impedance protection. Second...
www.audiosciencereview.com
Mystery solved! Credit to Douk Audio for actually supplying an answer:
The "hold to program" functionality actually has two variants. Holding any button until you get a double flash of the power light puts it into the "toggle" mode. The button you held now toggles inputs.
To get back to "direct select" mode, hold the currently programmed toggle button until you get a single flash of the power light, then let go. The power light will then double flash again, and the device will go back into the original "direct select" mode.
It is extremely sensitive and might take a couple of tries before you get the hang of switching it back and forth.
As far as my Googling can tell, and I'm in IT, so a professional Googler, this is totally undocumented. I haven't asked ChatGPT if it knows about this, but maybe it'll read this forum and figure it out for someone else.
Could this switcher be used without attached power? I mean like I set it to either A-B or A-C and it keeps the setting and allows to listen to music in off state even without any power?
Or does it needs to be powered and switched on to pass the sound?
Or does it needs to be powered and switched on to pass the sound?
Confirmed. It does not pass audio when it is powered off or unplugged.
The TC-7220 should do what you want.
It's still available to purchase from various spots around the Internet. It is unpowered -- purely a mechanical switch with buttons that physically move the contact points.
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