Sonic degradation thru classic AR's with speaker selector ?

[Guest postjob62]

I have an old Adcom GFS-3 speaker selector box which I was about to put on ebay when a light went off. It would seem to be a great tool for comparing and A-B ing speakers. The box is simple- it has one set of speaker-level inputs where the signal comes in from the amp, and three sets of individually (or simultaneously) selectable outputs to three discrete sets of speakers. There is also a selectable "protection" circuit to increase impedance when using speakers with too little impedance simultaneously.

I would use this with 3a's, 4x's and 2ax's primarily, none of which are notably efficient. My amp is a high-current piece with 100 wpc into 4 ohms and 80 into 8 ohms. As stated, I plan to only have one set of speakers engaged at any time. Would anyone hazard a guess as to whether there would or should be any sonic loss to the speakers under these circumstances? My guess is that any loss would probably be less than that attributable to any number of other factors, and likely not noticeable to my 56 year old ears.

Obviously I can and will hook it up and see, but thought I might get opinions before taking the system down.

Thanks,

Ed

[Guest nathanso]

I use a Niles A/B box for testing various speakers and it seems to work fine. Degradation, if any, should be equal amongst the speakes being tested.

[dynaco_dan]

>I have an old Adcom GFS-3 speaker selector box which I was

>about to put on ebay when a light went off. It would seem to

>be a great tool for comparing and A-B ing speakers. The box is

>simple- it has one set of speaker-level inputs where the

>signal comes in from the amp, and three sets of individually

>(or simultaneously) selectable outputs to three discrete sets

>of speakers. There is also a selectable "protection"

>circuit to increase impedance when using speakers with too

>little impedance simultaneously.

>

>I would use this with 3a's, 4x's and 2ax's primarily, none of

>which are notably efficient. My amp is a high-current piece

>with 100 wpc into 4 ohms and 80 into 8 ohms. As stated, I plan

>to only have one set of speakers engaged at any time. Would

>anyone hazard a guess as to whether there would or should be

>any sonic loss to the speakers under these circumstances? My

>guess is that any loss would probably be less than that

>attributable to any number of other factors, and likely not

>noticeable to my 56 year old ears.

>

>Obviously I can and will hook it up and see, but thought I

>might get opinions before taking the system down.

>

>Thanks,

>

>Ed

Hi Ed;

Interesting topic.

I would say this setup would be ok, except, mainly for the "protection circuit".

This should not be in the circuit anywhere, as it may introduce distortion and definitely a false load to the amplifier.

The box, cables and switches should be sound, substantial and stable.

If there is an option, simultaneous use of more than one pair of switching options should be disabled, if at all possible.

The box does not need to be shielded for just speaker leads.

The cables do not need to be shielded, but not less that than 10 guage or not lighter than perhaps 18 guage stranded wire inside the box.

The switches should not be of the shorted, make before break type, and with strong silver plated contacts.

The speaker input terminals, across each pair of speakers plus and minus input terminals from an amplifier, should have a wirewound 10 -25 watt 100 ohm resistor soldered across.

This is to provide a constant amplifier load, even when switching between speakers or not.

An instant off or instant on load may damage some lesser quality amps.

I have a Russound speaker switching box that I bought from a second hand store years ago.

I do not know why I bought it, other than I own more than one pair of speakers.

Way back, we used to have demos at different homes on weekends, a switching box would have been real handy then.

Overall, if you wanted to switch between each set of speakers, in the same room, on a regular basis then a switch box would save a lot a wire switching.

Have a great day.

[ar_pro]

I've actually used the GFS-3, Ed, and the results were excellent with a pair of 3a's and 2ax's. This was probably 15 years ago, and the amplifier was the old Adcom 555II. As long as the GFS-3 is working properly, it should sound just fine.