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yesmynameisking

Is it safe to run two sets of speakers on a Fisher 400 using a Switch Box (with protection)?

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Is it safe to run two sets of speakers on a Fisher 400 using a Passive Switch Box (with protection) like the one in the picture? 

 

One set of speakers would be vintage Grundig's (see photo) from the 1960's that I believe are 6 ohms. The second set of speakers would be a passive Pioneer S-W33 Subwoofer (see photo) that is 8 ohms with duel speaker inputs.

 

If it is safe, do I run the Fisher 400 in 8 ohm or 4 ohm mode?    

 

 

Thanks,

Mike

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Edited by yesmynameisking

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Is it safe to run two sets of speakers on a Fisher 400 using a Passive Switch Box (with protection) like the one in the picture? 

 

One set of speakers would be vintage Grundig's (see photo) from the 1960's that I believe are 6 ohms. The second set of speakers would be a passive Pioneer S-W33 Subwoofer (see photo) that is 8 ohms duel speaker inputs.

 

If it is safe, do I run the Fisher 400 in 8 ohm or 4 ohm mode?    

 

 

Thanks,

Mike

Howdy Mike,

 

Hopefully someone else on here knows whether or not that Adcom unit has an impedance matching autoformer in it? In any case, the Pioneer dual-sub is probably a 4 Ohm load by itself if you connect to both pair of binding posts. Once you add (parallel) the additional 6 Ohm load, you would be driving into a 2.5 Ohm load. My guess would be that would be bad for your Fischer 400 EVEN on the 4 Ohm taps. :( Remember, as the impedance swings with frequency you may be driving your amp into a "dead-short". Not advised.

 

But, what you could try is to run the whole deal "in series/parallel", so for now don't use that adcom thing at all, 1st wire the sub "in series" (you could also "play around" with the series wiring to run it "in-phase or out of phase", try this 1st, run a wire from the positive terminal of the fischer to the first positive terminal on the sub, then run wire from the first negative terminal on the sub to the 2nd positive terminal on the sub. Now run a wire from the 2nd negative terminal  on the sub back to the negative terminal on the fisher. What you have now is the sub wired in series with the fisher (16 Ohm load). Now, run a wire from the SAME positive terminal on the fisher to the positive terminal on the LEFT vintage grundig. Run another wire from the negative terminal on the same LEFT vintage grundig back to the negative terminal that is already occupied by the wire from the sub. So for the Left channel you will have a vintage grundig and BOTH drivers of the sub. (16 + 6 = 22/4 = 5.5 Ohm load) Wire the other channel from the Fischer the standard way. Set the Fischer to 4 Ohm impedance and you  will be in business. :)

 

Hope I've helped. :) 

 

Matt.

 

P.S. Just place the sub somewhere between the two Grundigs. :) you may have to move it around a bit but I think you'd be happy. 

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Matt,

 

The Pioneer dual-sub says it in 8 ohm on the label (see picture). Though is says "8 ohm", do you think it is really 4 ohms? Let me know.

 

Thanks,

Mike 

Edited by yesmynameisking

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Matt,

 

The Pioneer dual-sub says it in 8 ohm on the label (see picture). Though is says "8 ohm", do you think it is really 4 ohms? Let me know.

 

Thanks,

Mike 

 

Don't guess, check it at the terminals with an Ohm meter.

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Matt,

 

The Pioneer dual-sub says it in 8 ohm on the label (see picture). Though is says "8 ohm", do you think it is really 4 ohms? Let me know.

 

Thanks,

Mike 

 

Don't guess, check it at the terminals with an Ohm meter.

 

Yep, what Carl just said, if you measure something in the neighborhood of 6-7 Ohms, on EACH pair of binding posts, then the series connection I have described for the subwoofers will be accurate.

 

Matt.

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Dead short loads are only bad for sand amps. Most if not all tube guitar amps have a shorting jack so if the amp is played with the speaker disconnected the output transformer will not be damaged. It's an open load which looks like infinity (AC only) on the primary that will swing huge voltage spikes and short windings or tube sockets when a signal is present.

 

The Pioneer sub in parallel with the Grundigs will present a 3.4 ohm load so use the 4 ohm tap on the Fisher 400. So that's half the Pioneer sub and one Grundig per channel.

Edited by xxJPMxx

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