Ohms selector isn't right

[wallythacker]

Collector'S Jimi Hendrix Marshall SUPERJH100 AMP Full Stack ALL Accessories | eBay

Check out the ohm selector. Three settings that I can make out

8 ohms, 16 ohms and 100 volts. What? 100 volts?

WTF is a mains voltage selection doing on the output side? My 1974 SL50 has 8 ohms, 16 ohms and 4 ohms. I'm pretty sure volts aren't a choice.

Is this rig bogus?

 

[Marshallhead]

Nope it's correct.

100v output setting from the OT is for driving long chains of speakers, like in a church of factory, without signal loss.

The original Drake transformers had a 100v tap so this reissue does too.

 

[wallythacker]

Very cool information. I like learning new things. Thanks

So in the chain of speakers, all in series I imagine, the impedance would be massive, wouldn't it?

I need to do some more reading on this. I'm having a hard time getting my head around it.

 

[Blacque Jacque]

No each speaker is wired in parallel across the 100v line & each has a local step down transformer. Power transmission is more efficient over long distances using high voltage at low current.

This is precisely why power companies use hundreds of KV on power lines to reduce transmission losses.

 

[wallythacker]

No each speaker is wired in parallel across the 100v line & each has a local step down transformer. Power transmission is more efficient over long distances using high voltage at low current.

This is precisely why power companies use hundreds of KV on power lines to reduce transmission losses.

I immediately saw that as soon as I read local step down. Of course. They can have hundreds of speakers if they want.

 

[Blacque Jacque]

There is still the limitation that they can only draw as much power as the amp is able to supply, but for speaker output transmission over long distances, 100v line was hard to beat, sound quality was something else however.

100v line was (and still is I believe) commonly used in schools, libraries, churches offices etc where there was an installed pa system around the buildings.

 

[hazmat7719]

Blacque Jacque,
Here in the US, the common pa systems are 25 and 70 Volt. Most schools, churches and public areas that use these transmission systems are sending background music or pages. You can purchase better transformers than the standard paging system transformers that are used in these applications.

 

[Blacque Jacque]

Cool, thanks hazmat, I didn't know of the 25v & 75v systems, I've only ever encountered the 100v here.

It's no surprise that the US & UK have different specs for these things though.

 

[hazmat7719]

Some of the US amplifiers/systems have a 100 Volt tap.