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Post subject: Wiring guru needed...
Posted: Wed Jan 29, 2014 7:02 pm
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I want to wire an on/on toggle to a 2x12 cabinet so that I may use both an SCX2 head (using one of the speakers), or use the same 2x12 cab with my TRRI- not as an extension cab, but as a replacement for the speakers loaded in the amp.

I think it can be done but my lack of wiring know how is preventing me from drawing up a plan. Any help would be awesome! Thanks...


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Post subject: Re: Wiring guru needed...
Posted: Wed Jan 29, 2014 7:17 pm
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JamGuy wrote:
I want to wire an on/on toggle to a 2x12 cabinet so that I may use both an SCX2 head (using one of the speakers), or use the same 2x12 cab with my TRRI- not as an extension cab, but as a replacement for the speakers loaded in the amp.

I think it can be done but my lack of wiring know how is preventing me from drawing up a plan. Any help would be awesome! Thanks...



It's a little more complex than just a switch. The amps need to see a load when switched out. Weber has a box that puts a 200 watt dummy load on the amp that is not being used.
This might help.

https://taweber.powweb.com/store/2head.htm

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Post subject: Re: Wiring guru needed...
Posted: Wed Jan 29, 2014 7:36 pm
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I think you're thinking that I want to use both amps at the same time… I just want to be able to use the same cab for two different amps, but not at the same time. The toggle switch would basically be cutting one speaker out when it was plugged in to the SCX2. Flipping the toggle switch would allow me to use the cabinet as the speakers for my TRRI, using both speakers.


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Post subject: Re: Wiring guru needed...
Posted: Wed Jan 29, 2014 7:58 pm
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I can't do a diagram at the moment, but explaining off the top of my head.

Assuming you have a cab with the 2 (8 Ohm) speakers mounted, a speaker jack mounted, and a SPST On/Off switch mounted.

1. Starting from the jack run a wire from the sleeve (-ve) terminal of the jack to the -ve terminal of speaker 1.

2. Then run a wire from the -ve terminal of speaker 1 to the -ve terminal of speaker 2.

3. Then run a wire from the (tip)+ve terminal of the jack to the +ve terminal of speaker 1.

4. Then run a wire from the +ve terminal of speaker 1 to one side of the switch.

5. then run a wire from the other side of the switch to the +ve terminal of speaker 2.


That will give you a 4 ohm cab using both speakers (speakers in parallel) with the switch On or a single 8 Ohm speaker with the switch in the Off position. (speaker 2 disconnected out of parallel circuit).


Snowy


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Post subject: Re: Wiring guru needed...
Posted: Wed Jan 29, 2014 8:59 pm
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Perfect description Snowy.

JamGuy,
You might want to get a jack plate to mount the jack and toggle switch. This is the one that I used for a similar project. I cut a hole in the back panel of the cab for the plate, and had to ream out one of the holes a little for the switch.

http://forums.fender.com/viewtopic.php?f=13&t=91939

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Post subject: Re: Wiring guru needed...
Posted: Wed Jan 29, 2014 9:39 pm
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Maybe this will help. You can actually use either speaker setting, 1x12 or 2x12, with either amp, SCX2 or TRRI.

Image

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Post subject: Re: Wiring guru needed...
Posted: Thu Jan 30, 2014 8:05 am
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shimmilou wrote:
Maybe this will help. You can actually use either speaker setting, 1x12 or 2x12, with either amp, SCX2 or TRRI.


Thanks for the help guys…

I'm surprised that I could use either setting for either amp, but then, I'm not familiar with how ohms and all that stuff works. So then, is a TRRI wired in parallel as it comes stock from the factory? I just want to double check before I get this wired this up.

Cheers, JG


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Post subject: Re: Wiring guru needed...
Posted: Thu Jan 30, 2014 11:57 am
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Yes, the TRRI uses two 8-ohm speakers in parallel for a 4-ohm speaker load. You can safely use one speaker (an 8-ohm speaker load) with the TRRI, providing the total speaker wattage is high enough for the amp. You probably want at least 100 watts total speaker load with the TRRI, whether one or more speakers. For example, if each speaker is rated for 100 watts, using one would be able to handle up to 100 watts and using both would be able to handle up to 200 watts. If each speaker were only rated for less than 100 watts, you should use both with the TRRI for a total of 100 watts or more.

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Post subject: Re: Wiring guru needed...
Posted: Thu Jan 30, 2014 12:02 pm
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shimmilou wrote:
Yes, the TRRI uses two 8-ohm speakers in parallel for a 4-ohm speaker load. You can safely use one speaker (an 8-ohm speaker load) with the TRRI, providing the total speaker wattage is high enough for the amp. You probably want at least 100 watts total speaker load with the TRRI, whether one or more speakers. For example, if each speaker is rated for 100 watts, using one would be able to handle up to 100 watts and using both would be able to handle up to 200 watts. If each speaker were only rated for less than 100 watts, you should use both with the TRRI for a total of 100 watts or more.


cool beans… yeah, wattage is not a problem. Each Commonwealth is rated at 225 watts. :shock:


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Post subject: Re: Wiring guru needed...
Posted: Thu Jan 30, 2014 12:17 pm
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Excellent! 8)

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Post subject: Re: Wiring guru needed...
Posted: Sun Feb 23, 2014 1:13 pm
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Thanks folks... I finally got the rest of the parts needed to finish the cab project... the toggle works great. I do have one question though... it says on the back of the SCX2 speaker out,
"8ohm min". If I'm running 2, 8ohm speakers in the cab, isn't that a 4ohm load? Again, I'm not very knowledgable with wiring stuff and do not want to damage the speakers or my amp. Is it really safe to run the SCX2 as a 2x12? BTW, the cab sounds incredible as both a 1x12 and 2x12... despite being back-breakingly heavy, the Eminence Commonwealths are pretty sweet sounding speakers... I'm not ever going to splurge on vintage JBLs but even if these are a distant second, I'm content. I've heard they're loosely based on the old JBLs with the aluminum cones but who knows if that's fact or fiction. Thanks again! I'll try and get a picture up at some point. Cheers...


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Post subject: Re: Wiring guru needed...
Posted: Sun Feb 23, 2014 5:22 pm
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When using an 8 ohm speaker load, you will get the most power from the SCX2. Impedance matching is about getting full rated power from a tube amp. When using a 4 ohm or 16 ohm speaker load, you will have less output power. It is perfectly safe to use a 4 ohm or 16 ohm speaker load with the SCX2, and the sound is really the main consideration. Sometimes a slight mismatch sounds better than a match. Remember the 2 to 1 ratio (high or low) and you'll be good.

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Post subject: Re: Wiring guru needed...
Posted: Sun Feb 23, 2014 6:00 pm
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shimmilou wrote:
When using an 8 ohm speaker load, you will get the most power from the SCX2. Impedance matching is about getting full rated power from a tube amp. When using a 4 ohm or 16 ohm speaker load, you will have less output power. It is perfectly safe to use a 4 ohm or 16 ohm speaker load with the SCX2, and the sound is really the main consideration. Sometimes a slight mismatch sounds better than a match. Remember the 2 to 1 ratio (high or low) and you'll be good.


Oh, OK, that makes a little more sense. I have to say, I had been throwing caution to the wind all afternoon as the SCX2 sounds incredible pushing the 2 12s. It's sounds pretty impressive just pushing the one but 2 is magic. Glad to know it's not doing any harm. The combo of the Commonwealths and the SCX2 has me contemplating retrofitting another one in my SCX2 combo... though I'm not sure what I'd have to do to jam one in there. The other problem might be the sheer volume of the speaker... the magnet is huge and takes up a large amount of space. Here's a picture of the cabinet.
Image

Thanks again Shimmilou for the help is figuring this out!


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Post subject: Re: Wiring guru needed...
Posted: Sun Feb 23, 2014 6:05 pm
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Since this thread is calling knowledgeable eyes. A quick wiring question, of sorts.

A 4 ohm speaker and an 8 ohm speaker, wired in series would produce what ohmage?

As a thinking person, the answer with the formula for the answer would be much appreciated.

Thank you in advance.

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Post subject: Re: Wiring guru needed...
Posted: Sun Feb 23, 2014 6:09 pm
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well, if I understand what I've been reading, I'd guess 6 ohm... which doesn't fit with the 2 to 1 ratio. Let's see who chimes in and corrects me. :lol:


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