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Converting Spider III 150 Combo to a cabinet


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#1 Tk11

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Posted 05 April 2016 - 06:57 PM

I am going to convert my Spider III 150 Combo to a 2x cabinet to be powered by a Randall 1 watt head. If the moderator allows this to be posted, am looking for any lessons learned and input. Specifically on ohms. the Spider III speakers are 8 ohms, how do i ensure the correct ohms are achieved. the conversion looks very simple due to the open back Spider III. 

 

Thanks,

RocketDog


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#2 Tk11

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Posted 06 April 2016 - 01:26 PM

Found the very applicable and easy to understand parallel vs. serial site from the Cleveland Institute of Electronics (PDF below) if anybody else is interested.  At this point, I have enough information to be dangerous to myself and others. If you have actual electrical background please weigh in. Unless informed otherwise, I am going to rewire the 2x cab in serial which should result in a 16ohm cab. Randall head specifications say the speaker out from the head can be plugged into any 8ohm or higher cabinet.

 

From what I understand, serial wiring will increase the impedance load by adding the speakers (resistors) together.  In this case, I have 2 8ohm rated speakers, if I wired in serial the I would have a 16ohms cabinet (within tolerance of my Randall head).

 

If I wire in parallel, the ohms reduce by half for each resistor (speaker) or said differently, you divide the speaker ohms by the total number of speakers to get the the total cabinet ohms. in this case 2 8ohm speakers wired in parallel would result in a 4ohm cabinet (8/2=4) outside of my Randal head specifications.  

 

of note on tube amps from the same site, 

Solid State Amps Power ratings change as the impedance changes. The lower the impedance, the greater the power

Tube Amplifiers Power ratings do not change as the impedance changes. There is no power handling advantage to wiring speakers in series, parallel, or series/parallel when using a tube amplifier. 

 

http://cie-wc.edu/Se...rallel_9_14.pdf

 

http://www.speakerim...page=calculator impedance calculator if anybody needs one.

 

RD


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#3 Tk11

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Posted 08 April 2016 - 12:17 PM

So I converted my Line 6 Spider III 150 into a passive cab last night (just did it with wired alligator clips for now, will solder wires today and mount the input jack permanently). Was really really simple. Ended up wiring in parallel, it just made sense when i was doing the conversion. My Randall 1 watt tube amp is way more then enough power for the cab. Actually in my studio (spare bedroom) I can only turn the amp up to about the the 8 o'clock position (2-3 maybe) if I run the output directly from my amp to the cab, it's that loud. What you miss however is the overdriven tube amp tube break up, just can't get to a volume to drive the amp without shaking windows.

 

Randall has a great feature however (not meaning to sound like a Randall commercial, but.... and i"m sure most other manufactures have something very similar), the amp has an attenuated output that emulates a Randall 4x12 cabinet. It is mostly for headphone use or running the amp into a mixing board so not to damage the phones or board. What I found is the attenuated output is the perfect output to run to the new cab. it allows me to go to 3/4 if not max volume and gain to drive the amp into tube breakup, but isn't loud at all. 

 

I'll post pictures later today after I finish it. But reading the posts below about Spider III electronic issues, this is a really easy, cost efficient option to keep playing.  Very happy with the result and I seemed to have conquered the the Spider III 150 watt volume issue that has plagued me for years. How the amp goes from barely to BLASTING in a very small movement of the volume or a change in a setting. Don't have that issue anymore :)


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#4 radatats

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Posted 08 April 2016 - 01:50 PM

sounds like a fun project.  However, I suggest you go with the series vice parallel wiring.  On the Randall page it says 8 ohms minimum for the RD1H.  While it may handle the ohms, it could cause issues down the road.  It will work just as well at 16 ohms and safer for your amp.


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Quit complaining and DO something or help somebody with their issues...


#5 Tk11

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Posted 08 April 2016 - 02:01 PM

Thanks, it has been fun, I knew nothing about calculating ohms or power ratings, so good project for the head . Yes, read the Randall specs for my head, and agree series is the correct way. However last night when I was mocking it up with alligator clips, series just seemed to be easier, just to see if it would really work.  Today when I solder I will wire in series. 


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#6 Tk11

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Posted 10 April 2016 - 08:11 PM

Project complete less picture's.  the Spyder III 2x12 cab convert was very simple and sounds excellent driven by the 1 watt amp. the only stumble was mounting the 1/4 TRS input through the side of the Spider III.  The combo amp has a surprisingly thick cab, to thick for a standard guitar input jack. to overcome, I connected one 1/4 to 3.5 mm adapter to another 3.5mm to 1/4 adapter (to give me connections I needed but also the length to pass through the cab) which fits internally into the "guitar" input jack (confused?).   Drilled a hole and pushed the whole thing through. the only externally visible part of this whole project is a gold guitar input on the side of the cab.

 

My soldering skills are horrible, so that is delaying the pics, sorry, don't want to show my poor work. To do again, the speakers have connections for crimp on connectors, I would do that instead of soldering, but you work with what you have.  

 

So for the first time in my guitar life I have non-processed sound. Not to sound dramatic but the sound heard is the sound put in. It's really naked and a bit unsettling at first. the notes stop when you lift your finger and suddenly your not as fast as you were thinking you were,  or the notes buzz if you don't do it right and it's not hidden by a distortion effect. naked, unsettling, but I can already tell I am becoming a better guitar technician, maybe not a better artist yet, but technically better.

 

Take care

 

RD

 

BTW, whoever gave me the Neutral point thanks! Don't know what it means, but seems better than the warning points above it. :)


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#7 spidercrack

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Posted 24 May 2016 - 04:49 PM

what if the cabinet just have a speaker and the head is a 150w? I have a spider iii HD150 and a dead spider iii 75w combo, but the speaker works.

 I've connected only one of the outputs to the speaker but it's louder than a normal 75w combo. I'm affraid something bad happens.

Any advice?


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