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Topic: Sica Neo 15" for Fender Vibrosonic? |
Chris LeDrew
From:
Canada
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Posted 17 Mar 2012 2:59 pm |
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I'm picking up a SF Vibrosonic in a few days, and I was hoping to try a Sica neo 15" in it. Will it fit? I recall some talk around here before that there were issues with the Sica fitting on a Vibrosonic baffle, but I could be mistaken.
Any info would be appreciated, thanks!
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Jackson Steel Guitars
Web: www.chrisledrew.com |
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Tim Marcus
From:
San Francisco, CA
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Posted 17 Mar 2012 4:16 pm
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It should fit - the SICA speakers use standard spaced mounting holes. Nothing out of the ordinary. Will probably shave a few pounds off the overall weight too if you are pulling a JBL out of there
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Milkmansound.com |
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Chris LeDrew
From:
Canada
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Posted 17 Mar 2012 4:21 pm
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Thanks, Tim....yes there's a JBL in there now. It sounds killer as is but I'm curious as to the tone-weight ratio of a lighter speaker. The difference between a 25-pound speaker and 7-pound speaker would be a nice break on the load-ins. If the sounds wasn't too compromised I'd go with it. The neo is in my Session 400 now, so I'd just pop it out to give it a try, or run the speaker to the Vibrosonic to try it out before installing it.
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Jackson Steel Guitars
Web: www.chrisledrew.com |
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Tim Marcus
From:
San Francisco, CA
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Posted 17 Mar 2012 4:58 pm
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Definitely try it first before wrangling that JBL out of there!
I think you'll like it. I use the 350W model in the Milkman steel amps. Its a great sounding speaker for steel
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Milkmansound.com |
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Chris LeDrew
From:
Canada
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Posted 17 Mar 2012 5:03 pm
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Good to know! The thing is I'll be using the amp for steel and guitar, so I will have to see how it sounds with rock and roll on an SG or Strat before making the decision. The amp as it stands now is freakin' heavy, even more so than my SF Twin. But the reverb is the most lush I think I've ever heard. And the amp is untouched except for some grill cloth discolouration. $500. Not bad!
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Jackson Steel Guitars
Web: www.chrisledrew.com |
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Kevin Hatton
From:
Buffalo, N.Y.
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Posted 17 Mar 2012 5:51 pm
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| The Vibrosonics are 8 ohm, and i think the Sicas are 4 ohm. You might have a problem. |
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Chris LeDrew
From:
Canada
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Posted 17 Mar 2012 7:26 pm
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Yes Kevin I just came across that on another thread. Drag. Strange that a Vibro is 8ohms and a Twin is 4ohms.
_________________
Jackson Steel Guitars
Web: www.chrisledrew.com |
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Kevin Hatton
From:
Buffalo, N.Y.
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Posted 17 Mar 2012 10:04 pm
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| You can change the output transformer to 4 ohm. |
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Marc Jenkins
From:
Victoria, British Columbia, Canada
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Posted 17 Mar 2012 10:47 pm
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| The SICA are easily available in 8 ohm. |
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Chris LeDrew
From:
Canada
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Posted 18 Mar 2012 5:20 am
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Kevin yes that would be a good solution. I have a '71 Dual Showman and maybe could swap the transformers. Is that doable?
Marc, I was hoping to use the one I currently have instead of having to buy a new new one, but if it was worth it I would.
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Jackson Steel Guitars
Web: www.chrisledrew.com |
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Danny Naccarato
From:
Burleson, Texas
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Posted 18 Mar 2012 7:43 am
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| Chris, do a search on Ken Fox. There are extensive threads on this subject years ago. I had a 4 ohm in my DSR a few yeas back. If I recall, there were some threads about putting in a "dead" plug in the ext speaker jack. |
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Chris LeDrew
From:
Canada
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Posted 18 Mar 2012 11:28 am
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Danny I will do those searches and check out the threads....thanks a lot.
_________________
Jackson Steel Guitars
Web: www.chrisledrew.com |
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Ken Fox
From:
Nashville GA USA
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Posted 18 Mar 2012 4:32 pm
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| SICA come in 4 or 8 ohm, 250 or 350 watt versions. Also the hole spacing is standard on 15" but not on the 12" speakers |
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Chris LeDrew
From:
Canada
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Posted 18 Mar 2012 4:38 pm
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Thanks for the info, Ken...so would a dummy load in the ext. speaker jack allow me to run a 4-ohm in the Vibrosonic? I know you're busy and bombarded with questions all the time, but if the answer is "yes" then I'm gonna go for it!
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Jackson Steel Guitars
Web: www.chrisledrew.com |
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Ken Fox
From:
Nashville GA USA
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Posted 18 Mar 2012 5:27 pm
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| That only applied to the 135 watt models. However, I can't recall if it was an open jack or a closed (shorted) jack. First, let me know if it is the 135 watt model. It had a switching jack for the transfomer taps, the 100 watt model did not. |
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Chris LeDrew
From:
Canada
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Posted 18 Mar 2012 5:35 pm
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Ken thanks for your response...it is an earlier 100-watt version.
_________________
Jackson Steel Guitars
Web: www.chrisledrew.com |
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Tim Marcus
From:
San Francisco, CA
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Posted 18 Mar 2012 5:36 pm
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Another option is to pull 2 power tubes - that will give you about an 8ohm impedance at the secondary of the output transformer and match yor current speaker
You can yank the inner or outer two
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Milkmansound.com |
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Chris LeDrew
From:
Canada
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Posted 18 Mar 2012 5:39 pm
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Ah, I think I heard that before. Thanks again. I'd be down to 50 watts then, right?
_________________
Jackson Steel Guitars
Web: www.chrisledrew.com |
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Ken Fox
From:
Nashville GA USA
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Posted 18 Mar 2012 5:39 pm
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You can always buy the 8 ohm SICA speaker. Just a thought!
For the 135 watt only:
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Chris LeDrew
From:
Canada
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Posted 18 Mar 2012 5:42 pm
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I guess I can get a general idea of the speaker's sound by doing the above, and if I liked it I could order the 8 ohm. You have them in stock now, Ken?
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Jackson Steel Guitars
Web: www.chrisledrew.com |
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Ken Fox
From:
Nashville GA USA
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Posted 18 Mar 2012 5:44 pm
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| I drop ship them from distribution right to your door! I suggest the 350 watt model for extended high end and superb low end as well. It is on my website and there is an audio clip there as well for that speaker. |
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Chris LeDrew
From:
Canada
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Posted 18 Mar 2012 6:46 pm
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Great, Ken, I will keep in touch.
_________________
Jackson Steel Guitars
Web: www.chrisledrew.com |
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Brian McGaughey
From:
Orcas Island, WA USA
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Posted 18 Mar 2012 7:13 pm
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$500 for a Vibrosonic? Nice!
This thread got me thinking and I took a look...I've been powering a 4 ohm JBL with my Vibrosonic for a number of years. Haven't had a problem. Maybe I've been lucky? I don't push it hard. |
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Ken Fox
From:
Nashville GA USA
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Posted 19 Mar 2012 3:14 am
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Good info from the net:
Q: Why do I have to match speakers to the output impedance of the amp?
A: You'll get the most power out of the amp if the load is matched.
Q:Will it hurt my amp/output transformer/tubes to use a mismatched speaker load?
Simple A: Within reason, no.
Say for example you have two eight ohm speakers, and you want to hook them up to an amp with 4, 8, and 16 ohm taps. How do you hook them up?
For most power out, put them in series and tie them to the 16 ohm tap, or parallel them and tie the pair to the 4 ohm load.
For tone? Try it several different ways and see which you like best. "Tone" is not a single valued quantity, either, and in fact depends hugely on the person listening. That variation in impedance versus frequency and the variation in output power versus impedance and the variation in impedance with loading conspire to make the audio response curves a broad hump with ragged, humped ends, and those humps and dips are what makes for the "tone" you hear and interpret. Will you hurt the transformer if you parallel them to four ohms and hook them to the 8 ohm tap? Almost certainly not. If you parallel them and hook them to the 16 ohm tap? Extremely unlikely. In fact, you probably won't hurt the transformer if you short the outputs. If you series them and hook them to the 8 ohm or 4 ohm tap? Unlikely - however... the thing you CAN do to hurt a tube output transformer is to put too high an ohmage load on it. If you open the outputs, the energy that gets stored in the magnetic core has nowhere to go if there is a sudden discontinuity in the drive, and acts like a discharging inductor. This can generate voltage spikes that can punch through the insulation inside the transformer and short the windings. I would not go above double the rated load on any tap. And NEVER open circuit the output of a tube amp - it can fry the transformer in a couple of ways.
Extended A: It's almost never low impedance that kills an OT, it's too high an impedance.
The power tubes simply refuse to put out all that much more current with a lower-impedance load, so death by overheating with a too-low load is all but impossible - not totally out of the question but extremely unlikely. The power tubes simply get into a loading range where their output power goes down from the mismatched load. At 2:1 lower-than-matched load is not unreasonable at all.
If you do too high a load, the power tubes still limit what they put out, but a second order effect becomes important.
There is magnetic leakage from primary to secondary and between both half-primaries to each other. When the current in the primary is driven to be discontinuous, you get inductive kickback from the leakage inductances in the form of a voltage spike.
This voltage spike can punch through insulation or flash over sockets, and the spike is sitting on top of B+, so it's got a head start for a flashover to ground. If the punchthrough was one time, it wouldn't be a problem, but the burning residues inside the transformer make punchthrough easier at the same point on the next cycle, and eventually erode the insulation to make a conductive path between layers. The sound goes south, and with an intermittent short you can get a permanent short, or the wire can burn though to give you an open there, and now you have a dead transformer.
So how much loading is too high? For a well designed (equals interleaved, tightly coupled, low leakage inductances, like a fine, high quality hifi) OT, you can easily withstand a 2:1 mismatch high.
For a poorly designed (high leakage, poor coupling, not well insulated or potted) transformer, 2:1 may well be marginal. Worse, if you have an intermittent contact in the path to the speaker, you will introduce transients that are sharper and hence cause higher voltages. In that light, the speaker impedance selector switch could kill OT's if two ways - if it's a break befor make, the transients cause punch through; if it's a make before break, the OT is intermittently shorted and the higher currents cause burns on the switch that eventually make it into a break before make. Turning the speaker impedance selector with an amp running is something I would not chance, not once.
For why Marshalls are extra sensitive, could be the transformer design, could be that selector switch. I personally would not worry too much about a 2:1 mismatch too low, but I might not do a mismatch high on Marshalls with the observed data that they are not all that sturdy under that load. In that light, pulling two tubes and leaving the impedance switch alone might not be too bad, as the remaining tubes are running into a too-low rather than too-high load. |
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Brian McGaughey
From:
Orcas Island, WA USA
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Posted 19 Mar 2012 5:56 am
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Thanks Ken. I know that's probably a tired old question for you. Hope your rebuild project is going well. Perhaps you're done?
Now back to Chris's regularly scheduled thread... |
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