Author Topic: You Guys Brought Up Something I Read Elsewhere, And I Saw Something Interesting.  (Read 167 times)

Zut8083

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Hi, again,

I will try to make this post not so convoluted, nor attempt to destroy English, as I did earlier.  Apologies for that.

In providing an answer to my question from an earlier thread, adriaan stated that the wrong resistance in the speaker enclosure (be it set to 4, 8, or 16 Ohms), when paired to the current and wattage at a higher resistance from the output of the power stage of an amplifier, thus creates mechanical and electrical failure in the amplifier via burning out speakers, the most fissile part of the enclosure if they are not appropriate for the job (quoting adriaan on the "I Think This is The Right [Forum, sic] For a General Amp Question" thread started 2/2/2018: "- like the true fact that one can fry an amp by attaching speakers that present an impedance lower than what the amp is designed to work with").  Elwoodblue had the latest word with the RT/Lindsay Buckingham story behind "Rumors" and the enhanced output and current from Buckingham's immolating the power transformers in a few old Hiwatts, and the amps cycling through a boffin's work bench to repair them.  Daily.  Awesome.  (RT cited by elwoodblue, 02/03/18: "For Lindsey, my main contribution during Rumours was installing an Alembic “Stratoblaster” in his Strat exactly like the one I’d put in Lowell George’s guitar, the one you hear on Little Feat’s live album, “Waiting for Columbus.” For Lindsey, the sound of the electric on Rumours is his guitar with the ‘Blaster gain all the way up, basically destroying a succession of HiWatt amps. Evidently, the HiWatts did not have adequate current protection; they were fine with normal electric guitar output levels, but when we boosted that by nearly 12 dB, the amplifier just tried to pull more and more current through the power transformer, and after about 20 or 30 minutes of high gain sustaining guitar solo, the transformers would literally go up in smoke. Luckily, they had three of them, and every day one would go off to Prune Music to be repaired.")

I thought about these statements a bit, and compared them to what I had read earlier on a TalkBass Forum (https://www.talkbass.com/threads/if-you-use-a-guitar-amp-will-you-break-the-speaker-or-the-electronics.351246/), and these statements totally seemed to mesh with the implied thought experiment of a hypothetical bass being amplified by a guitar amp, and then providing aberrant current from an overly aggressive signal initiated by a bass playing through a guitar amp, which could then destroy a speaker and create a cone excursion (?) and possibly destroy the speaker's voice coil by the now enhanced current/wattage doing work on the adhesives and such that secure the coil, allowing the coil to free itself and burn itself out with the power amp output (the following reference is not where I originally read about this phenomenon, but it does has a nice diagram and some descriptions/details that supersede part of the scope of the original source: http://sound.whsites.net/articles/speaker-failure.html#s32). The end result is an abrupt disruption of the circuit in the speaker enclosure when the electrical potential from the amp engages the lower impedance of the speakers initially, then burning one out, and seemingly increasing the total impedance of the enclosure upon failure to the detriment of the amp (the original reference I mentioned apocryphally cites a jump from 8 Ohms to 100 Ohms in this case).   

Apparently, from the original source mentioned above, but also intuitively, these spikes in the resistance following failure in the enclosure's speakers, be it that the speakers are insufficiently hearty/rated for the application or if the speakers are old or defective, the end result is the same: the new speaker resistance overwhelms the signal conductance and then prevents power being pumped into the malfunctioning speaker enclosure, preventing the signal from going into the speaker to do mechanical, chemical, or electrical work, then picking the path of least resistance and cooking the output transformer (http://sound.whsites.net/impedanc.htm).  If that is an inaccurate synopsis, that mistake is mine.

Congruently, elwoodblue cited RT describing an input voltage/current so large from a raring 'Blaster circuit, that upon amplification by the preamp in a vintage Hiwatt circuit , the current over-ran the output transformer circuit, thus crossing the streams, and causing the the door to swing both ways and reverse the particle flow through the gate.  Basically.  And a very similar story where the path of least resistance focused on the end of the power stage to do some Van Dammage.

However, in the last reference for your consideration (http://sound.whsites.net/impedanc.htm), there is a section called "Speaker Protection Systems" and a subheading called "Poly-Switches".  Namely, it seemed to highlight the potential use of relay circuitry (maybe?) to provide a way to switch between parallel circuits by the switch's temperature as a means of dissipating the mechanical or thermal work from the amplifier after it cooks off a speaker.  This seems to have the potential to help restore the appropriate resistance of the enclosure during performance.  It seems to be an intuitive way forward to avoid speaker-mediated problems with an amplifier as the victim, and as the "sound.whsites.net" page above cites these "Poly-Switches", they seem to be occasionally integrated into speaker circuits.  It sounds like awesome protection of the amplifier by rerouting current and power away from the speakers based on the rising temperature at the switch generated impending voice coil failure.  That assumes I read that properly.

But my questions for the forum are "How common is this?"  "Is this a normal component of speaker cabinets/enclosures?"  It does not sound like it is very common based on what I've read. 

So, "Why not?"  That seems a little mean to me, man.  Enclosures are extremely expensive unless you build your own, and mostly you seem to pay for a manufacturer's logo in a number of cases; the least a manufacturer could do is to throw one such poly-switch and any associated circuits to dissipate the output from the amp.  "Do only some manufacturers regularly include these circuits in their cabinets/enclosures?"

Is Colonel Sanders only Justin Wilson in black and white film with darker glasses?

Inquiring minds want to know.

gtrguy

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No. I just make sure I use the right speakers or make sure to set the variable speaker ohm switch on the amp (if it has one) to the right setting, or correctly wire up multiple speakers, etc.


Some amps are more forgiving of mismatched speakers, as well. My Mesa MKIII 100 watter guitar amp has instructions that tell me it is it is not as important with that amp.


However, on the topic of blowing speakers, I have certainly done my share of that over the years. Mostly by overdriving them over the span of a year or two. Many old speakers, such as good old JBLs 15s etc are not designed to carry that much power (check the rating). I also like to use EV 15" guitar speakers for bass. They sound fantastic! However, the guitar speaker was not built to do the job that their bass speakers were, and they give out after a while. The last one I did that to came out of a gibson solid state L5 (or one of those) amp and finally gave out after a year of gigging. Oddly enough, I happened to stick it back in the L5 amp, and it continued to work fine for guitar! Go figure!

pauldo

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  • What chaos . . . ?
Confession -electricity is magic to me.

I had a Sunn Coliseum 300 running into a Sunn Beta bottom.  Ran the rig for sometime.. we were playing at an outdoor show and the system went silent.  Playing outside I was cranking things relatively loud (just out of high school and PA was only for vocals).

Later I took the amp in and was told that the output transducer blew because of wrong impedance matching.  That was almost 40 years ago, I did not repair the head (got a GK 800RB and haven't looked back) - point is I am not sure if the repair person saw me as a gullible teenager and was blowing smoke up my wazoo or not - why would a mis-matched impedance system work for several years and then die??
1984 Distillate Zebrawood

elwoodblue

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IIRC, the Coliseum 300 will work with a 2ohm load, and being solid state a higher impedance wouldn't
be detrimental if I'm thinking right.


If things were getting hot from playing hard and long in the hot sun, with a black amp, then maybe something went thermal.
 I think your tech was off base somewhat...but I'm just guessing.


5a quilt top

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Re: using a guitar rig for bass - I routinely use a PRS Sweet 16 all tube 16 watt head with a closed back EVH 1x12 cab loaded with the stock EVH 25 watt Celestion speaker to amplify my Rob Allen 4-string fretless "acoustic" bass. It works great unless I boost the amp's pre-amp gain too much or use too much bass or mid while reducing the amp's master volume. Doing that will produce a "tubby" slightly fuzzy tone, which sounds interesting, but is not what I need when I'm playing behind acoustic guitars and mandolins.


When set correctly, this rig produces a pillowy, fat midrangey tone with good definition and a lot of growl. I've received several compliments on the tone from other bassists who have heard this rig and are amazed to discover that it's a guitar amp.


That having been said, I don't think this rig would work well for any of my Alembics...

gtrguy

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I ran a Sunn Coliseum Lead guitar amp into an Acoustic 2X15 with horn cab for my bass for years, with frequent touring. I never even looked at what the ohms were on the cab. It never let me down.
Heavy as all get out though!

Some amps are sensitive and some don't care.