toddlgreene
3470 posts
Nov 30, 2011
11:23 AM
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On another thread I mentioned I just acquired a Silvertone 1482 amp head. Thanks to Hawkeye Kane, I learned I've got an 8 ohm output. Here's the question: Can I BRIEFLY hook up to my only cabinet, which is 16 ohms, without causing damage? At what point would doing something like this cause damage, and what exactly would happen? Enquiring minds want to know.
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Todd L. Greene
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MP
1895 posts
Nov 30, 2011
11:32 AM
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nothing bad will happen. it's just not right. no big deal. you are just useing double the specified impedence. your head may have to work harder but not much harder. some folks would use 4ohm to really make it grind. that is more dangerous.
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MP
doctor of semiotics and reed replacement.
"making the world a better place, one harmonica at a time"
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mercedesrules
113 posts
Nov 30, 2011
11:33 AM
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.....I believe you can always hook it up to a greater impedance. It is lower ones that do the most harm (in your case - 4,2). Higher ones will just be less efficient (quieter); lower ones might cause your amp to heat up.
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5F6H
997 posts
Nov 30, 2011
11:53 AM
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MP's & Mercedesrules' advice is on the money. Technically, this is a very complex issue, you really need to know the output transformer's turns ratio, or primary impedance to know the limits for sure, so what might work for one amp with a "middle of the road" OT might spell disaster for another amp with a borderline OT (common things in "budget" line amps).
However, in the real world, the one common rule is that speaker impedance is not "fixed", it rises with frequency response, ask your speakers to reproduce 3.5KHz and your 8ohm speaker becomes a 16ohm speaker (at your amp's rated output @ 1KHz, your 8ohm speaker is more likely to measure 10ohms)...hence the doubling of the load over design centre works pretty well...it happens every day in, er, "nature"?
As you go lower with frequency, speaker impedance does not drop significantly (the speaker's nominal rating is the lowest working impedance), so we can assume any amp is designed to at least the "minimum limit" regarding transformer/speaker match, which is why lower than stock OT primary impedances/speaker loads can be riskier.
BF/SF Fenders with parallel wired "ext. speaker" jacks are typically tolerant to halving & doubling the rated speaker load - EXCEPT Super Reverbs & Concerts, or any tweed basssman style amps with a single speaker jack plug, ~1ohm actual speaker load is just too much on the risky side for my liking, still fine to double though.
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www.myspace.com/markburness
Last Edited by on Nov 30, 2011 11:55 AM
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HawkeyeKane
498 posts
Nov 30, 2011
12:34 PM
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Let us know what happens when you try it out Todd! Can't speak for everyone of course, but I'm dying to know!
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Hawkeye Kane
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toddlgreene
3471 posts
Nov 30, 2011
12:52 PM
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I might get a chance tonight...hopefully it won't blow up.
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Todd L. Greene
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rbeetsme
488 posts
Nov 30, 2011
6:53 PM
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I researched this last week. My question was whether I could put speakers with different impedence in the same cab. From all of the information I found the answer was no. I guess my 16 ohm speaker will go solo.
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Greg Heumann
1359 posts
Nov 30, 2011
9:49 PM
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@rbeetsme - I don't see why you CAN'T put speakers of different impedance in a single cab. One speaker will work harder than the other - but you won't hurt anything and you might like the sound. You DO need to be sure that the impedance the AMP sees is within the bounds of its design spec, which in turn depends on what its output transformer was designed for. Let's say you have an 8 ohm and a 16 ohm speaker. If you wire them in series you'll have a 24 ohm impedance. If you wire them in parallel the formula is (R1*R2)/(R1+R2) = 5.3 ohms. You'd be safest to use an OT set up for 4 ohm speakers with the latter.
2 16's and an 8? Wire the 16's in parallel. Then put that in series with the 8 ohm speaker = now you have 16 ohms. The 8 ohm speaker has to absorb as much power as the 2 16's together - so the 8 should be heavier duty.
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/Greg
Last Edited by on Dec 01, 2011 8:38 AM
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5F6H
998 posts
Dec 01, 2011
1:40 AM
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What Greg says, using differing speakers with different impedances is possible & won't hurt the OT. Just be sure that the weakest link in the chain is up to the job wattage-wise. But that applies for different speakers of the same impedance too, the more efficient speakers to the bulk of the work.
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www.myspace.com/markburness
Last Edited by on Dec 01, 2011 8:46 AM
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toddlgreene
3472 posts
Dec 01, 2011
5:49 AM
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UPDATE:I plugged the old bugger in last night, and the tubes began to glow...only the red jewel wasn't illuminated. Ran a cable from the output on the 1482 to my speaker input on the Epi, then plugged my trusty EV631B into the 'microphone' input. There are three inputs, and at least one has 'tremelo'. Didn't mess with that yet, as time didn't permit.
I gave it a little volume, tapped the mic, it was alive! So i grabbed an A harp, and lit into it...whoa! Sounded damn nice. A lot of warmth, not too dark with 'Tone' turned all the way down. With the stock 12ax7s inplace, I could get a decent 'at home/practice' volume before it began to howl with feedback, but I was also in a semi-small room.
I then switched to my Epi, which is modded for harp. It will get MUCH louder before feedback, but the difference between the 2x 6V6 tubes and the 1 EL84 is noticeable-just a different sound. I seemed to get more bottom end from the Silvertone, plus it's got 'sag'. I'm ready to maybe try some preamp tube swaps on the 1482 and see what that does for feedback, plus I'm curious if there is any difference using the other two inputs-and what that tremelo sounds like, if it works.
All in all, a satisfying brief test!
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Todd L. Greene
Last Edited by on Dec 01, 2011 5:50 AM
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5F6H
999 posts
Dec 01, 2011
6:18 AM
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Tremolo should work on all inputs, it's tapped into the circuit just before the power tubes & after the preamp.
The instrument inputs just have a resistor in series with the signal to attenuate a little, they are all "hi-Z", use the one you like best.
The pilot is the regular 6V "Type 47" bulb as used in Fenders.
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www.myspace.com/markburness
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HawkeyeKane
500 posts
Dec 01, 2011
6:25 AM
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"...only the red jewel wasn't illuminated."
I've actually seen a couple 1482's with a blue jewel. I'm guessing this was done aftermarket, but it still looks really cool.
Good to hear you got the old girl working Todd! That's a helluva good amp.
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Hawkeye Kane
Last Edited by on Dec 01, 2011 6:26 AM
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Greg Heumann
1360 posts
Dec 01, 2011
8:40 AM
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@5F6H - good catch, thank you! I was vacillating between giving another 4 ohm example or a 16 ohm example. I actually did mean series, but the resulting impedance should be 16. I just corrected in the original post.
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/Greg
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Reverend Jimmie Jive
16 posts
Dec 01, 2011
11:33 AM
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If you parallel 2 16s and then put them in series with an 8 , you will have 16 total
if you parallel 2 16s and put the resulting circuit in parallel with an 8 , you will have nominally a 4 ohm load,, (3.2 actually I believe)
when you parallel speakers of dissimilar impedance.. the resulting impedance will always be lower than the lower rated speaker, \
everyone should remember, impedance is NOT resistance,, it is a combination of Reluctance and Resistance..and thus varies with frequency into it ..that is to say, lower notes will face less IMPEDANCE than higher notes will.
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Reverend Jimmie Jive
17 posts
Dec 01, 2011
11:36 AM
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in other words.. try to make certain your mike is not picking up the bass drum, floor tom, or rumble and footsteps from the stage floor ... and don't let your bass player plug into your amp ever, and more so if he plays 5 or 6 string bass
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5F6H
1003 posts
Dec 01, 2011
11:45 AM
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@Rev Jimmie "if you parallel 2 16s and put the resulting circuit in parallel with an 8 , you will have nominally a 4 ohm load,, (3.2 actually I believe)" The nominal impedance is still 4ohms in this example, the dc resistance might be about 3.2ohms. Dc resistance, when measured with an ohmmeter, is always a little less than the speaker's nominal impedance.
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www.myspace.com/markburness
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Reverend Jimmie Jive
19 posts
Dec 01, 2011
12:01 PM
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oh, yea, yer right, I forgot, that is the reading I get with an ohmmeter for resistance when I am quick like trying to identify an unmarked speaker,, and If I 'member right, 8 ohmmers measure 6.8 on the DC the ohmmeter puts thru em
Good catch and good info 5F6H..I think this is of practical use to folks , thanks
btw,, another topic perhaps.. how about 'splainin to the guys how to phase speakers with a D cell hooked across the terminals ..that is important too !!!
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5F6H
1004 posts
Dec 01, 2011
1:44 PM
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Good point Jimmie, yes, after ensuring the impedance is within perameters with an ohmmeter, check that all the speakers move in the same direction when a 9v stomp box battery is placed with the "+" to the speaker cable's jack plug, and the "-" to the barrel/ground. You shouldhear a sharp "dok" sound.
The amp should be off, the speakers/cab disconnected from the chassis. You might find you hear a preference with them moving either forwards, or backwards. Reversing the wires at the speaker jack plug decides which way the speakers fire. The important thing is that all the speakers in the cab all move together in the same direction.
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www.myspace.com/markburness
Last Edited by on Dec 01, 2011 1:45 PM
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