newb ohm question

[Last_Confession]

ok finally got home with enough time to hook up my 6505 and 1936
so i don't wana fuck this up i have stereo input on the cab for 16 ohm each or mono at 8
so can i run my amp stereo and does it need to set it at 16 or 8?

 

[John_C]

if the 6505 has 2 outputs that can both be set to 16ohms each then you can use that for a stereo setup, 2 leads going from the amp to the cab

EDIT: just looking at the 6505 manual, you should set the amp to half the sum of the immpedance if you're using both outputs at the same time. So for stereo with the 1936 set the amp to 16 ohms

 

[Last_Confession]

ok cool thats how i have it set i assume that having 2 leads isn't going to half the impedance

 

[John_C]

ok not sure what you mean quite.......

but here's the basic idea of impedance (and yes i'm going to pretend it's just resistance, as far as working out totals it makes no difference. Apologies to jbroll and other physics/maths people )

the total impedance of two components in series (in a row, as seen above) is just the sum of the seperate impedances. So two 8 ohm speakers in series have a total impedance of 16ohms


however: 2 components in parralel

this is more complicated

(ignore the bottom equation in that last pic)
in the case of components with the SAME resistance (like the speakers in your 1936), this can be simplified. The total resistance is half for 2 components, or a third for 3, or a quarter for 4 etc of the resistance of ONE of the components.

ie two 16ohm speakers connected in parralel have a total impedance of 8ohms

4 16ohm speakers in parallel would have a total impedance of 16/4 = 4ohms

Your 1936 has 2 16ohm speakers in it. The choice of wiring you have is either each one seperately (stereo) meaning each input is 16 ohms. The other choice is mono, which in this case is both speakers connected in parallel giving 1/2 of 16 = 8ohms

Now, if you are connecting 2 speaker cables to your amp, each one loaded at 16ohms each, the amp treats them as in series and therefore sees 16/2 = 8ohms
Hence, you need your 6505 set to 8ohms if you're connecting it in stereo to your 1936

NB: remember, you can only just take a half or a third etc if the things you're dealing with are of THE SAME impedance, if they're not then use the equation in the pic

 

[ßlackwater]

my head has officially exploded.

 

[Last_Confession]

cheers dude

 

[Mr. Brokenamp]

Basically what all those formulas are telling you is at 8 ohms the speakers are in parallel in stereo they are 16 ohms per speaker. Unless your amp has 2 output transformers you are not running in stereo so basically it's your call. If you use the 16 ohm outputs on your amp you will get a little more top end than on the 8 ohm out put. Just use the proper output on the back of your amp.

 

[John_C]

Basically what all those formulas are telling you is at 8 ohms the speakers are in parallel in stereo they are 16 ohms per speaker. Unless your amp has 2 output transformers you are not running in stereo so basically it's your call. If you use the 16 ohm outputs on your amp you will get a little more top end than on the 8 ohm out put. Just use the proper output on the back of your amp.

not quite. The 6505 and many other amps allow you to select TOTAL impedance.
So if he's running 1 8ohm load (ie the mono setting on the 1936), or 2 16ohm loads (ie the stereo setting on the 1936), he should have his amp set to 8ohms

as you rightly point out, unless the amp has two output transformers the difference between the two setups should in theory be nothing.
All you are effectively doing is either setting up the parallel wiring in the amp (stereo setting) or in the cab (mono setting). The output transformer sees the same load so IN THEORY there should be no difference in tone

 

[gabriel g.]

But I think your math is for constant tension ONLY.
Maybe I am wrong...

alternating voltage needs other math.

Or do guitar amps make alternating voltage to constant tension.

I´m not that into electrics...

 

[John_C]

as far as working out total impedances, the maths for resistance (direct current) and impedance (alternating current) is the same.