#1
You know, whenever I start a thread I always feel like beginning it with "I'm sorry" because some of my questions are so silly.


I've only ever played solid-state combos, it's actually kind of embarrassing that I'm ill-versed in amps aside from those.

Currently, I'm looking at tube amps. And while a lot of all-tube combos look extremely appealing, I'd be so satisfied if I could mix/match a head with a cab.

Now, from what I understand, you have to match impedance. My first question is this:

Why doesn't every single amp head and cab have their impedance clearly listed on the site? Some do, some don't, just doesn't make sense to me.

When I DO find the impedance, I know the cab should be equal or higher in ohms than the amp head, right? Second question:

If the cab is 16 ohms at 1x12, would there be a loss in sound quality/volume on a head that's 8 ohms?

Lastly, what's hanging me up the most:

How do you match impedance with more than one speaker? In an example, an amp head outputs 16 ohms and a 2x12 outputs 8, is that equivalent? How is cab impedance listed if it has more than one speaker?


Thank you guys so much! Appreciate the help, really.
Last edited by johnturner9 at Feb 11, 2014,
#2
a) useless, slack arsed ****ers.

b) With tube amps you should match the impedance. A higher impedance speaker relative to the amp is safer than a lower impedance one but it is still not good practice. Most tube amps will cope with a higher impedance cab but not all do it so well.
With your example you'd lose about 3dB, more or less.

With more than one speaker it depends on how they are wired up. If you are just using paralleled outputs on the amp (or daisy chained from the cab) then the total impedance follows this equation:
1/Zt = 1/Z1 + 1/Z2
The impedance written on the cab is the total impedance of all speakers combined. How that is calculated is dependent on how they are wired. So, forget about what each speaker inside the cab is, the figure written on the cab is all that concerns you. If it says 8 then your amp has to be at 8.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#3
Quote by Cathbard
a) useless, slack arsed ****ers.

b) With tube amps you should match the impedance. A higher impedance speaker relative to the amp is safer than a lower impedance one but it is still not good practice. Most tube amps will cope with a higher impedance cab but not all do it so well.
With your example you'd lose about 3dB, more or less.

With more than one speaker it depends on how they are wired up. If you are just using paralleled outputs on the amp (or daisy chained from the cab) then the total impedance follows this equation:
1/Zt = 1/Z1 + 1/Z2
The impedance written on the cab is the total impedance of all speakers combined. How that is calculated is dependent on how they are wired. So, forget about what each speaker inside the cab is, the figure written on the cab is all that concerns you. If it says 8 then your amp has to be at 8.



Quick response! Thank you!

Do you mind if I use a real world example?

This little guy, a hughes & kettner all-tube 5 watt has 8-16 ohm impedance range:

http://www.sweetwater.com/store/detail/TM5H/

So, I'm assuming that I go with the highest peak impedance for the best quality? That would be a 16 ohm impedance for the head.

And for some reason, I wanted to use this guy:

http://www.sweetwater.com/store/detail/1960B/

Now in reality, I wouldn't want to pair these two, but am in this hypothetical because of the cabs whacky impedance rating. It says 4-16 ohm mono. Does that mean it'll either use 1 speaker or all? With an 8 ohm stereo, it'd be coming from 8 ohms on each side?



If I wanted to use the 8 ohm stereo, would I set the head to 8 ohms? Or keep it at 16? Further, would using the 4 ohm mono speaker option blow the head?


Thanks, again, haha. I don't know if I'm explaining myself well or not here. Sorry for the long post.
#4
The 1960B has a switch that will select either 4 or 16 ohm (it changes the internal wiring topology). If you run it in stereo you get a left and a right input, each at 8 ohms, two speakers for left and two for right. That is moot though because you are talking about a mono amp.
You would simply use the 16 ohm output on the amp, the mono input on the cab, switch set to 16.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#5
Quote by Cathbard
The 1960B has a switch that will select either 4 or 16 ohm (it changes the internal wiring topology). If you run it in stereo you get a left and a right input, each at 8 ohms, two speakers for left and two for right. That is moot though because you are talking about a mono amp.
You would simply use the 16 ohm output on the amp, the mono input on the cab, switch set to 16.



I get what you mean, thanks .


Do you always go to the maximum possible ohm output on both the cab or amp? Or would there be a valid reason to get an 8 ohm cab and hook it up to the head with the 8ohm switch selected?
#6
It really doesn't matter, you just have to match the impedances. That combination you showed us would work just fine.

There is a slight difference in what impedance you choose but I'll be ****ed if I can hear it. I could bore you with the technical theoretical differences but at the end of the day it really doesn't matter.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
Last edited by Cathbard at Feb 11, 2014,