Two speaker cab - ohm options

[famous beagle]

Hey y'all,

So I'm almost finished building my Marshall 18-watt clone amp (see pictures), and I'm ready to wire the speaker cabinet. I have two 10" Weber speakers rated at 8 ohms each. The amp head has selectable impedance of 4, 8, or 16 ohms.

I'm curious if there are big sonic differences in wiring series (16 ohms) or parallel (4 ohms). I don't have any personal experience with this, and I'm wondering if anyone else has.

Thanks!

 

[Greg_L]

I'm curious if there are big sonic differences in wiring series (16 ohms) or parallel (4 ohms).

This is a hotly contested subject in some circles. I say there's no difference. I'd go with 16 ohms so you can add cabs if you want to.

 

[ocnor]

This is a hotly contested subject in some circles. I say there's no difference. I'd go with 16 ohms so you can add cabs if you want to.

^^^This^^^

 

[JCH]

Wire it both ways. See what you prefer.

Nice Lookin' Amp!

 

[ecc83]

Using the 16Ohm tap on an amp will be more efficient because it uses all the winding of the secondary and the ratio is at minimum.

There would be a noticeable difference in sound if you could quickly A/B the setup since putting speakers in series kills any damping the amp might provide, however valve guitar amps rarely HAVE any damping, much, to start with so go 16.

The legendary Vox AC30 used two 8's in series so you are in good company!

Dave.

 

[Lt. Bob]

Using the 16Ohm tap on an amp will be more efficient because it uses all the winding of the secondary and the ratio is at minimum.

this .... when given the chopice I always try to use all the windings in the tranny.

Hpwever .... they DO sound different .... it's not impossible that you might prefer one over the other.
Since you're doing the work of building an amp (purty BTW) why not do the little bit of extra work and try both?

 

[ranjam]

There may be slight/subtle differences, but you probably won't notice. Just before I try explain, I'd look around and see if you have any other amplifier heads laying about. If you have a Bassman head, they like 4-ohms. So to keep the cabinet versatile enough to use with other amps you have, check the impedance on those.
Now, if you don't use negative feedback, and many 18-watt schematics I see don't show a feedback resistor, I doubt there is any difference. Now, if you choose to use negative feedback, you typically put it on the 16-ohm tap. If you do that, and use the 4-ohm tap, the feedback signal has to 'travel' through a little inductance and minor added resistance. Now some egghead will have the formula, and have the phase angle figured, but the end result will still be that you won't likely notice any difference.
You can record it, and listen, or check the digital waveform to know for sure.