Amp Impedance - Attenuator on VOXAC15. Help please....

make-and-do

Just bought the Swart Night Light attenuator from Guitartone (thanks for the tip-off Alan).
Some really nice gear they've got - wouldn't mind a Reverend Flatrock ?
Also super nice and accommodating people! Thanks for the good service guys.
Anyways, I couldn't take my amp with me...so I haven't set the attenuator up yet.

I need your electronics wizardry/know-how, as I'm dangerously useless when it comes to anything electrical.
I don't want to end up frying (a) myself (b) my amp.

Inside the Swart leaflet for the pedal it says: set amp for 4 or 8 ohms.
So I would probably have to set my amp for 8 ohms for it to work at all then.
At the moment it looks like it's on 16 ohm.

Is the jack input on the left the 8ohm one? Seeing as the right side would be the 16 ohm one?
Or are both at 16ohm at the moment? And the switch to the right of the jacks determine what ohm settings both have??
Do I flick the impedance switch to 8ohm and that makes both jacks 8ohm? And if I do so, does it matter which jack I pop the attenuator into?
Left or rightside? This is starting to sound Monty Pythonesque.

AND..will the amp function normally at 8ohm? (I'm supposing it would - why would there be a switch to change it then ? )

I checked the AC15 manual as well which wasn't exactly helpful.
Please help, any techie minded folks! I wanna play my "new" amp.

Here's a shot of the AC15CC1 (Wharfedale speaker model).

shaunf

The way I read that is that you set the switch to 8ohm and disconnect the internal speaker and plug in the attenuator. What speaker cab do you plan playing through?

AlanRatcliffe

OK I read that as the stock speaker is 16 ohms. Amp and attenuator ideally have to work at the same impedance as the speaker.

SO it's not going to work unless you either:
- add a second 16 Ohm speaker and change the amp to 8 ohms (and run both from the output of the attenuator). Bit pointless as that will make the amp louder again.
- change your speaker for a 8 Ohm model and set both amp and attenuator for 8 ohms.

Nicholas-L

Don't they have a 16 ohm version? If so the swap it out. The other option would be is to add a huge 16 ohm 100W resistor in parallel with the speaker and put the Resistor on a heat sink

MikeM

I'd rather stick to the wattage of the speaker, and make sure it's one of those alu housed resistors. They have a bit of inductance so they will be more transparent.

make-and-do

Alan Ratcliffe wrote: OK I read that as the stock speaker is 16 ohms. Amp and attenuator ideally have to work at the same impedance as the speaker.

SO it's not going to work unless you either:
- add a second 16 Ohm speaker and change the amp to 8 ohms (and run both from the output of the attenuator). Bit pointless as that will make the amp louder again.
- change your speaker for a 8 Ohm model and set both amp and attenuator for 8 ohms.

Thanks for the input guys.

Yes, stock speaker at the moment is the Wharfedale and the impedance switch looks like it's on 16ohm.
So I can't just flick the switch to 8 and still play through the 16ohm speaker?

What is the difference between a 16ohm and 8 ohm speaker? Is the one "stronger" ?

So Alan would it work then if I changed the speaker to say a Celestion (not sure which one yet, price dependant) 12inch, 8ohm one?
What are the procedures then? Do I just install the new speaker and set the impedance switch to 8ohm and connect the attenuator and I'm good to go?
Or would the amp still need some sort of other technical re-adjustments made as well on the insides...? Yes I'm clueless with these things :-[

Nicholas-L

Rather not run the amp and attenuator in different settings. Damage will occur. Swapping out the speaker to say a Celestion greenback 12" 8 ohm will work perfectly with the switch on the amp set to 8 ohm and the Attenuator connected in between. If wanting to go for a Celestion check yebo electronics website. they don't stock them but they do get them for you at a great price. Bought my 2 Vintage 30's through them.

AlanRatcliffe

It's all down to how valve amps work and you must never run a higher impedance speaker than the amp is rated for (amp still puts out the same power, but the speaker only uses half of it and the unused power builds up and blows the amp's output transformer). I think if you set the amp and attenuator to 8 ohms, the attenuator will take the brunt of it, but the chance that something will give is good.

make-and-do

Thanks...okay it seems it would be the safer option to maybe return the attenuator then rather than end up overloading the amp because of a lower
impedance speaker. Guess I should just get a smaller amp then.