Advice On Amp Setup With A Hotplate?

[fenderman1972]

Hey guys, I need some advice on my setup. I have a Fender Hot Rod Deville 4x10 and a Fender 4x12 expansion cab. I want ot use a Hotplate, 8ohm version, with this setup using both cabs at the same time. I emailed THD about this and the response was that it would work fine I would just have to run the signal to the hotplate and the both cas from the hotplate. I would also have to put a "dummy jack" in my Hot Rod's ext speaker jack to change the transformer to 4 ohms. Would that work ok, I just don't want to damage anything. Let me know your thoughts. Oh yeah, and what would I use for a "dummy jack"? Anything in particular?

[drewl]

Which model (ohms) Hotplate do you have?
You need to match the amps output impedance to the hotplate.
If the amps output impedance is 4 ohms, you need a 4 ohm Hotplate.
You can then run 2 cabs out of the hotplate, the impedance doesn't have to match exactly, but the tone switches work best when they are matched.
I often use my 16ohm hotplate with my Marshalls set to 16ohms with 2 16ohm cabs.
The amp sees 16 ohms so it's happy, the hotplate sees 8, but doesn't care.

[sled]

what are the ohms of each cab?

[fenderman1972]

I have an 8 ohm hotplate. I was told by THD that the 8 phm would work with my setup? The Deville has an 8ohm ext speaker jack and my 4x12 is an 8 ohm cab. I currently run the 4x12 out of my ext speaker jack so that I have both the 4x10's and the 4x12.

[fenderman1972]

To my knowledge that the ohm rating for the internal speakers in 8ohms and I know my 4x12 cab is 8ohms.

[sled]

then with two cabs each 8 ohms, that's 4ohms load on the amp.

to run both cabs, you should have a 4 ohm hotplate and configure the head for a four ohm load.

are you basically after lower volume. in that case you could run one cab and parallel a 8ohm Hotplate (set to load) from the external spkr jack. this would be an equivalent 4ohm load.

[fenderman1972]

Now I am really confused? This is the response that I got from THD:

"You'd want the 8 ohm Hot Plate for it. That obviously would be a
match for the 4x10 cab, it also will be fine with any other 8 or 16 ohm cab. When you want to use both cabs you'll need to plug a dummy jack into the amps extension jack which will switch the transformer to 4 ohm and then run both cabs off the Hot Plate."

[sled]

I agree. if an 8ohm HP will run at 4 ohms, then why the need for a 4ohm hotplate.

I never unintentionally run mismatched loads.

[Primakurtz]

Better yet, sell your Hotplate. Buy a Tube Cube attenuator (he sells on eBay). Get the version with 2 speaker outs. As with the Weber attenuators, you can use any impedance load you want - any combination pf cabinets, and never have to worry about this again. Sounds just as good at moderate attenuation levels. I am guessing you don't want to use this rig for bedroom playing anyway?

[Ed DeGenaro]

Originally Posted by fenderman1972

Now I am really confused? This is the response that I got from THD:

"You'd want the 8 ohm Hot Plate for it. That obviously would be a
match for the 4x10 cab, it also will be fine with any other 8 or 16 ohm cab. When you want to use both cabs you'll need to plug a dummy jack into the amps extension jack which will switch the transformer to 4 ohm and then run both cabs off the Hot Plate."

Yes this is assuming you want a one size fits all approach. Which when mismatching would be the 8 ohm Hot Plate. When you want to use a Hot Plate with two different load one of them will be a mismatch. An acceptable one, but nevertheless it's a mismatch. Just like every other attenuator that is "one size fits all" it's 8 ohm...so to recap.
8 ohm amp with an 8 ohm Hot Plate=matched
you then add another 8 ohm cab you'll have a 4 ohm load. The fender switches output impedance with a switching jack. In order for the transformer to switch to 4 ohm you have to run a dummy plug (as the Fender manual states) in the external jack. This is just the 1/4 inch jack with no cable attached.
So...then you have amp set to 4 ohm>8 ohm Hot Plate>4 ohm load=acceptable mismatch.
If you run 2 8 ohm cabs the obvious choice would be a 4 ohm Hot plate, however that means when you want to run a single 8 ohm cab you still would have to do so off the 4 ohm setting (with dummy plug i the external speaker).
If you want to run a 16 ohm load, you'll be fine doing so off the 8 ohm setting (internal speaker jack with no dummy plug in the external jack) into the 8 hm Hot Plate into he 16 ohm cab.

[matt5150]

After talking to Ed, I use a 8 ohm Hot Plate with all my extension cabs (8 and 16 ohm) with no issues.

Matt

[SgtThump]

Originally Posted by matt5150

After talking to Ed, I use a 8 ohm Hot Plate with all my extension cabs (8 and 16 ohm) with no issues.

Matt

Just to confirm... Do you always keep your amps set to 8ohms into the 8ohm HotPlate, then into either an 8 or 16 ohm cab? The amp is always set to 8ohms in this scenario regardless of the cab rating, correct?

[tedm]

What do you recommend for the vintage amps that just have 8 ohm taps, but have an paralleled extension cabinet that can allow for 4 ohm loads (assuming extension speaker is 8 ohms), 4 or 8? I'm sure either will work, but what sound differences or output differences, if any?

Originally Posted by Ed DeGenaro

Yes this is assuming you want a one size fits all approach. Which when mismatching would be the 8 ohm Hot Plate. When you want to use a Hot Plate with two different load one of them will be a mismatch. An acceptable one, but nevertheless it's a mismatch. Just like every other attenuator that is "one size fits all" it's 8 ohm...so to recap.
8 ohm amp with an 8 ohm Hot Plate=matched
you then add another 8 ohm cab you'll have a 4 ohm load. The fender switches output impedance with a switching jack. In order for the transformer to switch to 4 ohm you have to run a dummy plug (as the Fender manual states) in the external jack. This is just the 1/4 inch jack with no cable attached.
So...then you have amp set to 4 ohm>8 ohm Hot Plate>4 ohm load=acceptable mismatch.
If you run 2 8 ohm cabs the obvious choice would be a 4 ohm Hot plate, however that means when you want to run a single 8 ohm cab you still would have to do so off the 4 ohm setting (with dummy plug i the external speaker).
If you want to run a 16 ohm load, you'll be fine doing so off the 8 ohm setting (internal speaker jack with no dummy plug in the external jack) into the 8 hm Hot Plate into he 16 ohm cab.

[plexistack]

If your hotplate and your cabinet(s) don't match in ohms, you'll get values in between them.

So if you have a 4 ohm cab & 8 ohm hotplate and you set it to '0' the amp just sees the 4 ohm cab with no hotplate

If you set the hotplate on "LOAD" then your amp sees 8 ohms.

The -4, -8, -12, and -16 settings will put you somewhere between 8 and 4 ohms depending on where you have it set.

Personally I'd be very very careful mismatching my amp, and I'd never mismatch my vintage amps.

[FrankieSixxxgun]

I used to run my 16 ohm Hot Plate at 8 ohms all day every day with no ill effects. It'll be fine.