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Post subject: Fender Twin Reverb '65 RI - 8 ohm Reactive Load Box?
Posted: Mon Jan 16, 2017 7:16 pm
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Hi guys - I'm looking at getting a Reactive Load Box for my FTR '65 RI. The challenge is that the amp says it is a 4 ohm speaker impedance (with no selector switch) and almost all of the reactive load boxes operate at 8 ohm.

The question: can I use an 8 ohm reactive load box with this amp w/o any issues / compromises? If not, what are the issues / compromises I should be knowledgable about?

I already posed this question to Suhr (re: their reactive load box) & they (surprisingly) weren't able to answer the question - pointing me to ask it of Fender.

Thanks in advance!!!


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Post subject: Re: Fender Twin Reverb '65 RI - 8 ohm Reactive Load Box?
Posted: Thu Jan 19, 2017 10:09 am
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Use Weber Mass attenuator, some other brand work in 4 ohms too.


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Post subject: Re: Fender Twin Reverb '65 RI - 8 ohm Reactive Load Box?
Posted: Fri Jan 20, 2017 2:31 am
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THD hot plate have 4 ohms attenuator ;

http://www.thdelectronics.com/product_p ... plate.html

Weber ; for any impedance

https://www.tedweber.com/mass


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Post subject: Re: Fender Twin Reverb '65 RI - 8 ohm Reactive Load Box?
Posted: Fri Jan 20, 2017 10:55 pm
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What is a "Reactive Load Box"? Is that a brand name?

In any event, and 8 ohm load on a Twin Reverb is no problem at all. In fact, a 4 ohm tube amp can safely handle any load from 2 ohms to 8 ohms.

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Post subject: Re: Fender Twin Reverb '65 RI - 8 ohm Reactive Load Box?
Posted: Sun Jan 22, 2017 3:21 pm
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Just because I like to complicate things:

If you want to check out what the difference in sound would be between running the Twin into a 4-ohm or 8-ohm load, you could do this:

If you have a spare 8-ohm speaker, hook it up to one of the Twin's speaker outs. Assuming you need silent recording, stick the speaker in a closet. It may not be totally silent, so use all the blankets and pillows in the house. Your wife will love you for it.

Connect the 8-ohm attenuator to the other speaker out.
Now, the load box is getting the eight ohms it wants, and the Twin is running at four ohms. It's a win-win.

Proceed to rawk.

(If I am wrong about this, I will never admit it. LOL.)


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Post subject: Re: Fender Twin Reverb '65 RI - 8 ohm Reactive Load Box?
Posted: Mon Jan 23, 2017 12:45 am
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That would defeat the purpose of using a loadbox, i.e. cranking the amp and lowering the output to the speaker.

Even easier, disconnect one of the amps internal speakers, that will give you an 8 ohm load. :idea:

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Post subject: Re: Fender Twin Reverb '65 RI - 8 ohm Reactive Load Box?
Posted: Wed Jan 25, 2017 6:41 pm
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[quote="shimmilou"]What is a "Reactive Load Box"? Is that a brand name?

There are nuances between a load box vs. attenuator:
- A load box is for using your amp w/o a speaker - in my case, to get the amp tone directly into a DAW for recording in my home at night w/o making noise and w/o needing to mic the amp. If you want, you can then use software to model different cabinets / speakers.
- An attenuator reduces volume to play thru a cabinet / speakers at lower volumes (which you'd record via mic-ing the speaker/cabinet).

The "reactive" is not a brand name but indicates that (unlike resistive) it will maintain the impedance curve - making the amp feel, sound, and respond similarly to when it’s connected directly to a cabinet.

Given I'm interested in a load box (not an attenuator), am I still fine using an 8ohm load box w/ a 4ohm FTR amp impedance? Are there any downsides to this?

I still can't find a 4ohm load box (they all seem to be 8ohm)?!?!?


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Post subject: Re: Fender Twin Reverb '65 RI - 8 ohm Reactive Load Box?
Posted: Wed Jan 25, 2017 8:13 pm
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You will not harm your amp by connecting it to a load rated at higher/more ohms than the amp was designed to see.
If you were going the other direction that would be very different.
Go ahead and use the 8 ohm box.
You could also use a 16 ohm box.
What you shouldn't do is use a 2 ohm box.
4 or bigger is fine.
Smaller is not fine.

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Post subject: Re: Fender Twin Reverb '65 RI - 8 ohm Reactive Load Box?
Posted: Thu Jan 26, 2017 10:24 am
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Here is a 4 ohm dummy load for $31 dollars. this might be what your after
http://www.parts-express.com/4-ohm-200w-non-inductive-dummy-load-resistor--019-025
mud


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Post subject: Re: Fender Twin Reverb '65 RI - 8 ohm Reactive Load Box?
Posted: Thu Jan 26, 2017 4:30 pm
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BMW-KTM wrote:
You will not harm your amp by connecting it to a load rated at higher/more ohms than the amp was designed to see.
If you were going the other direction that would be very different.
Go ahead and use the 8 ohm box.
You could also use a 16 ohm box.
What you shouldn't do is use a 2 ohm box.
4 or bigger is fine.
Smaller is not fine.


Thank you!!!


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Post subject: Re: Fender Twin Reverb '65 RI - 8 ohm Reactive Load Box?
Posted: Thu Jan 26, 2017 4:37 pm
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BMW-KTM wrote:
You will not harm your amp by connecting it to a load rated at higher/more ohms than the amp was designed to see.
If you were going the other direction that would be very different.
Go ahead and use the 8 ohm box.
You could also use a 16 ohm box.
What you shouldn't do is use a 2 ohm box.
4 or bigger is fine.
Smaller is not fine.


Actually, a 16 ohm load on a 4 ohm amp is approaching the danger zone, because too high an impedance is what is to be avoided. And a 2 ohm load on a 4 ohm amp is perfectly fine, no problem with too low of a load. Rule of thumb, a safe impedance mismatch is to stay within a 2 to 1 ratio, either low or high, and the amp will be perfectly capable of handling the load safely.

Remember, a short circuit on the output of an amp, such as a shorting output jack (0 ohms), will protect the amp in the event that no speaker is connected, whereas an open circuit (infinitely high ohms) will damage the amp. This applies to tube amps, while solid state amps are a different story entirely.

We have covered this topic so many times on this forum, I am surprised that some still don't get it. Go ahead and search the forums, not one instance of anyone harming their amp when using a safe impedance mismatch, not one single instance. Can't get more definitive than that. :wink:

harpua23 wrote:
...Given I'm interested in a load box (not an attenuator), am I still fine using an 8ohm load box w/ a 4ohm FTR amp impedance? Are there any downsides to this?..


No problem whatsoever as far as performance. The only difference when using a safe mismatched impedance is that the sound produced by the amp can be different (many times it will produce a more pleasing tone). I routinely use mismatched impedance with many of my amps because I prefer the sound. One of my favorite is to run my 8 ohm Mesa head into my 4 ohm Fender Bassman cab, it sounds really sweet, better in fact than using the 4 ohm output of the Mesa with the 4 ohm cab.

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Last edited by shimmilou on Thu Jan 26, 2017 4:49 pm, edited 2 times in total.

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Post subject: Re: Fender Twin Reverb '65 RI - 8 ohm Reactive Load Box?
Posted: Thu Jan 26, 2017 4:41 pm
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shimmilou wrote:
BMW-KTM wrote:
You will not harm your amp by connecting it to a load rated at higher/more ohms than the amp was designed to see.
If you were going the other direction that would be very different.
Go ahead and use the 8 ohm box.
You could also use a 16 ohm box.
What you shouldn't do is use a 2 ohm box.
4 or bigger is fine.
Smaller is not fine.


Actually, a 16 ohm load on a 4 ohm amp is approaching the danger zone, because too high an impedance is what is to be avoided. And a 2 ohm load on a 4 ohm amp is perfectly fine, no problem with too low of a load. Rule of thumb, a safe impedance mismatch is to stay within a 2 to 1 ratio, either low or high, and the amp will be perfectly capable of handling the load safely.

Remember, a short circuit on the output of an amp, such as a shorting output jack (0 ohms), will protect the amp, whereas an open circuit (infinitely high ohms) will damage the amp.

.


+1


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Post subject: Re: Fender Twin Reverb '65 RI - 8 ohm Reactive Load Box?
Posted: Thu Jan 26, 2017 4:55 pm
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This sums it up quite nicely. Impedance matching is about getting the most power from a tube amp, nothing more.

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Post subject: Re: Fender Twin Reverb '65 RI - 8 ohm Reactive Load Box?
Posted: Thu Jan 26, 2017 5:09 pm
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I don't know if that power versus volume thing applies to a box that just puts out a preamp level signal.
If it's going into a computer, there will be gain adjustments on the interface as well as in the DAW software.
Volume will be irrelevant, won't it?

As far as "approaching danger" goes, I have to think that as long as you're not actually crossing the danger line it shouldn't be all that big of an issue.
No?
Besides, he wants to use an 8 ohm device, not 16.

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Post subject: Re: Fender Twin Reverb '65 RI - 8 ohm Reactive Load Box?
Posted: Thu Jan 26, 2017 6:29 pm
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That's the rub. We know that an open circuit will harm the amp, and at some point approaching an open circuit will harm the amp, we just can't be sure at what point the impedance will be too high and cause harm. Hence, the rule of thumb of the 2 to 1 ratio is a sure safe zone.

And you make a good point, it is a TR, so the sound will be clean at just about any volume.

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