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Post subject: fender deluxe reverb oamage question
Posted: Mon Dec 26, 2011 9:51 pm
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If a deluxe reverb puts out 22 watts with a 8 ohm load,
What does it put out at 4 ohms?


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Post subject: Re: fender deluxe reverb oamage question
Posted: Mon Dec 26, 2011 11:18 pm
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Neither an original Blackface Deluxe Reverb nor a 65 Deluxe Reverb Reissue have a 4 ohm transformer tap and are not rated to drive a 4 ohm load.

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Post subject: Re: fender deluxe reverb oamage question
Posted: Tue Dec 27, 2011 7:41 am
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+1 to what Bill said...and it's not good to operate it with a 4 ohm load.


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Post subject: Re: fender deluxe reverb oamage question
Posted: Tue Dec 27, 2011 8:36 am
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It will not hurt the DRRI, or any other tube amp to run at 4 ohm speaker load. If the amp is rated 8 ohms, and you use a 4 ohm speaker load, the amp will not develop full power, so the output of the DRRI would be somewhat less than the 22 watts you will get with an 8 ohm load. Any tube amp can safely and easily handle an impedance mismatch of 2 to 1.

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Post subject: Re: fender deluxe reverb oamage question
Posted: Tue Dec 27, 2011 8:57 am
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shimmilou wrote:
It will not hurt the DRRI, or any other tube amp to run at 4 ohm speaker load. If the amp is rated 8 ohms, and you use a 4 ohm speaker load, the amp will not develop full power, so the output of the DRRI would be somewhat less than the 22 watts you will get with an 8 ohm load. Any tube amp can safely and easily handle an impedance mismatch of 2 to 1.


While that may be true, if the amp is under warranty and you run a speaker load other than what the amp is rated for or is specifically designed to accomodate and something happens, the warranty is void. Even if the amp is no longer under warranty, are you willing to guarantee to the OP that nothing will ever go wrong using a load that the amp is not rated for? We always talk about in this forum how vintage amps were overdesigned and could handle anything you threw at them. We also talk about how the current crop of reissue, or for that matter many modern amps, use inferior components compared to the vintage amps. While you or I may be willing to try things with our amps that could result in a problem, I'm not going to recommend that someone else do the same without knowing the condition of the amp in question or warning of the possible consequences. :wink:

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Post subject: Re: fender deluxe reverb oamage question
Posted: Tue Dec 27, 2011 10:27 am
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Lots of confusion and myth involved with impedance matching. Plugging a speaker into an external jack provided by the manufacturer will not void the warranty. A call to Fender might help to clear up the confusion. :wink:

There is nothing about any design parameters of any of the amp's components that are exceeded with an impedance mismatch of 2 to 1. It seems natural to assume that somehow something will be "overloaded", but that is not the case at all. No one can even say what they are concerned about with an impedance mismatch, it must be superstition, 'cause there are no facts to point to anything operating improperly.

Impedance matching is only about getting the most power out of an amp, nothing more. If the impedance is not matched, the tubes cannot develop full power, no magic involved. It wouldn't be very nice of Fender to provide an extra jack that has the potential to ruin your amp if used. :lol:

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Post subject: Re: fender deluxe reverb oamage question
Posted: Tue Dec 27, 2011 11:19 am
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Maybe the use of the word "warning" on the label for the speaker impedance for an amp, scares people. :?: This picture shows a more appropriate label about speaker impedance.

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Post subject: Re: fender deluxe reverb oamage question
Posted: Tue Dec 27, 2011 11:58 am
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shimmilou wrote:
Lots of confusion and myth involved with impedance matching. Plugging a speaker into an external jack provided by the manufacturer will not void the warranty. A call to Fender might help to clear up the confusion. :wink:

There is nothing about any design parameters of any of the amp's components that are exceeded with an impedance mismatch of 2 to 1. It seems natural to assume that somehow something will be "overloaded", but that is not the case at all. No one can even say what they are concerned about with an impedance mismatch, it must be superstition, 'cause there are no facts to point to anything operating improperly.

Impedance matching is only about getting the most power out of an amp, nothing more. If the impedance is not matched, the tubes cannot develop full power, no magic involved. It wouldn't be very nice of Fender to provide an extra jack that has the potential to ruin your amp if used. :lol:


I never said that "Plugging a speaker into an external jack provided by the manufacturer" would void the warranty. I said that an amp failure while operating outside of its rated value or design parameters would void the warranty. Big difference.

Based on the owner's manual and schematic

http://support.fender.com/manuals/guita ... manual.pdf

http://support.fender.com/schematics/gu ... ematic.pdf

the DRRi (Side note: This is the Vintage amp forum. You assumed in your first post that the OP had a Reissue and had just posted in the wrong forum. My responses have also been based on that assumption which could very well be wrong.) is clearly spec'ed at 22 watts into 8 ohms. The external speaker jack is in parallel to the main speaker. There is no 4 ohm transformer tap. There is no 4 ohm power rating.

Will the amp work with a 4 ohm load? Probably. Can you GUARANTEE that it will work with a 4 ohm load and not have problems? I can't and won't. Personally, I do not want to provide any advice to someone without letting them know that there may be consequences to their actions. I don't want a forum member sending their attorney after me as some other members have done when they did something stupid. :wink:

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Post subject: Re: fender deluxe reverb oamage question
Posted: Tue Dec 27, 2011 12:00 pm
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shimmilou wrote:
Maybe the use of the word "warning" on the label for the speaker impedance for an amp, scares people. :?: This picture shows a more appropriate label about speaker impedance.


A "warning" doesn't scare me, but it certainly makes me think about the consequences of my actions. Not everyone does.

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Post subject: Re: fender deluxe reverb oamage question
Posted: Tue Dec 27, 2011 12:25 pm
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Bluesky, you know Shimmy is correct about the impedance matching. A really good amp tech showed me a long time ago on a scope that the impedance of all speakers is only taken at 1kHZ, with a constant 1 watt input, by the manufacturer (he used an HP signal generator).

But, each speaker impedance varies from near 0-ohms to over 20-ohms (sometime 100-ohms) depending on the frequency. And this is with a simple sine wave signal generator. Complex music waves vary even more.

This tech told me that with tranny coupled tube amps, the impedance is not as critical as tubes are voltage driven monsters. Indirectly coupled to the speaker(s) by the Holy output transformer. Which is very forgiving, provided it is a well-wound tranny with good iron lammies.

With solid-state outputs it makes a world of difference as they are usually capacitor coupled--- and current driven. If the speakers drop too low in impedance there is nothing between the output transistors and certain death except a capacitor--- which is directly coupled to the output.

It's why most good SS amps SHOULD have fuses on their output.

Good dynamic cone speakers try to stay within a certain range of impedance. But, I know of quite a few very high end hi-fi SS-amps that blow fuses driving electrostatic Magnaplanar or sub-woofers.

Diagram is of 1 watt sine wave input, from 20-20kHz.


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Last edited by BMW2002Ti on Tue Dec 27, 2011 12:35 pm, edited 1 time in total.

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Post subject: Re: fender deluxe reverb oamage question
Posted: Tue Dec 27, 2011 12:34 pm
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Oh yes, DR or DRRI, same as far as speaker operation/impedance, but sorry to call it the wrong name. :oops:

As far as consequences, that's where the fear seems to be, the unknown. More false assumptions is all that happens from here. :? An assumption can't then be used as proof of an amp failure.

The response from Fender has been that it is no problem to use another 8 ohm speaker with the internal 8 ohm speaker in the DRRI. I seem to remember members here with original DRs that also use external 8 ohm speakers with the internal, as well as other Fender amps doing the same with no problems. The "assumption" is; the older amps could handle an "overload" better than a newer ones. There of course is no overload to begin with, but as you can see, it still snowballs into something inaccurate.

Should we assume that in order to use the external speaker jack in a Deluxe Reverb, you would have to change the internal speaker to a 16 ohm, and only use a 16 ohm external speaker with it? And then you would have a 16 ohm internal speaker that couldn't be used by itself? I don't think so. :wink:

Just saw your post when I hit preview, nice BMW2002Ti. I also like to point out the shorting output jacks for protection, they are nearly zero ohms. :)

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Post subject: Re: fender deluxe reverb oamage question
Posted: Tue Dec 27, 2011 12:59 pm
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Just a little blurb about why to use the "correct" impedance matched speaker. And is not because of damage to a tube amp, but...

Impedance output on a tube amp can make the biggest difference to the compliance (or control) of the woofer or bass.

This is because the impedance relates to the natural resonance frequency of the speaker (notice the peak in the graph about at 100Hz?). The woofer’s resonance (if typical 12-inch type) is around 100-200 Hz. The impedance match is important to add a kind of an LCR circuit (where voice coil’s inductance, speaker’s impedance, and the inherent capacitance of the wires in the coil) act to dampened the resultant “spike” (when looking at an oscilloscope reading of frequency versus speaker output) ----at this frequency.

The design of the speaker cone (whether paper is smooth or corrugated, etc.) also contributes to the specific resonance frequency and transient response. That is why good speaker has very lightweight paper, which is usually corrugated. This reduces standing waves (another resonance phenomenon) and helps stiffen the cone at the resonance frequency.

In English----the match results in better control, therefore better response in your speaker. EVERYTHING has an inherent resonance frequency---called the fundamental. However, in smaller speakers because of their small mass---the resultant "spike" is small and not as noticeable.

The bass resonance, also, seems to correspond to the roll-off point. Therefore, at an impedance mismatch your speaker will starting to roll off at 100-200 Hz. Really, the roll off is because below this resonance frequency, there is poor control over the movement of the speaker cone. Controlling, this point helps give to better compliance and tone, in not only the lowest frequency ranges, but also all the harmonic higher frequencies related to this fundamental.

Think of it like a car’s suspension. The springs, shocks, and control arm all act to control the inherent resonance of the car’s suspension. Without shocks, the car would hit a bump, and then go into a wild, uncontrolled up-&-down movement. The springs are equivalent to the inductance of a coil. The shocks are like the impedance or a resistor, and the control arm and wheels have a natural capacitance or in auto term, compliance. That is why good setups consider all three. Not just the springs or the shocks


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Post subject: Re: fender deluxe reverb oamage question
Posted: Tue Dec 27, 2011 1:18 pm
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bluesky636 wrote:
shimmilou wrote:
Maybe the use of the word "warning" on the label for the speaker impedance for an amp, scares people. :?: This picture shows a more appropriate label about speaker impedance.


A "warning" doesn't scare me, but it certainly makes me think about the consequences of my actions. Not everyone does.

It doesn't scare me either,and why in the world would I want to push the tubes in my DR into seeing a 4ohm load,with less power and possible earlier breakup?
....lower volume and breakup,that's what the volume knob and a good pedal are for. :lol:


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Post subject: Re: fender deluxe reverb oamage question
Posted: Tue Dec 27, 2011 1:32 pm
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Less power and earlier breakup without a pedal?!?! Why would anyone want that? :lol:

Seriously though, the tubes aren't being "pushed", and I believe that you proved my point about the unknown by assuming earlier breakup, and using the word "push" as if something is working harder. :idea:

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Post subject: Re: fender deluxe reverb oamage question
Posted: Tue Dec 27, 2011 2:23 pm
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Guys,

Why are you putting words in my mouth? Where in any of my posts did I say that shimmilou was wrong? What I did very clearly say was:

"Will the amp work with a 4 ohm load? Probably. Can you GUARANTEE that it will work with a 4 ohm load and not have problems? I can't and won't."

No one has stepped up and answered my question.

And BMW2002Ti, I am very well aware of how speaker impedance is measured and what it looks like across the frequency band. However, I would like to point out the the graph you provided is only of the magnitude of the speaker's impedance. Impedance is a complex number consisting of a magnitude and phase angle. That nice 4-ohm speaker (or whatever magnitude you wish to assign it), could very well have an extremely nasty reactive phase angle at some point in its impedance curve which can wreck havoc with an amp, transformer coupled or not.

I think we have beat this topic to death. I have anyway. If the OP is still with us, he is free to plug another 8 ohm speaker into the external speaker jack. Nothing bad will probably happen.

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