Yes it is a great circuit.
Sadly, Neither the pic of the amp in the link is original
(It's a Fender reissue)
nor is the amp chassis in the follow on picture.
(It's not even a good look-a-like)
About 2/3s of the way through the article
on the Deluxe Reverb Filter Cap Board
the "Tube Amp Doctor" Caps are okay,
better can be had cheaper
Then on the AB763 Filter Cap Board
are the caps we should never use in our
amps--(Dave Funk in his seminal work,
"Dave Funk's Tube Amp workbook".
Generally Rob's discussion is good.
Also, for the closest reproductions of the original
one needs to find the guy "off-shore" who has
duplicated the original face & back plates and chassis.
The MoJo cabinets are great!
For serious musicians I'd go with either a Deluxe Reverb Amp
or a Vibrolux Reverb Amp. These amps with modern Carbon Films
will be fine for up to medium sized gigs. More than that
just mic -em and you'll be fine.
How do I know?
Deena Carter's (Singing Carter Family fame) lead guitar player couldn't believe my "litttle" deluxe reverb amp sounded as good and kept up with
the Super Reverb he typically uses.
Remember how the Fender amps were designed to be used.
Mic in channel 1 for voice and plug into channel 2 for guitar.
There are some interesting amp picture finds in the Gallery area
here, that I posted, some y'all might find entertaining.
Cheers,
Sync
That depends A LOT on the speakers employed---a 40-watt Super Reverb puts out ~114 db SPL (max) into 4 x Jensen 10" speakers. A 20-watt Deluxe Reverb will put out ~116 db SPL (max) into 1 x JBL 15" D-130 (because it's much more efficient than the Jensens).
@Dotneck335, I think you are mixing up Vibroverb and Deluxe Reverb
amps. A Deluxe Reverb amp didn't come with a 15 inch speaker, I think the
cab is physically too small anyway. Don't get me lieing here, Some
folks jammed a 12 inch speaker in a Princeton Reverb Amp, but that
is the Mesa Story.
A 15" D-130 type would be used in something like a Vibroverb amp
and would be similar to the amp made famous by my home boy - Stevie Ray Vaughn.
Careful with the Vibroverb amps as they came in various speaker
configurations.
I don't recall a Deluxe Reverb Amp ever coming with anything other than
a 12 inch speaker. In my case, the Deluxe Reverb had Vintage 30
in it, or the Heritage, or a Custom made Weber VST, that Ted made
for me before he passed away.
What would a Super Reverb Amp's SPL be with four 10" JBLs?
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Yeah, I realize that the Deluxe was only equipped with a 12" speaker--I was just theorizing its use with a separate cabinet. BUT, if you put a 12" JBL D-120 in it, it would produce the same SPL level as the Super with Jensens. Here's a quote from steel guitar preamp guru Brad Sarno:
"The 10" JBL's (D, K, E110) use a smaller 3" voice coil and dustcap. They have a crisper, higher, sweeter treble than the 4" voice coil found in the 12" series. It's almost like a tweeter compared to the bigger voice coil. But when you get things rolling, they still have that JBL sound. A D110 may sound the best overall, maybe not as good with deep bass, and again, they are delicate. That's the cool thing about JBL's, their efficiency. If you put a K120 in a Deluxe Reverb, it'll make it as loud as a 40 watt Fender amp with a "normal" speaker."
Guitar preamp guru, eh? I didn't know they had those.
Are there also guitar treble control gurus? Input jack gurus? Toggle-switch gurus?
Just kidding, but I don't think gurus of any sort are the best way to determine speaker efficiency. How about a little acoustic physics instead?
The manufacturers published sensitivity (dB SPL @1 watt @1 metre) is a good starting point.
For multiple identical drivers, all closely spaced and driven from the same signal, the sensitivity goes up by about 3 dB every time you double total cone area (this is reasonably accurate for the range of frequencies that dominate a guitar signal, i.e., where the acoustic wavelength is much bigger than the speaker cone diameter).
So if you had a speaker with, say, a 97 dB @1W @1m sensitivity, and you use two of them, and feed the pair 1 watt total power (accounting for the new parallel or series speaker impedance), you get an SPL of about 100 dB (rather than 97 dB), because of the 3 dB sensitivity improvement from doubling the cone area.
And if you used four of those 97 dB@1W@1m speakers, driven with a total power of 1 watt, you could expect something close to 103 dB sensitivity, because you have doubled the total cone area one more time, in going from two to four drivers.
With the 1 watt baseline sensitivity of the single, dual, or quad driver now in hand, you can work out the approximate SPL at any other drive power in the usual way. For example, if you put 10 watts of power (that's +10 dBW) through that quad of speakers with the combined sensitivity of 103 dB, you can expect an ear-bleeding SPL of around 113 dB. (Ouch!)
Keep in mind these are usefully accurate approximations, rather than mathematically exact formulae. We have neglected various smaller factors, such as power compression due to voice coil heating, for example, which in practice will drop the actual SPL a little bit.
-Gnobuddy
Thanks Gnobuddy, I wanted to say I thought it added 3dB whenever we added another speaker (to the Deluxe Reverb Amp) but didn't feel like researching it. I think you summarized it quite nicely and better than I would have.
I thought that Super Reverb that I have sounded a lot better after I redid it, and even better when
I got the JBLs in it. I'm also glad it has rollers too. : )
Cheers,
I thought that Super Reverb that I have sounded a lot better after I redid it, and even better when
I got the JBLs in it. I'm also glad it has rollers too. : )
Cheers,
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Not sayin' I don't believe you, but have you actually MEASURED this?How about a little acoustic physics instead?
For multiple identical drivers, all closely spaced and driven from the same signal, the sensitivity goes up by about 3 dB every time you double total cone area (this is reasonably accurate for the range of frequencies that dominate a guitar signal, i.e., where the acoustic wavelength is much bigger than the speaker cone diameter). So if you had a speaker with, say, a 97 dB @1W @1m sensitivity, and you use two of them, and feed the pair 1 watt total power (accounting for the new parallel or series speaker impedance), you get an SPL of about 100 dB (rather than 97 dB), because of the 3 dB sensitivity improvement from doubling the cone area. And if you used four of those 97 dB@1W@1m speakers, driven with a total power of 1 watt, you could expect something close to 103 dB sensitivity, because you have doubled the total cone area one more time, in going from two to four drivers.Keep in mind these are usefully accurate approximations, rather than mathematically exact formulae. We have neglected various smaller factors, such as power compression due to voice coil heating, for example, which in practice will drop the actual SPL a little bit.-Gnobuddy
I haven't, but Printer2 did - at least, he did the experiment with first one, and then two, identical speakers, and an SPL meter. I think he used white noise (FM tuner) for the experiment. As far as I remember, he didn't do the quad experiment, probably because he didn't have four identical speakers and cabs to try.
In Printer2's experiment, he added a second speaker driven by the same signal, so the power into the speakers doubled. That should have produced a 3dB increase in SPL. Instead, the meter showed a 6 dB increase in SPL.
That extra 3 dB came from doubling the speaker cone area - the pair of speakers together acted like a single bigger (and therefore more efficient) speaker.
I agree with you that an actual measurement is very important, because we don't know what other factors we may have overlooked when we came up with our theoretical hypothesis.
But it's also important that there is solid scientific theory to back up an experiment - there are bad experiments too, and it is quite possible to measure something that doesn't actually exist, due to errors in the experiment or measuring equipment!
In this case, we know an 83 Hz sound (guitar low E in standard tuning) has an acoustic wavelength of over 4 metres / 13 feet, so even a whopping 15" guitar speaker is really tiny compared to the size of the sound waves it's trying to launch into the air.
It turns out that when an antenna trying to launch a wave is much smaller than the wave itself, it does a very bad job. Under these conditions, if you double the size of the antenna, you double the amount of energy radiated. In guitar speaker terms, that means if you double the cone area, you gain 3 dB efficiency, more or less.
As I mentioned before, there are "ifs" and "buts". For instance, this only applies to frequencies where the speaker is much smaller than the acoustic wavelength. So it doesn't really apply if you're tremolo-picking the high E on the 24th fret, high E string, of your Ibanez shred guitar, four octaves about that 83 Hz low open sixth-string E.
Fortunately for us, most of us don't play a guitar like a soprano ukulele, so in practical terms, most of the energy in guitar sound is at wavelengths much larger than the guitar speaker.
But, as Printer2's measurement showed, the result even applies to white noise - that surprised me, actually, because white noise has plenty of energy at high frequencies, unlike a guitar signal.
-Gnobuddy
I hear you on the rollers.
My lower back was hurt in elementary school when I was the victim of a malicious childhood prank by a cruel classmate. As usual, those old injuries come back to haunt you as you age. This last year, there have been many days when I've had to be careful even carrying my little Super Champ XD.
-Gnobuddy
An increase of amplifier power of 10x yields a 3dB increase in acoustic power ... thus 10w vs 1w is 106dB vs 103dB, not 113dB
There is a difference between electrical and acoustic power ratios; it's easy to forget but none the less that's the way she goes (and that is why speaker efficiency is so important).
Using a measured 2.83v amplifier output value, which is equivalent to a 1 watt/8 ohms, into 4 ohms (two 8 ohm drivers in parallel) it's 2 watts, into 16 ohms (2 8 ohm drivers in series) it's 0.5 watt.
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Johnny, I'm sorry, that's incorrect. You may be confusing decibels with the fact that it takes roughly ten times as much power to make a sound subjectively twice as loud.
To calculate the decibel change in power, you use the formula dB = 10 log (p2/p1).
Here, (p2/p1) = 10. The log of (10) to the base 10 is 1.0. Finally you multiply that answer by 10, because dB = 10 log (P2/P1); multiplying 1.0 by 10 gives us 10, so the answer is +10 dB.
Since our reference level was 1 watt, you can either say there was a power increase of 10 dB, or simply state that the new power level is 10 dBW.
No, that is also incorrect. A power ratio is a power ratio. But the loudness ratio is different from the electrical power ratio - maybe that's what you're thinking of?
Agreed, speaker efficiency is very important. That's because the least efficient speakers on the market (little Hi-Fi drivers with less than 85 dB @1W @1m sensitivity) require much more drive power to be equally loud compared to a very sensitive guitar speaker (some of the most sensitive are around 105 dB@1W@1m at midrange frequencies - see attached Rajin Cajun manufacturer frequency response curve between 2 kHz and 3 kHz).
In this extreme comparison, 105 dB is 20 dB more than 85 dB. And that corresponds to a power increase of 100x. The 105 dB speaker would need a hundred times less power from the amp to be equally loud!
This isn't an apples-to-apples comparison - it's very unlikely anyone would plan to use a 3" fullrange Hi-Fi speaker in their guitar amp! But it does illustrate the point you were making, that speaker efficiency plays a hugely important role in a guitar amp's ability to play loudly.
-Gnobuddy
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