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For my personal needs, the "underpowered" Princeton is just fine : at-home use and secondly accompanying jazzy fingerstyle a female singer. I also have a H&K portable PA, so if ever my Princeton lacks power, the H&K delivers plenty. My decision to buy the Quilter Aviator Cub is based on the excellent review by Rich Severson who proved the Cub to be an excellent amp for jazz (and that is all the Cub will be used for).
Originally Posted by jads57
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09-09-2022 12:41 PM
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I read your post, then went out and bought a Hiwatt. Originally Posted by Christian Miller
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Comparing to my Quilter TB202 this new TMPR does not have a Middle pot. And is there an update with a 5751 tube in V1?
I had a SFPR 1979 for a decade and could use it in jazz gigs after swapping 12” speaker in it, modding a middle pot in it and swapping a 5751 for the V1 tube.
So I’ll stay with my Quilter. (And DIY Tweed Deluxe & Deluxe Reverb.)
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I have a ‘78 Princeton Reverb. Mine happens to be appreciably louder than a PRRI (I know this from side by side comparisons on gigs). I was told by a tech that mine tests out at 16 watts rms (as opposed to 12), and it also has a Jensen C10Q rather than the stock C10R. The more efficient speaker probably explains most of the difference. Point being, if you have a PR that’s not quite loud enough for your uses, a speaker swap might do the trick. “Underpowered" is a bit of a moving target.
Anyway, there probably are gigs it couldn’t handle, but it’s loud enough for anything I’ve done. Still, in theory, more clean headroom could prove useful, as could a significant weight reduction (by my bathroom scale, my PR is 37 lbs, making it too heavy for bringing far without a handcart). So when I look at the TM PR, I don’t really see the point because it doesn’t solve either of those issues. Same form factor + lighter speaker and cabinet + power scalable from super quiet to the equivalent of 50 l-ish clean tube watts would be perfect, and would get me to sell my PR. But the TM PR as described would not.
The Quilter Aviator probably is a better solution. It’s louder and lighter. Its blackface tone comes close (but not quite, IMHO); I think tweed setting sounds great, though, so it’s tempting. But I played it next to a TM DR, and I have to say the TM DR sounded appreciably better than the Quilter’s BF setting played clean.
Long story short, my PR is safe for now. But if I didn’t have one already and wanted that vibe with lower weight and greater flexibility. I’d probably look at the Quilter, or (based on how much I like my Champion 20) a Champion 40.
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https://www.fender.com/en-US/guitar-...274400000.html
Looks like Fender is releasing a TM Princeton. Interesting that it uses a standard ceramic speaker.
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I love the gamesmanship in spec’ing power outputs for the new generation of amps. Fender wants us to consider a “50 watt” amp as the modern equivalent of a smaller tube amp: Originally Posted by rsclosson
“50W into 8 Ohms (Simulates 12W Tube Amp Performance)”
Others want us to consider their “rated output power” as being the equivalent of a bigger tube amp:
”SuperBlock fits the power of a 25 watt tube amp right on your pedalboard”
And my Microblock is “rated” at 45 watts. So it’s now pretty much impossible to know from its specs whether an amplifier is likely to fulfill your power needs without trying it in real life performance.
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So it is 50w? But they have a 25w speaker in there?
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Someone cleverer than me can probably explain the whole class D thing. I'm not quite sure how it relates to anything. Originally Posted by nevershouldhavesoldit
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Traditional amplification systems operate on constant power from their PSs and use the low power input signal to control a high power audio output signal. Output tubes have a constant high voltage power flow through them to maintain bias in our good old Twins and Boogies. Most of the constant energy is converted to heat and wasted. And some of the power supply’s output is shaped into the audio waveform that comes out of the speaker. But the whole process is inefficient and wasteful. Originally Posted by Christian Miller
Class D converts the audio input signal into a series of energy pulses (much like an analog-to-digital converter does, except that digital conversion is into a series of on-or-off pulses of equal width - only the amplitude changes with the waveform). In class D, those pulses turn the power to the output stage on and off instead of modulating the audio output signal. So a class D amp only draws power during each of those pulses and can be over 95% efficient. The audio output signal is “assembled” from those pulses, with both their amplitude (height) and their duration (width) shaping the output wave. But this is not a digital process because each pulse can be a different width and amplitude (as fits the audio waveform being amplified).
In digital amplification, those pulses are just electronic 0s (signal flow off) and 1s (signal flow on). The output waveform is reconstructed from the curve formed by the tops of those signal pulses. The power supply is still pumping DC energy to the output stage,where it’s shaped into an AC signal more powerful than the input. In class D (“switching amplification”, the pulses are analog power pulses rather than single electronic digits.
So class D generates very little heat and requires tiny power supplies compared to classes A, B etc. like digital amplification, there’s a very high frequency output component related to the pulses - and, like digital, there’s a filter on the output to remove this very high frequency signal.
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A class D amp is something like a switchmode power supply who's output voltage can be varied at an audio frequency rate. One feature it has that is crucial to the operation of the Tonemasters is that it remains efficent even at or below half power output.
All of the clipping behaviour of the Tonemasters is in the emulation software. The power amp module is rated well beyond the rated output power of the Tonemaster emulation so that the module itself can pass the spikes that come from the "output stage" of the valve amp emulation without clipping. If an ordinary class B amp were used for this job it would spend most of its time working with very low efficiency. For example, at 40% of the module's rated output, as much power would be lost in the output transistors as goes into the speaker if it were not class D.
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And the % of the power supply's output that never makes it to sound pressure is transduced into heat. Efficiency in an audio power amp is basically a measure of how much of the power supply's output becomes audio output vs how much of that energy is converted to other forms. The major loss of energy in audio amplifiers is through conversion to heat, which happens largely in the output devices. So the power supply in a class A or A/B amp is basically powering a big heater, with some leakage of energy into audio output. Originally Posted by aquin43
The main reason class D amps are so small and light is that their power supplies don't have to produce the power that's lost to heat in a traditional amplifier - they only have to produce enough power to generate the rated audio output power, plus the inevitable minor losses to signal path resistance etc. And since that heat is not generated, there's no need to dissipate it. So there's no need for massive transformers and caps, and there's no need for massive heat sinks.
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So if that’s true why is the wattage so high on the class D amps compared to trad?
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I assume you mean the audio output power in watts. Because a class D amp is 90-95+ % efficient, it can convert a much higher % of the line power coming in directly to audio output than a class A, A/B, or B circuit can do. If its power supply is drawing 1 amp at 120 volts, it can put out 90+ % of that (~100 W) as audio power. And it needs very little heat sinking to dissipate the 10% loss as heat - it’s about the same heat a 10 watt incandescent bulb would generate. Originally Posted by Christian Miller
To generate 100 watts at the output jacks, the power supply in a typical class A or A/B amp with 45 to 50% efficiency has to provide the output power plus the power needed to maintain bias, to offset / repel the electrons that are flying off the hot cathode when there is no signal applied, to heat the filament, and to supply the energy lost to heat, resistance etc from each output tube. So it has to provide at least 200+ watts and have a way to dissipate the heat and maintain operation. It also has to have enough room inside for components (resistors, caps etc) that are large and robust enough to handle the increased voltages and currents without degrading from the heat. A 1/2 watt resistor is a lot smaller than a 2 watt resistor, for example.
It needs bigger transformers, more robust rectification, and power smoothing, which means big caps. And because of the higher temps and power flows throughout, tiny chip circuits simply can’t handle the stress.
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I was thinking the Deluxe Reverb TM might be the sweet spot between the Princeton and Twin. At 24 lbs, it's certainly light enough to carry anywhere.
Anyone want to chime in on Princeton vs Deluxe TM?
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It is still a rated wattage of solid state hardware at the end. Beyond the rated wattage the clipping distortion is a hard clipped signal with horrible sound and a risk of thermal runaway causing component burnout unless a thermistor circuit shuts it down first. Originally Posted by Christian Miller
tubes behave differently. The clipping is soft and compressed progressively the further you go. The 12w is only a description of how much power of linear amplification within a band of acceptable distortion. Beyond 12w you are getting progressively more distorted and your amplification becomes less linear (getting compressed). This effect sounds surprisingly good for electric guitars.
Hard clipping sounds bad.
Here is the crux though. We never apply a constant DC signal when we play. Instead we inject a pulse of voltage (pick strike) that decays depending on the instrument.
Tubes amps can handle the strike of voltage fine because of all the valve compression - like punching a wall made of foam.
SS there is no foam- just brick. So better make sure the wall is well out of arms reach. 12w vs 200w. SS will try to soften the sound with circuitry added along the way but the wall is still there.
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It is also worth noting that it is possible to buy 50w amps with common tube pre/power sections but with switch mode power supplies. They are light, run efficiently (cooler) and have no need for the heavy iron weights.
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I suspect the ceramic speaker is to keep the ticket cost down at the expense of weight. If the used the same speaker as the TMDR then the cost would be too close to the TMDR but a significantly lower “wattage”. I also suspect (no proof) that the amplification hardware inside the two is identical but the Princeton gets a different preamp config and a derated output potential. Originally Posted by rsclosson
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How does the RMS rating of a tube amp compare to the watt rating of a Class D?
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I haven’t found any data to support a definitive answer. But I suspect it has to do with the differences in power supplies and in the more rapid rise of THD near maximum output of class D amps. The sustainable RMS output power of an audio amp into a stated load at a given frequency (or within a given frequency range) at a specified THD is limited first by the maximum output the power supply can sustain. The chosen THD at which to spec it is a compromise between the appeals of lower distortion and higher power, since THD rises more rapidly than power output as the output limit is approached. Class D chips usually achieve 75% or more of their maximum output power at relatively low distortion - but it rises rapidly to heights that will displease potential buyers on paper even though no one will ever push the amp to that level. Originally Posted by ccroft
So the same amp may be correctly and accurately rated at 100 WRMS from 20-20kHz @ 0.05% THD or at 150 WRMS @ 1000Hz @ 1% THD or at 200 WRMS @ 1000Hz @ 10% THD.
Now throw in “peak power”. Class A and A/B amps have huge caps in their power supplies to dump extra current that temporarily boosts the PS output for transient peaks. Interestingly, no maker I’ve ever encountered rates peak output for the length of time it can be sustained. The only number spec’ed is the voltage itself, which is kinda dumb considering that a sustained triple forte orchestral passage could demand peak output of significantly longer duration than a single even louder blast of horns and percussion. But the PS is the prime determinant of both steady state RMS and transient peak amplifier output power.
Even though they don’t have or need huge power transformers and caps, the best power supplies designed for class D amps are not deficient in peak power capability. For example, TI specs a reference PS for their best class D chips that puts out a sustainable, continuous 200 W with a peak output of 800 W. Here are the complete specs. Assuming a decent design, a class D amp using this PS could easily put out a steady state 150 WRMS @ low THD. But the nature of class D amps includes more of a rise in distortion close to max output than is typical of a class A or A/B amp of equal sophistication. So 10% THD may occur as low as 200 W - and that output would still be sustainable rather than peak. But a 10% distortion level is a serious turnoff for most buyers.
Bottom line? I suspect that class D amps do not carry peak power ratings like class A and A/B amps do because they’d look bad if given along with the distortion at that level. But their power output ratings are the same as RMS ratings for traditional amps. A Quilter Superblock has a class D power amp chip inside that’s rated at 25W output. It’s the equal of a 25W class A tube amp in maximum usable SPL, and no peak rating is offered or needed. The simple truth is that transient peaks are so brief that higher distortion is probably inaudible anyway. And we don’t generate peaks with our guitars that even come close to those in orchestral and other dramatic music.
I hope more knowledgeable participants will correct, modify, augment or otherwise refine the above. It’s only my 2c, but I think it’s basically correct.
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