Tube vs solid state power amp volumes and speaker load

[sibo]

If you're not interested in all of this you can just scroll down to the question at the bottom of this post.

I am in the middle of a transition from a 50W tube amp (Marshall 2550) and a Kemper with a retrofit Ritter power amp.
The problem in short is with my SS power amp I'm not getting anywhere near the volume I used to have with my old valve power amp. The sound, however is really brilliant!

Setup 1 with enough loudness:
Marshall 2550 50W tube head
Orange PPC212 rated 120 W at 16 Ohms

Setup 2 without enough loudness:
Kemper Profiler into Ritter Camplifier 180 - 180 Watts at 8 Ohms, meaning 90 Watts at my cabs 16 Ohms
Orange PPC212 rated 120 W at 16 Ohms

So I understand somehow tube power is more loudness per watt - obviously.. I think I get pretty much half the volume with my 90W Camplifier as I do with my 50W Marshall. Now I totally get that the Kemper is leaving a weaker signal as I had to adjust "volume" between settings to balance it out, but this is just too low. I got the Camplifier knowing that if it wasn't enough I can return it but that really doesn't solve my problem.. So far I only tried wiring the amp through the KPA's "Main Out" and someone suggested trying the "Monitor Out" which is supposed to leave a stronger signal but since I haven't been in a band situation for some time I haven't had the opportunity to try it..


Q: I would gladly take suggestions on how to maximize volume from my Kemper to my 120W@16Ohms cab without harming the speakers. How much SS power amp Wattage can I load into my cabinet? I can't seem to find other retrofit solutions than above mentioned but maybe I am just looking in the wrong places?

Oh and I already considered FRFR powered speakers and decided to go with regular guitar cab solutions.

[loudthud]

Can you post a picture of the business side of the Camplifier or better yet, a schematic? The mains power rating seems a little light for a true 180WRMS rating. If it only weights 2 Kg, it would have to use a switch mode PS and a Class D PA.

[Mike Sulzer]

Q: I would gladly take suggestions on how to maximize volume from my Kemper to my 120W@16Ohms cab without harming the speakers. How much SS power amp Wattage can I load into my cabinet? I can't seem to find other retrofit solutions than above mentioned but maybe I am just looking in the wrong places?

Oh and I already considered FRFR powered speakers and decided to go with regular guitar cab solutions.

Another approach is to try to gather some information. Watts delivered versus watts specified is always an interesting question. But the louder one really ought to have a higher rms ac voltage across the speaker. Do you have a friend with a meter (and a set of ear plugs)?

[The Dude]

I have to wonder if you are supplying enough input to the power amp to drive it to full power. The amp is rated at 360W peak power, which should be able to get substantially loud. I haven't fiddled with a Profiler for a while, but I seem to recall settings for global output level (a dB setting if my recollection is correct). They do this to match various configurations, for instance the difference in required input from guitar amp to standard power amp. Have you tried adjusting the output level of the Profiler and/or do you know if you are indeed able to drive the amp to full output with your current settings?

[g1]

And to do a fair comparison, you would run the Profiler into the FX return or Power amp IN on the Marshall.
This may help show any level issues mentioned by The Dude above.

[Enzo]

And if you are comparing loudness at some "setting", that is meaningless. If you turn both of them all the way up, it might be fairer, but preamps all do not have a standard sensitivity.

[sibo]

Can you post a picture of the business side of the Camplifier or better yet, a schematic? The mains power rating seems a little light for a true 180WRMS rating. If it only weights 2 Kg, it would have to use a switch mode PS and a Class D PA.

I will carefully rip it apart and do that if I need to after trying the below suggestions. Thanks

Another approach is to try to gather some information. Watts delivered versus watts specified is always an interesting question. But the louder one really ought to have a higher rms ac voltage across the speaker. Do you have a friend with a meter (and a set of ear plugs)?

Sadly, I do not.

I have to wonder if you are supplying enough input to the power amp to drive it to full power. The amp is rated at 360W peak power, which should be able to get substantially loud. I haven't fiddled with a Profiler for a while, but I seem to recall settings for global output level (a dB setting if my recollection is correct). They do this to match various configurations, for instance the difference in required input from guitar amp to standard power amp. Have you tried adjusting the output level of the Profiler and/or do you know if you are indeed able to drive the amp to full output with your current settings?

I will have a look at all those intimidating menus later tonight and see if I find something like that.

And to do a fair comparison, you would run the Profiler into the FX return or Power amp IN on the Marshall.
This may help show any level issues mentioned by The Dude above.

Thanks, I'll try that!

[printer2]

So I understand somehow tube power is more loudness per watt - obviously..

Q: I would gladly take suggestions on how to maximize volume from my Kemper to my 120W@16Ohms cab without harming the speakers. How much SS power amp Wattage can I load into my cabinet?

I don't understand tube watts somehow being louder than SS watts. The speaker does not know if you are feeding it a watt from a tube amp rather than a SS amp. If the tube amp is louder it is because you are feeding more power into it or the spectral energy is greater where the ear is more sensitive.

[Enzo]

No no no. The argument is not that a one watt from a tube amp is louder than one watt from a SS amp. What the claim says is that a "50 watt" tube amp can make more sound than a "50 watt" solid state amp. The argument is that a tube amp can exceed its power supply voltage "limit".

[printer2]

No no no. The argument is not that a one watt from a tube amp is louder than one watt from a SS amp. What the claim says is that a "50 watt" tube amp can make more sound than a "50 watt" solid state amp. The argument is that a tube amp can exceed its power supply voltage "limit".

And I am saying if the one amp is much louder than the other the speaker is getting more power from that amp. The OP had a concern about how much power he can safely put into his speaker with the SS amp. I said the same amount of power as what was coming out of the tube amp. I guess that was not made clear enough. If the SS amp is not loud enough and it still does not sound objectionable,

The sound, however is really brilliant!

then I would think there might be more on tap from the amp. Now if the amp is being played to the point where clipping sounds objectionable then maybe a compressor/limiter before it might be in order. Whether it is a true C/L or a distortion box that clips the signal the average level should go up to the point of what the tube amp is providing.

[J M Fahey]

There's many possible explanations here, only bench testing will tell which one applies.

1) Preamp/emulator might not be driving power amp to full power, because signal levels do not match, as Enzo suggested.
Which sounds plausible to me.
I have tested SS and tube amps side by side countless times, clipping tube amps sound *somewhat* louder than same nominal power SS ones, will comment on that later, but it's not that big a difference.
Driving same speakers, a 100W SS amp easily matches a 50W tube one, yet you say that a 90W one (practically same as 100W) is WAY weaker than the Marshall, WAY means at least a 6dB difference and that's definitely not right ... unless the SS one is NOT driven anywhere near clipping.
Once SS amps clip, they don't lose power by any means, but the ruler flat waveform tops kill definition and harmonics, sound becomes muddy, instrument loses character, "all sound the same" , and that will be perceived as: "they don't cut in the mix or onstage" .but not that they have less *volume* , just flatter boring sound.

I'll show some clipping waveforms so you see what I am talking about

Marshall 18W, famous for its biting aggressive sound, so much so that some (mistakenly) add "buzz caps" to tame it; notice the sharp peaks, they are heard very well, believe me:


a standard tube amp, where one tube is weaker than the other so it clips earlier and has trouble reaching the same peak as the good one, not shown but I guess the PI is also clipping, we have the transformer which is a bandpass filter changing shape, the PI>power tube coupling cap also changes waveform shape, anything changing waveform away from a sinewave will add harmonics and our ear may hear them better:


here you see different clipping methods, used in SS amps and pedals, notice that NONE of them looks or does the same as a tube amp clipping , even if some pedals using them call themselves Tube Screamer or Hottubes
The last one, showing an Op Amp clipping, is the exact same square, flat top waveform of an SS power amp clipping ... for the very good reason that a standard SS power amp is just a "large" Op Amp, large enough to drive speakers


other SS clipping waveforms, one barely clipping , the other somewhat more, in any case different from tube ones:




some SS amps add special feedback to become "constant current" or "high impedance" outputs, emulating *one* tube characteristic (they still miss many others), in that case the square wave reacts to the speaker voice coil inductance and creates a front edge peak which adds some bite, look at the bottom waveform, and look for a similar peak at the "18W" clipping:


our friend Loudthud has generously posted tons of scope capture waveforms, very enlightening.

[Mick Bailey]

I always compare outputs at the onset of clipping - set the output just at the point where the tops of a sine wave flatten off (as viewed on my scope). Listening to an amp gives a perception of loudness that's especially skewed once clipping sets in. With any modelling situation you want the cleanest power achievable, otherwise the colouration will not give a true reproduction of the modelled amp, particularly if you're listening to a library sound. I have four customers who use Kemper setups and rather strangely two of them have commented that in a band situation they don't sound anywhere near as loud or 'cut through' like the original tube amp does. Maybe then the output level isn't optimized to the correct level to effectively drive the power amp.

Watts is Watts whether it's SS or tube, just as a pound of flour weighs the same as a pound of sand. The test is to measure the output of both setups.

One thing to note is the XLR balanced output offers the highest signal level (+22dBu against +16dBu).

[Mike Sulzer]

Juan, am I correct in thinking that the sharp peaks in the 18W clipping are a result of the cathode biasing? I do not see them in a grid biased pair of EL84s.

[pdf64]

Juan, am I correct in thinking that the sharp peaks in the 18W clipping are a result of the cathode biasing? I do not see them in a grid biased pair of EL84s.

My guess is that extreme overdrive pushes the power tubes effectively into class C, so the spikes are crossover artifact.
Due to the combined effects on the operating point of bias shift at the control grids, 'squish' as the cathode voltage rises, and 'sag' as the screen grid HT voltage drops.

I think that your fixed bias and 100k control grid stoppers may act to reduce / eliminate those effects.

[nickb]

In the AES journal, May 1973 article titled "Tubes versus Transistors: Is There An Audible Difference" concluded:

“Vacuum-tube amplifiers differ from transistor and operational amplifiers because they can be operated in the overload region without adding objectionable distortion. The combination of the slow rising edge and the open harmonic structure of the overload characteristics form an almost ideal sound- recording compressor. Within the 15-20 dB "safe" overload range, the electrical output of the tube amplifier increases by only 2-4 dB, acting like a limiter. However, since the edge is increasing within this range, the subjective loudness remains uncompressed to the ear. This effect causes tube-amplified signals to have a high apparent level, which is not indicated on a volume indicator (VU meter). Tubes sound louder and have a better signal-to-noise ratio because of this extra subjective headroom that transistor amplifiers do not have. Tubes get punch from their naturally brassy overload characteristics. Since the loud signals can be recorded at higher levels, the softer signals are also louder, so they are not lost in tape hiss and they effectively give the tube sound greater clarity. The feeling of more bass response is directly related to the strong second and third harmonic components, which reinforce the "natural" bass with "synthetic" bass [5]. In the context of a limited dynamic range system like the phonograph, recordings made with vacuum-tube pre-amplifiers will have more apparent level and a greater signal to system noise ratio than recordings made with transistors or operational amplifiers.”