Bill, I would think that would depend on the power supply. A hefty supply would keep up and as long as the waveform doesn't clip any of the stages of the amp, it should keep its tone.
I haven't seen many amps inside, but my Ampeg SVT-3 Pro has a huge toroidal tranny. Supply capacitance is not what I would like nor are the diodes HEXFRED, but I will say it holds tone really well.
Bass amplifier question
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soundmasterg
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"Amps running at 2 Ohms typically aren't supposed to sound as good as they do running at 4 or 8, weather they're designed to or not. Sure, you get more power but at a loss of tone. 4 Ohms seems to be a sweet spot."
That is pure opinion and has no basis in fact.
When someone designs an amp, they design it to operate under certain conditions. A tube amp is designed to work under a given load, whatever the load may be, and it will make it's best power at that load. It will work into other loads within a range, but make less power, and have more distortion at those other loads, and the tonal spectrum will change. If you go outside the range, the tube amp won't be able to handle it and the output transformer or tubes will arc and self-destruct.
A transistor amp makes more power as you get closer to a dead short, without actually getting to a dead short, because the power transistors would blow. So at a 2 ohm load it will make more power than at a 4 ohm load. You don't need an output transformer with transistor amps, although some have used them in the past, especially earlier designs. The transistor amp can be directly connected to the speaker, which is a big reason why transistor amps have a higher damping factor than tube amps. (Damping factor is how well the amp controls the movement of the speaker) The transistor output section is designed to never distort on it's own because when it does so it sounds terrible due to the sudden onset of harsh, odd order distortion and hard clipping, and it goes into thermal runaway very quickly at that operating point. If a transistor amp is distorting, it has been designed into the amp to do so using different methods than just overdriving the power transistors, such as diode bounding for example.
As humans, we each hear differently, and there is a different threshold for everyone as far as when your ear gets overloaded due to a loud sound source. When your ear gets overloaded with too strong a signal, it actually becomes less sensitive to input to a certain extent and acts somewhat like a compressor. Because this happens at a different SPL level for everyone, it is hard to generalize. What may be a loss of tone to one person could be just the ticket for someone else. Engineers design an amp to do a specific task. An example would be marketing saying to engineering "We need a 200 watt bass amp for this price range." So the engineer makes decisions that shape his design from that point on. Tubes or transistors? Mosfets, Jfets, BJT's, etc. Head or combo. 10 inch speakers or 15 inch speakers, etc. The budget determines the quality of the components and how much effort is spent on the design. Obviously no company wants to design something that will fail and cause them warranty issues, so most stuff is designed to perform at least to a basic level. Transistor amp designers often skimp on the power supply design and tend to use lots of feedback to make an amp stable. The more feedback you use, the less touch responsive an amp is. The more you skimp on a power supply, the louder the hum level is, and the more the supply sags when high current levels are demanded of it. Most tube amps have what is considered very poor power supply regulation. If you use solid state rectifiers, you can go very high in filter cap values without any concern of rectifiers blowing, and you can make a tube amp sound as clinical and lifeless as most transistor amps. It is all in how it was designed, but the sound of the amp doesn't really have very much to do at all with what load it is running at, assuming the load and speakers are matched up properly. Tube amps won't make more power at a 2 ohm load anyway unless that is where their optimum load is. Transistor amps will make more power at a 2 ohm load than a 4 ohm load, but their tonal spectrum doesn't change at that operating point except in the case of acoustic considerations relating to your ears.
That is pure opinion and has no basis in fact.
When someone designs an amp, they design it to operate under certain conditions. A tube amp is designed to work under a given load, whatever the load may be, and it will make it's best power at that load. It will work into other loads within a range, but make less power, and have more distortion at those other loads, and the tonal spectrum will change. If you go outside the range, the tube amp won't be able to handle it and the output transformer or tubes will arc and self-destruct.
A transistor amp makes more power as you get closer to a dead short, without actually getting to a dead short, because the power transistors would blow. So at a 2 ohm load it will make more power than at a 4 ohm load. You don't need an output transformer with transistor amps, although some have used them in the past, especially earlier designs. The transistor amp can be directly connected to the speaker, which is a big reason why transistor amps have a higher damping factor than tube amps. (Damping factor is how well the amp controls the movement of the speaker) The transistor output section is designed to never distort on it's own because when it does so it sounds terrible due to the sudden onset of harsh, odd order distortion and hard clipping, and it goes into thermal runaway very quickly at that operating point. If a transistor amp is distorting, it has been designed into the amp to do so using different methods than just overdriving the power transistors, such as diode bounding for example.
As humans, we each hear differently, and there is a different threshold for everyone as far as when your ear gets overloaded due to a loud sound source. When your ear gets overloaded with too strong a signal, it actually becomes less sensitive to input to a certain extent and acts somewhat like a compressor. Because this happens at a different SPL level for everyone, it is hard to generalize. What may be a loss of tone to one person could be just the ticket for someone else. Engineers design an amp to do a specific task. An example would be marketing saying to engineering "We need a 200 watt bass amp for this price range." So the engineer makes decisions that shape his design from that point on. Tubes or transistors? Mosfets, Jfets, BJT's, etc. Head or combo. 10 inch speakers or 15 inch speakers, etc. The budget determines the quality of the components and how much effort is spent on the design. Obviously no company wants to design something that will fail and cause them warranty issues, so most stuff is designed to perform at least to a basic level. Transistor amp designers often skimp on the power supply design and tend to use lots of feedback to make an amp stable. The more feedback you use, the less touch responsive an amp is. The more you skimp on a power supply, the louder the hum level is, and the more the supply sags when high current levels are demanded of it. Most tube amps have what is considered very poor power supply regulation. If you use solid state rectifiers, you can go very high in filter cap values without any concern of rectifiers blowing, and you can make a tube amp sound as clinical and lifeless as most transistor amps. It is all in how it was designed, but the sound of the amp doesn't really have very much to do at all with what load it is running at, assuming the load and speakers are matched up properly. Tube amps won't make more power at a 2 ohm load anyway unless that is where their optimum load is. Transistor amps will make more power at a 2 ohm load than a 4 ohm load, but their tonal spectrum doesn't change at that operating point except in the case of acoustic considerations relating to your ears.
Greg, a tube amp, when matched to it's output impedance load, will always put out the same power whether at 2, 4, 8, 16, etc., provided that is its design. By that I mean the tube stage's load is the primary of the output tranny and that is always the same given the secondary load is matched output tap to speaker load. Whether the output load is the 2 ohm tap into a 2 ohm cab load or it is the 4 ohm tap into a 4 ohm cab load is immaterial to the tube/primary windings circuit. Same power.
Also with tube amps with SS rectifiers and large capacitance supplys, that doesn't make them sound clinical and lifeless, but makes them able to maintain their characteristic sound to maximum designed power output. When the supplies sagged, that created the softer, mushy sounds tubes used to be known for. It also added larger amounts of even order harmonics - what some call the golden warmth of tubes. Look at the power supply in an Ampeg SVT - huge power tranny and good filtering. That makes for a very punchy sound. Crank one up and the jump factor is scarey.
Also with tube amps with SS rectifiers and large capacitance supplys, that doesn't make them sound clinical and lifeless, but makes them able to maintain their characteristic sound to maximum designed power output. When the supplies sagged, that created the softer, mushy sounds tubes used to be known for. It also added larger amounts of even order harmonics - what some call the golden warmth of tubes. Look at the power supply in an Ampeg SVT - huge power tranny and good filtering. That makes for a very punchy sound. Crank one up and the jump factor is scarey.
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soundmasterg
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John, maybe I wasn't clear enough in what I was trying to say. I completely agree with you about a tube amp and power output as far as if a 2 ohm tap into a 2 ohm load is just as loud as a 4 ohm tap into a 4 ohm load, etc.
What I was trying to say was that if you have a 4 ohm tap and run it into a 2 ohm load or into an 8 ohm load instead of a 4 ohm load, the power output goes down, and the harmonic spectrum changes, assuming the 4 ohm tap/4 ohm load setup is designed for max power anyway. Sometimes amps aren't designed for max power, like the Marshall JTM 45 which used a 6600 ohm secondary in the output transformer when a 4000 ohm secondary would have given more power.
When I was talking SS, I wasn't talking about rectifiers in tube amps, I was talking about actual SS amps. If you stiffen up the supply in a tube amp by using a SS rectifier and increase filtering to something like the SVT, then you get a very punchy sound because the power supply is able to keep up with what you're demanding out of it. If you go up further on the level of filtering to what they often use in a SS amp, (6000uf for example) then a tube amp will sound almost as lifeless and clinical as many solid state amps. Then add in the amount of negative feedback they have to put in SS amps to make them stable, and then you're in the same lifeless territory even with tubes. One of the main benefits to tube amps and their sound is that the circuits can be stable and run fine on little to no feedback and very little power supply filtering or AC spike protection. SS amps often have to have lots of feedback and spike protection and voltage regulation to even work ok, and these contribute to a lousy sound.
Jared, that part you mentioned about this:
"And I thought that the 'tone' was partly a function of how many windings are in the OT vs the tap at half, 25%, 75% etc."
sounds like Gerald Weber gobblyspeak. He's full of **** sometimes and this is one of the things he said thats ridiculous and is designed to help him sell his products. Read the FAQ at www.londonpower.com and Kevin O'Connor mentions something about that there unless he took it down since I last read it.
What I was trying to say was that if you have a 4 ohm tap and run it into a 2 ohm load or into an 8 ohm load instead of a 4 ohm load, the power output goes down, and the harmonic spectrum changes, assuming the 4 ohm tap/4 ohm load setup is designed for max power anyway. Sometimes amps aren't designed for max power, like the Marshall JTM 45 which used a 6600 ohm secondary in the output transformer when a 4000 ohm secondary would have given more power.
When I was talking SS, I wasn't talking about rectifiers in tube amps, I was talking about actual SS amps. If you stiffen up the supply in a tube amp by using a SS rectifier and increase filtering to something like the SVT, then you get a very punchy sound because the power supply is able to keep up with what you're demanding out of it. If you go up further on the level of filtering to what they often use in a SS amp, (6000uf for example) then a tube amp will sound almost as lifeless and clinical as many solid state amps. Then add in the amount of negative feedback they have to put in SS amps to make them stable, and then you're in the same lifeless territory even with tubes. One of the main benefits to tube amps and their sound is that the circuits can be stable and run fine on little to no feedback and very little power supply filtering or AC spike protection. SS amps often have to have lots of feedback and spike protection and voltage regulation to even work ok, and these contribute to a lousy sound.
Jared, that part you mentioned about this:
"And I thought that the 'tone' was partly a function of how many windings are in the OT vs the tap at half, 25%, 75% etc."
sounds like Gerald Weber gobblyspeak. He's full of **** sometimes and this is one of the things he said thats ridiculous and is designed to help him sell his products. Read the FAQ at www.londonpower.com and Kevin O'Connor mentions something about that there unless he took it down since I last read it.
Greg - agreed. But let me add a decently designed SS amp, one where each stage was correctly designed by someone who knows what they are doing, doesn't need a large amount of negative feedback.
I have a Nikko SS amp (120W/ch) that is a very decent sounding amp to start with (runs class A up to a couple watts), and I added big amounts of ps capacitance (30,000uF total per rail) and front end voltage regulation to it and it sounds as good or better than my tube VTL and McIntosh amps. Which really suprised me. In fact I sold it to a friend, shortly later wishing I hadn't, and a couple years later bought it back. I still use it.
As to adding supply capacitance to a tube amp and it sounding lifeless and clinical I disagree. On my Dynaco Stereo 70 I kept adding capacitance to the three higher voltage supplies until I saw no ripple in the supply voltage with dynamic music content. It retained all the virtues of tubes, but with more tautness and clarity.
I have a Nikko SS amp (120W/ch) that is a very decent sounding amp to start with (runs class A up to a couple watts), and I added big amounts of ps capacitance (30,000uF total per rail) and front end voltage regulation to it and it sounds as good or better than my tube VTL and McIntosh amps. Which really suprised me. In fact I sold it to a friend, shortly later wishing I hadn't, and a couple years later bought it back. I still use it.
As to adding supply capacitance to a tube amp and it sounding lifeless and clinical I disagree. On my Dynaco Stereo 70 I kept adding capacitance to the three higher voltage supplies until I saw no ripple in the supply voltage with dynamic music content. It retained all the virtues of tubes, but with more tautness and clarity.
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soundmasterg
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John, is that SS Nikko amp for hi-fi? If so, then I don't think you'd notice the difference as much as compared to the tube/SS comparison with guitar amps. The application is completely different and hi-fi guys aren't trying to distort the **** out of their rig like most guitar players do. When overdriven to completely clipped is where you would notice the regulation and capacitance difference and is mainly what I was addressing. It is certainly possible to design SS stuff without much negative feedback and have it work ok, but the designers are often too lazy or inexperienced to do so, or the pricing of the unit is such that they can't take the time.
On your Stereo 70, were you still using the tube rectifier, and if so, how high did you go on the filtration? The GZ34 specced for those can only have a 60uf max for the first cap without failure risk, and I've heard of modern GZ34's having trouble at 50uf. The Sunn 200S is like a Dynaco Mk.3 and I went to 110uf and 50uf on the first two filter stages in mine, and switched to a solid state rectifier and it is much better now.....for bass. I'd suspect that if you went to 30000uf in that amp that it may sound ok, because bass is the intended application, but I still think that if you went to 30000uf on a Fender 4x10 Bassman with a solid state rectifier, AND added the level of feedback that often is used in a lot of solid state stuff that it would lose a lot of it's tube character and the sag that blues players love so much would be gone.
On your Stereo 70, were you still using the tube rectifier, and if so, how high did you go on the filtration? The GZ34 specced for those can only have a 60uf max for the first cap without failure risk, and I've heard of modern GZ34's having trouble at 50uf. The Sunn 200S is like a Dynaco Mk.3 and I went to 110uf and 50uf on the first two filter stages in mine, and switched to a solid state rectifier and it is much better now.....for bass. I'd suspect that if you went to 30000uf in that amp that it may sound ok, because bass is the intended application, but I still think that if you went to 30000uf on a Fender 4x10 Bassman with a solid state rectifier, AND added the level of feedback that often is used in a lot of solid state stuff that it would lose a lot of it's tube character and the sag that blues players love so much would be gone.
Greg, yes the Nikko is in my home audio room. On the Stereo 70, I kept adding 20uF 500V caps - some to the main power, some to the resistor-isolated front-end supplies. I think I ended up with 5 or 6 added caps along with the original Dynaco can capacitor. Yes the GZ34 is still in there, no problems with it. I would think the resistor isolators keeps the rectifier tube from being overloaded on inrush current spikes.
Putting 30000uF into a 600V+ tube amp would be one HUGE bank of caps, and one I would not want to be around at all!
As to the Fender Bassman statement, the added excess feedback would be the spoiler, I would think.
I hadn't considered guitar players wanting the low regulation and distorting circuit designs. With my home audio and bass amps I want tight regulation and firm supplies. Bass needs about twice the power to be the same room volume as other instruments, and you'd want it to be firm and solid.
This has been interesting and a learning experience!
Putting 30000uF into a 600V+ tube amp would be one HUGE bank of caps, and one I would not want to be around at all!
As to the Fender Bassman statement, the added excess feedback would be the spoiler, I would think.
I hadn't considered guitar players wanting the low regulation and distorting circuit designs. With my home audio and bass amps I want tight regulation and firm supplies. Bass needs about twice the power to be the same room volume as other instruments, and you'd want it to be firm and solid.
This has been interesting and a learning experience!