1000W is only twice as loud as 100W. Someone who has 1kW is going to want to play louder than someone with just 100W, otherwise what use has all that extra money gone towards? So more watts will never be the answer to clipping.
Did you get normal or expedited shipping for the book? Still waiting for mine here...
Did you get normal or expedited shipping for the book? Still waiting for mine here...
normal shipping to save cost. 
The book contains so many valuable information. It may be classified by the mainland custom.
some commercial amps may have their protection partially acting too early. If we can disable the circuit, the amp may sound differently.
My amp clips frequently. It is fun to listen the difference between clip or not.
The book contains so many valuable information. It may be classified by the mainland custom. some commercial amps may have their protection partially acting too early. If we can disable the circuit, the amp may sound differently.
My amp clips frequently. It is fun to listen the difference between clip or not.
Yeah, me too - 4 other books in the same order which were in stock arrived ahead of schedule in around 2 weeks. Can't have been on a ship Yours must have travelled by air too to arrive so quickly.
My first amplifier was a NAD3020, I still have it even though I recall selling it on to my younger sister at some point. She gave it back to me to fix as its volume control had gone noisy - never did get around to sorting that. This amp had as one of its USPs 'soft clipping' - I haven't examined the circuit but I believe it operates prior to the output stage. There's a slide switch on the rear to defeat it.
Yours must have travelled by air too to arrive so quickly.My first amplifier was a NAD3020, I still have it even though I recall selling it on to my younger sister at some point. She gave it back to me to fix as its volume control had gone noisy - never did get around to sorting that.
This amp had as one of its USPs 'soft clipping' - I haven't examined the circuit but I believe it operates prior to the output stage. There's a slide switch on the rear to defeat it.You've also forgotten the effects of the voice coil inductance which is a major source of high frequency distortion. It varies both with the diaphragm displacement and the current in the voice coil
Hi Pete,
That A/B test was one of those tests where many people were surprized in several ways, including myself. The tube amp in question was one that I had designed myself solely for the purpose of hearing the difference between a tube amplifier and a SS amplifier where the listening conidtions were well-controlled AND I was familiar and trusting of both designs. Up to that point, I had not designed a tube amplifier since I was in high school. So I designed the tube amp with more modern knowledge and some updated techniques. For example the tube amp used transistor current sources for the tube differential pairs and screen voltage supplies that were regulated with MOSFET pass transistors. Some may call this cheating
Anyway, I was surprized at how good the 35 wpc tube amp sounded.
I subsequently took the amp to a tube-head meeting where it was compared with other tube amps in the usual uncontrolled way. It was well-liked, so I guess it had at least some legitimate tube pedigree despite some of the modern circuit techniques. (those push-pull KT88's, loafing at 35 wpc, really stepped on the SETs).
At the HE2007 workshops, my recollection is that a decent number of people could hear a difference, but about half were wrong in identifying which was the tube and which was the solid state. Similarly, I think that about half preferred the one that was solid state and about half preferred the one that was tubed.
Cheers,
Bob
One reason why any difference was heard was that the peak level was well over 100W (or was it 200W, 230W comes to mind) as I recall from the SS amp. It was level matched so the tube amp (35W) was well into clipping. It was amazing that they sounded as close as we observed since this does not in any way meet the requirement for no clipping. This demonstrates that the tube amp is an excellent compressor!
I've been thinking for years that I'd like to rebuild a ST-70 with 6550s or KT88s seems tubes need to be derated also.
Richard Modafferi likes the idea of using emitter followers in tube power amps:
Audio frequency power amplifier with ... - Google Patent Search
As a solid-state centric designer for many years, my first reaction on hearing the tube amp was that it doesn't have a right to sound that good.
BTW, I always try to keep in mind the distinctions among:
amplifier is musical
amplifier sounds good
amplifier is neutral
Ideally, a well-behaved neutral amplifier always sounds good, but some program material and loudspeaker combinations sound better with an amplifier that is synergistically not neutral.
It seems that tube amplifiers have always had a reputation of being more musically tolerant to clipping than SS amps. We often hear something like "A 35-watt tube amp can play louder than a 35-watt SS amp".
I included optional dynamic soft clip (I called it the Klever Klipper) into my Super Gain Clone (SGC) amplifier and also described it in a chapter of my book. It does indeed give the SGC a more tube-like tolerance for signals that will clip it. It sounds good, even though THD begins to rise significantly at power levels above about 1/3 power in the SGC, which is rated at 40-50 watts. I show a curve of THD vs power for the SGC in the book with the Klever Klipper turned on and off.
Cheers,
Bob
Yeah, me too - 4 other books in the same order which were in stock arrived ahead of schedule in around 2 weeks. Can't have been on a ship
My first amplifier was a NAD3020, I still have it even though I recall selling it on to my younger sister at some point. She gave it back to me to fix as its volume control had gone noisy - never did get around to sorting that.
Hi abraxalito,
One of the key things of interest in soft clipping circuits is whether they are inside a feedback loop or not. They work much better if they are ahead of the amplifier-proper and not inside the feedback loop, since feedback tends to sharpen up the clipping too much if the clipping is inside the feedback loop.
Cheers,
Bob
Hi Bob
You say 'a feedback loop' and then 'the feedback loop'. Are these the same feedback loop? I ask because I've designed soft clipping circuits before that have what might be called an envelope feedback loop. This is in addition to the normal NFB which is applied to the power amp. So they operate in the same way as a compressor - sense the output envelope and feed that back to an AGC stage to lower the overall gain.
In a former job I used to design active subwoofer amps. One of the big challenges there is to handle overloads gracefully - the sound of the compressor played one of the biggest parts in the overall sound of the device.
With a subwoofer, the power supply is one of the most expensive parts so an engineering optimisation is called for to get the most out of it. Supplies sag when under load, and the drive unit's load varies with frequency so a clipper based on predicting what the power supply is going to do is almost impossible. I played with a feedback system from the output rails - I did this by using a rail-to-rail opamp, driven from a resistively divided version of the output rails. It can be arranged that this opamp clips at 90% of the maximum output voltage of the power amp - its clipping generates an error signal which feeds back to lower the gain at the input. There's absolutely no added distortion then below 90% of output, below the clip level of the modelling opamp.
errata: page 257 "for this reason, trimmer R22" referring to Figure 12.8 on page 256. There is no R22 in the schematic, so I guess this was referring to R12.
(I'm cheating a bit by reading ahead, but I was thinking to apply the error correction concept to a Leach amplifier circuit I'm using as a test bed, which will also be used to try out the On Semi Thermaltrak parts.)
I'm glad to see some introductory coverage of basic circuits and concepts, which was assumed knowledge in Self's and Slone's books. Not all of us are starting out with EE degrees.
(I'm cheating a bit by reading ahead, but I was thinking to apply the error correction concept to a Leach amplifier circuit I'm using as a test bed, which will also be used to try out the On Semi Thermaltrak parts.)
I'm glad to see some introductory coverage of basic circuits and concepts, which was assumed knowledge in Self's and Slone's books. Not all of us are starting out with EE degrees.
In all cases in that post I was referring to the amplifier's global feedback loop. The kind of clipper I was referring to as my preferred approach is a soft clipper that precedes the amplifier, so that the amplifier, with its global feedback loop, never clips.
The use of a dynamic soft clip circuit means that the clipping threshold of the soft clip circuit tracks the average available rail voltage so that some degree of dynamic headroom is retained. The Klever Klipper merely uses passive silicon diodes for the clipping action. Those diodes are normally reverse-biased by the clip threshold control voltage.
The Klever Klipper is described in Chapter 17 of my book.
Cheers,
Bob
Hi Damon,
Thanks for bringing that errata to my attention. You can also email me directly at bob [at] cordellaudio [dot] com.
I'm delighted that you liked the introductory coverage that I included in the book. As you can see, I've aimed to serve a broad spectrum of readers.
Cheers,
Bob
I received my copy today and have just had a brief look through it, and I must say I´m deeply impressed! Loads and loads of useful info, good explanations that made me think in different paths, and a written language at just the right level to keep things interesting but never overwhelming. At least it suits me, not speaking English as my native language. To anybody out there not sure about buying the book, all I can say is go ahead and buy it! You won´t be disappointed! This is what I have been looking for the last few years. Thanks Bob!
/Rikard
/Rikard
Jan, where did you order it? I did it via amazone uk and i have to wait until december.
To Bob Cordell
In your book, do you analyze the influence of a reactive load on crossover distortion.
I am puzzeled by the fact that crossover distortion is happening when the current goes through zero in the output transitors. Due to the phase of the input impedance of the load, the voltage can be high at that moment and will then have a glich. Could it then happen that again due to the phase of the voltage input, pressure ouput transfer function of the system, the output pressure could be high and experience at that moment a glich which makes it louder than what would be expected from a zero crossing signal.
The same can be asked for the optimum bias current if the load is reactive.
If this is true, custom phase equalization of the system becomes a very important topic at least for diy.
JPV
Copyright 2011??? Did I miss a few months somewhere?
Steve.
Wow, you've really got sharp eyes. Good proof reader. I hadn't noticed that. I don't know whether it is a mistake or just the way they date things with copyrights. Go figure.
Cheers,
Bob
I received my copy today and have just had a brief look through it, and I must say I´m deeply impressed! Loads and loads of useful info, good explanations that made me think in different paths, and a written language at just the right level to keep things interesting but never overwhelming. At least it suits me, not speaking English as my native language. To anybody out there not sure about buying the book, all I can say is go ahead and buy it! You won´t be disappointed! This is what I have been looking for the last few years. Thanks Bob!
/Rikard
Thanks, Rikard. These are very very kind words. I'm really glad you like the book and hope that you will enjoy it and that it will inspire you to good ideas.
Cheers,
Bob
Hi JPV,
I do not recall saying much about the influence of a reactive load on crossover distortion, however your point is well-taken. Crossover distortion is a function of the output current of the output stage. While the net output current crosses through zero at 0V for a resistive load, this is not the case for a reactive load. So the answer is yes, the crossover glitch could occur at a point in the output signal where the output voltage is moderately high if a reactive load is being fed.
I don't think this observation has any implications for what the optimum quiescent output stage bias should be.
Cheers,
Bob