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Cutoff vs. Saturation vs. ?


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7/25/2005 12:24 PM
Matt Cutoff vs. Saturation vs. ?
The "Planned distortion. Design for Saturation or Cutoff?" thread reminded me that I don't know enough about this stuff. Any recommended reading to get a good explanation of it? Hopefully not too technical but not dumbed-down too much either. I did read a paper that Ray Ivers (I think) suggested called "Vacuum Tube Nonlinearity as part of the Electric Guitar sound" and it helped. But I still doubt I could properly explain it to someone else (which, I was taught, means I don't really understand it well enough). TIA!
 
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7/28/2005 7:13 AM
kg
what kind of explanation are you looking for?  
 
there's a lot of tube technical stuff on my website.  
 
http://ken-gilbert.com  
 
hth  
ken
 
7/28/2005 7:53 AM
Matt
Thanks kg. I knew you had a site with some info but forgot about it. I'll definitely give it a look.  
 
One thing I would like to find (even though it's not what I originally asked for) is audio samples of different types of 'distortion'. Even though words like 'farty' distortion are somewhat descriptive, they still can be misinterpreted. Audio samples that would show what excessive crossover distortion sounds like, or blocking distortion, excessive IM, etc. And if these audio samples were also accompanied by an image of the waveform you were listening to, that would be even more informative.  
 
For example, when I play an amp I hate any sort of 'fuzz-like' distortion (i.e. distortion that to me sounds like a bad fuzz box). I've had people tell me it's blocking distortion and others tell me it's just 'asymmetrical' or 'loaded with odd-order harmonics' and probably a few other things. So I still don't know what it is. I've built some high-gain circuits that sound terrible and only a couple that sound good (one of them great IMO). And I don't know why the bad ones sound bad or why the good ones sound good (sometimes the exact same circuit but in a different amp). About all I've 'learned' is that it appears that the PS plays a much bigger role than I thought (and I'm not even sure about that).  
 
Now that I've written all this, it really looks like I just need to pony up the dough and get a 'scope and dig in.
 
7/28/2005 8:38 AM
Ray Ivers

Matt,  
 
I hadn't replied because I really wasn't 100% sure what you wanted, and also because practically all the heavy-duty 'classic' texts (Radiotron Designer's Handbook, Terman, Seely, Spangenberg, etc.) took me many years to 'dumb down' to a usable level for myself. ;) I found that once I got a reasonably-good understanding of what was going on, I stopped thinking in terms of words and more in terms of 'mind pictures', for lack of a better phrase - so it's quite possible for you to understand completely without being able to describe exactly; does that make sense?  
 
Do check out Ken's site, it rocks. Leave yourself the better part of a morning. :) There's also Steve" target="_blank">http://members.aol.com/sbench101/">Steve Bench's site which is a great read as well - and I'm sure you've already been to the legendary Aiken" target="_blank">http://www.aikenamps.com/TechInfo_2.htm">Aiken Amps tech section.  
 
If you have a tube amp with a cascaded-gain-stage preamp, MV, and a push-pull output stage, you have almost everything you need to answer all of your questions regarding distortion. You'll have to invest a bit more time than it would take to surf the Web for samples, but it will be worth it - in fact, IMO there's absolutely no substitute for it.  
 
If you have such an amp and are interested in trying this out, let me know and I ( and certainly many others here) can tell you what minor mods to make to get each of your desired distortions.  
 
Ray
 
7/28/2005 8:40 AM
Ray Ivers

Matt,  
 
I hadn't replied because I really wasn't 100% sure what you wanted, and also because practically all the heavy-duty 'classic' texts (Radiotron Designer's Handbook, Terman, Seely, Spangenberg, etc.) took me many years to 'dumb down' to a usable level for myself. ;) I found that once I got a reasonably-good understanding of what was going on, I stopped thinking in terms of words and more in terms of 'mind pictures', for lack of a better phrase - so it's quite possible for you to understand completely without being able to describe exactly; does that make sense?  
 
Do check out Ken's site, it rocks. Leave yourself the better part of a morning. :) There's also Steve" target="_blank">http://members.aol.com/sbench101">Steve Bench's site which is a great read as well - and I'm sure you've already been to the legendary Aiken" target="_blank">http://www.aikenamps.com/Techinfo_2.htm">Aiken Amps tech section.  
 
If you have a tube amp with a cascaded-gain-stage preamp, MV, and a push-pull output stage, you have almost everything you need to answer all of your questions regarding distortion. You'll have to invest a bit more time than it would take to surf the Web for samples, but it will be worth it - in fact, IMO there's absolutely no substitute for it.  
 
If you have such an amp and are interested in trying this out, let me know and I ( and certainly many others here) can tell you what minor mods to make to get each of your desired distortions.  
 
Ray
 
7/28/2005 8:43 AM
Ray Ivers
Funny how some links work in the 'Preview'...
and not when you post. And you can no longer go back and correct your posts like before... but I don't think I could get the Bench link to work even if I could re-edit it. Oh well.
 
7/28/2005 9:41 AM
Matt
Thanks Ray. I might have to build another amp with a cascaded preamp/MV/fixed-bias PP output (actually I have an unfinished amp that should work great). My most recent amp was a dual effort of mine and another poster here and it sounds so good I hate to mess with it! I spec'd the PT and choke from Heyboer and used a MM 100W plexi OT but he designed/assembled the amp, then I 'rebuilt' the preamp using the web version of the XTC OD channel (with some minor tweaks). I've built that circuit in a hacked BF Bandmaster (with a Marshall-type 50W OT) and it sounded terrible but this amp sounds great (best amp I've ever played!) and is amazingly quiet for the amount of gain it has.
 

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