gofar99 Messages: 1949 Registered: May 2010 Location: Southern Arizona
Illuminati (5th Degree)
Hi, Oh yes. Many moons ago, I thought that you should be able to get a clean square wave out of any amp . Not so with any that have coupling caps or transformers. A good rule of thumb that someone passed along to me is that in order pass a clean square wave the response must be linear at both 10 time above and 10 times below the test frequency. It seems to hold true. Some SS gear ( I have one amp like this) can pass DC to 400K. It produces nice square waves at any audio frequency you choose... it just sounds dull and uninteresting. Everything I cook up with the exception of the recent phono preamp can do nice squares from about 100HZ to 4K. Below that you will find some top slanting and above that some slight rounding or an occasional overshoot. I design for -3db at 5HZ and 30K so this is about what you would expect to see. Gear like phono preamps (not IC ones though) will have rather wild looking squares (more like triangles) because of the method of equalization. I have considered what would happen if you used a linear phase IC to do the equalization in a tube based phono preamp. Not a purist thing for sure, but might be nice.
Finally, I like to measure what I can, but my ears are the final judge. If it doesn't sound right, then I'm not measuring the right things and need to go back to the drawing board.
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. Not so with any that have coupling caps or transformers. A good rule of thumb that someone passed along to me is that in order pass a clean square wave the response must be linear at both 10 time above and 10 times below the test frequency. It seems to hold true. Some SS gear ( I have one amp like this) can pass DC to 400K. It produces nice square waves at any audio frequency you choose... it just sounds dull and uninteresting. Everything I cook up with the exception of the recent phono preamp can do nice squares from about 100HZ to 4K. Below that you will find some top slanting and above that some slight rounding or an occasional overshoot. I design for -3db at 5HZ and 30K so this is about what you would expect to see. Gear like phono preamps (not IC ones though) will have rather wild looking squares (more like triangles) because of the method of equalization. I have considered what would happen if you used a linear phase IC to do the equalization in a tube based phono preamp. Not a purist thing for sure, but might be nice. 
