D.A.(Tony)Stewart
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With Slew rate limiting and diode soft compression on gain , tube performance can be emulated with solid state design.
Normal limiting on solid state produces square waves from a single tone which are only odd harmonics and tubes & xfmr's produce limit with even harmonics. A triangle wave makes only even harmonics with no odd harmonics. There is more to it than that, but I have not attempted to emulate it.
My only tube amp was the Bogan Stereo I had since '70 with my 12" Philips speakers, in cabs. I made with tuned Helmholtz resonators to extend the bass.
The Bogan final A-B tube stage started to glow with blue corona , I think from spurious oscillations in its last days of use before I replaced it with a Technics unit which always had that solder resin flux smell to it.
That Bogan with the -15dB contour switch is still today the most sensible alternative to the "loudness" switch used to today. Where the "loudness" switch adds mostly boomy bass, the "contour" switch was used to cut the mid-range when you wanted to cut the sound but maintain the EQ according to human Fletcher-Munchen EQ curves. Our ears tend to be flat EQ near the max levels and then need compensation to cut midrange and lower levels which is exactly what Bogan's design did.
I loved it, but my buddy who graduated in EE before me had already designed/built tube amps for pre-amp and power amp. They amazed me for low S/N ratio, in fact total silence at max gain. Perfect silence and then the music would vibrate the house with a punchy bass, I had never heard before, until I found a disco in Hull with quad 15" woofers and a rack of DC300's in parallel. It was a 70's vintage RC church converted into a disco, just across the river from Ottawa. I found it late at nite searching for the bass seismic waves.
Tony in Toronto.
Normal limiting on solid state produces square waves from a single tone which are only odd harmonics and tubes & xfmr's produce limit with even harmonics. A triangle wave makes only even harmonics with no odd harmonics. There is more to it than that, but I have not attempted to emulate it.
My only tube amp was the Bogan Stereo I had since '70 with my 12" Philips speakers, in cabs. I made with tuned Helmholtz resonators to extend the bass.
The Bogan final A-B tube stage started to glow with blue corona , I think from spurious oscillations in its last days of use before I replaced it with a Technics unit which always had that solder resin flux smell to it.
That Bogan with the -15dB contour switch is still today the most sensible alternative to the "loudness" switch used to today. Where the "loudness" switch adds mostly boomy bass, the "contour" switch was used to cut the mid-range when you wanted to cut the sound but maintain the EQ according to human Fletcher-Munchen EQ curves. Our ears tend to be flat EQ near the max levels and then need compensation to cut midrange and lower levels which is exactly what Bogan's design did.
I loved it, but my buddy who graduated in EE before me had already designed/built tube amps for pre-amp and power amp. They amazed me for low S/N ratio, in fact total silence at max gain. Perfect silence and then the music would vibrate the house with a punchy bass, I had never heard before, until I found a disco in Hull with quad 15" woofers and a rack of DC300's in parallel. It was a 70's vintage RC church converted into a disco, just across the river from Ottawa. I found it late at nite searching for the bass seismic waves.
Tony in Toronto.
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