Post by Owen Y on Jun 3, 2020 15:05:58 GMT 12
Part 1 - some take-outs: About design philosophy & voicing of some of the recent First Watt amps: " The SITs definitely give a nod towards triodes.... there's this larger market of people who are tempted either by tubes or the sound of tubes.... I would like to push my aim a little off the tube centre & grab the solid-state guys " About warm-up of SS amps: " Temperature makes a lot of difference.... it becomes a different amplifier as it warms up " About power cables: " We get big, fat, copper cable. We don't do anything exotic with power cable. "
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Post by Owen Y on Jun 3, 2020 15:11:39 GMT 12
Part 2: Hear what power amp/s Nelson Pass uses himself in his own living room.. The next SIT amp design - will use "big" SITs (industrial VFETs). Nelson recently purchased some Heil AMT drivers (which are being made again) - hear about his loudspeaker side-hobby. Steve Guttenberg is going to sponsor a Amp Camp Amp DIY build - " I can't solder & I can't see! "
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Post by Owen Y on Jun 3, 2020 21:50:24 GMT 12
About warm-up of SS amps: " Temperature makes a lot of difference.... it becomes a different amplifier as it warms up " We had a discussion thread on Warm-up time, a while ago.
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Pundit
Post by peter0c on Sept 20, 2020 16:18:15 GMT 12
A bit more on harmonic distortion from shop.ehx.com/vacuum-tube-faq/. Would any musician like to express an opinion? "The harmonic content of an overdriven tube amplifier consists primarily of 2nd order and 3rd order harmonics with some 4th order harmonics. The harmonic content of an overdriven transistor amplifier is primarily 3rd order with suppressed 2nd order harmonics. 2nd and 3rd order harmonics are the most important from a viewpoint of electronic distortion. Musically the 2nd harmonic is an octave above the fundamental and is almost inaudible, yet it adds body to the sound, making it fuller. The 3rd harmonic is a musical 12th. Instead of making the tone fuller, a strong 3rd harmonic makes the tone softer. The odd harmonics (3rd, 5th, etc.) produce a "stopped" or "covered" sound. The even harmonics (2nd, 4th, etc.) produce a "choral" or "singing" sound. Adding a 5th to a strong 3rd harmonic give the sound a metallic quality that gets annoying in character as the amplitude increases. A strong 2nd with a strong 3rd harmonic tends to open the "covered" effect. Adding the 4th and 5th harmonics to this gives an "open horn" character. The higher harmonics, above the 7th, give the tone "edge" or "bite.""
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Post by colinf on Sept 21, 2020 2:47:25 GMT 12
Nice link, thanks! I guess anyone wanting to know a little more on valves would do well to read this. It has a section on valve testers as well. Air has harmonic distortion as well. Next to the point of vibration, a compression heats the air slightly and causes the air to increase density. Similarly a rarefaction cools the air slightly and reduces its density. Because a rarefaction reduces the air density the air pressure reduces by a lesser amount than the increase in pressure caused by increased density for a compression. So a little 2nd harmonic is produced. The amount of 2nd is partly used by the ear to detect how far away something is. An amplifier with positive 2nd harmonic would make the sound appear closer/more forward. Negative second makes the sound more spacious/distant. (At least I think I’ve got that right, I’m not an acoustician. Acoustic engineers please chime in!)
AMR-iFi R&D
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Pundit
Post by peter0c on Oct 4, 2020 12:10:39 GMT 12
Probably the wrong thread (First Watt F8) but this set me thinking. The F8 has .012% second order negative phase (only) distortion which I think I'm correct in saying is independent of gain and .015% THD distortion at one watt. Saint Nelson arrived at this negative phase figure by having early customers report their preferred dial position on their SIT1s (the knob and dial altered the phase and level of 2nd order distortion although this wasn't explained at the time) at this particular point. No informed consent for this 'blind' experiment though! Now let's revert to conventional speakers. When a positive ac voltage is first applied the cone moves forward and to complete the cycle the reverse occurs. In a positive cycle the cone is dampened by the air to the front (i.e. your room) and to an unknown extent, a partial vacuum in the cabinet. In the negative cycle the compressive effects of the cabinet provide the dampening (ideally the total speaker Q should be .7) and if it is a ported cabinet, there is no dampening whatsoever below the port tuning frequency. So conventional cone speakers in a cabinet are inherently unbalanced at least at low frequencies, which might partially explain the popularity of OBs and planar / electrostatic speakers which also have the same profile (i.e. not convex and concave cones) both sides. So my friends what does this mean in terms of positive and negative phase even-order distortion from the speakers (rather than just the amplifier) and what does it mean in terms of matching amp and speaker combinations?
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Post by Citroen on Jan 26, 2021 8:41:08 GMT 12
Steve's latest chat with Nelson Pass. He designs amplifiers for First Watt and Pass Labs.
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