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In Reply to: RE: Don't Know That !! posted by cpotl on June 01, 2015 at 00:53:55
The 60/120Hz hum/buzz would probably cause the driver's diaphragm some excursion but make little noise through the horns . I have no doubt that 250mV ripple would cause some nasty distortion .
I spent a great deal of effort to get a dedicated amp quiet enough on my TAD TD4001 which incidentally also have 110dB sensitivity . Even 1mV of ripple at the output terminals was unbearable . 250mV would be horrendous !
Al
Follow Ups:
You are confusing mVAC at the output transformer's secondary, with the primary. The mVAC on the primary can be much higher as it is stepped down by the turns ratio of the output trannie, primary to secondary.
Also, with a DHT, there is a certain amount of mVAC from the DHT's filament when we AC excite a 2A3's Ef.
Jeff
Ok , maybe I got confused with that but what you suggest , even at the output termianls would be horrible on 110dB drivers . I aim for 1mV maximum at the output terminals with 97dB speakers . I couldn't manage that even with DC filaments with that amount of ripple . How quiet are your amps ? What about pentode SE ? What sort of maximum ripple would you suggest is allowable ?
Al
Hiah Al,Generally, I think building a supply for lowest hum is a mistake in a amplifier.
An amp that "plays the music to us in the music's time frame, and not the amp's time frame, with maximum possible dynamic contrasting", is the goal I seek and value the most in designs. This requirement and " lowest possible hum" are at odds with each other, design wise.
Playing back the music in music's time, is the one thing, for example, that a no-feedback amp can begin to give us.
Well, today I layed my main supply caps, and Rk bypass caps into my Type 45 amp chassis. I coated the chassis and the bottom of the caps heavily with GE Silicone II, and mated them together, so that , when cured, the DC LINK Vishay and WIMA caps will be elevated about 1/4 of an inch off the steel chassis. Caps sound better when they don't touch the chassis, and, when they don't touch each other.
BTW, that fellow Barry in London, "Smart845" that I wanted you and Andy Evans to visit and give me a report, has started a blog on audio. Check out his center tapped 45 Globes, a new design from EML.
http://smart845.blogspot.co.uk/
As for SE Pentode, I have no idea what kind of supply that needs. But I KNOW G2 has to be super stable and ideally - separate from the B+ supply, to do it right.
But, why would anyone want to build a Pentode output stage, and have two things going on at once, when simple triodes like the 2A3 and 45 exist ?? That is why I never messed with SE pentodes.
Regards and best wishes,
Jeff Medwin
Edits: 06/03/15 06/03/15
I don't know why you think that I go for minimum hum . I go for a power supply that provides acceptable hum and the best sonics using what iron and caps I have available in stock .
SE pentodes have far less immunity to power supply ripple so a power supply for a SE pentode needs to be approached slightly differently to that of a triode . As for the extra grid and feedback , so what ? If you have not experimented with SE pentodes , you should
I have told you and your creepy cheerleader this already . I don't have the time or the inclination to go and listen to someone elses amp who is a nightmare journey the other side of town .
Al
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