Has anyone here ever contemplated an output transformer for a transistor amp ? It would make for nicer voltage levels inside the amp ( multiple devices at low voltage +/- 55V ) . The amp could be direct connected also . An auto transformer could be used , it might be better .
Some people say if class D has a sonic advantage it is the need to remove the modulation carrier wave . Sony in 1979 told me that the choke to be obvious and rather nice . You never know the output transformer might do the same . As a way of minimizing crossover distortion it is good . The amp would run at a constant gain without a volume control . The volume would be by taps . Doubtless a level ( tweak ) control a nice idea . It means you could eliminate much nasty circuitry like the volume pot . Tweak could be by feedback loop gain ( +/- 3dB ) .
If you know about transformers . Is there a sensibly priced metal better than M6 ?
Some people say if class D has a sonic advantage it is the need to remove the modulation carrier wave . Sony in 1979 told me that the choke to be obvious and rather nice . You never know the output transformer might do the same . As a way of minimizing crossover distortion it is good . The amp would run at a constant gain without a volume control . The volume would be by taps . Doubtless a level ( tweak ) control a nice idea . It means you could eliminate much nasty circuitry like the volume pot . Tweak could be by feedback loop gain ( +/- 3dB ) .
If you know about transformers . Is there a sensibly priced metal better than M6 ?
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100V line systems do this as per normal....EWIS systems require amps that run on 24V DC......transformer coupled outpputs is the norm.
I agree, D Class amps could well benefit with a suitable output trannie....1:1 would work, maybe different ratios might be subtly better.
Tapped output autotransformer and related switching would be far too expensive for typical gear.
Dan.
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I think McIntosh uses output transformers on some SS amps.
I don't know if it is possible to extrapolate from microphones but SS mics with output transformers sound more 'tubey' than tube mics without them.
Agreed - I think the HF roughness is a result of very poor PSRR at those frequencies and insufficient attention paid to supply decoupling. But I'm relatively new to the class D game....
I was thinking only yesterday about putting a trafo on the output of class D - but I reckon a similar effect can be obtained by paralleling chips. Gotta do a fair amount of experimenting....
I was thinking only yesterday about putting a trafo on the output of class D - but I reckon a similar effect can be obtained by paralleling chips. Gotta do a fair amount of experimenting....
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This is a Stan Gould ( 1988 ) Class A + H amp said to be used by Turbosound ( Flashlight and Floodlight amps ) . It has high efficient ( 70 % compared with AB 52% ) and real 20 W class A .
Interesting to look at class D . Usually feedback of 20 dB is about the limit . This requires high intrinsic linearity . Seeing as Hypex do OK they must be highly linear . The Hypex amps are very simple ( deceptively ) . If not the problems would get out of control . Thus by default they make an amp in my style .
My class AB output transformer is in fact a gear box ( auto TF ) . As I think Dan was saying not unlike 100V line when wanting output above the rms of the amp direct . My proposal was to use the transformer as a volume control . Just think how nice to use an amp always at it's best linearity . Also the drive into difficult loads would be excellent at critical listening levels ( < 10 V rms ) . I dare say it rolling off at 60 kHz no bad thing . Feedback taken which ever way works best . I will have to try a mains variac and see where is goes ( smoke ? ) . It might not be as awful as it seems . I tried a toroidal mains transformer as output device and was rather surprised .
PSU design seems to be important . All the usual things . Use a scope and analyzer to see what's going on inside the PSU and seek solutions . I really don't think SMPS is a good idea as it isn't synchronized with the output oscillator . Make the PSU as large as you would for class AB . The project I did recently didn't have that luxury which caused me much trouble . If the RF that comes from the amp is only the self generated stuff I am reasonably happy to say as good as most class AB .
My PA friends say Class AB 100 kg ( 220 lbs )
Class H 50 kg
Class D 25 kg
Most prefer class H on all counts ( Turbosound ) . Broken backs v sound quality .
Cant say i have ever heard a Class-H amp, name names ...
Carver is close . Many car stereos . All variants of Hitachi Dyna-harmony class G amps .
Thoughts Dvv ?
http://www.vxm.com/21R.69.html
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Courtesy of ESP Audio , a concept class G circuit . If the rails are changed the lower circuit can be class A . It could be 16 W 4 R and reverting to AB if above that ( biasing using Vbe as here will do that ) . What I like about this circuit is the simplicity . Sure it will have switching spikes . These are in some ways easier to deal with than AB distortion . If the lower amp is class A a very nasty problem is avoided ( AB ) . If you think about it two simple switching problems are better than one impossible class AB problem . Dvv your fix for AB is about the best you can do . It is highly frowned upon by book writers . However the idea that a bias tracking system works as they say I found to be unlikely . The music itself alters bias .
Dvv your amp behaves almost like a class G where the A bit is a couple of watts . You too have two spikes ( gm doubling ) . Why not ? At least then it isn't a kazoo . Under-biased AB ( B ) has MP3 effects . Sometimes called optimum bias class B . I have doubts it is . That doubt is I never got the bias to stay where it should . I used examples given as perfect , they were not much better .
Don't dismiss Carver . The Sunfire class AB with tracking PSU can do very high current .
Bob Stewart's Meridian 105 was said to be a totem-pole as in the early days . It isn't . Dvv it echos your amp a bit . I liked it especially with Gale 401's or LS3/5A . Totem pole ( Bean stalk ) and class G look similar .
http://www.meridian-audio.info/public/105_v1_service_manual[3908].pdf ( Page 10 )
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Of course, the weight ratio between linear supply and smps is easily 2:1 or more, so put it in a matrix.
From what I heard, pa has pretty much turned to class D for new investments, for mobile approaching 100 %. Also because it sounds great.
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