Its a linesource Dutchie , only 3db drop every doubling and z-min on the revised speaker is 1.3ohm, .85 was 12-22k range that has been rectified and its 1.3 currently . Regardless the amp has to keep chugging regardless if 1.: or .85 , some models used are also 8 ohms , others 4 nominal 2 zmin.
80- 100watts @8 ohm is whats desirable , with welding capabilities, 8pr gets us pretty close , this will make a great amp for you too Dutchie ..
You are a party breaker Jacco, those heatsinks will cure the thermall runaway of under-compensated OPS anyway...
Dutchie ..?
What's to say, a Locanthi triple is less easy to thermally stabilize as a double EF output stage. (and Hfe x Hfe x Hfe is a frigg.. large number
)If the output stage is undercompensated by the Vbe multiplier, bias goes up as the OS heats up and you have thermal runaway.
The complementary BD-pair in the Vbe multiplier may compensate for the different behaviour of the NPN/PNP devices in the output stage.
But even glued on top of the output devices, there's epoxy inbetween, thermal resistance between the die of the output device and the one of the BD. Both connect to the heatsink, so thermal resistance of the heatsink to ambient (the C/W) also becomes a factor in the equation.
Idle dissipation of the output stage is ~87W (130mA x 42V x 16)
In case of your 20A out, 440W.
1 : 5 (Jimbo Early effect will also pass by).
Even the Vas current is a factor.
Long story, the OS has to be overcompensated. (overcompensate too much, and distortion will not be pretty into a 1 ohm impedance)
A Vbe (Vgs) multiplier like the one on the schematic is what e.g. John Curl uses, on a MOSFET driver and BJT power device output stage.
For an (all BJT) EF triplet you'd have to think diode strings á la Leach & Locanthi, or enhanced 2-transistor Vbe multipliers that can be (e.g. tempco) trimmed.
Btw, check how poorly a classic Vbe multiplier performs : www.hagtech.com/pdf/vbe.pdf
(in case you missed this one : http://www.diyaudio.com/forums/atta...plifier-diy-ribbon-elektor-ribbon-amp-001.jpg I have the magazines with the articles, but in Cheese only)
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The 3dB is for distance, not voltage.
Yours looks ~60'' high, don't wander off too far. (definitely not an infinite line at 20 paces)
Jacco,
As we both know, there are many ways to make a Vbe multiplier, far too many to even list. The one I used here I always liked because with some selection of the BD trannies, one can find a matched pair with a Hfe of 120 or better, I've even made 140 on several occasions. In my experience, which may well be smaller than yours, this has enever failed to do the job, and do it properly.
Problems can, and probably will, appear when one uses the BDs with a low Hfe figure, and they can go down to 60, which is too low for most purposes. I have also used MJE 340/350 in the same configuration, but again, after some selection, as they too can vary quite a bit with their Hfe figures.
But, however you look at it, the heat sinks are the key. If they are very efficient, the overall heating up will be less, and vice versa. One of the reasons I'm sure which helped in my never having thermal runaway problems is the fact that I have always used very generous heat sinks, typically 300x40x100 mm German made Fisher types, with main body thickness of 10 mm. Also, I've never done any REALLY hard condition amps, such as pro amplification, when an amp is called upon to dissipate trenedous currents, at relatively high voltages, for long periods of time, I've done only home audio gear, which is never really pushed too hard. On such a heat sink, you can easily fit 4 pairs of 200W output devices plus drivers, enough for one decent channel, and have no problems under normal circumstances.
And, if push came to shove, I could always use the same heat sink, but 400 mm long, for still better heat exchange. Ultimately, I could use forced air cooling as well. It appears Wayne has pre-empted this by obtainig cooling fans as well, so I really don't see how this could go seriously wrong anywhere, worst case being that he gets to hear the air whoosh of the fans when he starts to irritate the neighbors with very loud music. Then, heat will become a problem, but that heat wears blue uniforms and has guns.
As we both know, there are many ways to make a Vbe multiplier, far too many to even list. The one I used here I always liked because with some selection of the BD trannies, one can find a matched pair with a Hfe of 120 or better, I've even made 140 on several occasions. In my experience, which may well be smaller than yours, this has enever failed to do the job, and do it properly.
Problems can, and probably will, appear when one uses the BDs with a low Hfe figure, and they can go down to 60, which is too low for most purposes. I have also used MJE 340/350 in the same configuration, but again, after some selection, as they too can vary quite a bit with their Hfe figures.
But, however you look at it, the heat sinks are the key. If they are very efficient, the overall heating up will be less, and vice versa. One of the reasons I'm sure which helped in my never having thermal runaway problems is the fact that I have always used very generous heat sinks, typically 300x40x100 mm German made Fisher types, with main body thickness of 10 mm. Also, I've never done any REALLY hard condition amps, such as pro amplification, when an amp is called upon to dissipate trenedous currents, at relatively high voltages, for long periods of time, I've done only home audio gear, which is never really pushed too hard. On such a heat sink, you can easily fit 4 pairs of 200W output devices plus drivers, enough for one decent channel, and have no problems under normal circumstances.
And, if push came to shove, I could always use the same heat sink, but 400 mm long, for still better heat exchange. Ultimately, I could use forced air cooling as well. It appears Wayne has pre-empted this by obtainig cooling fans as well, so I really don't see how this could go seriously wrong anywhere, worst case being that he gets to hear the air whoosh of the fans when he starts to irritate the neighbors with very loud music. Then, heat will become a problem, but that heat wears blue uniforms and has guns.
He won't hear the neighbours, the 'heat'.....or the fans........It appears Wayne has pre-empted this by obtaining cooling fans as well, so I really don't see how this could go seriously wrong anywhere, worst case being that he gets to hear the air whoosh of the fans when he starts to irritate the neighbours with very loud music. Then, heat will become a problem, but that heat wears blue uniforms and has guns.
Dan.
The 3dB is for distance, not voltage.
Yours looks ~60'' high, don't wander off too far. (definitely not an infinite line at 20 paces)
Total height is 76 in ..
Greetings pilgrims , did Borno kill the party ....
Good news on the home front , finally got around to updates and new motor system and revamped diaphragms have boosted performance beyond expectations, short story sensitivity is bettered by 10 db ..!!!!!
Now looking for a good SET amplifier and recommendations ....
Rhetorical ...
Good news on the home front , finally got around to updates and new motor system and revamped diaphragms have boosted performance beyond expectations, short story sensitivity is bettered by 10 db ..!!!!!
Now looking for a good SET amplifier and recommendations ....
Rhetorical ...
How about regular triode, in parallel banks of 50.
Though Mr Tent can vouch that I totally misbehaved during three days of hard liquor and a grand total of 5 hours of sleep/showers at the 2010 ETF, this thing still echoes in my aural sensory system.
etf2010/cg/PB270718
(as my history with Guido goes back to him being 25 years younger, my recommendation may be somewhat biased)
Thsts what I'm talking , go big or go home .....
Most potent poisons come in teeny weeny small glass ampules.
No, SETs, Square Emitter Triodes
(Russian dual triodes, which makes two 25-valve quadrants a 100-device PP output. Can think of very few SS amps with output stages of equal/larger number)
Perhaps because they don't need such massive output stages?
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