High Current Leach/leach super amp

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A Crown VZ5000 has kind of a wimpy power supply, it only goes up to 2.5KW at 2 ohms (stereo) from 2KW at 4 ohms. If you use a bigger transformer it will do more.

The VZ5000 is a bridged design running on ±82.5V with only four pair of MJ21195/96 per half, a total of sixteen outputs per channel.

The MJ21195/96 have 240W SOA at the 80V the amplifier runs at, and only cost USD$2.46 in small quantity.
 
bowdown,
i hope someone share a step drive solution for your quest,
this is according to DJK,
The AB International 1100A uses the Leach topology with a tiered power supply and does 1000W+1000W@2R with only three pair of MJ15024/15025 with rails at +/- 0, 48, and 95VDC.
isn't it great?rather than going on 14 pair? better use tiered a CLASS H LEACH:)
 
2000W into 2r0 requires 89.4Vpk at the resistor.
The resistor will draw 44.7Apk

Now replace the 2r0 resistor with speaker/s that have an effective impedance of 2ohm.
The reactive load can draw up to 130Apk.
A 3pair output stage using conventional audio BJTs cannot deliver that current even if the ClassG or ClassH or Classx,y,z is implemented.
 
"A 3pair output stage using conventional audio BJTs "

True, but four pair might handle the current.

The 2x 2500W/2R rated Crown VZ5000 is a class H bridge with only four pair in each quadrant (16 outputs per channel). Originally they used the MJ15024/25, and currently use the MJ21195/96. 15A driver transistors are used. The outputs are mounted without insulators on a copper tunnel for best thermal performance.

You can always use more devices. I probably would, they don't cost that much.
 
Gents:

Don't forget that the W.M. Leach Super amp has a totem pole (cascade) output stage that greatly increases the SOA by dividing the Vce seen by each power transistor by 2 thus allowing each transistor to operate in a much more favorable area of the SOA. These are not normally labeled as output pairs but rather output quads as it takes at least 4 output transistors to complete an audio cycle instead of standard two.

Cheers’

Philip
 
bowdown,
i hope someone share a step drive solution for your quest,
this is according to DJK,
The AB International 1100A uses the Leach topology with a tiered power supply and does 1000W+1000W@2R with only three pair of MJ15024/15025 with rails at +/- 0, 48, and 95VDC.
isn't it great?rather than going on 14 pair? better use tiered a CLASS H LEACH:)

It is not that difficult to do with an S-Leach or any similar amp. A few component changes, a commutation diode (and snubber, not shown) and you're on your way.
 

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2000W into 2r0 requires 89.4Vpk ..........
The reactive load can draw up to 130Apk.

"A 3pair output stage using conventional audio BJTs "

True, but four pair might handle the current.
How?
What would be hFE for a peak transient current for 130/4A=33A?
What current would the driver/s need to supply?
What would be the hFE of the driver/s at that peak current?
What would the Pre-driver or VAS need to supply?

The impedance seen at the output reflects back through the stages.
 
How?
What would be hFE for a peak transient current for 130/4A=33A?
What current would the driver/s need to supply?
What would be the hFE of the driver/s at that peak current?
What would the Pre-driver or VAS need to supply?

The impedance seen at the output reflects back through the stages.

Nobody said that distortion would remain at 8-ohm levels driving a sub-2-ohm reactive load. If it delivered 90A peak or so safely without gross distortion, it would be good enough for most users to bridge into a 4 ohm 2x18 (or labhorn, or whatever). At 22.5A, the Hfe might be about 8 which is tolerable with a triple EF and a TO-247 or TO-3 driver.

And if you've ever studied the impedance curves of actual speakers you'd know that whenever you hit a local minimum, it's always pure real, as in resistor. It's at the point of maximum rate of change that you get the largest phase angle. And a speaker with a 90 degree phase angle (zero power factor) would produce no sound at that frequency, which is undesirable.
 
"How?"

Ask Crown. Ask Carver. Ask AB International.

Carver just uses a double EF connection, Crown and AB International use a triple.

The Crown will drive 2.5KW/2R without a problem, some guys have loaded them down even lower. The ODEP lights might flash when pounding four 18" 8R woofers in parallel, probably 1R5 and a 45° load (but not at the same frequency).

You might get very alarmed to see what Carver does in the PM1.5, ±125V and all the current through one pair. I doubt the gain is higher than 5 at the 25A peak current these will deliver at 4R. The 2SA1302/2SC3281 have a gain of about 100 at that 5A, so they need about 50mA peak current from the front end (a complementary pair CFP driven by an opamp).
 
2000W into 2r0 requires 89.4Vpk at the resistor.
The resistor will draw 44.7Apk

Now replace the 2r0 resistor with speaker/s that have an effective impedance of 2ohm.
The reactive load can draw up to 130Apk.
A 3pair output stage using conventional audio BJTs cannot deliver that current even if the ClassG or ClassH or Classx,y,z is implemented.

sir andrew please teach us more of CLASS X,Y,Z:D
 
The reactive load can draw up to 130Apk.

It is high time you better show me any link or any piece of valid proof of information which says reactive loading apart from making voltage and current shift in phase, also draws more current than with resistive load of some finite ohmic value, say 2 ohms.

2000W at 2 ohms won't take more than 50Amperes peak , agreed.

How come with reactive loads it will take upto 130pK.

Are you ignoring the DCR of voil coil which doesn't changes and remain somewhat constant and variation is little even in high temperatures.



Kanwar



Below is my 4kw 3-step Class-H module, 12 pairs of 17A devices at output stage capable of more than 200A pk, Triple EF stage.
 

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Cordell's recently published book confirms the 3times as acheiveable for the test conditions he used to show the effect.

2000W at 2 ohms won't take more than 50Amperes peak , agreed.
50Apk into 2r0 is equivalent to 2500W into 2r0 for a sinewave signal.

A 44.7Apk or 50Apk limit will cripple the output when feeding a 2ohm speaker. This will be current clipping.
 
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A 44.7Apk or 50Apk limit will cripple the output when feeding a 2ohm speaker. This will be current clipping.

Probably. Four 18's in parallel with a 5.6 ohm DCR will go down to about 1.4 ohms at box tuning. So instead of 50A, you need 70. But not 130. The woofers just simply can't draw any more than this unless you feed them more voltage. Any other effect, be it reactance, back EMF, or horn loading will cause the impedance to RISE not fall. So design for 80+, and call it good.

At other higher frequencies the impedance may indeed go down, possibly in the midrange (where bandbpass gain may be employed to match sensitivities) but it could be easily analyzed or measured to see if more current is desirable. At these higher frequencies the durations for these overloads are so short that they won't hurt anything and won't even cause the protection cirucits to fire. If it causes distortion, you can design for more current. But in these applications you won't be using a 2kW amp, you'd be using only 100 or two.
 
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