Leco amp stable 2 ohms

DjLeco

Moderator
Upgrading this amp http://www.forum.poweraudio.ro/viewtopic.php?f=64&t=19182 with newer versions of Leco Amp modules, with the recovered modules from it, I decided to make another Leco Amp with transformer and those 2 modules.


Output devices used are a little special with SOA of 2,5A/80Vce/1Sec, MJL21195 and MJL21196.
http://www.onsemi.com/pub_link/Collateral/MJL21195-D.PDF

Power transformer is from Crest VS1100, wich assures after bridge rectifier and storage capacitors, +/- 78Vdc in idle.

http://www.peaveycommercialaudio.com/media/pdf/vs1100_5-20-97.pdf

As storage capacitors I used 4 pieces of 12000uF, 2 parralel on rail + 2 pieces of 3300uF per rail wich is around 27000uF/rail or 54000uF total storage.

Is one amp real 2 ohm load per ch, output current limiting occuring at 35A rms.

As relevant, Crown Macrotech 5000VZ has current limit set at 30A rms.

Suporta full 4 ohm in configuratie bridge, sau 2 ohm/canal si ofera un sunet exceptional de calitativ, pe drivre suna demential, cit si in bass sau full range.

Freq range with less than 0,5db deviation at extemes of bandthwith is 5Hz-50kHz at full power/2 ohm (approximed on oscilloscope readings).

Some pictures during construction:









I made some tests on different dummy loads, 4 ohm, 2 ohm, and 1 ohm, also with music on real speakers:


Testing output current at 4 ohm/50Hz:

https://www.youtube.com/watch?v=BwVYN2zZTeU&feature=youtu.be

Testing output current at 2 ohm/50Hz:

https://www.youtube.com/watch?v=7qaz_T0hb4c&feature=youtu.be

Testing output current at 1 ohm/50Hz:

https://www.youtube.com/watch?v=_s_fFe3W46g&feature=youtu.be

Testing squarewave 2 ohm 50Hz+10kHz+20kHz+40kHz:

https://www.youtube.com/watch?v=V9vQmmy6zNE

Testing squarewave 8 ohm (standard rise and fall times measurement):

10kHz+20kHz+40kHz+60kHz:

https://www.youtube.com/watch?v=ojQ0OBJAVxs&feature=youtu.be

Linearity on output between 1000Hz and 100000Hz:

https://www.youtube.com/watch?v=1vpoI9xnJEM



And final test on music on real speakers Ch 1 loaded with 2 ohms, Ch2 loaded with 4 ohms, choose 1080p on youtube for max audio quality:

https://www.youtube.com/watch?v=IZ5flhHV8C0&feature=youtu.be
 
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DjLeco

Moderator
The moment of truth, wich represents output of amp loaded with under 1 ohm resistor, and shortcircuit the output too.

I put 1 ohm 1000W resistor, parraleled with another 4 ohm 300W resistor ro obtain around 0.8 ohms load+ wires resistance, to be around 0,85-0,9 ohms on binding post outputs of the amp.

One GOERTZ SHUNT 50Amps/100mV, where we read tension correspondent to that seried current on the circuit.

The maximum tension read (under clipping) was 71mV, wich corresponds to 35,5 Amps.

In that circuit on the first movie is seried one 25A slow blow fuse, to "see" the current on it, until get's RED and fails.

Movie with 25A fuse in circuit:


https://www.youtube.com/watch?v=FmxJ0CPngeY&feature=youtu.be


Movie without fuse and shorted output:

https://www.youtube.com/watch?v=wchyrZ7qLAk



The "dead" fuse:







Mine protection kills differential input stage, including VAS and bias too, and as you see if on 0,8-0,9 ohms, on "normal condition" is around 35,5 Amps on output, on shortcircuit condition, output current is limited at around one tenth, at 3,3 amps.

Most of "classical amps", limits on output in shortcircuit case, at the maximum output current available, forcing the final stage to dissipate alot of heat until fails if no overtemp protection acts quickly.

As instant the short dissapears, output is again able to offer 35A rms.
 
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