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Cactus Sound ELT.12 - Output Replacement
Cactus Sound ELT.12 - Output Replacement
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Old 21st May 2019, 07:46 PM   #21
Perry Babin is offline Perry Babin  United States
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The biggest problem I have with these big amps is that the owner will reconnect it the same way and blow it again... and expect it to be repaired at no cost.

If an amp this size comes in, I'll check it to see whether it's working or not but if it's blown, out it goes.
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Old 21st May 2019, 07:55 PM   #22
MarioRestucci is offline MarioRestucci  Italy
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Quote:
Originally Posted by JMFahey View Post
Sorry for this, but ... do you think that given the massive destruction it´s worth trying to repair it?
I´m seeing 64 MosFets per amplifier in that picture, a massive short which cracked half of them and shorted the others must also have blown traces ... plus I don´t think you have a Service manual or at least a schematic.

I worry final repair cost (including your Bench time of course) will exceed replacement price.

Happens to me many times, customer does not want to pay the estimated bill , plus he´s typically impatient, and just replaces it.
The customer accepted the quote I proposed and given the difficulties in finding original components, he agreed to wait for the right time to avoid doing other damage by going too fast.
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Old 23rd May 2019, 03:28 PM   #23
MarioRestucci is offline MarioRestucci  Italy
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Back on this damn amp:
I excluded the IXYS because I realized that I can run into problems.
I decided to solve by choosing a mosfet with a VDS far superior to IRFP4242.
FDH44N50 support the same current and have a VDS of 500V, so I believe that we are far above the rail voltage avoiding overvoltage problems and various explosions.
Also taking a look at the datasheet:
https://www.tme.eu/Document/435ad476...2/FDH44N50.pdf
even the on and off times seem to be almost compatible and should also be easier to drive.
What do you think about it?
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Old 23rd May 2019, 07:52 PM   #24
manlog is offline manlog
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Quote:
Originally Posted by Perry Babin View Post
The biggest problem I have with these big amps is that the owner will reconnect it the same way and blow it again... and expect it to be repaired at no cost.

If an amp this size comes in, I'll check it to see whether it's working or not but if it's blown, out it goes.
How So Much RIGHT you are here, Perry...

Day by day we have looked at wattage of MOBILE amplifiers going up and up to iper-galactic numbers and most of their users ignoring totally the basic Volt x Ampere law.
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Old 23rd May 2019, 08:35 PM   #25
caraudioguy2100 is offline caraudioguy2100
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Wouldn’t the IRFP4868 work for this amp ?

Asking this because they are used in an Orion 8k very similar design
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Old 23rd May 2019, 09:02 PM   #26
MarioRestucci is offline MarioRestucci  Italy
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Quote:
Originally Posted by manlog View Post
How So Much RIGHT you are here, Perry...

Day by day we have looked at wattage of MOBILE amplifiers going up and up to iper-galactic numbers and most of their users ignoring totally the basic Volt x Ampere law.

I don't understand your comment!
irony? what are you referring to?



Quote:
Originally Posted by caraudioguy2100
Wouldn’t the IRFP4868 work for this amp ?

Asking this because they are used in an Orion 8k very similar design


Probably ORION 8k uses these because it doesn't have a high rail voltage like this amplifier.
IRFP4868 has 300volt VDS but it is not declared for VDS (avalanche) which (correct me if I'm wrong) allows a surplus of rail voltage at times when, at rest, or when the battery pack of your system is in great shape and the voltage it is higher than 14v.
As this CACTUS reaches voltages close to 320-330v at 14.4v of battery voltage, IRFP4242 can guarantee up to 360v, IRFP4868 no!
Perhaps in the ORION 8K the rail voltages at 14v are more contained and the 300v of IRFP4868 can keep these at bay.

Anyway, what do you think of FDH44N50?
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Old 24th May 2019, 03:52 PM   #27
MarioRestucci is offline MarioRestucci  Italy
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Nobody? anything?
I know that many of you will think that to know if they are okay, I have to try, I want to know something absurd.
Unfortunately, sometimes these components also cost a lot of money and buying them, only to discover that they are not suitable or worse still break them at the first ignition, it would mean throwing a lot of money into the garbage.
FDH44N50, as well as other mosfets I've noticed, cost between 5 and 7 euros each, meaning 140 € thrown away.
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Old 24th May 2019, 04:01 PM   #28
Perry Babin is offline Perry Babin  United States
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This isn't the answer you likely want but... you had the choice to refuse the repair as soon as you saw the parts were unavailable.

In this business, there is little support and there may not always be a perfect solution. Anyone who has been in this business for any length of time has wasted time and money. It's part of the cost of doing business.
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Old 24th May 2019, 05:51 PM   #29
manlog is offline manlog
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Hi Mario,
you probably are misunderstanding my post and you shouldn't have to as I did clearly quoted the post by Perry I was referring to... so no obscure sense or ironic, just what it is... however you just begun this thread as follows, remember?:
Quote:
Originally Posted by MarioRestucci View Post
Good day everyone.
I just opened a CACTUS SOUND ELT.12 amplifier (13.5kw amplifier).
I found the power supply exploded and some output mosfets shorted.
I really believe this is the reason for the failure.
Due to the careless owner, too low impedance or limited supply current, the output section gave way and put the power supply under stress which then exploded. ...
so, you suggested and advised a "careless owner, too low impedance..etc" that is what is day by day happening (good for technicians and labs?!) as in this forum are recently more frequent requests for "tenth thousands watts" amplifiers dead, I saw, and you all, guess...
I was pointing out we are in a CAR Audio forum, or anything that has to be mounted in a mobile machine driving around cities and countries streets.. (hoping degrading our one-planet as minus possible)... and if these thou'ds watts beasts are used in spl contest&shows and they got blown as well (that's sure the most cases around) would you define a professional installer that audio system owner?

Going back to your issue about which output fets choose between fdh44 I -modestly- find in agreement with caraudioguy2100 for irfp4868 which are higher amp than fdh and much similar to the original in RDS and other specs... this considering that the owner -as you advised- has a very low impedance load and it would request higher amperage at output stage.... while voltage could not increase unless anyone would modify vehicle alternator or adding 2volts cells and similar artifacts...
good evening
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Old 10th June 2019, 06:53 AM   #30
MarioRestucci is offline MarioRestucci  Italy
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Back to this amp...
I finally had time to install the new mosfets (FDH44N50):
For safety, before installing the new mosfets, I checked all the diodes in parallel with the 22ohm resistors, they were all good.
Since the FDH44N50 is easier to drive, I replaced the 22ohm gate resistors with 33ohm.
I installed the new mosfets only on one of the two amplifiers (remember that this amplifier is a "2 bridgeable channels") and I turned it all on.
The amplifier works and I have rail-to-rail oscillation, but the new mosfets heat up quite quickly and by observing the signals on the gates of the high side and low side mosfets simultaneously, I realize that while the high side switch ok, the low side has a small defect (perhaps ringing) which keeps it slightly in conduction when it should be the high side in conduction.
I was thinking of reducing the value of the pull-down resistor (gate to source) to force mosfets to shut down faster. What do you think?
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