Old-school Earthquake/Hifonics power fets

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Good evening guys, does anyone have an open amp like this can share the part numbers on the power supply fets (gate resistors are 220 ohms).
Or by design if there are any replacement that are considered stronger or a much better subs. I really don't have the name plate for the amp but I know it's either Hifonics or an Earthquake.


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If the amp has a regulated power supply (fairly sure it does), the reduction in duty cycle could be masking a serious problem if deadtime isn't built into the system. If you ever get the amp back on the bench, reduce the 12v supply voltage to as low as possible without shutting down the amp. If the idle current increases at the lower supply voltage, there is insufficient deadtime.
this is interesting as it looks to be a PA2300 and I'm actually working on a PA4300 at the moment and the FETs are IRFZ44N with 220ohm gate resistors. I'm looking at swapping the gate resistors to somewhere between 68 to 100 ohms on Perry's advice :) I'm guessing modern mosfets are built different to original mosfets? maybe have a different capiacitance?

good look to the project and I look forward to following it!

Gate resistors

Do not change the gate resistors to lower values.

The PA2300 was an almost direct copy of the Hifoncs Zeus without the multiple rails.

The reason I designed in 220 ohm gate resistors in the Hifonics was because of leakage inductance in the main transformer and this helped to slow down the MOSFETs

Changing to low Qg MOSFETs will not help as the leakage inductance is still these.

Check that you have at least 0.25v of deadtime measured at pin 4 of the TL494

Steve Mantz
Zed Audio
If you don't recommend changing the gate resistors, what would you suggest if the amp draws excessive idle current due to cross conduction when the duty cycle is at it's greatest?

I've had similar amps that, with identical part number FETs as replacements, would have an increase in current draw and significant heating.

The pa2300 has multiple rails.


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Hi everyone,

I went up and down this thread and I'm a bit confused as in post #1 Formas did put a photo of an "exhumed" amp and you all identified as PA2300 by Earthquake, thereafter Perry shows a photo in post #13 stating it PA2300 but it is evidently different than the first one showing the second toroid on m.b. while the one posted by Perry it has not of course...
Are they different releases of same PA2300? Please anyone can clarify this?

As I have the 1990 Earthquake catalog have being famous for showing in the central pages the PA2300 reversed pics simulating a very big amp -what PA4300 would have been a couple years later- there, anyone could have seen 1 only toroid in the m.b. so, no doubt only Perry's pic truly is a PA...

Re. Hohmann name, in the same page in catalog you can see Earthquake Sound Co. heading, at the time located in S. Mateo, CA was a branch of / or likely owned by HERMANN HOHMANN International Co., and Factory at Lang Road, Burlingame so close to AUTOTEK plant in Cowan Road, sheer chance...!

Pls Abuzafi, can you explain what law-suit did happen... that time I was selling Earthquake and Autotek as representative in my region and I didn't realize any of such a cases... also I was asking myself who this Hermann Hohmann was as in 1993 I met Mr. A. Sahyoun owner and export sale manager of Earthquake and he said chief owner was his brother Joseph, company's chief engineer too...
As for my difficulty to shot good pics I avoid for now to post photo of the catalog (of that time I only keep PA2075 and PA2040, not big ones...) but if anyone want to watch, just ask to....
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