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Our Guitar Dept brought over an EBS HD350 that sounded distorted. I opened it up, and saw again (to my horror) the stack of folded aluminum heat spreaders that were supposed to be bolted down to the 3/16" thick aluminum plate were not even tightened down (with mgt screws bottomed out not going any tighter). Saw one of the 2SK2221 Renesas/NEC N-CH MosFET's cracked in half, that half of the output stage shorted.
Absolutely NO Thermal compound between any of the heat dissipator fins so no real way to get heat out. I've seen this now on four different EBS Amps, so I have to believe their concept of heat dissipation stops at the base plate. They are at least using insulator pads, though those are higher thermal resistance than greased mica.
Also, not having any service documentation, I'm looking at this amp, seeing 4 pair of N-Ch/P-Ch MosFET's straddling the supplies, Drains directly connected to the output buss. I guess that's how they're getting away without using individual low-ohm summing resistors as we're used to seeing.
No spec on Rds in the data sheets I downloaded.
I don't have any inventory of 2SJ352 P-Ch or 2SK2221 N-Ch Mosfets....only a collection of recently matched and batched IRFP240's and IRFP9240 on hand, that I use on the Ampeg SVT Pro series MosFET amps. What's the thought out there about using those in place of these Renesas/NEC or Hitachi MosFETs?
After asking our department manager if we own or EBS owns our inventory of their products, I find they own them, having them here for exposure with all the high-end clients that come thru using our rehearsal stages. I guess it's time to touch base with their engineering department, as this is just unacceptable manufacturing methods.
Absolutely NO Thermal compound between any of the heat dissipator fins so no real way to get heat out. I've seen this now on four different EBS Amps, so I have to believe their concept of heat dissipation stops at the base plate. They are at least using insulator pads, though those are higher thermal resistance than greased mica.
Also, not having any service documentation, I'm looking at this amp, seeing 4 pair of N-Ch/P-Ch MosFET's straddling the supplies, Drains directly connected to the output buss. I guess that's how they're getting away without using individual low-ohm summing resistors as we're used to seeing.
No spec on Rds in the data sheets I downloaded.
I don't have any inventory of 2SJ352 P-Ch or 2SK2221 N-Ch Mosfets....only a collection of recently matched and batched IRFP240's and IRFP9240 on hand, that I use on the Ampeg SVT Pro series MosFET amps. What's the thought out there about using those in place of these Renesas/NEC or Hitachi MosFETs?
After asking our department manager if we own or EBS owns our inventory of their products, I find they own them, having them here for exposure with all the high-end clients that come thru using our rehearsal stages. I guess it's time to touch base with their engineering department, as this is just unacceptable manufacturing methods.
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