Hi all, I normally don't venture out of the car audio forum, but Perry Babbin suggested I look for some advice here.
I have an a/d/s amplifier that I'm working on. It was a bit of a Frankenstein from several previous techs repair attempts. I've finally isolated my major issue, and it is that sometime in the past someone replaced the 2SJ77/2SK214 mosfet complimentary pairs with what appear to be counterfeit parts. The 2SJ77/2SK214 mosfets have a lead order of Gate Source Drain. These counterfeit transistors are all the more common GDS lead order.
The originals pairs are now long obsoleted and I'm looking for some possible substitutes. The tabs are not needed, so the package does not necessarily have to be to-220. They are sandwiched between the board and the heat sink though, so the package would have to be of similar thickness.
Thank you all in advance!
Jason Campbell
I have an a/d/s amplifier that I'm working on. It was a bit of a Frankenstein from several previous techs repair attempts. I've finally isolated my major issue, and it is that sometime in the past someone replaced the 2SJ77/2SK214 mosfet complimentary pairs with what appear to be counterfeit parts. The 2SJ77/2SK214 mosfets have a lead order of Gate Source Drain. These counterfeit transistors are all the more common GDS lead order.
The originals pairs are now long obsoleted and I'm looking for some possible substitutes. The tabs are not needed, so the package does not necessarily have to be to-220. They are sandwiched between the board and the heat sink though, so the package would have to be of similar thickness.
Thank you all in advance!
Jason Campbell
GDS is usuall vertical mosfets.
GSD is usually lateral mosfet.
It will probably work ok with verticals but lack of source resistors wont make it react to heat so good unless it has a proper Vbe multiplier.
Maybe they have turned down bias current to compensate ?
GSD is usually lateral mosfet.
It will probably work ok with verticals but lack of source resistors wont make it react to heat so good unless it has a proper Vbe multiplier.
Maybe they have turned down bias current to compensate ?
Well, this shows how little I know in this subject. I was not even aware what a lateral mosfet was until you said that and I looked it up. I normally work only on automotive amplifiers, and while I'm no stranger to mosfet based linear amplifiers, this is the first time I've run across these fets. Typically mosfet based car audio amps use irf540/9540, irf640/9640, or similar, which after my brief Google education appear to all be "vertical fets".
How would one go about narrowing down a distributors offering to these lateral fets? Basically I'd love to find replacements that are the same lead order as the stock parts, I just don't know how to start looking for them. There has to be a better way than finding similar specced parts then pulling the datasheet to find out if it has this lead order.
Thank you!
Jason
How would one go about narrowing down a distributors offering to these lateral fets? Basically I'd love to find replacements that are the same lead order as the stock parts, I just don't know how to start looking for them. There has to be a better way than finding similar specced parts then pulling the datasheet to find out if it has this lead order.
Thank you!
Jason
At least to the date of their release, those amps were among the finest for sound quality that could be obtained. Those latfet drivers are a big part of the reason. There is no substitute available. If you want to restore this amp you might want to see if you can cannibalize one from eBay. If you end up fixing it correctly, certainly don't waste it on a subwoofer.
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Lateral mosfets are very rare now and when you can find them they are usually very expensive.
I think Profusion is about the only seller left selling laterals. They might have something compatible.
If not then its probably down to ebay if you dont mind risking fakes.
The rareness of laterals is probably why your amp was converted to verticals.
I think Profusion is about the only seller left selling laterals. They might have something compatible.
If not then its probably down to ebay if you dont mind risking fakes.
The rareness of laterals is probably why your amp was converted to verticals.
I designed a lateral mosfet amp a few years ago.
I think the mosfets were about £4 then.
I recently looked at making some another and was shocked to find the high power ones are about £20 if you factor in p+p !
So just built up a vertical mosfet amp instead.
To be honest I cant tell the difference in sound between lateral and vertical mosfet amps. So laterals are wasted on me. Someone with better hearing will probably disagree.
The amp wasn't converted to verticals, it has correctly labled parts in it, but those parts test out to have the VGS lead order and are the whole reason that the amp came to me for repair. I assume one of the previous techs went the eBay route and ended up with counterfeit relabled vertical fets.
It was a jfet input bipolar out amp of beautiful discrete simplicity. I wish I still had the schematic to share. Back in the day it was easy to tell when the salesmen left the ads amps selected while going past the autosound display area.
But verticals and laterals have different pin outs.
So you cant swap them without some pin twisting.
The ebay route should ok if its a working amp they are taken from.
I got caught out with ebay mosfets that lasted 10 minutes !
I unplugged my soldering iron and the glitch on the mains blew the mosfets.
So I replaced them with RS genuines and try as I might I couldn't get glitches on the mains to blow them.
The fakes must have had low breakdown voltages and the glitch killed them.
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Exactly, that's my point as to why I assume they are counterfeit. These parts are labeled j77/k214 but the center lead is most assuredly a drain lead, not source.
I too wish you had the schematic. This had been a challenge to work on, mostly due to the fact that there is no component silk screen on the board and that it's been through a few people attempting repairs in the past. I've spent a lot of time just undoing work that's been done just to figure out what the issues are.
Here you go. They are kind of tough to photograph. I'm curious why you think they aren't fakes with just the discussion so far. I can't see why the lead order would differ from the datasheet except if they were fakes...
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Thank you for taking the effort. You see, I was curious and doubtful, but now I am certain: they are clearly fake.
It was no big trouble. It was more difficult to remember to take the pictures while I was in the shop. I have 10 pair coming from China. They look a lot more respectable than these, but I fully expect them to be fakes as well. I somehow doubt that there were 10 pair of these in a Shenzhen market stall just waiting for me to buy them... I'll post more pictures of them once they are here...
Thanks,
Jason
Thanks,
Jason
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