Oh, that's very interesting, and even more reason not to pursue the "alternative IGBT" route. And this might explain why Forte spent a lot of time individually hand-testing each transistor and installing a little round sticker on them with the value, then having to assemble boards with transistors of the same value. Although it simplified the circuit (which these were all about), the time investment would make it hard to maintain a good margin in the "value price" market.True, but the Toshiba parts were specifically designed around audio. My own complaint with them was that they were a compound of Fet And BJT with no pin access to adjust relative biasing of the two components. This also complicated matching for parallel operation. In any case it is moot - Toshiba dropped the parts.
On Michael's behalf, (from what I've learned, anyway), the IGBT had adequate operation frequency (although not as good as a MOSFET) but much higher current capability, and that might have been what he was after. (?)
Second item of note: since I am now replacing components in the M6 board, I tested everything in the output stage that I could test while it was still on the board. Low and behold, the opposing transistor's emitter resistor was also blown open, so I removed it, as well as the N-channel IGBT for replacement. Is that just coincidence, or when one goes, will it commonly take out the other?
They never caught on in audio, and as MOSFETs got super low RDS-on resistances (sub milliohm, now) the IGBT no longer has much advantage anymore.
I remember reading that there were issues with latchup with those IGBTs also.
They quietly came and and disappeared from the scene pretty quickly. Must have been a reason other than cost ....
mlloyd1
They quietly came and and disappeared from the scene pretty quickly. Must have been a reason other than cost ....
mlloyd1
Right to both. I've removed the IGBTs from the M5 boards - how does one go about selecting a pair of MOSFETs that would most likely preserve that nice Forte sound from the many available?
Thanks
Thanks
I've purchased a set of Toshiba 2SC5200/2SA1943 MOSFETs for the model 5, and I will post the results when they are installed. 🙂
Sure they are Mosfet?...I thought they were bipolar.
And most likely fake...
Go for alternate genuine parts...
Which is why I told you to buy a ready populated board.
Any amplifier which changes the sound is interfering with it, so that particular thing is your choice.
And most likely fake...
Go for alternate genuine parts...
Which is why I told you to buy a ready populated board.
Any amplifier which changes the sound is interfering with it, so that particular thing is your choice.
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Yes, you did. And several other people have offered their opinions as well. And I want you to know that I appreciate all the people who have taken time to share their knowledge. 👍 🙂
Well Naresh, you might be right. On Digikey, a search for 2SC5200 brings up a bipolar STMicroElectronics part. What I purchased (after a short course on Duck Duck Go) was the Toshiba version of that part number, which is (supposed to be) a MOSFET - but doesn't even exist on Digikey. Probably the guy who made the video recommending them is the same guy who's manufacturing them in his kitchen and shipping them world-wide. Clever little dude, eh...? 🤓
Well, what's the worst that can happen? We try them out, take a listen, and see how we did. If anybody else has some suggestions for a good set of MOSFETS, let me know!
https://www.salconelectronics.com/product/4-mosfet-power-stereo/
They have many varieties of ready populated boards.
They work.
Learn from this site, no compulsion to buy.
And the parts will be the commercial variety, easily replaced. Mostly good Chinese.
The Keltron kit variants use Keltron (Sprague licensed) capacitors, which are very good. Worth the higher price.
China may be a better source for you for this type of populated board.
They have many varieties of ready populated boards.
They work.
Learn from this site, no compulsion to buy.
And the parts will be the commercial variety, easily replaced. Mostly good Chinese.
The Keltron kit variants use Keltron (Sprague licensed) capacitors, which are very good. Worth the higher price.
China may be a better source for you for this type of populated board.
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Well, let's see...
Nelson Pass says "I believe you should be able to fit complementary mosfets into that topology."
and NareshBd says "I told you to buy a ready populated board. Mostly good Chinese."
Hmmmm.... decisions, decisions....
Nelson Pass says "I believe you should be able to fit complementary mosfets into that topology."
and NareshBd says "I told you to buy a ready populated board. Mostly good Chinese."
Hmmmm.... decisions, decisions....
That doesn't mean that you can just magically drop them in without identifying and making any necessary circuit changes.
True, but I think the biggest concern is the bias voltages for the outputs. Your average mosfet will want something like 3 volts Vgs, but I don't have the figures for the IGBT's.
Thanks, Marcus - definitely no magic here. Could you maybe expand on that a little with some of the possible changes one should look for when changing output devices? Thanks
Nelson, are you talking about the bias voltage at the .47 ohm emitter resistor, or the trigger voltage controlled by (what is now) the150 ohm resistor at each gate? Thank you
Oh. Okay. So "identifying and making any necessary circuit changes" basically just boils down to "the bias voltages for the outputs". Doesn't seem like such an ominous undertaking. Thank you for pointing that out! 😉
Nelson, a DDGo search showed me that the Vgs bias voltage is the voltage from gate to source, or what I called the "trigger voltage" (is that even a word in the electronics world? 🤔), which comes across the 150 ohm resistor at each gate right now. Oddly, I don't see Vgs identified on either data sheet. Is this a generic voltage for MOSFETs in general, or unique to each transistor?
Nelson, a DDGo search showed me that the Vgs bias voltage is the voltage from gate to source, or what I called the "trigger voltage" (is that even a word in the electronics world? 🤔), which comes across the 150 ohm resistor at each gate right now. Oddly, I don't see Vgs identified on either data sheet. Is this a generic voltage for MOSFETs in general, or unique to each transistor?
It is also called Vth or V(threshold), the voltage at which the device turns on.
It is different for each device but generally between 2 and 4V for power devices.
Jan
It is different for each device but generally between 2 and 4V for power devices.
Jan
Thanks, Jan,
That is helpful! With a little research on Digikey, I see that each MOSFET has a voltage range of operation, a threshhold at which it becomes active (albeit minimally active at that threshhold), and a saturation point; and they are unique to each transistor.
Interestingly, IGBT transistors are not listed with the same parameters - my initial thought was that I could look up the Vgs and Vth for the current GT20D201/101 and try to get as close to that as possible with the new MOSFETs, but I don't seem to have the data to work with. Barring that, I'm thinking that I can measure the voltage between the gate and source on the amp now (at idle?) to be sure I am selecting transistors that will work with the current voltage, or adjust the Vgs by changing the 150 ohm series resistor.
I think there are still quite a few 25-30 year old Fortes out there, and they are really nice sounding amps available for a really nice price. It would be a shame if, as the IGBTs start to fail, they all became bookends. So I'm hoping that we can come up with a workable solution here that might help a few folks out.
That is helpful! With a little research on Digikey, I see that each MOSFET has a voltage range of operation, a threshhold at which it becomes active (albeit minimally active at that threshhold), and a saturation point; and they are unique to each transistor.
Interestingly, IGBT transistors are not listed with the same parameters - my initial thought was that I could look up the Vgs and Vth for the current GT20D201/101 and try to get as close to that as possible with the new MOSFETs, but I don't seem to have the data to work with. Barring that, I'm thinking that I can measure the voltage between the gate and source on the amp now (at idle?) to be sure I am selecting transistors that will work with the current voltage, or adjust the Vgs by changing the 150 ohm series resistor.
I think there are still quite a few 25-30 year old Fortes out there, and they are really nice sounding amps available for a really nice price. It would be a shame if, as the IGBTs start to fail, they all became bookends. So I'm hoping that we can come up with a workable solution here that might help a few folks out.