Aspringv,...or not, perhaps. I used a value of 0R68 for R1 (instead of the listed 0R56) mainly because thats what I had on hand at the time.
Unfortunately, after biasing up to about 1.7A it now looks like the below.
Guess I'll need to replace that wee guy as well 😱
Nice board! I did a quick calculation to see how much wattage that resistor dissipates with 1.7 Amps flowing. I think you are at about two watts. What wattage resistor is it? I am using 3 Watt Panasonics at that level and have not seen them burn like that. Also, metal film or oxide type? Wire wound?
Is there a possibility you have a high frequency oscillation going on?
Any more impressions as to the sound quality or characteristics?
I still have not heard them play music yet. Very frustrating to have these devices and not yet time to work with them.
@Mikegranger I wish I could take credit for the board, but it's one of teabag's F6 boards (and it is lovely). The resistors were ebay 0R68 3W metal film units, so after that I've no idea as to anything else about them, although dissipation shouldn't have been a problem. I've since replaced them with some 3W wirewound 0R56 and we seem to be all good now.
With regards to oscillation, I haven't as yet checked if that was indeed the problem, but it would make sense to do so. I'll get back to you.
Re how it sounds? No idea yet! I'd like to finish boxing it properly or I run the risk of never doing that at all... 🙂
With regards to oscillation, I haven't as yet checked if that was indeed the problem, but it would make sense to do so. I'll get back to you.
Re how it sounds? No idea yet! I'd like to finish boxing it properly or I run the risk of never doing that at all... 🙂
I have some nice vishay resistors and another good brand.
Not sure whether the resistance value would suit your needs. I think they are 0.47Ohm.
I'd be happy selling a few at less than cost if that gets you going again.
Not sure whether the resistance value would suit your needs. I think they are 0.47Ohm.
I'd be happy selling a few at less than cost if that gets you going again.
slowly slowly
Hi 2 picoDumbs - thats a very kind offer, and much appreciated. I think I've got it sorted though so hopefully your offer of help won't be needed
No progress tonight, so here's hoping I'll have it finished by the weekend! 😎
Hi 2 picoDumbs - thats a very kind offer, and much appreciated. I think I've got it sorted though so hopefully your offer of help won't be needed
No progress tonight, so here's hoping I'll have it finished by the weekend! 😎
Cree spins off power division
Cree's Power and RF Division is Now Wolfspeed!
I hope this is a good thing for us.
Cree's Power and RF Division is Now Wolfspeed!
I hope this is a good thing for us.
Another propeller-head internet marketing name.
Why "Wolfspeed" when "Crapulent" is still available?
😎
Why "Wolfspeed" when "Crapulent" is still available?
😎
Finally heard the CREE SiC mosfets play in an Amplifier I am building. It is a push-pull all n channel output circuit similar to the PLH design from Papa. I have used the IRFP 240 in the same circuit before and the 240's were always very stable. The CREEs biased up very smoothly but both channels of the amplifier were prone to very high frequency oscillation and unstable. I played around with various methods of compensation but things just got worse. I finally put a 10 UF polycarbonate film cap across both speaker outputs and tried the amplifier again. This time it made music and there was no further oscillation evident on the scope display.
I am wondering if I need to include a snubber or Zobel network in the amp to provide a high frequency load? I did not connect the amp to my good speakers and won't until I can trust the amp a little more. So all I can tell you so far is that they do work and sound pretty good on my test speakers.
I have always marveled that Papa can design circuits that don't need Zobel networks on their output for stability. I would love to know why......
I am wondering if I need to include a snubber or Zobel network in the amp to provide a high frequency load? I did not connect the amp to my good speakers and won't until I can trust the amp a little more. So all I can tell you so far is that they do work and sound pretty good on my test speakers.
I have always marveled that Papa can design circuits that don't need Zobel networks on their output for stability. I would love to know why......
Did you try larger gate resistors, before installing the output shunt 10uF cap?
The cap is a brute force approach to set a low dominant pole.
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Rayma and 2 PicoDumbs
Thank you for your responses to my post.... I very much appreciate your interest and help! I have not tried increasing the gate stopper resistance. The circuit has 130 ohms there currently, but I certainly will try increasing that to 1k or at least higher than 130.
Thanks for the suggestion. I will report back when I get the chance to change them.
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Thank you! I suppose that since the stopper resistor is part of a low pass network with the gate capacitance, if you decrease the gate capacitance by going with a different mosfet you would have to increase the stopper resistance to keep the cutoff frequency the same.
Might want to try some ohms between the high speed buffer chip and the
transformer: winding capacitance.
😎
transformer: winding capacitance.
😎
2 PicoDumbs rayma and Papa...
You guys are the best! Tried your suggestions and now both channels are rock solid and sound very good to my ears. I will let the amp settle in a few days and then let some of my golden eared friends do some critical listening. They will let me know what it really sounds like! Thanks again for the help!
Best....
You guys are the best! Tried your suggestions and now both channels are rock solid and sound very good to my ears. I will let the amp settle in a few days and then let some of my golden eared friends do some critical listening. They will let me know what it really sounds like! Thanks again for the help!
Best....
What did you end up doing, and not doing? More than a few here may end up doing the same.
I think Nelson may have me mixed up with Aspringv. He is building the F6 with a high speed I C buffer front end. I did not have to address transformer winding capacitance because my circuit is more like the PLH topology. You and 2 PicoDumbs both suggested increasing the gate stopper resistors to somewhere between 500 and 1000 ohms. I went for the 1000 ohm value. I put them in and turned the amp back on with the film caps still across the outputs. When I saw no more oscillation, I removed the shunt caps and the Amp was still stable. The amp was easier to bias than the same circuit with the IRFP240s installed.
I did not mention which Crees I used. They are the C2M0080120D parts.
Good stuff Mike
Congrats on the new amp.
I've got my eyes on those parts too. Good to hear they are working well.
Congrats on the new amp.
I've got my eyes on those parts too. Good to hear they are working well.
My son and his buddy from work that I'm building the amp for stopped by just before I installed the new resistors. They stayed to see if the amp was going to work. It was three hours later when they left because they kept wanting to hear "just " one more cut. This was on my junk test speakers nonetheless ! Their impression was (and they have heard my amp with IRFP240 outputs) that the Crees sound impressive. We want to set up a test listening with two identical amps side by side one with Cree outputs and the other with 240's. That way we can switch them out quickly and maybe tell better what differences in sound there may be. The Crees certainly didn't seem to hurt performance from our first impressions.