Formantjim,
Congratulations on your successful Cree output F6 startup! I am really liking the amp I built using them. Nice pictures..... Is that a Tektronix 456 B I see? Happy listening!
mikegranger thank you and yes it is indeed a Tectronix scope
SjoerdSmits as 2 picoDumbs has mentioned lower capacitance therefore er frequency response. This does not make any difference with the F6 with IRF's or Crees I have measured both with my trusty Tectronix and function generator the frequency is limited by the transformer exactly as Nelson mentioned in his article.
I have now rebiased the F6 and took the current up in baby steps at 1.2 Amps the F6 came alive louder and wider sound stage. I'm currently running at 1.425 Amps and the heatsinks are warm but not hot. Takes about an hour for the F6 to come up to this current from cold but very stable. This is where she will stay for the time being as I'm going to just enjoy listening.
SjoerdSmits as 2 picoDumbs has mentioned lower capacitance therefore er frequency response. This does not make any difference with the F6 with IRF's or Crees I have measured both with my trusty Tectronix and function generator the frequency is limited by the transformer exactly as Nelson mentioned in his article.
I have now rebiased the F6 and took the current up in baby steps at 1.2 Amps the F6 came alive louder and wider sound stage. I'm currently running at 1.425 Amps and the heatsinks are warm but not hot. Takes about an hour for the F6 to come up to this current from cold but very stable. This is where she will stay for the time being as I'm going to just enjoy listening.
Ciss 200pF!
That is marvelous!
However, Rds(on) is as high as 1ohm.
But then, paralleling 3 of those would still keep the Ciss at just 600pF, which still is marvelous...
12pcs /stereo amp, not cheap though...
Did you make any THD measurements? How does the harmonics look like?
Edit:
C3M0065090D
???
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D
Deleted member 24284
Yes, that has the lowest gate capacitance.
Here is Mouser's chart sorted by gate capacitance:
Cree, Inc. Through Hole MOSFET | Mouser
No I do not possess the tools to measure THD unfortunately maybe one day. All I can measure is nice clean waveforms and it clips just like a tube amp no harshness. (Although at these levels it cracks the drywall 
)
But this amp sounds fantastic I'm hearing details in music that I never knew were there!
)But this amp sounds fantastic I'm hearing details in music that I never knew were there!
myhui Thank you for the list of the Crees at Mouser some interesting devices there and some not too expensive. Just when I have finished the amp now I'm curious but to take the F6 apart after just building it I now may have to build another one. This hobby is so addictive!
Just a question then what would the benefit be of using a lower Rds on? Lower THD?
Just a question then what would the benefit be of using a lower Rds on? Lower THD?
2 picoDumbs I would love to know how to go about doing that can you explain or point me to somewhere that shows me how. I'm sure there are a lot of hobbyist's out there like me that has only the basic tools like a scope and frequency generator would love to learn how to do this.
We all make these amplifiers and if they sound better than the last one then we are happy until some new design comes along and catches our interest. I'm not sure I could hear some of the distortions anyway but for the sake of curiosity it would be nice to see.
We all make these amplifiers and if they sound better than the last one then we are happy until some new design comes along and catches our interest. I'm not sure I could hear some of the distortions anyway but for the sake of curiosity it would be nice to see.
You have a computer.
Does it have a soundcard?
Download ARTA or RMAA or something similar.
If bad quality soundcard (take loop back THD), get a good external.
A good soundcard is the first buy for an enthusiastic audiopile.
I use SoundBlaster X-Fi HD.
On good weather it can get down to 0.0009% loop back THD.
Which is good enough for F6 measurements.
Best I could squeeze out from my F6 was 0.009%/8R/1kHz/1W. Although I use different PCB and different input buffer than the DiyAudio version...
Edit:
Here at 1.5A bias:
I have also Lundahl transformers on my table here. I just need to find time to put those into the circuit and see what happens then...
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Thanks palstanturhin I will definitely look in to purchasing a decent sound card soon. Which software produced that graph?
Pretty impressive figures and I would love to see your results with the Lundahl transformers.
Whilst testing the prototype F6 at around 3.8 KHz there was definitely an acoustic noise coming from the Jensen. I tried putting limiting resistors on the output of the HA5002 buffer chip to see if I was over driving the transformer but it still did it. Anyone else encountered this phenomena?
Pretty impressive figures and I would love to see your results with the Lundahl transformers.
Whilst testing the prototype F6 at around 3.8 KHz there was definitely an acoustic noise coming from the Jensen. I tried putting limiting resistors on the output of the HA5002 buffer chip to see if I was over driving the transformer but it still did it. Anyone else encountered this phenomena?
Papa mentioned that you may want to add some resistance but did not go into detail. Here is a section from data sheet regarding adding components for added stability:
"The HA-5002 can become unstable with small capacitive loads (50pF) if certain precautions are not taken. Stability is enhanced by any one of the following: a source resistance in series with the input of 50Ω to 1kΩ; increasing capacitive load to 150pF or greater; decreasing CLOAD to 20pF or less; adding an output resistor of 10Ω to 50Ω; or adding feedback capacitance of 50pF or greater. Adding source resistance generally yields the best results."
They also mention adding current limiting resistance on the output stage power supply connections to prevent over current.
Are you powering the 5002 with bipolar supply?