Using the opa541 is a handy solution. They are good sounding and fairly rugged chips. You’re getting only 6watts? Would the opa549 also work?
mdaudio !
the power is limited by the pin fin heatsinks. 6-8 watts is the upper limit which is enough for me. OPA549 is nice looking but no FET inputs. The DC Servo for the output offset requires a low input bias current otherwise the dc coupling cap would become fairly large.
the power is limited by the pin fin heatsinks. 6-8 watts is the upper limit which is enough for me. OPA549 is nice looking but no FET inputs. The DC Servo for the output offset requires a low input bias current otherwise the dc coupling cap would become fairly large.
Here is the FFT. 100hz @ 1w @ 7R. A healthy does of 3rd order. Mr tubecad has designed an AC coupled I to V converter. The cathode signal is tiny compared to the plate and the circuits needs serious gain (@ 200) It’s my mistake for not picking the error out. there is no way this circuit will operate as ‘shown‘ in TUBECAD. Gonna change directions again with a dc coupled super triode pcb. It’s a beast.
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You need to be very careful with his designs. Most of them were never ever built....
Here is the latest and greatest.. solid state load, bipolar regulated ps, dc servo ( no blocking caps ). based on the 6922 (100v/10ma) tube and a single to-247 exicon (+-18v@2a). Mono block design. I have been delaying this approach due to its complexity. Go big or go home 😉
dwight
dwight
Ok. I ended up switching directions. One more attempt using an 6922 / lm3886 In a super triode configuration. The cathode follower servo circuit is from tubecad. Look up ’no gain, no pain , tubecad’. I have also built a couple preamps on this circuit. See attached. the to-264’s are for the regulated power supplies (+/- 20v & 6.3v). 8w @ 8/4r. This creature is designed to replace 2a3 and 300b tube amps. I luv the EML 2a3 but it is expensive !
https://www.diyaudio.com/community/threads/ecc99-cathode-follower-with-servo.364335/#post-6446453
https://www.diyaudio.com/community/threads/ecc99-cathode-follower-with-servo.364335/#post-6446453
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Revisiting da Super Triode Direct Coupled concept -
supertriode circuit requires 3 design points (per tubecad) -
the circuit driving the load inverts
the tube does not contribute to the load
a ‘stiff‘ ccs so the plate resistor can act as the local negative feedback path
my 1st layout was based on the lt3092. 10k @ 10khz leaves to much noise @ the plate.
it was suggested to design a cascode ccs circuit. Found an article from Jung on the subject. See attached
dwight
supertriode circuit requires 3 design points (per tubecad) -
the circuit driving the load inverts
the tube does not contribute to the load
a ‘stiff‘ ccs so the plate resistor can act as the local negative feedback path
my 1st layout was based on the lt3092. 10k @ 10khz leaves to much noise @ the plate.
it was suggested to design a cascode ccs circuit. Found an article from Jung on the subject. See attached
dwight
Hi, just found your post about the super triode connection. I did build one using OPA541 before, using the TubeCAD info. I listened to that for a couple of months and was not satisfied. I still believe that this STC concept can give better results.
I note that you do build a couple of configurations, switching from one to another. Till now which one you feel best? And if I plan to build a new one, which configuration you recommend?
By the way, you have tried LM3886. According to the info, you need an amplifier which is unity gain stable. Do you see any oscillation etc with the LM3886 version?
I note that you do build a couple of configurations, switching from one to another. Till now which one you feel best? And if I plan to build a new one, which configuration you recommend?
By the way, you have tried LM3886. According to the info, you need an amplifier which is unity gain stable. Do you see any oscillation etc with the LM3886 version?