Hi!
Can I have choke loaded the MOSFET in circlotron output section of this circuit? What about depletion mode MOSFET CCS loaded 2SK1058?
Amplifier End by Andrea Ciuffoli
Pros and Cons?
Can I have choke loaded the MOSFET in circlotron output section of this circuit? What about depletion mode MOSFET CCS loaded 2SK1058?
Amplifier End by Andrea Ciuffoli
Pros and Cons?
Mr. Ciuffoli still manages to surprise with the lack of basic electronics knowledge. 2SK1058 is NOT a depletion mode MOSFET, it's an enhancement mode LATERAL MOSFET which gives it inherent thermal stability for the usual currents it is used at.
Your question has little sense as the MOSFETs in a circlotron essentially load each other. Unless you are asking about putting a transformer coupled output.
Your question has little sense as the MOSFETs in a circlotron essentially load each other. Unless you are asking about putting a transformer coupled output.
I think Tubenstein is trying to suggest loading a 2SK1058 with another type, i.e. a depletion mode type.
I don't know that is any better either, but it's a different meaning.
I don't know that is any better either, but it's a different meaning.
Sadly, no - he was quoting A. Ciufolli from the link, where he keeps on mentioning the K1058 is a depletion mode MOSFET and even saying it's now a new fashion to use depletion mode MOSFETs as well as other inferences that have nothing to do with the MOSFET type. Clearly no idea what he's talking about but that's nothing new 🙁
Even so, there is no sense additionally loading the halves of a circlotron output as the current passes through both halves and respective PSUs in series. Whatever you load the halves with goes in parallel with the load and when there is no signal, net DC on it is zero. So, any loading just adds a load in addition to the regular speaker load - and does not affect idle currents and voltages at all.
Yes, the circlotron is actually nothing more than one possible topology of a push-pull output stage, and not basically working different from other topologies. John Broskie pointed it out clearly in his web pages (Tube CAD Journal).
Yes, this is exactly what I meant either load the 2SK1058 by a choke or a depletion mode MOSKET CCS:
K & K Audio - Lundahl Transformers, audio DIY kits and more
Just saw this discussion... - better late than never, I guess.
True that Circlotron is just another push-pull arrangement. And true that depletion mode MOSFETs are normally ON and need negative BIAS. Whereas enhancement mode MOSFETs are normally OFF and need positive BIAS. The more BIAS, the closer we get to class A. A class A/B Circlotron amplifier is possible using either...
What I have found however is that source followers are much easier to get to behave. And that - when BIASed high enough (200mA - 300mA for class A/B) have little overall impact on the final sound. After all, you want the MOSFET output stage to amplify current and not necessarily the voltage - as voltage gain is much easier to achieve.
Now to the thoughts about where to put the choke. Easy: in the power supply. Pi-filter - like we do in a SE tube amp.
So: think of the depletion mode MOSFET as a fat tube. One that easily can crank out 8A across say 50V. And just like a tube, it needs negative BIAS. And it needs a coupling cap at the gate. Now we have something that follows the input signal from say -3.6V to say 25V or so. Nice. But that is only the half of the overall amplitude. So we need another one driven in the opposite phase so we can deliver +3.6V to 25V relative to the speaker. Enter the Circlotron. That is the perfect topology to do just that. Have a PI-filter in each half and you will have very clean power. Plus the common mode rejection of the topology will make your speakers dead quiet.
The only thing that now is left to do, is to feed the two phases of the output MOSFETs with a +/1 25V signal. Something that is easy to do with tubes. Denis Vilfort BAF 2019 Final - YouTube
I see little benefit in choke-loading the depletion mode MOSFET when used as a follower. Anything can be done of course - but Pi-filter and tube drivers will deliver a solid amp that will sound like a tube amp with balls.
Have fun & good luck.
True that Circlotron is just another push-pull arrangement. And true that depletion mode MOSFETs are normally ON and need negative BIAS. Whereas enhancement mode MOSFETs are normally OFF and need positive BIAS. The more BIAS, the closer we get to class A. A class A/B Circlotron amplifier is possible using either...
What I have found however is that source followers are much easier to get to behave. And that - when BIASed high enough (200mA - 300mA for class A/B) have little overall impact on the final sound. After all, you want the MOSFET output stage to amplify current and not necessarily the voltage - as voltage gain is much easier to achieve.
Now to the thoughts about where to put the choke. Easy: in the power supply. Pi-filter - like we do in a SE tube amp.
So: think of the depletion mode MOSFET as a fat tube. One that easily can crank out 8A across say 50V. And just like a tube, it needs negative BIAS. And it needs a coupling cap at the gate. Now we have something that follows the input signal from say -3.6V to say 25V or so. Nice. But that is only the half of the overall amplitude. So we need another one driven in the opposite phase so we can deliver +3.6V to 25V relative to the speaker. Enter the Circlotron. That is the perfect topology to do just that. Have a PI-filter in each half and you will have very clean power. Plus the common mode rejection of the topology will make your speakers dead quiet.
The only thing that now is left to do, is to feed the two phases of the output MOSFETs with a +/1 25V signal. Something that is easy to do with tubes. Denis Vilfort BAF 2019 Final - YouTube
I see little benefit in choke-loading the depletion mode MOSFET when used as a follower. Anything can be done of course - but Pi-filter and tube drivers will deliver a solid amp that will sound like a tube amp with balls.
Have fun & good luck.