What To Do With Those 2SJ28's

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For lower distortion? I'm surprised you don't get better cancellation with two of the same sex.

I did try bridging two same sex on LtSpice, and it suggests that the THD is better, but I am doing something silly: I mirrored the circuit leaving two independent CCS's to enable independent adjustment of the idle current. But of course the circuit clips at the same point as with a single device. I assume whats happening is that as the current goes back and forth through the load, the maximum current limit is hit on `one side' and then the other and is limited by the CCS in either case. So it doesn't help dissipation or max power. I either need to get smarter or failing that I'm trying a circlotron
 
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Vfet circlotron?

I keep looking at the attached and I am hoping (expecting) for someone to educate me on the inevitable flaws in this cunning plan... apart from 600W of heating and (with luck), some good vibrations.

The Aleph CCS addition does make the CCS device `see' both sides of the amp, and to this end perhaps I could put the sensing resistor in the drain path of the gain device and shield it from the contribution of the other side with the cap in schematic (I tried this and couldn't seem to make it work). It would allow independence and better matching perhaps

Does cancellation via complementary pair or `balanced single ended' or circlotron pairing start to kill the `character' of a SIT and if so should we focus on a single device single ended toy?

As an aside how much influence does the choice of the device for the CCS make on the sound of the output? It seems a bit extravagant to run two 2sk180s in a single ended stage (one as the gain device and the other as the CCS). On the other hand, I'd guess as soon as you start using the mu or Aleph CCS then the 'CCS device' starts to play an increasing role

BeardyWan
 

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As an aside how much influence does the choice of the device for the CCS make on the sound of the output? It seems a bit extravagant to run two 2sk180s in a single ended stage (one as the gain device and the other as the CCS). On the other hand, I'd guess as soon as you start using the mu or Aleph CCS then the 'CCS device' starts to play an increasing role

BeardyWan

JAMA on this forum has already built the amp you are asking about: using the IXTN46N50L (a linear part, not a switch) as the CCS and driving 2x K180Ds. He even measured its H2/H3 performance and it's a deadringer for a 45 triode amp he built earlier. In other words, he has built a parallel 2SK180 SE amp that delivers 50W Class A into 4 Ohm!

Attached please find the approximate schematic and his own descriptions are here: http://www.diyaudio.com/forums/pass-labs/280950-baf-2015-coverage-87.html. Great work as usual, JAMA!
 

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Hi Ci11,

I was aware of JAMA success with this circuit, but I wasn't aware that he had tried multiple different CCS devices and found it made no difference to the sound.

I do not know JAMA had tried diffeent devices for CCS including the K180, but he did deviate from the original BAF2015 circuit which uses the IXFN140N20P in both CCS and output. The linearity of the IXTN46N50L made it far easier to achieve a stable bias.

As to the sound, his schedule for the second channel build is later this year so he probably has not heard it on speakers yet - but his FFTs showing the amp's harmonic balance and that very lovely 10kHz square wave response are very interesting: what I glean from those measurements is a quiet, powerful SS amp with lightning fast reflexes and the harmonic character of a tube amp.

If he has time, I am sure he will weigh in and provide a lot more insight...he's a really great guy and a fearless builder.
 
For what it's worth,

The simplified schematic of post #96 is now the SIT-3, and I have the pilot
production run near completion. Below is that image and also three
graphics of measurements on it.

Nice thing about this particular circuit is that accommodates all the remaining
SIT devices including the Sony parts, and you just reverse the polarities for
P vs N channel SITs.

The second piece of news is that the Sony VFET project has turned out
sufficiently reliable that I can release some of the VFETs that were being held
against repair needs, so I think we will be making arrangements shortly for
a small offering. Looks like one more chance to get in on the VFET action
for those who missed the three previous releases.

And if you miss this one, the circuit works fine with a regular Fet as well.

Subscribed. I have a pair of 2sk82 ja-33. I would like to try the kit. Please update when they are available.
 
Hi All,

I am curious about the pros and cons of a transformer as an voltage gain stage as opposed to adding extra active devices like a capacitor coupled BA3?

There is widespread appreciation of the F6 and M2, although Nelson has stated that transformers measure worse than capacitors, and there are certainly those who will run screaming from a few uF. The whole Zen philosophy of fewer components and more elegant designs with less feedback making for a more enjoyable experience (less harmonious?), would suggest fewer active components.

Without building several examples of each topology... Is there a consensus or a discussion (or even a list of pros and cons to contemplate)?
cheers

Beardy
(sitting on 3 pairs of 2sk180 and wondering about SIT-3 versus a BBA3/SE CD topology)
 
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