Total Domination VFET (TDV) Amp (using 2SK2087C)

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^ All I should add to that is... Ditto!


I know I post a lot... but I'm also a notorious lurker. I cut and paste notes into files that will (hopefully) be my own build instructions for future projects.

To some, this seems to come naturally. For me, I pick up a bit here, and a bit there, then I forget about it for a while. If I did not document a step-by-step approach that some could likely do intuitively with one eye closed... the likelihood of success would be zip-zero-nada. Also learning a bit more about how these devices behave in various configurations is fascinating.

Conversations like the previous posts around @rickmcinnis's build are vital.

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I had kludged the bundle of resistors for which I am going to do a proper job of tonight.

Upon startup the Vgs seemed to bounce around more than I would have expected but once it selttled down it was stable.

I tend to think the tacking on of parallel resistors might have had somehting to do with that.

Seems like the amp is behaving just as Ben Mah's calculations predicted.

Take care, ra7
Amplifier is working very well.

I hear the absence of what cody called "sweetening" and it is good riddance. You do percieve a further cleaning of the window with TDV. The fundemental sound is the same just more transparent. But then that is only hearing it for a couple of hours and one out of four amplifiers,

I do find that it is necessary to connect a wire from pin 1 on the DAC to the input ground of the amplifier otherwise there is a buzz.

I had my "tweeter" down 19 dB with the SINGING BUSH and with TDV51 I am at 9 dB down - I was expecting something much close to 0 so I guess no gain is needed at all. I still wonder if a mosfet follower following the DACs might be a good idea.

Power consumption is approx. 100 watts versus the 140 of the SINGING BUSH. A nice advantage when using an inverter.

Now to get the other three done,
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Working on the second amplifier - not paying good attention while finishing up.

Installed the zener backwards and got a small puff of smoke from a twenty watts 1R resistor.

Did not take it more than a couple of seconds to reach that temperature.

The resistor returned to its stated value after cooling down but measured as a short after I turned the amplifier off.

So for those who wondered what would happen when the zener is installed backwards I have saved you the trouble of finding out for yourselves ...

This afternoon: install the zever correctly and replace the 1R resistor. I do not trust it after abusing it like that.

Thsi was not the result of working on the amp after cocktail hour. I have no good excuse other than mindless excitement at having my left channel back in operation.
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Joined 2010
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If you apply 69vdc of avionics power, current limited to 3A, backwards across the leads of a 5V, 1/4w diode you get a one inch, white jet of flame... this will happen after you've blown all the caps on the circuit, taken out all of the semiconductors and will burn through five layers of a ten layer board.

It will also burn through the conformal coating (used for environmental protection).

The worst part will be filling paperwork with a number of company safety departments for the next six months.
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I am in dread of that possibility.

I do have one spare.

Reminds me of the page in early CROWN owners manuals -titled Murphy's Law -

My favorite was the protection circuit will protect itself and leave the circuit on its own.

Not fully applicable here - but if I had elected to not use the zener at all I would not have this hovering over my head.

I discovered a week or so ago when I began this conversion project that two SINGING BUSH do not have any zener protection at all and I have never had any problems with them. I never remove interconnects with the amplifiers on and the amplifiers are always tunred on last and turned off first. I have no idea why the zeners were left out. But I bet it has something to so with mindless excitement again.
The device did not fail.

Second amp came up with no drama. What a great relief.

This one is using a big HAMMOND choke in the power supply instead of the LUNDAHL LL2733.

I only have 6 of the LL2733 and I have two of the HAMMOND 100 mH/0.1R chokes which I am using for the amps for the woofers.

This gives slightly more B- - I had to use an additional 5R resistor and I switched out the one 1R resistor, an OHMITE "audio" resistor - non-inductive winding - for three 3R 12 watts OHMITE BROWN DEVILS which were used very often for cathodes in 300B amplifiers - so that makes three 3R and 4 5R - 10 watts resistors. They get just above warm after fifteen minutes. I am sure after an hour of listening they will get warmer than that.

Just below 2.5 amps Iq - - not able to measure the resistor bundle's exact resistance - I figure this is close enough.

Vgs - just above 3.6 volts and Vds just above 38 volts

Ran out of time so I did not get to put it into the system,

So far, this is damned easy; it is almost like magic.

For those planning something similar using a 30 volts secondary power transformer and the THF51 - starting with Ben Mah's recommened 1R and working ones way down with Ohm's Law calculator and a parallel resistor calulator on the computer I do not think one can go wrong with ra7's concept. As he says it IS the easiest implentation by far. Don't let the selection of the resistor scare one off.

Installing the input transformer is all that is left to do but I did not feel like doing it last night.

Should be making some kind of noise this afternoon.

I figure like a 300B amplifier - with so few components every componenet becomes important. Unlike the fellows who would try ten different gate stopper resistors - I am too lazy for that so i use pieces that have done well for me in the past.
I am using 1 watt SHINKOH for the gate stopper and the TEXAS COMPONENTS TX2575 for the 6.9K load resistor. When there are so few pieces needed one might as well go fuill audio kook deluxe.

Just to annoy ZM I am using DUELUND input capacitors but then, I do not think I could annoy him any more than I have.

For the output caps I am using the KEMET 10mF slit foils along with a DUCATI 1500 uF PP the size of a large motorcycle battery. I havce had these in use for years with various amplifiers. For the tweeter amp I use a 5 uF round capacitor that was recommended by Jeff Medwin.
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As a bookend to my foolish question about pin one from my DAC and where to connect it - I connected the "bass" amplifier last evening and did not think about the orientation of the output capacitor - left it as it was with the SINGING BUSH even though this is a TDV with a "negative" power supply. That did not occure to me at the time.

Well it definitley makes sound. I was thinking there was something not quite right and about ten minutes later I hear this sizzling sound. My first thought was that somehow that rather large HAMMIOND choke in the power supply filter had some kind of inexplcable problem only to quickly realize it was a capacitor well on the way to destruction.

That thing was HOT!

Had to default to using only the 1500 uF PP and was curious how this might affect the response - it did seem to be a little thin.

Will listen with a new electrolytic oriented correctly this evening in combination with the big PP. Should be much better.

I figure these mea culpas are good for me and might be of use to others.

I did find that the Iq continues to fall for an hour and then becomes stable. VERY slow decrease. Started at 1.415 at start up and descends to 1.39 eventually. I listened for about 1.5 hours. Will see if it decreases further tonight when I have a chance to listen longer.

These amps are only drawing 60 watts each per the inverter's meter. A drastic reduction for the 140 watts of the SINGING BUSH. I will be able to listen for five hours continuoulsly once all are converted.

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