L'Amp: A simple SIT Amp

[maxlorenz]

Hello,

I've been having trouble locating any reasonably priced SITs except for the 2SJ28 - KF33 grade and while I have build a few amplifiers in kit form I'm interested in trying my hands at a scratch build.

What does it mean when people mention reversing the polarity if one plans to use the 2SJ28?

Reasonable price is a relative concept. Think like you were buying NOS triode for your dream tube amp...
I bought recently (not yet arrived) a pair of 2SK180 Tokin SIT from this Japanese seller with 100% feedback:
1pc 2SK180 NOS TOKIN V-FET(SIT) Original, Made in Japan, similar 2SK77 | eBay

I hope they are as cool as they look.

To Dady:
Thank you, dear. I couldn't find the sibling for the heat sink: out of stock.
I will have to be manage with only one but I cannot increase bias current.

Cheers,
M.

 

[kf_tam]

It may be also worthwhile to check out Joshvi to see whether he still still have these in stock (esp. in matched pairs):
http://www.diyaudio.com/forums/swap-meet/283642-fs-tokin-sit-2sk180-2sk180c-tokin-2sk-180-d-4.html

Or maybe some 2SK60:
http://www.diyaudio.com/forums/swap-meet/294359-fs-vfets-2sk60-2sj18-pair-2sk79.html

Best Regards,
Edward Tam

Reasonable price is a relative concept. Think like you were buying NOS triode for your dream tube amp...
I bought recently (not yet arrived) a pair of 2SK180 Tokin SIT from this Japanese seller with 100% feedback:
1pc 2SK180 NOS TOKIN V-FET(SIT) Original, Made in Japan, similar 2SK77 | eBay

I hope they are as cool as they look.

To Dady:
Thank you, dear. I couldn't find the sibling for the heat sink: out of stock.
I will have to be manage with only one but I cannot increase bias current.

Cheers,
M.

 

[slimecity]

I also have a pair of unused 2SK180D's which I bought from Joshvi (I also have the curves) which Im happy to part with as I have now bought the Pass Sony kit from the diyaudio store.

 

[maxlorenz]

So I connected my featherweight SMPS powered SE SIT SK82 amp to my big Autographs with Beyma 15KX coaxials and they can move them Not the best bass but the transparency and immediacy are exquisite.
As I am now collecting the parts for a SK180 Tokin amp I wanted to ask some questions beforehand.

1) What sonic improvements are to be expected with a pseudo-parafeed configuration?

2) I chose the following parameters from Michael's youtube post about biasing the 180 (if I understood correctly) for the SE amp: SMPS with B+= +85V-->variable power regulator--> R= 25 Ohm (200W)--> VDS= +35V (variable) ; Vbias from -12V upwards, low noise.
Did I understood it correctly or did I go it wrong?

Thank you very much.
M.

 

[asanden]

I am planning a L'amp...
Got some nice bulbs, got a full range Mark Audio CHR-70g3 in a pencil cabinet to drive (8ohm). I am lucky to have 2x 2SK82, 2x 2SK60 and 2x 2SK180's (i'll experiment with them), I have the Ids/Vds/Vgs plots...
I even read about the thd/static/dynamic load lines...
The goal is to drive the speakers with not too much class A power that gives a satisfying sound/volume.
The issue/question is about my trafo's I have on hand and I would like to use, I have two identical trafo's, each 230VAC 2x38VAC (2x80W) center tapped (so 3 wires). Each trafo rectified will give about 2x 50VDC.
They are not optimal I know, but what would be the best way to implement them? (in one case, no mono blocks). I could parallel the secondary's, but I want to use the whole trafo.
Look forward to see and hear the L'amp!

 

[bonzo15011978]

Inductors question

Good evening DIYers,
I wrote on this thread some times ago, but still no amp made yet.
I have a question about inductor:
I have a big dual inductor (two coils in the same core, as you can see in the picture below), do you think I can use it for a stereo amp? Each coil measure 100mH, dcr is 1 ohm and they are rated for 4A each.

I ask it because I fear that the mutual interaction of the bobbins could cause bad channel separations at least.

Thank you for any help

 

[DIYBras]

Good evening DIYers,
I wrote on this thread some times ago, but still no amp made yet.
I have a question about inductor:
I have a big dual inductor (two coils in the same core, as you can see in the picture below), do you think I can use it for a stereo amp? Each coil measure 100mH, dcr is 1 ohm and they are rated for 4A each.

I ask it because I fear that the mutual interaction of the bobbins could cause bad channel separations at least.

Thank you for any help

In fact, the mutual coupling will be a issue. Probably is interesting to use it with coils wired in series, in one channel only. If you have 2 of it, will be perfect.

 

[bonzo15011978]

In fact, the mutual coupling will be a issue. Probably is interesting to use it with coils wired in series, in one channel only. If you have 2 of it, will be perfect.

Maybe too much resistance? It would be near 2ohm.
It's a pity I have only one, I think I will use it for filtering purpouse (at least I think I can use it in a CLC filter, one bobbin per rail or both bobbins in series separated by a capacitor)

Thank you very much for the help DIYBras!

 

[slimecity]

OK so dumb question (I have a few of these....!)

If the speaker wires accidentally short what is the likely outcome to the amp?

Is it worth installing speaker fuses, would these be likely to prevent damage? (I have no room in my enclosure for a separate speaker-protect relay board).

thanks!

 

[vdi_nenna]

If the speaker wires accidentally short what is the likely outcome to the amp?

It will draw current until the output device and supporting components burn.

Build output protection or don't short it.

Add fuses to the power supply lines.

 

[slimecity]

Add fuses to the power supply lines.

Cheers, will do, would 3 Amps for the fuses be adequate?

 

[vdi_nenna]

There's probably some rule and considering this amp is constant current, you have to be sure the fuse doesn't break easily yet breaks when the current goes out of safe operating area of the vfet.

 

[maxlorenz]

The other condition to worry about is when the bias supply goes off for whatever reason: D-S becomes a short.
I thought about 10A fuse for the Tokin SK180 supplies, and 5 amps for testing, calibrating.

Slowly getting there...

 

[Soundhappy]

Protection by Zener diode 9V1

Remember from Papa schematic on BAF2015 vfet protection by 9V1 zener diode between drain and source pins.
Was for guys who use tube preamplifiers. Protect the vfets is always priority.
Any comments or recommendations how we can more secure L'Amp circuit ?

 

[Michael Rothacher]

(Assuming we're talking about the L'Amp circuit with the light bulb) Let's have a little fun and turn this into a puzzler:

Who can tell me what will happen to the voltages and currents in the bulb and transistor if the bias voltage drops towards zero?

Think about it before answering.

 

[cwtim01]

Think about it before answering.

I'll give a try ...

Almost the whole Vcc goes across the two bulbs, and they get brighter (Unless Vcc is above 110V, the bulbs are going to be fine).

The current is limited by the resistance of the bulbs, so the SIT will be fine.

 

[Michael Rothacher]

Well done.

Let's go to the next puzzler (again assuming the light bulb circuit):

What will happen if you place a short across the speaker terminals?

 

[plasnu]

Remember from Papa schematic on BAF2015 vfet protection by 9V1 zener diode between drain and source pins.
Was for guys who use tube preamplifiers. Protect the vfets is always priority.
Any comments or recommendations how we can more secure L'Amp circuit ?

I was wondering if adding a main power supply relay on/off by bias voltage can avoid bias loss accident.

 

[maxlorenz]

(Assuming we're talking about the L'Amp circuit with the light bulb) Let's have a little fun and turn this into a puzzler:

Who can tell me what will happen to the voltages and currents in the bulb and transistor if the bias voltage drops towards zero?

Think about it before answering.

You are right. I was thinking about my "non l'Amp" version with plain R load...sorry.
Anyway I cannot get a pair of those bulbs here.

Cheers and thanks for the inspiration.
M.

 

[Michael Rothacher]

Tim's answer applies to a resistor or light bulb.

Any takers on the second puzzler?