Article: Beast With a Thousand Jfets

[Nelson Pass]

Actually I do have a "mini beast" which uses about 700 Jfets per channel,
and Mr. Fullrange is making me some nice boxes.

It could be a kit in the near future, but is more expensive than the usual.

 

[MEPER]

The PCB layout can be very compact if only SMD components are used?
This could have some sonic benefits like shorter signal path and less noise pickup?
Components can be mounted on both sides of the PCB?

 

[Nelson Pass]

The heat that gets generated calls for more space than you would otherwise
expect, and we also use the other side of the board to dissipate some of it.

 

[Lazybutt]

A rough calculation:

2000 per channel = 150mW x 2000 = 300W per channel or 150W with a 50% safety margin

4000 JFETs would cost roughly 500 €/$
Count about a tenth of that for SMD film resistors

Basically that's a 1k$ project.... less if you already have the casing and PSU.

Not so cheap in the end despite the huge cost difference between 2SK170 and 2SK209... still that would be a very entertaining project.... plus the joy of buying a whole 3000 parts reel from Mouser lol !

 

[Lazybutt]

I have a name for it.. B1-thousand

 

[MEPER]

Hopefully they don't need to be matched!
How many 2SK209 do you think they have in stock?
There should be enough for us DIY's without prices goes up?
Mounting that many…...it has to be done by machines?
Of course it could be good practice to hand solder SMD's……
10 - 20 pr. day…….it would take some time...….

 

[Zen Mod]

run them with 150mW each........ say goodbye to amp very soon

 

[obh]

You can glue 2 thousand 2SK209 on a big heatsink dead bug style with thermal glue
and wire peer to peer. Depending on offset tolerance you probably need to balance
the two sides.

 

[Zen Mod]

that would be definition of masochism

 

[R-K Rønningstad]

To me this sounds like an automated assembly line job, in which case quite a lot of boards should be assembled to bring the cost down. Regarding heat the transistors should be pressed against a heat sink, perhaps via some flexible gasket to get uniform pressure.

 

[Zen Mod]

heat will faster go from poor critter through gate pin , as I am informed few years ago

that's why I made substantial pads for 2SK2145 gates , where I'm using these

 

[Dennis Hui]

I hope the mini beast uses through-hole parts.

 

[Zen Mod]

somehow a Proper Beast is more likeable to me , at least now


nothing wrong with 2 pcs of THF51 or 2SK182 , stacked

 

[avtech]

To me this sounds like an automated assembly line job...

Sounds like cheating. Part of the attraction to this amp was the fact that is was all hand-soldered. Kind of like, I can print a very good copy of the Mona Lisa, but I'd rather look at the real thing.

Any good candidates for a 'Beast With a Thousand Op-Amps'?

 

[R-K Rønningstad]

Absolutely. But I earn my money in the electronics business , and we loathe too much SMD soldering. On the other hand, a hobby project towards the holy grail of amplification is an entirely different case.

 

[MEPER]

I discovered that RS Components offer these N-channel jfets in SOT23 ceramic package:
https://docs-emea.rs-online.com/webdocs/0f92/0900766b80f922bf.pdf

Can they be used for audio amp applications?

Ceramic package may make them more temperature stable?

 

[rayma]

I discovered that RS Components offer these N-channel jfets in SOT23 ceramic package:
https://docs-emea.rs-online.com/webdocs/0f92/0900766b80f922bf.pdf
Can they be used for audio amp applications?
Ceramic package may make them more temperature stable?

These are special RF parts costing ~ $44 each. So stereo 4000 x $44 = $176k?

 

[MEPER]

Ok.....but a very reliable amp?
We may get them for 10 cent each if we tell them they are for "The Beast".

 

[Lazybutt]

run them with 150mW each........ say goodbye to amp very soon

Which is why I'm considering a 50% margin

Using thick copper, and large pads should greatly help dissipate heat

 

[Lazybutt]

With a beast of a thousand 2SK209, "B1 style", this could actually be soldered on a proto board
or a series of parallel wires

Cut-to-length according to the power needed