Beast with a Thousand JFETs

[udailey]

nelson its way to intriguing to us.
I vote to.
although it can be figured out via the pics I think.

 

[Rembulan]

collecting a thousand P-Jfet is beyond my wildest dream but Pass always can put me on the list for read His article/thread here.

 

[Nelson Pass]

nelson its way to intriguing to us.
I vote to. although it can be figured out via the pics I think.

This is not a democracy. It is a benevolent meritocracy owned by a
Serbian national monopoly contracting with an orbital data haven with
a ten year leaseback provision held by Codex Capital.

With that out of the way, here is the basic schematic:

 

[Zen Mod]

and there is real one , leaked ditto from FW

 

[Zen Mod]

btw.
I'm seriously thinking about starting , best ever , periodical ;
it will be called either Nonlinear Audio or Audio Slowness .

off course that Pa will have special treatment as Author , but even he will not be allowed to write about sissy gadgets ;


conditions will be set by power dissipation :
-for line level signal stages - nothing under 100W (for both channels , somewhat relaxed conditions )
- for power stages - nothing under 300W , per channel

 

[EUVL]

The schematics is no news. 😉

I am more interested in what the real sonic performance is like, and your subjective impression.

And BTW even if 2SK74 is unobtainium, you can still do this with 2SK170 alone using modulated current source.
See the DAO TCS (Taylor current source) for reference.


Patrick

 

[Johnloudb]

No voltage gain. Looks like another job for the Impasse preamp. And that would really be something!

 

[EUVL]

With 14V rails, you don't need much gain.
A modified blowtorch will do.


Patrick

 

[regiregi22]

With 14V rails, you don't need much gain.
A modified blowtorch will do.


Patrick

Looked for but no luck, schematic please?

Thanks!

 

[Johnloudb]

With 14V rails, you don't need much gain.
A modified blowtorch will do.


Patrick

Or an op amp. You'd want a preamp that could put out a high quality 13 volt signal.

I was thinking with the Impasse and two Beast amps, you can turn that 13 volt output into 26 volts peak output per channel. But, how much power can this amp dish out? Suppose that could be too much to ask into an 8 ohm load, don't know.

Looked for but no luck, schematic please?

Thanks!

Yes, I'd like one too.

 

[regiregi22]

A thousand jfets at, let's say 10mA idss each one, amounts to 10 amps peak, right?

 

[Zen Mod]

"actually 2352" Jfets

say that 2352 goes to two channels

say that each channel is made of two SE bridged ;

say that each SE is made of 2352/2/2 jfets , which means 588/2 = 294 paralleled complementary followers ( I'm lazy to count them on pics)

lets say that each follower cell is biased to conservative 5mA

so each SE is biased with 294 x 5mA=1A47

say that each follower have output impedance of conservative 35 ohms ; divide that with 294 ..... so it have pretty low 0R12

let again say that two SE stages are bridged ; that means 0R24 of output impedance , each half with 1A47 Iq , meaning that peak current can be at least twice that

so - I think power is more than impressive , even if Beast Watt is certainly mucho expensive one

in any case - Beast is fun for Papa and - in same time Demonstration of Brute Force - tossing that number of preputium made Toshibas in a toy , while some other audio manufacturers are not having that number of Jfets to put in regular production

disclaimer - maybe I slipped somewhere with "2" divider , so if I erred , it was in decreasing some value and/or number

 

[jacco vermeulen]

A thousand

In that case you'd need 4K of the JFETs for the boards.

( i'll take the ones below 10mA Idss when you're done selecting )

 

[Zen Mod]

ya Dutchie Elephant .......

ya certainly remember those numbers form BAF - how many W on 8 , how many WW on 4 and how many WWWW on 2R ?

 

[VladimirK]

Guys, this Nelson's "toy" inspired me for, as appeared, excellently sounding integrated jFET amp with paralleled KP903A at the output, and jFETs at other stages.
If the target is not to finish completely the K170 stores, KP903A provides definite advantages (Idss=400mA, Ciss=18pF, Pdiss=6W, transconductance nearly 90mS, stud mount case), especially in transconductancer/Ciss ratio.
I already have experience in finding and shipment of few hundreds pcs, could try to repeat this adventure.

 

[Luda]

Hi.

As you can read here: http://www.diyaudio.com/forums/headphone-systems/233559-simple-headphone-amp-spare-parts.html I'm currently looking for a simple design for a headphone amp that I can build from spare parts.

I bought some (8) 2SJ74s a while ago just in case I decided to mod the input of my Zen V4. I guess they were cheaper back then. 8 2SK170s are available as well. The rest of the idea should be obvious ;-)

OK, time for some math:
First of all: AFAIK current headphones aren't designed for 120 Ohm sources any more, so I'll just ignore the calculations I just did and calculate that stuff again, without that resistor.
My headphones are:

- Sennheiser HD570 64 Ohm, 102dB@1V, max 100mW
- Sennheiser HD280 64 Ohm, 102dB@1V, max 500mW
- Etymotic HF2 16 Ohm, 105 dB@0.1V, max 120dB

I'll assume the source produces 2 V peak or sqrt(2) V RMS.

Since the "Beast" doesn't have any voltage gain, and neither does my B1, 2 Volts peak or sqrt(2) Volts RMS will be the maximum voltage.
- The 64 Ohm headphones with 102 dB @ 1 Volt* will deliver 105 dB @ sqrt(2) Volts RMS and draw roughly 31 mA (peak) per channel.
- The 16 Ohm in-ears With 105 dB @ 0.1 V* and 120 dB max will produce 120 dB @ ~0.56 V RMS and draw 35 mA (peak) per channel.

At my desk I usually use the closed HD280 and wear ear-plugs underneath, just to get rid of all ambient noise.[special= What the f***?]%[/special]
It's not my preferred option for listening to music, but it's what I (have to) do for now. At least for a couple of hours every day.
105 dB minus 20 (or more) dB due to the earplugs... mh.. I guess 6 dB voltage-gain wouldn't hurt. Especially if I don't want to get in huge trouble when turning on the power amps without checking the volume control on the B1 first ;-)

If I understood the article on the "Beast" correctly, each pair of 2SK170/2SJ74 will deliver 20 mA max, so with just 2 pairs per channel I won't need any voltage gain. If I want any voltage gain, I have to use all 8 SJ74s.


So, before I try to figure out any more details on my own, especially the voltage-gain-stage: Could this actually work?


*RMS?

 

[Zen Mod]

will buffer work for headphones ?

 

[JimT]

ZM,
The Szekeres headphone amp is a mosfet follower buffer. With my Sennheiser 595's, about the same efficiency, I run it about 8 o'clock for normal listening. Seems like a buffer would normally be fine, but adding ear plugs to the mix could be an issue.

Luda,
I would suggest changing to the small headphones for portables and put some safety headphones overtop. The hearing protectors I use when using noisy power tools reduce noise by 25dB and cost $25.

Hearing Protectors - Lee Valley Tools

As for the design of the buffer, hopefully ZM has time to help.


Jim

 

[pidesd]

yes if you are doomed to put something inside your ears anyway, why not use earphones(buds) with a noise supressing headset. this way you would not need voltage gain.

by the way i built a beast of 20 jfets (roaoarrr), or 10 parallel buffers, for phones(senn 52 ohms) and in my experience, the more jfets the better. It sounds supremely transparent this way but had i more fets i d double that number, at least.

2V for headphones this sensible is already loud, at least on my hd 570, why dont you try it first? it s the simplest circuit i know of

 

[maxlorenz]

Talking about the "beast", instead of a board, why don't use a 3D aproach, like a pair of "fortune wheels", one (or series of) for N-ch and one (or series) for P-ch? 😎

Just an idea.
M

PS: and immersed in oil 😀