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Old 13th December 2011, 03:46 PM   #271
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A thousand jfets at, let's say 10mA idss each one, amounts to 10 amps peak, right?
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Old 13th December 2011, 04:04 PM   #272
Zen Mod is offline Zen Mod  Serbia
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"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
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Old 13th December 2011, 04:04 PM   #273
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Quote:
Originally Posted by regiregi22 View Post
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 )
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Old 13th December 2011, 04:09 PM   #274
Zen Mod is offline Zen Mod  Serbia
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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 ?
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Old 14th December 2011, 04:27 AM   #275
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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.
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Old 8th April 2013, 02:18 PM   #276
Luda is offline Luda  Germany
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Hi.

As you can read here: Simple headphone amp from spare parts 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. What the f***?
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?
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Old 8th April 2013, 02:41 PM   #277
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will buffer work for headphones ?
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Old 8th April 2013, 03:40 PM   #278
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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
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Old 8th April 2013, 07:24 PM   #279
pidesd is offline pidesd  Canada
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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

Last edited by pidesd; 8th April 2013 at 07:30 PM.
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Old 8th April 2013, 07:37 PM   #280
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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

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