SSTART Preamplifier

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#3
Luke said:


I think this is the art pre Grey talks about in the article.

http://www.geocities.com/rjm003.geo/rjmaudio/diy_ls.html
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Try this link, instead:

http://www.conradjohnson.com/It_just_sounds_right/a-art.html

Note that the ART itself has been discontinued. There is a similar model called the ACT2 in the current CJ product line; the general idea is the same.
The circuit is inexpensive to build and as simple as you could wish for. It's also modular, which gives you the ability to change the gain to suit your needs.
Although I generally use PC boards, the SSTART is simple enough that it can be built using point to point wiring without undue difficulty. It can be built in an hour or two, which is nice if you're in a hurry, and there's not a lot of junk in the signal path to screw up the sound.
I happen to have about a zillion J271s on hand (a P-ch part very similar to the J310, though not technically a complement) and I keep meaning to throw together a P-ch version. Just never seem to find the time.

Grey
 
#5
Given that the original ART used ten tube sections (5 x 6922, all sections paralleled) and the one you linked to shows four sections, total, I'd say it's a definite no. Besides, he says it isn't--just read a review and got excited. He says he hasn't even built the thing.
I glanced at the schematic and saw something that looked a little odd, but I'm so tired I'm cross-eyed and might have misread things.
File it under "inspired by" and go from there.
I've got a small pile of 6922s and had thought about making a run at the ART, but decided to go with solid state. I've got another tube preamp circuit that I'd probably do first if I were to do tubes. Either 6SN7s or 6922s...remote chance I'd use 12AX7s, who knows? I'll cross that bridge when I come to it.

Grey
 
#14
Cobra2 said:
How much gain does it give (or how do I calculate gain)?

Arne K
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Gain = 20dB, plus or minus a smackeral


twitchie said:
250 pieces of J310 on the way to me ... I'll give this one a shot. I can't promise anything before 2009 however :angel: :smash: :santa2:

Thanks for this one Grey :cheers:

P.S. Will it work as a headphone amp?
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If you need more current, parallel more devices...jeez, am I gonna revoke your DIY license?
Note that this will increase your gain if you leave the rest of the circuit as-is. My suggestion is to throw as many JFETs into the mix as you like, then resize the load resistor to split the difference between the rail and the voltage at the Gate of the cascode device. As it is, there's about 17V across the load resistor. If you're running a 50V rail, you've got about 35V of output swing, which is substantial for headphones, but comfy for normal preamp duties; the philosophy being to only use a fraction of that. If you double the number of JFETs (at the same bias current), then halve the value of the load resistor. Something in the range of 120 to 150 Ohms would do pretty well. Yes, you can parallel two 270 Ohm resistors to get 135 Ohms and to handle the heat.
You can parallel any number of devices that floats your boat. The J310 is a low capacitance device and the cascode reduces the effect even further, so capacitance won't be a problem. The MOSFET cascode will take the current from quite a few JFETs before it starts getting antsy.
Don't forget to increase the capacitance at the output if you're using it to drive headphones. Think in terms of an electrolytic bypassed with a film cap.
As I've said, I've got a screaming blue million of the J271s and have been toying with the idea of a single-ended, massively parallel amplifier to use a few of 'em up. A scaled down version would do rather nicely for headphones.
One of the nice things about J310s is that they're cheap. Build a SSTART to listen to, then use the leftover parts for Evil Experiments. Who knows, you might come up with something really, really cool.

Grey
 
#15
Grey
I know you know.
But like with may Nelson Pass 'keep it simple' amplifiers
we need to take good care of providing a Clean power supply.

A shunt regulated 50 Volt, with one IRF610 bypass transistor
with enough capacitance filtering
would be one of my options.
 
#16
Me too, I have 100 j310 waiting for a work 😀:

Lineup, I agree with your comment.

Maybe ZenMod can help us...
Master :rofl: ZenMod, will the Shiny go up to 50V?
Or is beyond the 317 max in-out limit? (but - correct me if I'm wrong - is not a matter of absolute Vout, but only Vin-Vout)

I'm currently playing (very slowly) :snail: with a lot of projects

Have a look on this (http://www.diyaudio.com/forums/showthread.php?postid=1643803#post1643803 (Shinyy is a dual Shiny)
and http://www.diyaudio.com/forums/showthread.php?postid=1627519#post1627519

Grey,
what about IRF510 instead of IRF610?

Last question:
START: will it drive the F4? 😀 😀

Guido
 
#17
GuidoR said:
......
Master :rofl: ZenMod, will the Shiny go up to 50V?
.....

......
Grey,
what about IRF510 instead of IRF610?

Last question:
START: will it drive the F4? 😀 😀

Guido
Click to expand...

- yes - it will work (Shiny) on 50 V for output (look in small "how Shiny works " post

- (even if just my beard is gray :rofl: ) ........ 510 is OK

- yes - it will drive F4 ...... SSTART is not your Mamma everyday preamp ........ :clown:
 
#19
Did anybody think to replace the JFets with a 6DJ8?
35-40 V at its anode will suffice to get a nice operatiing point....


A question for Grey: in the article you mentioned the 2SK246 as a possible subtitute for the J310. It's a direct replacement (despite of the different pinout) or should I change something?.
I have some Toshibas handy.....
 
#20
Today I hooked up a SSTART prototype to a storage osciloscope with a FFT feature..

If I you lower the cascode to about 4.14V, I got a very nice 2nd harmonic cancelation.. .. your milage might avy however, my Idrain were about 20mA/JFET..!
 
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