Build your own High End OpAmp (Jensen 918)

[Brymus]

I found this and thought it is pretty cool:
http://www.waltzingbear.com/Schematics/Jensen/JE-918_documentation.pdf

One directory up has pics of a completed unit top and bottom,sorry of someone has already posted this here.
If not someone will probably have a vero version within a week.

[R.G.]

I have a PCB layout for the precursor or "son of" that one somewhere. The JRE9?? has been around for a while.

On a lighter note, there are some changes that would improve it, notably a current mirror on the input diffamp load.
[edit] Found it. Look up "JRE 990".

[Brymus]

I have a PCB layout for the precursor or "son of" that one somewhere. The JRE9?? has been around for a while.

On a lighter note, there are some changes that would improve it, notably a current mirror on the input diffamp load.
[edit] Found it. Look up "JRE 990".

Here or at your site RG?
I would like to etch a couple of these when I do another batch of PCBs

[R.G.]

I don't think I published it. (the PCB, that is)

[PRR]

> Here or at your site RG?

Google found it fast.

Deane Jensen ran a range of opamp lumps. The _990_ earned great respect (even though it aint a lot different from the 918).

Deane has left this world. His company still does his fine transformers but not his opamp. John Hardy took up that project and his paper gives much detail.

[Brymus]

WOW 50$   for a single op amp,albiet discreet but still  
Hairball Audio has a complete  kit for 25$,still a bit pricey,but etching that 1.5" x 1.5" PCB would be hard using toner transfer method.

Something I would like to try at least once,but not for a pedal.Maybe when I build a HiFi Gainclone.
Or use it as a driver for a 100/200 watt Mosfet or Tip series Si amp.
It would probably sound better than using a TDA2040 as the driver stage which is pretty popular for DIY home amps.

Oh well I will keep it in mind and hopefully remember when I actually have money to throw at this type of project.
I was hoping it was something I could build with standard components like 2N3904 transistors or such.
By just sorting a batch for a matched pair.
A bigger version (3" x 3") would be better for me but the high end specs are critical of the layout and parts type from what I read.
Edit:corrected the size and the Si part #

[PRR]

You can build a "990" with jellybeans. I don't think any changes are needed. While the output won't be short-proof and won't put a whole Watt into 150 ohms, the noise figure won't be much worse, and in some applications the offset may not be a problem.

But 990 is a dead-end. It comes from days of expensive opamps, minimizing the number of opamps, and maximizing the work each one does. Days when men were men and wore white shirts; when loads were True 600 Ohms and we might drive several at once.

And when alternatives were nasty. 741 has hiss and won't carry a cymbal crash transparently. 709 (I had a whole broadcast console full of 709) dies instantly if the output is shorted, and the input is fussy.

It is a pig for power. It is "low low hiss" only for low source impedances. It has a lot of parts. And gobs of gain (begging instability).

In hi-fi you never take original sound (from microphone), only from preamps or pickups already optimized so that any "reasonable" amplifier does not define your system hiss. You never see a 600 Ohm load. For such uses the venerable '5532 is probably a better choice spec-wise.

[wavley]

Yeah, but there is something special that happens when you put a pad after a JE990 or API2520 based preamp's output transformer and push that op amp/transformer combo hard.  There's a fattening to the lows and low mids that's really great sounding.  I started in this direction building an RG inspired Hum Free ABY to break some ground loops and ended up pushing the iron with regular DIP op amps with a "one of these days, I'm going to drive these with 2520s fed by a FET input" I haven't gotten around to it and most likely won't because I like the way it sounds now and I have preamps to push like that when recording anyway, and really... it's overkill, the op amps sound great just the way they are.  But, every now and then I still think that an overdriven API 312 inspired stomp box would be awesome, but certainly not a cheap build.

[Brymus]

Thanks for the replies PRR and Wavely.
It's hard discerning hype from practical when perusing the HiFi threads.
Some people swear by 5532's others say only OPA IC's sound good,ect...
I would like to build my own "op amp" just because it fascinates me,time permiting (which it never does)
I will draw up a layout,a little bigger and see what happens.