Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
918 discrete opamp schemo request
« on: July 17, 2005, 07:08:17 AM »
Hi
For my endless research on discrete opamps I would love to study the secrets of the 918, a parent of the 990; D. Jensen designed the former for a company called "Pacific Recorders and Engineering".

A web search made me believe that this company is not in business any more, so I hope it is OK to ask for the schemo.

Thanks,
Samuel


Bo Hansen

918 discrete opamp schemo request
« Reply #1 on: July 20, 2005, 08:51:53 AM »
Samuel,

I remember I have something about Pacific Recorders & Engineering Corp. version of JE-990, but the 918 I don`t remember.

In the end of 1990`s,  there was also a other company "The Sound Steward" that made a own 990 version, the TSS-990.

Here is what I find in my archive:

--Bo



I met a man with a dollar, we exchanged dollars, I still had a dollar.
I met a man with an idea, we exchanged ideas, now we each had two ideas.

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
918 discrete opamp schemo request
« Reply #2 on: July 20, 2005, 09:22:11 AM »
Thanks, Bo, for this documentation!

http://www.soundsteward.com is still alive; the owner Steve Hogan posted about the 918 some time ago. I'll ask him about the schemo.

Samuel

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
918 discrete opamp schemo request
« Reply #3 on: August 15, 2005, 04:20:25 AM »
Today I got mail from Jensen with 9 pages of schemos, application info, measurements and orignal notes by D. Jensen. The circuit is public domain, so I'd be happy to scan/redraw/retype these pages if interested.

Samuel

pucho812

918 discrete opamp schemo request
« Reply #4 on: August 15, 2005, 10:47:18 AM »
samuel. I would be much interested in that. If you need a place to host them I can do that too.
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
918 discrete opamp schemo request
« Reply #5 on: August 15, 2005, 02:00:26 PM »
918_documentation.pdf, 5.9 MB.

Scans from a copy, so not perfect reading.

Looks like it would make an excellent APIish mic pre with a 1:8 or 1:10 transformer. Probably easier to build than a 990C, but very likely with similar distortion performance at low and medium closed loop gains with reasonable loads.

The mentioned +/- 24 V extra sheet is unfortunately not included, but I believe that changing the three 27k resistors which bias the diode strings to 43k is all that is needed.

Who is making boards? :cool:

Samuel

pucho812

918 discrete opamp schemo request
« Reply #6 on: August 15, 2005, 02:53:49 PM »
here is link to the JE- nine 90 schemo

http://www.dibsplace.com/design/CIRCATS/je-990.pdf
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

Bo Hansen

918 discrete opamp schemo request
« Reply #7 on: August 15, 2005, 04:07:16 PM »
Samuel,

Thanks for your schematic scans, very nice to have this among the other pro-audio discrete op-amps in my tech archive.

As you probably allready know, Dane Jensen have design a lot of op-amps around the years, I think some of them was when he work for Quad Eight and maybe also Electrodyne.

BTW, besides my own development of discrete amp design, include op-amps, I have as a hobby to collect old time solid state pre-amps tech/schematic information, (and even orginal potted modules and cards) for both pro-audio and high end Hi-Fi gear.
It is very interesting to study why different euquipment sounds and behavior in a particularly way.

There are some designs that I`m very currios to examine, build, measure and listen on:

1. The very old "Holzer op-amp" (octal plug-in type)  designed by David/Howard Holzer, the Haeco company USA.
I have heard that this op-amp was involved in many consoles that A&M studios use in the late 1960`s

2. The OP-amp Labs 360 and 425 series (octal plug-in type)

3. The console amp designs that the Sheffield Lab Recording/Douglas Sax and Bill Schnee use on the "Missing Link" records and the Telma Houston "I`ve Got The Music In Me"

4. And of course George Massenburgs older Op-amps types that he use in the first genaration equalizers and mike preamps.

I have search for this information under many years, but without result, if some of you have any idea, please let me know.

--Bo
I met a man with a dollar, we exchanged dollars, I still had a dollar.
I met a man with an idea, we exchanged ideas, now we each had two ideas.

Gus

918 discrete opamp schemo request
« Reply #8 on: August 15, 2005, 05:51:17 PM »
Samuel

  Thanks for the scans.  This looks like a fun easy circuit to build.

 This is my opinion, good designers often lay out the schematic almost as a good PCB layout.

  What I mean page two could be used as a top view of a PCB

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
918 discrete opamp schemo request
« Reply #9 on: August 16, 2005, 02:30:06 AM »
Bo, I don't know if you have seen my post in the discrete opamp META about the opamp history document: Web_ChH_final.pdf
It does not cover any of the opamps you mentioned and it is not audio-related, but I found it very interesting nonetheless. Many schemos and descriptions of toobe- and solid state discrete OAs.

BTW, does someone understand the remark to R3 on page 4 of the 918 docu? I read "required only on 318". 318? Another discrete opamp? He does not reference to the IC, does he?

Samuel


Bo Hansen

918 discrete opamp schemo request
« Reply #10 on: August 16, 2005, 06:15:08 AM »
Samuel,

Yes, I have this OP-amp history dokument, very nice reading.

Regarding the R3 resistor, some time you must put a resistor in front of a input terminal to get rid of unstable behavior and RF-interferense.
(like a grid-stopper on a tube)

--Bo
I met a man with a dollar, we exchanged dollars, I still had a dollar.
I met a man with an idea, we exchanged ideas, now we each had two ideas.

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
918 discrete opamp schemo request
« Reply #11 on: August 16, 2005, 06:38:36 AM »
Sure, but why is he refering to a "318"?

Samuel

Bo Hansen

918 discrete opamp schemo request
« Reply #12 on: August 17, 2005, 01:59:40 PM »
Samuel,

I have notice you live in Switzerland.
For 10 years ago I have contact with two company i Switzerland that made discrete mic preamplifers.

Sonosax company in St-Prex, with the FD-M4 modular mic. preamp and the FM-Acuostic company in Horgen, with the M1 Presision mic preamp.

Do you know what they use for type of discrete amp design ?

--Bo
I met a man with a dollar, we exchanged dollars, I still had a dollar.
I met a man with an idea, we exchanged ideas, now we each had two ideas.

rickc

918 discrete opamp schemo request
« Reply #13 on: August 25, 2005, 08:57:11 PM »
the reference to the '318' is to the LM318, which was just about the fastest monolithic (IC) opamp you could buy in the timeframe that Deane designed the 918. Deane determined that the input stage in many opamps, discrete and otherwise, had a possible parasitic oscillation, and the cure was the 1k stop resistor in series with the non-inverting input.

I don't know the mechanism involved; I was just fortunate enough to have known Deane during his lifetime.

I have built and used these opamps before. You should note that the design dates back to the late 1970's. At one time, I had a pcb design for this that fit into the API-2520 physical format.  It was a b**ch to stuff. You had to do it in layers.

--rick chinn

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
918 discrete opamp schemo request
« Reply #14 on: August 26, 2005, 02:03:17 AM »
Thanks, Rick, for the answer. If it happens that you find your PCB design, I would be very interested! Do you know of other unknown opamps designed by Jensen?

Bo: did you check your e-mail?
Samuel

rickc

918 discrete opamp schemo request
« Reply #15 on: August 26, 2005, 02:29:10 AM »
no, AFAIK, the 918 and 990 are the only discrete opamps that Deane designed. Now I'm not counting anything that he may have done while he was at quad-eight. Does anyone know if he ever worked at Electrodyne? Both of those companies had very similar (at least externally) products.

waltzingbear

918 discrete opamp schemo request New
« Reply #16 on: May 05, 2007, 03:30:55 PM »
I know this is an ancient thread, but I do have a pile of 918 op-amps from PR&E. attached are links to scans of the top, bottom and cover of the unit. enjoy

Alan Garren
Waltzing Bear Audio

http://waltzingbear.com/ProAudio/Jensen%20918%20cover%20copy.jpg

http://waltzingbear.com/ProAudio/Jensen%20918%20board%20top.jpg

http://waltzingbear.com/ProAudio/Jensen%20918%20board%20bottom.jpg
« Last Edit: December 15, 2009, 05:26:06 PM by waltzingbear »

rickc

Jensen 918 opamp
« Reply #17 on: May 05, 2007, 06:29:35 PM »
I could probably find my pcb layout for the 918 in a 2520 pinout.

But someone needs to ask for it.

Waltzingbear: thanks for posting the photos. I always wondered why Deane designed the 918 (aside from the exercise). He also did some designs for PR&E that used the LM318 and a class AB emitter follower pair. They used these in some of their broadcast consoles.

They also later made a version of the 990 opamp.

Bill Whitlock @ Jensen Transformers could fill in a lot more of Deane's early history with the LA console manufacturers. You can contact him thru the Jensen Transformers website.

rafafredd

918 discrete opamp schemo request
« Reply #18 on: May 08, 2007, 07:42:24 PM »
Quote
But someone needs to ask for it.


Do we?  :razz: So... here it goes.

I would love to see it!


 

Related Topics

  Subject / Started by Replies Last post
0 Replies
1526 Views
Last post July 27, 2004, 07:46:45 PM
by Steffen
0 Replies
1310 Views
Last post July 31, 2006, 01:20:40 PM
by bbuz
6 Replies
2867 Views
Last post December 02, 2007, 12:47:25 PM
by jensenmann
4 Replies
1206 Views
Last post March 30, 2012, 08:40:07 PM
by pucho812