918 discrete opamp schemo request

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Samuel Groner

Well-known member
Joined
Aug 19, 2004
Messages
2,940
Location
Zürich, Switzerland
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
 
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

Pacific%20JE-990,%20a.jpg

Pacific%20JE-990,%20b.jpg

The%20Sound%20Steward%20%20TSS-990.jpg
 
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
 
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
 
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
 
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
 
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
 
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
 
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
 
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
 
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
 
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.
 
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
 
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.
 

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