P511 High Performance AC Amplifier
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- Опубліковано 4 жов 2024
- From the Vault to the Bench - a close look at a precision amplifier for use with EKG's and other bio level electric signal recorders. Enjoy!
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Great stuff, I really enjoy seeing industrial / military electronics from this era. The construction methods, connectors, pots, switches... beautiful. So glad you are showing it off. Love those chunky knobs too, they're the correct choice.
I notice that your intro leads straight into a box of meters. I was just poking through my 3 small boxes of meters and thinking how i can never get rid of them.
As a sales engineer, I used to sell Analog Devices components to Grass Instruments back in the 80's. The company was very secretive about what they did and the property was surrounded by a barbed wire fence and gate. The company was bought out and is now gone. Very strange company.
Prob. some shell company for some gov. pgrm.
A money factory if cost of operation ant material of your plant is, "however much you want dollars".
@@resipsaloquitur13Or simply a government contractor
@@resipsaloquitur13 Theres an auto air parts factory here in puerto rico. It hasnt been active in the 10years ive been here, yet the lights are always on and theres never a spot of dirt or grime (it stands out as being very clean). Always makes me chuckle.
Must have been located in a rough neighborhood.
So I used to deal with these in my old job. I worked in hearing research and they were used to record the ABR (auditory brainstem response) from mice. (you might want to clean this thing off, you have no idea what might be living on it) What is crazy is that the P511 had a long life, like super long. The oldest one we had in the lab was from the 1960s and had a small family of vacuum tubes sticking out the back. In the engineering department we had schematics for every version almost up until Grass was bought by Natus who ended the product line. The revisions went from a to v at least. All the way up until the end they continued to use a lot of hand wiring to the front panel. Eventually I met some other people who knew the owners of Grass from their time as recipients of the "grass fellowship". Apparently they were very proud of how many people they employed in manual assembly work. Those knobs you like, they were made by Grass. Natus basically killed off the product, initially they tried to sell it with a very noisy switchmod supply, later they just ended all the non-human targeted products. These things *require* a +-12V linear supply which if you ever find you should save because it's really nicely constructed.
They made a few different input cables. The most common one had a set of zeners with fets to disconnect everything in the event a non-heart-safe amount of current was leaking. These could be deceptive in that they looked like they just had 3 x 5way binding posts so you assumed they were a breakout. The input stage used matched fet pairs to get a nice high input impedance (by the standards of the day). The version you have might have epoxied these pairs into the TO-5 packages you are finding. I never found one but I know they made a DC coupled version. I imagine this required a lot of manual tuning using padding resistors or something. Later versions kept the input stage fet pairs and the later stages changed to conventional opamps (nicer Burr Brown stuff OPAxxx). They made a battery powered version that used 9V batteries and ran on +-5V, initial versions of that used 1 x 9V with a flyback dc/dc that they tamed to be low noise (wish I had saved a schematic). Later one the portable version changed to dual 9V. That used LT made linear regulators in SOT5 packages. I remember opening that one for a repair and falling out of my chair at the sight of something so modern in a Grass design. The P511 architecture has an odd implication, some equivalent configurations of gain and filtering have different noise floors.
Eventually I designed a replacement for the P511 for ABR recording. Mine fit a subrack that I also made a standard for our lab. It also could run on dual 9V. Because it was just for ABR I dumped a lot of the adjustments that made the Grass P511 kind of fancy. ABR we used the settings of 300Hz, 3KHz with the 60Hz notch filter being optional. I also contributed to a heart rate monitor for use with this class of amplifier that had alarms and an output to our lab computers.
As to using these for audio, keep in mind they are not low noise by modern standards. If you are looking for more to match the unit you have they sold a larger product that they called the "Grass Polygraph" which featured a stack of these in a rack and a multiline strip chart recorder. These turn up on ebay periodically and biologists often buy them hoping to scrounge a few working units out of them. About the capacitors, they don't tend to die even when they are operated for decades in 95F ambient.
This setup was used for neural coding research for cochlear implants. I worked on the design of the current sources used to drive the implants and the recording of the "synthetic ABR" was done using the stack of Grass P511's.
Today you could build one of those just for the cost of the front panel knobs I guess. That’s progress. I still like the old design though. It has class.
I always find it interesting to see how much circuit boards from the 1970s on back vary from what is normal in this day and age, both in color and layout. Same for components.
Yeah the curved traces are always such a joy! And funny that the wires are at an angle.
Fran, a very happy new year to you, hope you had a great Hogmanay. Thanks for all the hundreds of hours of wonderful engagement you’ve given me over the years. I’d love to be able to contribute to your Patreon (I’m due you and Anton Petrov a fortune) but am currently financially embarrassed by the cost of heating here in Scotland. 😂 Love you and your amazing videos, this being one of the best.
As a med student in 1988 these were being used in the cardiac OR for pressure transducers.
simple and effective engineering. discrete components level knowledge was much more prevalent back then. good times!
Grass Instruments of Quincy? I happen to have a SIU-4B stimulus isolation unit from that company. Teeny tiny and totally tubular, uses a steel octal pentode and some RF circuitry. A thing of beauty and a joy for ever. I'm keeping it as a museum piece, will do a teardown of this thing... RealSoon.
Lovely build quality, and excellent manual! I can only imagine the touchyfeeliness of the controls... They used really fine parts :)
I wonder if it could be hooked up to a vital signs monitor, e.g. Tek 410. I've got one... still need to get it going and show it on my channel, it's well worth it.
LM317 PSU, the tried and true! You've got a multi-lifetime supply of 317, re-create all you want :)
And the video I promised (and waited until Fran's went public):
ua-cam.com/video/qsWcHUyEc4I/v-deo.html
I just love nerding out on your videos. We seem to share that "I wonder what makes that tick?" gene. Subscribed and happy about it.
I knew it. I had that feeling all long. I am not only one out there with a vault containing these things.
Wow! A Grass! Fantastic biomedical equipment. I spent thousands of hours listening to sapphire tipped Grass pens scratching on miles of fan folded paper.
i see the precision resistors are just 1% tolerance. The 5% resistors show sharp corners, which tells they are Allen-Bradley hot molded type, military qualified as high reliability parts, although probably cheaper industrial versions -not gone through the expensive burn-in. I thought the black tubular molded semiconductors might be matched pairs, such as TD101, TD201 and TD401 that I have at one time used for my differential amplifiers. However, the schematic showed they were FET/bipolar combos. Neat! I was also hoping to see the part number of the metal can ICs. At the seventies, there were already some amplifiers that were sold as better replacements for the ‘741. The front panel listed frequencies suggest something faster, anyway.
Might make an interesting microphone/instrument preamp, with the right connections added. The input is balanced, very high impedance (22 Megohms between high and low input leads), and it has an unbalanced, emitter follower output capable of maybe three volts RMS undistorted. Happy New Year!
It was/is not uncommon to use lower tolerance (less accurate) parts where better ones are not needed by the circuit. I doubt that Grass' rationale was to just use what they had on hand.
Those few black round potted devices are almost certainly transistor pairs, with two BJT's joined together thermally and potted. Sprague was well known for having a whole series of variations on that theme, and they look just like that. These days, we can buy monolithic packages with several matched & thermally tracking transistors in a DIP or other package, but back in the early 70s these were probably all that there were.
That wiring practice might or might not be influenced by military preference.....I have torn into quite a few pieces of military electronics and while I have seen lots of the square bends, I have seen just as many device with normal sweeping bends. But in normal non-military industry, I have never seen a manufacturing specification that did not prohibit square bends in wiring of any kind. Having said that, back when my engineering job included inspection of panels and assemblies built by subcontractors, I quite often had to reject on the basis of seeing square bends, in violation of specs to the contrary, and the culprit always turned out to be some ex-military technician who thought he knew better and to hell with the specification. I also wonder why anyone would have ever preferred square bends, when doing it that way is just asking for metal fatigue due to vibration (less critical of course in equipment that is not likely to be exposed to vibration), and so much military stuff DOES get exposed to vibration.
And yes, I would tend to agree that somebody at Grass was probably ex-military and just had to use those awful squared-off 'knobs'. The military likes them probably because they can be more easily operated by gloved hands, injured hands, etc. And the very stiff detented switches also suggest an intention to use in some kind of military, or similar, environment. But this equipment seems to be specialized biomedical or something like that, so the ergonomics seem all wrong. Again, it might just be that somebody at Grass (and from the sounds of it, it might have been a small operation with few people) was ex-military and just could not think differently.
I'm a retired Neuroscientist and these were modules used in a large rack mount Polygraph using Ink plot pens onto paper like a Richter scale (commonly recognized). You are absolutely correct that these are the HIGHEST quality electronics, They are extremely clean and accurate, I call them NASA grade. You can see them as "Lie Detectors" in old crime shows like Drag Net, Each Module Pre-amp was connected to one of 17 channels in a large rack for blood pressure, heart rate ECG, respiration rate, skin conduction, EEG or whatever extremely small signal or transducer you want. They were our E-Phys "tinker Toys" I saved every one from our Dept in 2000's for my retired Guitar shop electronics It is Rumored that "Dumble the Great" started out at Grass! His organization of the circuits are clearly seen in these Preamps! They are easy to HACK for guitar purposes. . I can share pics, transducers and cords if you wish. We used them for over 30 years...NASA Grade. Respect!
Top notch electronic parts and construction for the 1970's.
thanks for sharing Frannie, reminds me of reading about the first string Galvanometers used for ECGs back in the 1800s...Electrophysiology, the study of biological voltage changes, is fascinating stuff, especially historically, if you look into it. I also read that for ECG you need bandwidth of about 1 to 30 Hz. You should totally try to get it fired up with your recorder & fashion some sort of crude ECG or EEG experiments.
Wow. Grass Instruments. This is so cool.
I'll bet these cost a pretty penny back in '77! Those knobs (machined aluminium?) are great.
I've seen brain-wave monitor systems, took up half a rack and had like a dozen of those Grass amplifiers. Looked expensive but nobody bought it at the surplus store. Not a lot of applications for those.
I love audio gadgets.
Nice knobs, thanks for showing this piece of engineering.,
Interesting to see technology on the cusp.
It would be interesting to see, from the schematic diagram, where they thought it was important to use high vs. low precision resistors / capacitors. I'm also curious about the maximum bandwidth of the amplifier. Since Grass Industries built biomedical instruments, it might be "high fidelity for low frequencies".
If I had to take a wild guess this is probably originally purpose built in-house for God knows what.. That case is so crudely designed even by 1977 standards with a lot of old surplus parts. Very strange
You would have a bunch of these in a rack with a multichannel chart recorder, typically used in medical applications usually for EEG measurements.
Yes, hence the duplicated input and output connectors on the rear, they would be all wired internally in the chassis so the front starys uncluttered.
Nice ac amplifier 😊
Those RN60D resistors are Corning Glass Works precision military grade metal film resistors. The component catalog [sic] that I found these in doesn't specifically state that the body is glass substrate, just metal film, so I'm guessing they're ceramic like a normal metal film resistor.
I've seen a few microphone preamps that leveraged instrumentation amps for their front end.
I think Eddie Ciletti had a schematic in EM back in the 90s or early aughts.
The knobs are impressive
Fran, I'm a 50 year old Filipino/White (french) mix in the SF Bay Area.
I'm an entertainer here teaching folks how to paint for the first time while we drink alcohol.
It's hilarious!
Just wanted to let you know I think you are so cool.
I truly appreciate all your energy it takes for this show.
May your next meal be delicious!
14:08 "brain muscles", must be like the aliens in the original Star Trek "the cage".
It's been a long time since I've seen a Grass preamp. Grass used to be top of the line EEG equipment.
"Knobbage." Wonderful!
Nice to hack into a cool audio amp.
Especially with that chassis/case.
I'm betting that the T-05 resin impregnated packages are matched pairs of FETs.
Very cool piece. Loved the video Fran....thumbs up as always!!!
I think those “potted” black components are matched transistor packs, maybe matched and potted by the manufacturer..?
Get ahold of me about those connectors, I probably have at least one. It would be cool to see this working!
Love the teardowns, any older tech... Seeing the circuit design is always fascinating
Those rn60d resistors are metal film I think? I have heaps of them from old industrial instrumentation. The ones I've burnt up are metal film at least haha
0:50 well in that case I demand both the vault tune AND the lab tune 🤓
Very much appreciated.
Cool, old school stuff....
Happy New Year Fran!
Pretty snazzy. Wonder why they didn't also loom the wiring? I mean, it's probably not going anywhere where vibration is consideration, but if it's hand-assembled by a company that builds mil-spec... 🤷 Maybe some effort at cost-cutting?
Happy New Year, Fran.
Additional info: High Performance AC Preamplifier for Evoked Potentials, EEG, EMG, ERG,
etc.
Benchtop configuration - Model CP511
Rackmount configuration - Model P511
The 511 series features high gain, adjustable filters, low noise and an output which is easily interfaced with peripheral
devices such as computers, tape recorders, oscilloscopes and recorders.
The CP511 is enclosed in a compact, rugged, all-metal chassis that is easy to stack vertically or horizontally. Optional
rack-mount hardware allows two units to be mounted side-by-side in a standard 19" rack while using only 3.5" of vertical
space.
The P511 is a rackmount unit designed to take up less than 2 inches of 19" rack space.
Hello from Kansas City, thanks for the video lil lady.
nice knobs.
Happy New Year
Those look like level slides for a sound board. Not a piece of rack mounted eq.
I thought that was going to have vacuum tubes in it cuz I have two of those that have tubes and a few transistors but mostly tube
14:48 LM317 fanboy here
I wonder what would happen if you put a guitar signal into it and used it as a guitar preamp 🤔🤔
You'd go to 1100... probably a waste of precision if you're clipping that hard.
Very few electrolytics? Whats the output gain?
Seems pretty old fashioned for 1977, more like something you'd see from the late 50's or 60's.. Like the case, knobs and board were all crudly constructed in-house. Very strange.
I tend to prefer Bourne to Allen-Bradley for potentiometers, but that's just me.
رائع
Pardon my total ignorance. Is this an audio device? OK, guess not.
More info in the description.
AND the manual is in REAL English!!!!!
AB wrong deduction .............they are there for a reason !
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I only come here because I love you.
Happy New Year, Fran!