Idea for a dedicated Rhodes preamp, need help !

[Migs 31]

So I just ran the autorouter, somehow it won't work for me at night, probably due to too much traffic on the server.
But it worked fine this morning.
117 connections, 0 fails, 1 via;

That doesn't look too bad to me ?

How would you normally approach this ? Click the order button ? or would you start editting stuff ?

Hi,

I second/agree with what @rock soderstrom mentioned on previous posts. I think you got it.

Also PermO, can I suggest you make also a DIP version (SOIC to DIP adaptors are common now).
There's still a lot of good DIP chips available out there. Just to have the choice.
And not all of us (old/ageing folks) are comfortable with SMD soldering.

My two cents.
M

 

[rock soderstrom]

What I also notice is that the autorouter changes layers in an unmotivated way. I would only try to change the layers if it is necessary or makes more sense.

Some examples

 

[PermO]

I felt the same way...I was amazed at how quickly I got into the game. My main criticism is the component handling in the transition from the schematic to the PCB design.

Yes sometimes you pick a "nichicon 33uF 35V" from the list and... 100uF 50V from China ends up on the board... pfff.
So I'm now only using these components to get the right footprint.
I'm sitting here with a handfull of parts and a piece of prefboard "counting holes"

@Migs, I've been thinking about doing just that, as I now have found a supplier that still carries the DIP versions. for both chips. So I will remove all SMD components from the board, and enlarge it a bit.

I'll also be adding some extra gainsteps so the total nr wil be 12 instead of 8

 

[PermO]

The bit on the right side of R9 I have corrected this was also caused by net labeling.

The bit on the left side is correct as it only connects to "P" wich is a ground contact.

Don't worry about this layout, I'm updating the schematic now.

 

[rock soderstrom]

Yes sometimes you pick a "nichicon 33uF 35V" from the list and... 100uF 50V from China ends up on the board... pfff.
So I'm now only using these components to get the right footprint.
I'm sitting here with a handfull of parts and a piece of prefboard "counting holes"

I think it basically boils down to the same thing in all PCB design programs. In the long run, you will put together your own portfolio of component symbols and footprints that you trust because they have proven themselves.

Then it becomes really good and fast.
Simple editors for that and good import functions are important for me. EasyEDA does this relatively well.

 

[PermO]

So I've updated the schematic with the updated woo & foofery on the FX output.


I'll have to add a bunch of pads for the switches and pots as they will not be on the board... or maybe they will ?

It could look something like this in a 145 x 120 x 40mm stompbox, frontpanel explains the switcheroo...


Now cook some dinner....

 

[ccaudle]

There's an unbalanced instrument input (source in general is floating) and an unbalanced FX or reamp output that share the same groundpin on the PCB.

That should work out well, the unbalanced connectors are on the same side of the chassis as the XLR connector in your recent drawings, so you can have the unbalanced connectors connect directly to the chassis, and that pin you have drawn becomes the single point that the circuit board ties to chassis.

 

[PermO]

Makes sense now, thanks a lot !

 

[orphanaudio]

I have been following this thread for a while and it seems that no one (AFAIK) has brought up the necessity of mechanically fine-tuning the Rhodes tines & pickup system for best tone balance and harmonics, so your new preamp will be able to do its intended job.

Comments about dull tone and less than expected results for what is likely a really great preamp, are in most cases not the fault of the preamp or its design, but more likely just an out of adjustment piano.
Just as any acoustic piano requires regular tuning, maintenance, regulation and adjustment to perform at its peak, a Rhodes electric piano is no different and requires regular care and feeding to sound like the Rhodes we have all heard on hit records for decades.

Mechanical tuning, registration and precision placement of Rhodes tines, pickups, hammers and harp were the bedrock of the legendary Dyno-my-Piano mods from the great Chuck Monte (briefly mentioned earlier in this thread), as heard on Rhodes owned by players like George Duke, Joe Zawinul, Herbie Hancock, Tom Coster (and countless others) as well as one particular Rhodes available from Leeds Rentals LA that had graced countless Top-10 hits over more than 35 years. There was even a "Percussion Pedal" mod that changed the position of the harp/tines with respect to the pickup array to allow the performer to completely change the tone of the piano while playing.
The DynoMyPiano active preamp system actually came later to allow capturing all the tone those mechanical mods brought to the table, as well as related contributions from Songbird (Tri-Stereo Chorus, et-al) and several famous LA-based recording console designers who lent their genius to even more advanced Rhodes/DynoMy preamp designs.

Check out these links for enjoyable musical history lessons, a huge database of useful information, technical data and interviews with Chuck Monte and the players who still love his work.
You will also find complete Rhodes service manuals at the fenderrhodes.com site.

https://www.facebook.com/DynoMyPiano/http://www.fenderrhodes.com/history/dyno.html

Below are links to Vintage Vibe for Rhodes restoration kits and repair parts, their tech-tips pages, and the Electric Piano Forum for endless discussion on similar topics.

https://www.vintagevibe.com/https://ep-forum.com/smf/index.php?PHPSESSID=d3a7794864e0806dcea0770d9bc547ee&https://www.vintagevibe.com/blogs/news/tagged/tech-tips
Please understand the intent of this is not to send you down a long rabbit hole of research and learning away from your original preamp project, but as a fellow Rhodes owner, to find all the ways you can drastically improve your instrument with just a little mechanical tweaking,..... and get even more out of your preamp and piano.
Decades on the road as a keyboard tech and live sound engineer and hours spent inside my own my Rhodes (and many other vintage keyboards) have given me a world of knowledge and enjoyment of these instruments to pull from. Just experimenting with the sonic effects of tine alignment to the pickups (see attached image from Rhodes service manual) using my ears, an oscilloscope and some basic spectrum analysis tools, have offered incredible results.
Even a small change in proximity, elevation or alignment of the pickup or tine can drastically change the harmonic content and volume of each note.

There is a LOT more inside a Rhodes to understand and adjust (hammers, escapement, dampers, snubbers, tone bars & clips.....), but take it slow, mark positions or write notes on where things were before you start making changes and make small adjustments. Its VERY easy to get things out of whack and a lot of effort to get them back if you don't have an idea of where they were to begin with.


Please enjoy the data above. I hope you research as much as you brain can handle and report your success back to hungry GDIY members.


Ken Hirsch / Director of Engineering
Orphan Audio www.orphanaudio.com
Quad-Eight Electronics www.quadeightelectronics.com
Electrodyne Audio www.electrodyneaudio.com (a division of Orphan Audio)


"Education is the cure for everything"

 

[PermO]

I don't have a dodgy piano in the sense that it was bought fully restored and setup by a respectable local company.
And I went trough all this information when I was planning on buying one.

But good to have it here

So, back to the preamp.

After some delay by out of stock parts, I'm back to the Preamp.
I've got a box and some hardware so I can play with...

Form factor;


I wanted to keep it as small as possible and this box should just fit all the parts including the batteries.
145 x 120 x 40mm
I setteled with Elma rotary switches as I got a good deal on them.
I printed a drilling template on self adhesive paper so I can design the final lasercut vinyl sticker from the same template to match the holes.

The pin 1 problem, it keeps bugging me...

Pin 1 ties to chassis, it's a shield, not ground... yup, clear.

But if we have metal jack inputs outputs, unbalanced, directly on the same chassis ?
With an instrument as input, just fine.
But now a synth, with a powercord, and we use the box to reamp it into a guitar amp to mic it, and that amp.. has a powercord ?

So I went with isolated jacks now so I have a choice... would a added ground lift switch make sense ?
And where to lift ?

The thing is, you'll never know what people are going to do with it.. non of these boxes function on their own, it's the interconnectivity that makes them play. And as it has no transformers this box could be the main culprit in causing groundloops ?

(Boxes don't cause groundloops, people do)

 

[abbey road d enfer]

Form factor;
View attachment 121286

Nice job!

But now a synth, with a powercord, and we use the box to reamp it into a guitar amp to mic it, and that amp.. has a powercord ?

Ground loop, of course. Conflict of interest between audio performance and safety regulations.

So I went with isolated jacks now so I have a choice... would a added ground lift switch make sense ?

It may...

And where to lift ?

Try lifting pin 1.
However, it would not be as good as eliminating the primary cause, i.e. the differential voltage between chassis. Making sure both sender and receiver are powered from teh same outlet is key.

The thing is, you'll never know what people are going to do with it.. non of these boxes function on their own,

Education...

 

[PermO]

Ok, so how to design a circuit board on a screen that will exactly fit all connections in the real world ?

I came up with this;


I used a piece of prefboard to make a mock up, the prefboard shares the same grid pattern as the software, so now I can count holes on my screen and be pretty shure the thing that I am drawing will actually fit.

The metal studs are just placeholders to keep it in place, eventually I'll probably use two stick-on studs at the battery side of the circuit board.

The white dots are my pot connections.

Groundlift switch added.

I'll make sure to oversize the mounting holes for the jacks to have some margin.
I also notice the jacks should be mounted slightly lower, but that's what prototypes are for.

The XLR may be connected with a small piece of screened wire directly to the THAT chip outputs.

The goal for me is easy assembly...

 

[MidnightArrakis]

Ok, so how to design a circuit board on a screen that will exactly fit all connections in the real world ?

[how to design a circuit board on a screen that will exactly fit all connections in the real world?] -- My answer to your question -- may -- be beyond either your mechanical expertise and/or CAD-software capabilities, but at least this is how I accomplish what it is that you are asking:

First off -- You will need to have a fairly capable 3D mechanical design CAD-modeling program.

Secondly -- Either from Digi-Key, Mouser, SnapEDA, Ultra-Librarian or other CAD-model providers.....you will need to download a library of 3D CAD-models of all of your primary-important components.

Third -- Within your mechanical design program, you just need to create a CAD-model of your PCB using the dimensions required for your project.

Fourth -- (The "FUN" part!!!) - Again, within your mechanical design program, you first import your PCB CAD-model back into it as your foundation. From there, you simply start importing the CAD-models of your components (i.e., switches, pots, LED's, connectors, battery-holders, etc.) and then placing them onto the PCB exactly where you want them to be. Once you have this step completed, you then "SAVE" the entire PCB and components as an "Assembly".

Fifth -- Assuming that you have already downloaded a CAD-model of your enclosure, you import it into a "New" assembly file and now it becomes the foundation for your "Project Assembly".

Sixth -- After you have imported your enclosure CAD-model into your mechanical design program, you then import your "PCB Assembly" model into the enclosure CAD-model. Once you have the "PCB Assembly" placed within your enclosure CAD-model, all that you gotta do is then use the mechanical design programs' measuring tools to obtain the dimensions of where all of the enclosure hole cutouts are going to be.

Seventh -- From there, and once you have all of the dimensions obtained, you go back into the enclosure CAD-model and perform the function of placing all of the enclosure cutouts into it (in my software it is called "Extrude Cut"). Now you have a 3D CAD-model of your enclosure that has all of the component cutouts placed into it. YAY!!!

[I find the traces and many soldering pads too small] -- YES!!! ALL of the tracks on your PCB are WAY TOO SMALL!!! Forget about using the auto-router and route the board manually by hand. Since the PCB is double-sided anyway, don't be afraid to insert a couple of vias on one track so you can "jump over" another track. Using a shorter route is typically preferred over a long and winding track just to avoid a couple of vias. My 2-cents.

>> Your HAMMOND enclosure:




/

 

[PermO]

Yes, I understand, in the digital world it's all perfect, but in the end there's a box on my desk and a bunch of parts and there's a drillpress in the corner.
I'm kinda old school, and in this case a paper template is more help than a perfect picture on my screen.

The box is not of Hammond origin, it's 145x120x40mm a size Hammond does not have.

I actually have the "home" version of Fusion360 but that's not going to help me with this project as I am not having anything manufactured exept for the circuit board (that design is far from finnished as I need mechanical design concept first to get a fit)
The mechanical design is done, I like how it looks and feels, next step is to take the circuit board design from the mock up, use the right trace width and pad sizes, footprints etc...

And use my template to have a nice "frontpanel" vinyl sticker printed and lasercut with all the holes in place.
Boxes will go to a local powdercoater.

If I would need to make a lot of these I would have a local company cut me a steel drillguide, but for 5 pieces a paper template will do just fine.

For me as a hobbyist this is the easyest, fastest and most fun way of doing it...

 

[MidnightArrakis]

The box is not of Hammond origin

use the right trace width and pad sizes, footprints etc...

For me as a hobbyist this is the easyest, fastest and most fun way of doing it...

[For me as a hobbyist this is the easyest (easiest), fastest and most fun way of doing it] -- And.....I get it!!! Different strokes for different folks!!!

However, what I detailed in my previous response is what I do even for my own personal projects and I am only having a single unit made. That's just my normal work-flow whether I am designing something for myself or for some defense contractor. The designing process is all the same to me no matter what.

[The box is not of Hammond origin] -- In one of your earlier posts, you had made mention of using a particular HAMMOND enclosure, so I just went ahead and downloaded it.

[use the right trace width and pad sizes, footprints etc.] -- GOOD TO HEAR THAT!!! YAY!!! Check these out:











>> BEST OF LUCK ON YOUR PROJECT!!! <<

/

 

[MidnightArrakis]

next step is to take the circuit board design from the mock up, use the right trace width and pad sizes, footprints etc.

For me as a hobbyist this is the easyest, fastest and most fun way of doing it...

[next step is to take the circuit board design from the mock up, use the right trace width and pad sizes, footprints etc.] -- May you find untold mental enlightenment and newly found PCB design engineering insights within the URL link provided below:

850MB+ of PCB Design Reference Materials
https://mega.nz/folder/6uRS0bqZ#6OoLf3qKN2F474FcSM2JdQ
/

 

[PermO]

Thanks !

Having the thing in front of me, playing with som bits and parts inspires me, that's how things grow on me.

Testfitting;


By swapping the instrument input and FX output labeling the layout will make more sense, so that's what I'll do.

THAT output driver sits close to the XLR, OPA sits close to the input.

PSU filtering starts outwards so I will end up with a filtered + / - 18V in the middle of my board, close to the IC's.

Going trough my parts I found that I have a huge load (50+) of Beyerdynamic TR/BV310 001 001 200Ohm output transformers, I'm thinking about using them on the FX output, TRS balanced. Having that transformer there, the chance of groundloops happening will be less I guess.
When an unbalanced jack is used the transformer will keep the "dirty ground" away from my circuit board. Sleeve will only connect to the enclosure.

Another thing that I would like is some form of battery indication, on the previous version I put some isolated pins on the outside of the enclosure so in the off position you can probe these with a multimeter, I don't want to do this as you can have this box sitting in your pocket, and trow in your keys as well, it might end up as an out of controll pocket heater and you will probably have to buy a new jacket and someone is going to complain about the carpet when you deadshort 4x 9V Lithium batteries. (My first version still reads 36.2V now after many hours / days of use)

The circuit can drop quite a bit in voltage and still function just fine, there's no voltage regulaters that will crap out, so it will just very slowly fade away, probably still fine way below 20V.

I think I will tweak my LED in such a way that it no longer lights up at +/- 20V, the LED should die way before the audio does, so if you no longer see a LED it's time for fresh set of batteries.

This could work I guess.

I'll do some breadboard experiments with the passive part / tonestack of the FX output, listen to it, try a transformer see how that fares...

 

[PermO]

 

[MidnightArrakis]

Thanks !

Having the thing in front of me, playing with som bits and parts inspires me, that's how things grow on me.

try a transformer see how that fares...

[Having the thing in front of me, playing with som bits and parts inspires me] -- You need to play with things "in reality", whereas I am able to play with things "virtually".

[that's how things grow on me] -- Like mold on outdated bread!!!

[try a transformer see how that fares] -- Based upon the information I could glean from a 1976 BEYERdynamic "Input Transformer" catalog (Page-10), I went ahead and created a 3D CAD-model of your TR/BV310 001 001 transformer. I have saved the CAD-model also as a -- .STEP -- file, which "may" be imported by your FUSION 360 program. Since I don't know anything about FUSION and its capabilities, I don't know if it is able to import .STEP files. Perhaps you can fire it up and let me know what types of files that it CAN import and, if necessary, I could do a "Save As" as one of those other file formats. A good one to look out for is a "ParaSolid" format file, which is either -- .x_b or .x_t -- extensions. Those work really well.




Of course.....in order for me to be able to attach this CAD-file here in this forum thread, I had to rename the file and add-on the extension of -- .pdf -- to "trick" the system. So, all ya gotta do is rename the file again by removing the -- .pdf -- extension and you should be "GOOD TO GO"!!!

/

 

[PermO]

Nice job on the transformer !

I have not tried putting it in Fusion360 yet, I think it will work, I tried with the Hammond box file and that opens just fine.

But I don't have the file for the box that I have.

The thing is, creating this thing in Fusion360 for me will take way more effort than to just build it in the real world.
Recreating all parts on my desk will be a tremendous effort... If I want to see if it fits, I just grab one, and see if it fits.
And even when I would have a perfect digital design with all bits and pieces placed perfectly,... it's NOT going to help me, I don't have a robot assembly line and I am not producing 100.000 units in China.

There's a box of parts, and some tools on my desk, how is Fusion360 going to turn that in the actual thing ?
It won't.

It's callipers, protractors, pencils, templates, a drillpress... and me, in my lovely little workshop.
Also, I don't want to outsource the work that I love doing, I see so many people complaining about mechanical work "Oh I need to drill a XLR hole, oh the horror" ...outsourcing everything is not the DIY spirit.
I drill, paint, letter / label all my panels by hand, I love it ! it's my ZEN time, it's how I forget about this deranged world I'm living in and have all my focus on creating something nice, something beautyfull.




I love that !

I really appreciate your effort, and I will gladly work with you on the more sophisticated rack unit we have discussed, so keep the transformer, as we might use it in the rack version also.

This is just me doing a small run of 5 units for close relations, and if more demand arises I will do some more, I see it as a nice small side hussle if I could occasionally sell one of these.