Dyno my piano

[Bernardduur]

I would be quite interested.......

Seeing your sig; Nederlander?

[Eb7+9]

i'm very curious about your disstatisfaction with the suitcase preamp. There is of course this big contradiction: the standard config Stage + Twin with definite tubesound versus the ('full-version') Suitcase (full but solid state). It's quite a different sound but if your (also) a guitar man you're bound to prefer the tubes. I have a 1977 stage 73 myself, but in my current band I'm mostly playing guitar, so the the keyboad player uses the Rhodes on his solid state amp, it sounds terrible. When I plug it in to my BF-ed Super Reverb, it's magic. Do have to adjust settings radically, but still very well-defined, clear sound, with barking dynamics. With your amp, I'm not suprised you want  to straightjack it...

I don't think I mentioned being dissatisfied with the Suitcase pre ... the problem I had with my Satellite had to do mainly with the ground loops between the twin powered monitors and the pre - which I fixed using isolation transformers ... my concerns had more to do with recording - for live playing it's no big deal ... aside from this I have reasons for thinking the Dyno circuit is inspired by the tone circuit of certain tube amps - any mid/high powered Fender BF/SF amp - since they are nearly identical in "double hump" filtering function - and the hump frequencies are not that far off from each other in these cases ...

Why does it need a noise gate? From the time I spent reading Rhodes fora last year, I seem to remember that they are very susceptible to noise because the pickup field is so broad. If you look at the pictures from the VV board, notice how they completed wrap it in copper shielding. I'm just freewheeling here..

I wondered about that too - part of the noise situation with the Rhodes has to do with the length of the feed from the PU to the front of the keyboard where the pre is - about 2-1/2 feet long ... since the Dyno is capable of a fair amount of gain in the hump regions, and also because the circuit isn't balanced, and because the Rhodes cavity isn't shielded either one would have to shield all the components to help minimize total/overall noise ...

Another question still preventing me from having breadboarded the current design is the 15V. Is that really necessary? For the same reasons of noise, I was imaging a stompbox that I could jack between Rhodes and amp and would sit on the Rhodes - maybe not even a bypass on/off...

this is a headroom issue - you can run the circuit on 9v but because the Rhodes PU signal is hotter than a guitar PU signal and the filter has considerable gain with treb/bass controls maxed there's some chances clipping will occur at the output when running on a lower supply ... the circuit will obviously run on 18v and higher - I'm not sure why they selected 15v exactly ... I would breadboard the circuit and try it with 9v and 18v ...

Logically, I would say, through away the noise before you start amplifying anything. I saw it was located at the power source, but you removed it in your drawing. They would go where now is the 1k and ** cap, after the input cap -- is it superfluous because 1k and cap ** perfrom that function?

... then you're not gaiting the hiss produced by the active tone circuits - it's probably best to gate the output of the overtone path, I think that's where it's meant to be ...

So if you really needed a dyno effect, you could wire one up with a ABY box, a mixer and and broadband eq?

I think so - that's the whole deal with the frequency response curves - they tell us what frequencies to shoot for, at least at first ... a broad graph eq might come in somewhat close provided there's no phase-shift issues (which usually happens only when one band is set and min/max and an adjacent one is set contrary to it) ... I suspect there might be some difference in feel between the two - but again, in a band situation you might not hear that difference much ... again, noise/hiss would probably be higher with a multi-band eq ...

Another question I was wondering: what make that a cap should be polarized in the design? Are the ultrasonics polystrene caps?

the ultrasonic can be anything but polystyrene is probably best, the source bypass caps would typically be polarized electrolytics

... hope to see some "official" values as well

~JC

[zjokka]

i'm very curious about your disstatisfaction with the suitcase preamp. There is of course this big contradiction: the standard config Stage + Twin with definite tubesound versus the ('full-version') Suitcase (full but solid state). It's quite a different sound but if your (also) a guitar man you're bound to prefer the tubes. I have a 1977 stage 73 myself, but in my current band I'm mostly playing guitar, so the the keyboad player uses the Rhodes on his solid state amp, it sounds terrible. When I plug it in to my BF-ed Super Reverb, it's magic. Do have to adjust settings radically, but still very well-defined, clear sound, with barking dynamics. With your amp, I'm not suprised you want  to straightjack it...

I don't think I mentioned being dissatisfied with the Suitcase pre ... the problem I had with my Satellite had to do mainly with the ground loops between the twin powered monitors and the pre - which I fixed using isolation transformers ... my concerns had more to do with recording - for live playing it's no big deal ... aside from this I have reasons for thinking the Dyno circuit is inspired by the tone circuit of certain tube amps - any mid/high powered Fender BF/SF amp - since they are nearly identical in "double hump" filtering function - and the hump frequencies are not that far off from each other in these cases ...

I'm sorry, didn't know about your speaker problem, just inferred you plugged from the harp for reasons of sound.
It's seems we're rapidly moving towards to conclusion that the dyno was initially developed to lend some fender 'tube'-like grit to the solid-state Suitcase config? Because why built it into a Rhodes that is played thru a Fender tube amp that has this eq as inherent response? This probably has to do with recording. In the 60-70s they would have preferred to put it directly onto the mixing board to avoid track leakage.

If some dyno are very shril they might not be that by themselves, but due to combintation of dyno + fender tube amp and you might never get eq-ing right on the amp if you want ovetones from the dyno. double double hump?

because the Rhodes cavity isn't shielded either one would have to shield all the components to help minimize total/overall noise ...

"The Dyno Shielding Kit was an option that helped in dealing with 60-cycle hum and other sources of interference. By installing a metal shield on the underside of the harp cover or the Dyno flat top, noise that would normally be amplified by the harp was greatly reduced, if not eliminated completely."

http://www.fenderrhodes.com/history/dyno.php

But wouldn't it be possible to build it as a standalone unit with patch cable to the input like a stompbox?

I have breadboarded most of the design now apart from ultrasonics and diodes. So now I'm wondering:
* If the ultrasonics are in the range you described (0,001uF - 0.01uF), does it matter what type?
* Protection diodes, standard diodes will do? Maybe use leds?
* How do I balance the to filters, by measuring voltage or does it have to go my ear?

BTW BTW: how's yours coming along?

... hope to see some "official" values as well

I have a feeling they are coming shortly...

and ps: another one bites the dust on ebay at +$400

[zeerust2000]

It's been a while since there's been any activity here, but I have sketched the schematic of my own unit and will be building it soon.  Before I post the schematic I want to be sure that a) it works (there are some issues with my dyno unit as it is) and b) that I have indeed got the schematic right.  In the meantime I found what appears to be an authentic schematic buried in a German sit at <www.tasteundtechnik.de>  Just go to the section marked 'manuals and schematics'.  I had my computer translate the site for me, and it's understandable, although I was surprised to find that in Germany Rhodes are avialable in 'steam turbine' and 'gas turbine' models (is this German for 'stage' and 'suitcase' I wonder?)................Good luck, JH
PS....I would post this schematic directly but I can't work out how to attach images here.  Can anyone help out?..........Thanks!

[geertjacobs]

[zeerust2000]

Thanks!..................John H

[zjokka]

Wow, great, cannot believe I never found that, but then the site's gone online only recently, a year or so. The fact that he just put this sacred schematic online is, proof of his selfconfidence as a tech. He's says, you make soldered up your own preamp board, but I've got something that far better, his own Rhodes preamp. I bet it's a hell of a preamp.

Noteworthy that different FETs keep turning up in the different boards.


But there's another point. I had completely forgotten about this, but some years ago a friend allowed me to have a look at his Rhodes. He's a musicology student and excellent drummer who had bought this Mark II off a friend who moved to France for 400 EUR. He used it, but never plugged it in, just used it acoustically when he needed to write out some music. It was strange in the sense that the front panel had a power socket built in where the original nameplate used to be, and indicator LED, on/off switch and HIGH pot instead the bass boost.



When you plugged in the piano and powered it, a terrible hum filled the room. No wonder, with a built in power converter so near to the pickups, I would think and when I put it to the Rhodes forum, they could only agree. No way this was going to work:



I offered to repair the piano, ie rip the active electronics out and rebuild the standard passive circuit. But the guy was kind of protective of the piano, which is strange, with it being uplayable and all. Then he even went to Tanzania for a year, leaving the piano locked away (from me).

I had little interest in or attention for the preamp section that is also included, and thought it would be interesting to add here, as it is IC based. I really should get back to this guy to trace the circuit, now he's back. In the meantime, I just have these 3 year old pictures, which reveal more craziness like a internal (why?) gain pot. At least the IC number is visible (i hope)








...just wanted to add this, will think about getting a better look at the piano and maybe ask to trace it.
JC, didn't you say it would be easier with ICs?

zj

[Eb7+9]

Noteworthy that different FETs keep turning up in the different boards
...just wanted to add this, will think about getting a better look at the piano and maybe ask to trace it.
JC, didn't you say it would be easier with ICs?

(!) ... very interesting and useful info posted here lately - thanx for latest the pics and providing the link to Jacobs schem ... yes, I did mention the possibility of using op-amps for achieving the prescribed transfer - now, I don't know if it's necessarily easier to achieve with op-amps but one thing's for sure with op-amps you don't have to worry about biasing issues and you do get more signal headroom for a given supply voltage than you do with single-ended gain stages, and with op-amps you can elliminate the participation of the Driving-Point Impedance of the gain stages in its role to affect overall transfer profile ... that's unless we want to adhere to Thevenin equivalency - ie., by including an output resistor to simulate non-ideal DPI ...

otoh, like I said before, I like to entertain the possibility that reduced headroom in such a circuit might provide desireable dynamic "mojo" activity - to many this might be a moot point, whatever ... either way a dynamically clean circuit is probably very desireable in the end ... I'm just stating this so we're clear on what the issues are - in the end we would match the op-amp emulation response to the original anyway ... which brings us to our next subject ...




Thanks to the great generosity of Mr. John Della-Vecchia, moderator of the Yahoo "Rhodes-Tech" forum, I was able to put my hands on an original DMP900 preamp board and reverse the values from it ... although there is more work to be done measuring bias conditions and simulating the transfer in Spice I'm posting what I have for now so we can get the ball rolling ... below is a copy of the schematic John Hines sent me a while back of his reversed clone - I added values in RED indicating DMP900 values as they deviate from his schematic ...



when I get a chance I'll get back with some analysis results and ideas on what we can do with all this stuff ... for now pls consider the info incomplete and unverified - I'm still double checking things when I got time ... got a backlog of old amps to revive at work, I'm putting on a Zappa video nite this weekend, and my latest Vibe using a new wide-range constant-amplitude sine LFO I've been developing just came to life yesterday ... yeh!

~jc

[zeerust2000]

Hi there.  My schematic is the one above being compared to the an original DMP circuit.  Originally I had some problems with the unit I copied the schematic from, and suspected a dud component of some sort, probably one of the FETs.  I've just finished building a clone with identical values, and it works fine so obviously the problems I was having were hardware based. Has anyone else had experience with a unit they've actually constructed and Rhodes-tested?  I'd be interested to compare notes on the effect the preamp has on the sound of different Rhodes'.

[rockgardenlove]

What value pots are those?

Thanks

[zjokka]

What value pots are those?
Thanks

Dual concentric 100k Audio pots
Are you building it or prototyping? Was hoping to start on this one as well, but so much on the bench right now.

zj

[zeerust2000]

I've built a unit into an outboard box with four seperate pots.  I'll rebuild one into my Rhodes to replace the faulty one in there.  I find that with the 'overtone' up full, you can hear the percussive attack of the tines a little bit too much, particularly in the bass.  This manifests itself as a 'dinging' noise on the attack of the note.  I can eliminate this in the middle and high registers by pickup adjustment, but the the lower registers it doesn't seem possible to do this.  Overall though, it sounds great.  I got the J310s from Mouser.  I'm in Australia so the postage cost more than the transistors, but it was worth it.

[rockgardenlove]

So, anybody tried this with guitar?

[bleubleu]

Hi!

I know this is a very old thread, but just though I'd let you know that I built the German's guy version (hand drawn circuit in this thread) using the PCB found by EB7+9 (slightly modified) and it works great! I installed it on my brother's Rhodes and we immediately noticed a much more powerful and richer sound. The overtone pots really gives more harmonics. You can do everything from a soft mellow sound to a very percussive sound with strong attack. It would take hours to explore all the different sound this baby can generate.

On the technical side... I added a 15V voltage regulator at the beginning of the circuit. Right now it temporarily runs with two batteries, but I should add an external power supply soon. I remove the original volume and passive bass boost knobs and added 2 more pots for a total of 4. I could not find any of those dual concentric pots so I used 4 100K log pots. 100K seems to be a bit to much. Some pots only works up until half way (the sounds stays the same for the 2nd half) so 50K or lower might be better. We cut the RCA cable and added the circuit right after it.

Some pictures.











Mat

[Black Pearl]

Hi There

Given the age of this thread I appreciate this is a long shot, but I'm interest in building one of these preamps for my Rhodes MK1 Stage.

If anyone has built this using the PCB layout and/or has extra PCB I'd be interested to hear from you.

Thanks

Rob

[aron]

Yeah, post it if you can.

Thanks!

[gwike]

Hey guys,
I've just dropped off my 1973 Fender Rhodes 88 key stage model to get the Dyno preamp installed in it along with proper voicing and some restoration that will be done by Tim Warneck of Retrolinear in North Wales, PA. I managed to get all the caps, resistors, JFETS, etc but I was a little unsure on the pots. I wanted to get dual concentric pots placed in the preamp like in the original design and I managed to find two AB 100K dual concentric log pots from a guy in England selling them off of eBay. They look really similar to the original pots in the Dyno preamp. I don't know the dimensions of the original dual concentric pots but I'll include pics of the ones I got along with the dimensions. Any of you all know the dimensions of the original pots or have access to an original preamp to take some measurements of them? Any help solving this would be greatly appreciated

eBay Pots:

http://thumbs.ebaystatic.com/images/i/141265654572-0-1/s-l225.jpg

eBay Pot Dimensions:

Diameter: 24mm
Depth: 23mm
Bush diameter: 3/8"
Inner spindle: 3.85mm diameter, 26mm in length
Outer spindle: 5.90mm diameter, 17mm in length

[gwike]

Also here's a link to the preamp schematic I'm following minus the 4 single pots:

http://www.untrue.ch/test/dynoMyPiano/Dyno_My_Piano_Perf.gif