Author Topic: An alternate Volume/Tone control circuit for Mk1 Stage EPs  (Read 693 times)

Offline sookwinder

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An alternate Volume/Tone control circuit for Mk1 Stage EPs
« on: March 11, 2018, 05:26:58 AM »
I have had my 1973 Mk1 Stage Rhodes for just shy of a year now. Love it.
What I don't love is the crappy volume/tone controls. I know in Leo's day, everything was done to reduce production costs, for example design attributes in valves amps that we would just take for granted these days (including safety features that lower the risk of destroying the valves) were just not even considered back in the day.

Most likely that mind set was continued once Leo retired and obviously the Rhodes production was not immune.
But seriously the volume and tone controls circuit fitted to my Mk1 stage is amateurish at best.
The tea lady (or coffee lady) would have had a better chance of designing volume and tone controls for the Stage Rhodes.

There are many issues that arise.
The circuit is noisy.
Most of the signal is lost to ground because of ridiculous component (size) choices.
The bass boost circuit really doesn't do what its name suggests or at least does it partially but at the same time has a detrimental affect on the volume.
The circuit disobeys fundamental design rules as far as output/input impedance when connecting the Rhodes to a standard guitar amp, which causes reduction in frequency response  (ie. make it sound like there is a wet blanket over the speaker).

In short it actually causes the player to rely on the control on the amplifier to fix up the short comings of the signal coming out of the Stage Rhodes.

So given we have a long weekend here in Oz, I decided to investigate.

Initially I just set up a cable connected directly off the harp RCA through to the Phono jack on the name rail, bypassing all of the circuit.  Yes this did seem to improve the frequency response, but it also seemed to add a continuous static, not (white) noise but a static noise. Grabbed another cable and the results were the same. Encouraging, but not a solution.

Next idea was to change the value of the volume pot in the circuit.

One of the members here (Sean) had shown in another thread the following circuit for the Mk1 Stage:



The circuit in my 1973 Mk1 is different again.
I checked each of the pots and they both are 1973 production. 
Thanks to Max from CEPCo for the hand modelling services.


So I built up a wiring loom exactly the same as what appears to have been shipped with the EP back in 1973, except I changed the volume pot to 1M.  Given that many guitars utilise 1M volume pots, this should not have caused any issues.  (Typically Strats with single coil pickups have 250k pots, Les Pauls etc with humbuckers have 500k and sometimes 1M volume pots. Jaguars and Jazzmasters use 1M pots)

While I still felt the frequency response of the output was under par, there was a distinctly noticeable volume increase.

After some deliberation I decided to approach this issue as if I was designing a section of an amplifier.

The design would need to take into account that it needed to be compatible with amps that have high input impedance. (ie the classic valve amps for the 60s and 70s that we all love).  The correct choice of components, in particular the potentiometer for volume control, should allow the vast majority of signal to get to the amp and not be lost to ground.
 
The Bass boost function is a complete waste of time.  I have never known of anyone, be it in a studio or live, stop and say "my Rhodes stage EP does not have enough bass, damn! I need more bass boost".  Every player I know is always reducing the bass controls on the attached amplifier in the vain hope of dialling in some brightness and chime.

So I thought about how one would go about designing a bass roll-off control. It is better to try and get the signal coming out of the Rhodes as close as possible to what you want, rather than relying on the amp to control it.

I went for the classic High Pass Filter route.

For those who were asleep in classes, this is a high pass filter.  As the name suggests it lets through the high frequencies and blocks the lower frequencies.  There is a frequency called the cut off frequency, this is where the signal had dropped 3dB.  It doesn't mean everything below that frequency suddenly vanishes, but rather at that point that is the start of the roll off of all lower frequencies.



I wanted a design that allowed the cut off frequency to be adjustable.
If you wanted everything, that should be available.
If you wanted a little attenuation on the bass notes, likewise this should be able to be dialled up.
And lastly if you wanted the bass way down this should also be achievable.

Half a day of experiments and some calculations led me to the following design:

 , where the relationship between R1 : R2 is about 1:4.5 or 1:5. 
I had chosen the Volume pot to be 1M and the Bass roll off pot to be 250K, which meant that (using the standardised fixed resistor values) R1 could be either 47K or 56K.
The relationship between the combined R1+R2  (remembering that R2 is variable) and the capacitor then gives the range of the possible cut off frequencies.


I also added an extra function, using a CTS 1M pot that has an inbuilt switch. The switch is a SPST, and is independent of the functionality of the rest of the pot.  I.e. it does not turn the pot on or off, but rather the switch is activated by pulling the shaft/knob out and deactivated by pushing it in and allows 'something else" to be activated by this SPST switch.  I used it to have an additional capacitor added or removed from the circuit.  The circuit has two possible ranges of cut off frequencies (that overlap slightly).



The table below shows the cut off frequency relative to the percentage of Bass Roll-off control being selected. (and for each of the two possible - useable - values of R1 (47K or 56K)


Here is the layout drawing and some installation photos.
Note 1: there is just enough room between the harp and the name rail, at the far left, to be able to carefully locate the larger CTC 1M pot (with switch) without the need to remove the name rail
Note 2: you will need to cut off (with a hack saw) about 5mm of the shaft for the CTS 1M pot. Take about 10 minutes from go to whoa.  For what ever reason these CTS 1M pots with the switch feature have extended shafts.






So how does it sound... well great .. just what I hoped for.
The signal level is much louder, there is less (white) noise, no static noise and the bass cut off function is very easy to operate.
Fully counter clockwise the is no bass roll off (the starting frequency at those position is 26Hz, below the piano, below your ears).
Then just rotate the knob clockwise to gradually reduce the bass notes relative to the higher notes.
What I particularly liked is that I can set it up so I can clearly hear in the signal the physical striking of the tines on the upper register keys. This has often been overwhelmed by the lower notes.

The circuit is in the Rhodes and is staying put.
Enough said.

Time for dinner

David






« Last Edit: March 12, 2018, 04:47:07 PM by sookwinder »
Late 60s Pianet N - Late 70s Pianet T - Ensoniq ESQ1 - Hammond XK2 - Wurli 206A converted to a 200A - 1973 Rhodes Stage 73 - Roland RD150 - Vintage Vibe 64 EP on order - shit load of guitars, basses & amps

Offline jimbobothy

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Re: An alternate Volume/Tone control circuit for Mk1 Stage EPs
« Reply #1 on: March 11, 2018, 10:39:37 AM »
Nice, if I ever get a Rhodes I’ll be doing this mod  8) Thanks for the detailed post.

Offline Tim Hodges

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Re: An alternate Volume/Tone control circuit for Mk1 Stage EPs
« Reply #2 on: March 11, 2018, 03:45:28 PM »
Funilly enough I was going to put up the schematic for the older stage preamp with the 1UF capacitor last week but forgot to.

Excellent write up for the alternative, will give it a go.
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Offline d-rock

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Re: An alternate Volume/Tone control circuit for Mk1 Stage EPs
« Reply #3 on: March 12, 2018, 10:16:48 AM »
Excellent!

I think we all struggle with the low volume and noise coming out of our Rhodes. I've been boosting mine with a preamp pedal (Tech21 Liverpool) and have gotten good results but there is still a good bit of hiss that I just live with. This is really nice.

Offline pnoboy

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Re: An alternate Volume/Tone control circuit for Mk1 Stage EPs
« Reply #4 on: March 13, 2018, 04:01:51 PM »
I'm going to express a contrarian viewpoint, and I hope I can do so respectfully.  The OP presented 2 Fender stage-piano schematics--one hand drawn and one printed.  The printed one represents what Fender used for most of the life of the stage piano, and, except for the component values, I think that it is quite a good circuit, and better than the one designed by the OP.  Before I explain my opinion, let me mention my experience with my Rhodes stage pianos.  I have owned 2--the second of which I currently own.  In both cases, I found that the pianos could sound tubby if not properly equalized, and the tubbiness originated in the 100 Hz to 200 Hz frequency range.  Lower down the bass end of the piano, less equalization was required.  I think this results largely from the fact that most guitar speakers severely roll off bass as one goes below 80 to 100 Hz. 

Therefore, my experience was that a bit of a reduction in the 100-200 Hz range without too much reduction further down in the bass was just the ticket for good sound.  Of course, the amps, speakers, and speaker cabinet have lots to do with the sound of the piano, so my experience can't be considered universal.  I gigged with the 1st piano, and played it through 2 12" speakers in an open-back cabinet.  I think that speaker arrangement is pretty typical for many Rhodes players.

The Fender tone control provides what is often called a shelving high-pass filter.  The capacitor and volume-control resistance makes the high pass, and the resistor across the capacitor creates the shelf.  BTW, Fender calls this control a “bass boost,” but that’s just some marketing nonsense—it’s actually a bass-cut control.  In fact, it's kind of a 1/2 bass control.  Whereas most bass controls go from cut at one extreme, to flat in the middle, to boost at the other extreme, the Fender control goes from cut at one extreme to flat at the other.  Consider the image below .  It shows the frequency response with the bass control set for full cut and partial cut.  At the partial cut shown, it reaches a shelf of -6dB, where it flattens out.  At full cut, it's heading for a shelf, but doesn't quite get there at 20 Hz.
I find this type of control very useful.  It can cut the mid to upper bass frequencies without completely suppressing the lowest frequencies.  The OP's circuit cannot do this--as a simple high-pass filter its, bass rolloff never stops.  I have found that I never need that type of frequency shaping with my Rhodes pianos. 

As to the selection of component values.  It seems that Fender likes to suppress the sound of the hammers hitting the tines--I think of it as a ping or ting.  I say this, because, in general, Fender has used low input impedances in their pianos.  The Peterson preamp has a 33k input impedance, the stage pianos has a 10k input impedance, the early Janus preamps have a 10k impedance, whereas the late MkII preamps had a 47k impedance.  If one wants a higher impedance to let through more of the ping, the components used in the Fender schematic can be scaled as long as the RC product remains the same.  For example, one can multiple the potentiometer values by 10 and divide the capacitor's value by 10--hence, a 100k volume pot, and 500k tone post, and a 4.7nF capacitor.
The OP also mentions static or hiss.  I have never encountered this with my stage pianos--they have all been very quiet.  I wonder if the OP's problem relates more to his amp than piano?  The 10k pot does reduce amplitude, but if increased to 50k or more, that problem is resolved.  In short, I have no real criticisms of the Fender circuit--it does what the manufacturer wanted it to do in an efficient way.  In that sense, I think it's rather an elegant design.  If you want more ting in your sound, scale the pots up and the capacitor down. 

Offline sookwinder

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Re: An alternate Volume/Tone control circuit for Mk1 Stage EPs
« Reply #5 on: March 13, 2018, 06:22:36 PM »
I have 10+ amps of various sizes, designs (6 of them designed/manufactured by me) all very quiet.  All exhibit the "noise" level that I mentioned I experienced when plugging in the Rhodes.  The same noise never occurs with any guitars or other EPs.
The noise IMO is because of the miss match of components (in/out impedance mismatch) is a function of the circuit ... an EE would immediately comment of  the miss match of impedances and warn about loss of high frequencies which would result in noise being more prominent.

Further in my assessment of the circuit I did not even plug into an amp as such ... I used the valve preamp I have designed which is a the front end of an amp design, but doesn't have the power section for speakers as I then go DI.  I.e. it boosts the signal to line levels adding the "valve" sound and levels of compression associated with valve amps.  So I have negated any issues associated with good or bad speakers.

I do not know if you have played a stage Rhodes with the particular circuit I had in my stage (the one with the 2 x 10K pots and 0.1uF cap) but in reality when it was used, and the "bass boost" utilized, the overall volume reduced even further.  So you had a situation where, if you wanted bass boost you turned it up only to find that the overall volume has been reduced. Yes a tonal change has occurred but so has the volume dropped, almost counter acting the desired affect. IMO a crap design.

Volume/tone control circuits are a strange beast. 
There are many that are used or have been designed for amps over the years, but historically the one that is used is the FMV (fender Marshal Vox) style.  Not  because it is the best  (it certainly isn't) but because it has been the most commonly used, because it appears to be the simplest design that musicians (not amp designers) can understand and use successfully and because the component numbers are low - good for mass production.  Another reason is that FMV circuit is a good (general) circuit for ALL types of music.   
Likewise I would put forward that the circuit that was in my Stage Rhodes (10k/10k/0.1uF) was based upon cost reduction for production rather than any particular notion of "let's design it to allow a boost here or there in the bass because of speakers that may be not as efficient at particular areas".

David
« Last Edit: March 13, 2018, 08:11:26 PM by sookwinder »
Late 60s Pianet N - Late 70s Pianet T - Ensoniq ESQ1 - Hammond XK2 - Wurli 206A converted to a 200A - 1973 Rhodes Stage 73 - Roland RD150 - Vintage Vibe 64 EP on order - shit load of guitars, basses & amps

Offline Jenzz

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Re: An alternate Volume/Tone control circuit for Mk1 Stage EPs
« Reply #6 on: March 14, 2018, 02:35:57 AM »
Hi .-)

The 'noise' you mention is only a small matter of components... Do you have your sustain bar grounded? To me, this is the most important thing to do on any Rhodes, since any static of RF noise is coupled via the sustain bar into the the pickup colis, esp. in the lower keyboard range, because bar and pickups are pretty close there.

The 10K / 10K / 1uF circuit was just a treble roll-off design, it doesn't affect the bass. It indeed affects the overall volume if you turn up full, since the 1uF cap cuts out too much treble.

Jenzz

Offline sookwinder

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Re: An alternate Volume/Tone control circuit for Mk1 Stage EPs
« Reply #7 on: March 14, 2018, 04:31:31 AM »
Jenzz, G'day there...
The Rhodes was completely restored by CEPCo 10 months ago...  no issues from that perspective.
The noise I speak of is the standard noise you get from single coil pickups. The Rhodes, last time I looked, had quite a few single coil PUPs.

I am still trying to come to grips with the concept that a Rhodes needs (or needed) a bass boost.  Every amp I have ever used, or player I know who plays a Rhodes, have always had to reduce the bass via the amp controls.

FYI, with the circuit that was in my Rhodes, as the Bass Boost was rolled off  (ie the level of bass relative to the treble reduced) the overall volume of the treble decreased as well.  I measured this with a signal generator. That circuit, 10k/10k/0.1uF, is a dud circuit.  Even the 50k/10k/0.047 version circuit would have been better.  I even built up a copy of the 10k/10k/0.1uF circuit with brand new components and the results were the same.

Irrespective of the above ...  the Rhodes I have was manufactured with a crappy designed volume/tone control which was useful at basically one combination of the volume/tone controls.  I have looked at the issue from the way I would if I was designing an amp/guitar combo and come up with a circuit that is useful at the entire range of positions.

the Rhodes sounds awesome ... even better than it did.
And people can use the circuit if they wish or ignore it ...  that's what forums like this are for.

David
« Last Edit: March 14, 2018, 04:35:42 AM by sookwinder »
Late 60s Pianet N - Late 70s Pianet T - Ensoniq ESQ1 - Hammond XK2 - Wurli 206A converted to a 200A - 1973 Rhodes Stage 73 - Roland RD150 - Vintage Vibe 64 EP on order - shit load of guitars, basses & amps

Offline pnoboy

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Re: An alternate Volume/Tone control circuit for Mk1 Stage EPs
« Reply #8 on: March 14, 2018, 09:27:24 AM »
Jenzz, G'day there...
The Rhodes was completely restored by CEPCo 10 months ago...  no issues from that perspective.
The noise I speak of is the standard noise you get from single coil pickups. The Rhodes, last time I looked, had quite a few single coil PUPs.

I am still trying to come to grips with the concept that a Rhodes needs (or needed) a bass boost.  Every amp I have ever used, or player I know who plays a Rhodes, have always had to reduce the bass via the amp controls.

FYI, with the circuit that was in my Rhodes, as the Bass Boost was rolled off  (ie the level of bass relative to the treble reduced) the overall volume of the treble decreased as well.  I measured this with a signal generator. That circuit, 10k/10k/0.1uF, is a dud circuit.  Even the 50k/10k/0.047 version circuit would have been better.  I even built up a copy of the 10k/10k/0.1uF circuit with brand new components and the results were the same.

Irrespective of the above ...  the Rhodes I have was manufactured with a crappy designed volume/tone control which was useful at basically one combination of the volume/tone controls.  I have looked at the issue from the way I would if I was designing an amp/guitar combo and come up with a circuit that is useful at the entire range of positions.

the Rhodes sounds awesome ... even better than it did.
And people can use the circuit if they wish or ignore it ...  that's what forums like this are for.

David

Which tone control did your Rhodes originally have?  The older one that you showed in a hand-drawn schematic, or the newer one that I commented on?  If it was the older one, then, yes, the circuit was worse than worthless.  Re noise, an impedance mismatch does not cause noise per se.  For example, your new circuit uses a 1 meg pot, but the output impedance of the Rhodes harp is much, much lower than that.  One can say the same of guitars--the impedance of a guitar pickup is a few k ohms, but guitar volume controls and amps have a much higher impedance.  For an audio amp, an impedance mismatch is often good--and usually the input impedance of an audio amp is purposely made  to be much higher than the output impedance of what is connected to it.  I'd have to do a noise analysis to show this, which is well beyond what I'm willing to do for this forum.  I am still confused by the noise you report.  You have pictures of your Rhodes with your preamp sitting right on top of it.  Have you tried moving your preamp away from the Rhodes to see if that alters the noise?  I have owned 3 Rhodes--1 suitcase piano, and 2 stage pianos.  All are/were very quiet.   I really couldn't tell when they were plugged into an amp.  I can plug my current Rhodes into my amp and listen, then unplug it, and I don't hear any difference unless I put my ear right near the speaker.   Remember, that the Rhodes' single-coil pickups are connected in reverse polarity in groups of 3.  So, collectively, they really function as a sort of large, distributed, humbucker design

Offline sookwinder

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Re: An alternate Volume/Tone control circuit for Mk1 Stage EPs
« Reply #9 on: March 14, 2018, 05:36:37 PM »
Yes, if you read my original post, I had the hand drawn circuit in my Rhodes. 
I agree .. next to useless.

And no I do not play with the preamp sitting on the Rhodes top....  that was an artistic set up for the photo  ;D
I understand the concept of electrical interference.
Late 60s Pianet N - Late 70s Pianet T - Ensoniq ESQ1 - Hammond XK2 - Wurli 206A converted to a 200A - 1973 Rhodes Stage 73 - Roland RD150 - Vintage Vibe 64 EP on order - shit load of guitars, basses & amps

Offline pnoboy

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Re: An alternate Volume/Tone control circuit for Mk1 Stage EPs
« Reply #10 on: March 15, 2018, 06:28:28 AM »
OK--I was just trying to figure out why you were experiencing noise, and was grasping at straws to come up with some ideas.  BTW, last night I repeated my noise test to be sure I had remembered it correctly.  I turned my amp way up, stuck my ear right next to the speaker, and listened for a difference in noise between having my piano plugged in and having nothing plugged in.  In the latter case, the shorting jack shorted the amp's input.  Once again, I could barely hear the difference. 

Offline sean

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Re: An alternate Volume/Tone control circuit for Mk1 Stage EPs
« Reply #11 on: March 19, 2018, 06:19:10 PM »
I built the above circuit from sookwinder and the one from pnoboy, and I tested them in my state-of-the-art recording studio basement.



The bottom panel has sookwinder's circuit on the left (note the outrigger switch that adds the second capacitor), and pnoboy's circuit on the right.  The DPDT switch in between toggles between the two circuits.

The top panel is just the original Rhodes Bass Boost and Volume controls as shipped from the factory. 

The test gear included:

Namerail circuitry to test:
sookwinder's circuit with 250KΩ bass rolloff pot, two .01μF capacitors, switch, and 1MΩ volume pot.
pnoboy's circuit with 250KΩ bass boost pot, .01μF capacitor, and 50KΩ volume pot.
Harry's circuit with 50KΩ bass boost pot, .047μF capacitor, and 10KΩ volume pot.
Direct-off-the-harp RCA-to-1/4" cable, no volume or tone pot.

Tone sources:
1979 Rhodes 73-key Mark I Stage Piano.
1983 Rhodes 73-key Mark II Suitcase Piano top, without Janus preamp.

Amplifiers:
DIY headphone amp based on TDA1308 chip, with AKG K55 headphones. Solid-state full-range fidelity, battery power.
Fender Princeton Chorus guitar amp with two ten inch speakers.  Nice cheap solid-state guitar amp.
Crate Vintage Club VC20 (2112RB) guitar amp with one 12" speaker.  Cheap all-tube guitar amp.


Here are some comments taken from my testing notes:

sookwinder's circuit:
With the volume knob set at maximum, the piano sounds great, amazingly percussive above middle C.  With the headphone amp, I could not detect any change in tone when moving the "bass rolloff" pot from zero to 100%.  With the Crate tube amp, and with the Fender amp's bass and midrange controls set to 10, I was able to hear a slight change in the sound when turning the "bass rolloff" controll on sookwinder's circuit.  It was a very subtle change, and it required moving the pot through its full range of travel.  Moving the volume pot down from 10 makes a drastic changes to the piano volume, rather than the expected smooth decrease in volume.  The volume control was useful from between 8 and 10, but the piano was uniformly quiet between 1 and 8 (meaning setting the volume to 3 sounded just like setting the volume to 6).

pnoboy's circuit:
Sounds perfect with both knobs set at 10.  Volume pot movement between 8 and 10 makes powerful changes in piano volume, rather than the expected smooth change in volume.  With the headphone amp or the Fender Princeton Chorus amp, the bass boost strongly affects the tone, even on notes from C40 up to C64 (the tube amp didn't seem as sensitive above C40).  On the solid-state amps, the bass boost control strongly affected the tone of the low notes as expected, but also strongly controlled their volume.  I did not feel that settings below 7 were useful, because of the decreased volume of the bottom two octaves of the piano.

Harry's circuit as shipped on Rhodes Stage Pianos:
The bass boost knob affects the tone of the notes below C40, and maybe as high as C52.  The overall volume of these notes is not strongly affected by the bass boost knob.  I feel that the full range of the bass boost knob provides useful tonal control (I can set the bass boost to zero, and still find that musically useful).  The volume knob provides smooth control of the piano volume between settings of 5 and 10, so it provides intuitive control of the piano's volume without hesitation or re-correction required.  The bass boost and volume controls provided a wide variation of control of the Rhodes sound with all three amplifiers tested here.

Direct from the harp RCA connector to the amp, no intervening circuitry:
The piano sounds great, but no different from Harry's or pnoboy's circuit with bass boost and volume set to maximums. 


None of the amps I have owned have struggled with the stock bass boost and volume controls on the four Rhodes Stage Piano's that I have owned.  The testing that I performed was certainly limited in scope, and I don't own a Fender Twin, Fender Bassman, nor a Roland Jazz Chorus; so I cannot comment nor predict how these amps might interact with any of these tone control and volume circuits. 

So, for me, I will stick with the standard Rhodes namerail control circuit.

Sean

P.S. - By the way, I would not recommend using a Crate Vintage Club guitar amplifier with your Rhodes Piano. 
« Last Edit: March 19, 2018, 06:22:01 PM by sean »

Offline pnoboy

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Re: An alternate Volume/Tone control circuit for Mk1 Stage EPs
« Reply #12 on: March 21, 2018, 06:22:52 AM »
Thanks for your testing, Sean.  I would like to make a quick comment about the standard stage controls that I discussed and you tested.  There is a noticeable change in tone and volume if one is using the 10k volume pot that came with the pianos or if the component values are scaled to use 50k or higher volume pot.  In the latter case, the volume is higher and the tone brighter., with more of the hammer-strike sound.

Offline 4kinga

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Re: An alternate Volume/Tone control circuit for Mk1 Stage EPs
« Reply #13 on: March 21, 2018, 09:46:10 AM »
Sean,
Did you make those face plates?  Those are great!

Offline sean

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Re: An alternate Volume/Tone control circuit for Mk1 Stage EPs
« Reply #14 on: March 21, 2018, 12:12:55 PM »


4kinga - Yes, those are homemade drop-in replacement control plates for the Mark II stage and Suitcase pianos.

See writeup in other thread from today: https://ep-forum.com/smf/index.php?topic=9800.msg54393#msg54393

Sean

Offline The Real MC

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Re: An alternate Volume/Tone control circuit for Mk1 Stage EPs
« Reply #15 on: March 22, 2018, 10:23:31 PM »
The Rhodes pickups are very sensitive to impedance loads.

If the impedance is too low, it drastically impacts the tone.

Suitcase preamps have an input impedance of 1Mohm or better.  Fender Twin Reverbs (input #1 jack) has 1Mohm impedance.  That's why they sound better.  The passive circuit on the stage piano is nowhere near high enough and it sucks tone.

When I tested DIs of different input impedances right off the harp, I could hear the difference in tone.  Best sound I got was using a Countryman Type 10 which has an input impedance of 10Mohm.

Offline pnoboy

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Re: An alternate Volume/Tone control circuit for Mk1 Stage EPs
« Reply #16 on: March 23, 2018, 06:10:53 PM »
Actually, the suitcase preamps didn't have 1 megohm input impedance.  The Peterson preamp had a 33k input impedance--
http://www.fenderrhodes.com/org/ch11/fig11-8.jpg
The Janus preamps had a 10k input impedance--
http://www.fenderrhodes.com/org/ch11/fig11-1.jpg
The late Mark II preamps had 46.4k input impedance--
http://www.fenderrhodes.com/pdf/late-mark2-suitcase.pdf

Offline cemo69

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Re: An alternate Volume/Tone control circuit for Mk1 Stage EPs
« Reply #17 on: June 06, 2018, 07:44:38 AM »
Hi everyone.

I'm new on this forum. i'm french and owner of Rhodes stage 73 (1979).
Great job Sookwinder !
On your opinion,about the sound, in whitch way does your system have improve your Rhodes ?
How does it affect the sound ?
To be honnest , i want to test, but i hope significatif improvement compare to the original shema

Cemo