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Preamps, Modifications & Upgrades / Re: Help with 4 Pin Preamp!
« Last post by ggoerl on Yesterday at 07:06:41 PM »
If you have the preamp out of its case, try touching with your finger the spot at which the input from the harp connects to the preamp.  If you hear no hum, your problem is likely to still be in the preamp.  To be sure, you could unsolder the input wire so that there is no signal connected to the preamp's input.  Then, once again touch your finger to the input.  If there is still no hum, then your probably is almost surely with the preamp.

Well unfortunately what I thought was the RCA cable isn't, I replaced the old with the new and still no sound. So now it's back to the preamp. I'm honesty not sure what else it could be as I've replaced so many of the components already.
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Buying / Re: Early Wurlitzer 200 leg
« Last post by elpresidente on Yesterday at 11:13:45 AM »
Thank you for this information. It is very helpful!
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Buying / Re: Finding a replacement Suitcase for Mk2
« Last post by Oregone on Yesterday at 10:24:21 AM »
Avion studios sells just the power supply section, of the power supply. The circuit board that is. Its like $20. Then you have to buy a project box, 5 pin jack, power switch, power jack, 1/4" out jacks, fuse holder etc... but it works out great.

I am into the power supply breakout box for about $60, and it works flawlessly. Of course, I had the 5 pin cable, which would be another $50. I also had some other odds and ends, wire/jacks etc.

If you had to buy all of the parts, including the 5 pin cable, it would total about $125. That's pretty close to the VV cheekblock PS, which is really slick. If I would have had to buy the cable too, I would have went with VV. I just couldn't justify ponying up that kind of cash, plus shipping, so I build my own.
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Hi .-)

The piano will work even without this wire. The wire doubles the connection that is already established by the aluminum tape that connetcs all pickup mounting brackets to ground.

The bare wire is used to connect the damper bar to ground, thus eliminating hum and buzz. If the damper bar is not grounded, capacitive coupling into the damper arms will induct hum and buzz to the pickups. Remember, the damper arms are going under the pickup coils, esp. in the upper ranges.

Jenzz
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The Fender Rhodes Electric Piano / Re: Distortion in Janus Preamp with volume past 7
« Last post by sean on January 17, 2018, 04:50:10 PM »

Duh.  The wild swing of the long bass tines is obviously a much better explanation for the crazy waveform.

And I guess the humped asymmetric output at E56 is inductive, but not core saturation.
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The Fender Rhodes Electric Piano / Re: Black wire running along length of pickup rail?
« Last post by pnoboy on January 17, 2018, 11:36:33 AM »
Usually, that's the wire used to ground the aluminum damper bar.  At the right edge of the harp, where the last pickup is, you should see a wire from the last pickup to something.  Usually, that's the black wire, but in your case it's something else, I guess. 
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The Fender Rhodes Electric Piano / Re: Black wire running along length of pickup rail?
« Last post by Gescape on January 17, 2018, 08:39:27 AM »
Hello and thanks for the replies. There is in fact a bare wire, looks like picture frame hanging wire, in the back behind the harp RCA output, not quite sure what or where it’s attached to, but that could be the answer. I’d post a pic but am at work, away ftom the piano. So at least now  I don’t have to worry about the missing black wire.
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The Fender Rhodes Electric Piano / Re: Distortion in Janus Preamp with volume past 7
« Last post by pnoboy on January 17, 2018, 06:42:13 AM »

The first preamp stage is not to blame here.   If the first stage was clipping, then turning the volume below 7 would not clear up the distortion.

Since pulling the pickups back provided some satisfaction, maybe the offensive noise is not the fault of the preamp.  The bass notes can provide some fat flabby buzz if the pickups are pulled in close, and moving the volume knob doesn't clear it up (hitting the keys softer does clear it up).  I believe this sound is due to saturation of the magnetic core in the pickup, but it could be the fault of having so many inductors in series.

The core saturation causes a pronounced kickback that distorts the ideally sinusoidal output from the pickup.  The resulting waveform has an additional lobe or lump in each cycle, or strongly asymmetrical north and south lobes. 

With the pickups in close to the end of the tine, and a good strong hit on A13, the output looks like:



This oscilloscope screenshot pretty clearly shows that the output is not nearly as sinusoidal as ideal.  There is a pretty steep spike on this note, and it sounds like a fat flabby buzz that eventually goes away as the note fades out.  When the pickup is moved back a bit, the steepness of the attack smooths out.

A strong hit on E56 shows one lobe is much smaller than the other:


I like the distorted sound I get in the bass notes when I hit them hard.

Sean


Your comment about the 1st stage of the preamp is right on--I missed the information that turning down the volume cured the issue.  However, your comment about the pickups producing a pure sinewave is not correct.  The ends of bass tines swing quite a distance when struck hard.  As such, at the extremes of their travel, they are quite far from the pickups, and the pickups' sensitivity to their motion is very low.  As they travel to their mid position, which is close to the pickups, the pickups and tines couple much more strongly, and thus we have the fact although the swing of the tines is sinusoidal, the output of the pickups is not.   Also, I don't see any mechanism for the pickups to become saturated.   Consider the simple case of a single pickup connected to an infinite impedance amp.  In that case, there is no current in the pickup, so the pickup produces no power.  Now consider the real case--there is very little change in the response of the bass pickups between their being directly connected to a 1 meg input impedance guitar amp and being connected to the Janus amp shown or to the stage piano's volume control, both of which have an input impedance of 10 kohms.  At one point, I electrically isolated one pickup from the rest and connected its output only to my amp--there was no particular change in tone.
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Buying / Re: Early Wurlitzer 200 leg
« Last post by Tim Hodges on January 17, 2018, 05:53:50 AM »
These were made by Decar, infrequently they seem to turn up on either etsy or eBay.com when people have no idea what they're from.

These for example slot in the Decar mounting plates (but there is no wingnut and it's hole doesn't align) they are a few inches longer so they sustain pedal cable would need replacing:

Set Vintage Chrome Mid Century Modern Table Legs
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The Fender Rhodes Electric Piano / Re: Distortion in Janus Preamp with volume past 7
« Last post by sean on January 16, 2018, 09:32:38 PM »

The first preamp stage is not to blame here.   If the first stage was clipping, then turning the volume below 7 would not clear up the distortion.

Since pulling the pickups back provided some satisfaction, maybe the offensive noise is not the fault of the preamp.  The bass notes can provide some fat flabby buzz if the pickups are pulled in close, and moving the volume knob doesn't clear it up (hitting the keys softer does clear it up).  I believe this sound is due to saturation of the magnetic core in the pickup, but it could be the fault of having so many inductors in series the wild swing of the long bass tines.

With the pickups in close to the end of the tine, and a good strong hit on A13, the output looks like:



This oscilloscope screenshot pretty clearly shows that the output is not nearly as sinusoidal as ideal.  There is a pretty steep spike on this note, and it sounds like a fat flabby buzz that eventually goes away as the note fades out.  When the pickup is moved back a bit, the steepness of the attack smooths out.


There is evidence of an inductive kickback that distorts the ideally sinusoidal output from the pickup.  The resulting waveform has an additional lobe or lump in each cycle, or strongly asymmetrical north and south lobes. 

A strong hit on E56 shows one lobe is much smaller than the other:


I like the distorted sound I get in the bass notes when I hit them hard.

Sean
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