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Does Anyone have a Schematic for a Sound City Joanna Piano Keyboard?

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Old May 20th 19, 03:03 PM posted to rec.audio.pro
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Default Does Anyone have a Schematic for a Sound City Joanna PianoKeyboard?

On 5/14/2019 10:52 PM, Paul wrote:
> On 5/13/2019 10:53 PM, Paul wrote:
>> On 5/13/2019 1:00 PM, Paul wrote:
>>> On 5/13/2019 8:45 AM, ChrisG wrote:
>>>> On 5/13/2019 6:03 AM, Paul wrote:
>>>>> On 5/13/2019 3:48 AM, Paul wrote:
>>>>>> On 5/12/2019 3:16 AM, Paul wrote:
>>>>>>> Mine looks just like this one:
>>>>>>> **** https://www.matrixsynth.com/2017/07/...ty-joanna.html
>>>>>>> The power switch LED turns on, but nothing on the output.
>>>>>>> A schematic would sure be helpful....
>>>>>> *** Oh, nevermind.* It works.
>>>> I used to successfully employ heavy guitar strings on Farfisa and
>>>> Vox organs. They would need to be wound with a metal that could be
>>>> soldered though, bronze maybe? I later learned that the original
>>>> busbars and springs on better quality instruments were often gold
>>>> plated, so I probably caused a lot of destructive wear and tear, but
>>>> I didn’t know and didn’t care in those days. I just wanted the thing
>>>> to work when I needed it.
>>>> Everything corrodes, but gold on gold is pretty good until it wears
>>>> through. If they’re gold, it may be worth transplanting old springs
>>>> from the upper keys to the midrange to preserve the busbar, and
>>>> kludge the lesser-used contacts.
>>> ****** OK, that sounds like a good idea. Heavy guitar strings.* I don't
>>> think these are gold-plated, but I could be wrong.
>>> ****** I just compared them, and the guitar strings are definitely
>>> much stiffer, and less pliant, than the original springs, but it
>>> looks like it should work.
>>> ****** Still, is there a source for the original raw spring
>>> material?* It
>>> would be better, because the stiffer guitar string would definitely
>>> affect the action and feel of the keyboard a small bit.
>>> ****** But this all answers the question of why there were 10 springs
>>> missing in the first place!* They were clearly taken from this unit,
>>> and put into another keyboard.* And I noticed on the Vintage Synth
>>> website, that they are selling these springs USED, for about $4 a piece!
>>> ****** Hmmmm....no wonder people like to buy old keyboards for the
>>> parts only!
>>> ****** :/
>>>>>> *** I just need to clean the key springs, and buy new ones
>>>>>> for the ones that are missing.
>>>>>> *** But a weird sounding keyboard for sure!* Nothing like
>>>>>> that old Italian analog sound!
>>>>> *** Ok, can I just go to somewhere like Home Depot, and
>>>>> get stock spring, to replace the old, worn out key
>>>>> springs?* Like get a long length of it, and cut them
>>>>> to size?
>>>>> *** Here is a picture of similar Crumar key springs:
>>>>> https://xbs111.files.wordpress.com/2...-springs-2.jpg
>>>>> *** Thanks for any advice.

>> ***** Ok, the guitar string idea works great!* 0.052"!
>> ***** There isn't really an issue with a difference
>> in the feel of the action, because like most organs,
>> each key is only ON or OFF.* There is no velocity
>> information, and most of the forces on the key, come
>> from the thicker main spring of each key, not the thin
>> contact springs.* So consequently, I don't feel a
>> difference in the action, on the keys with the guitar
>> string replacement.
>> ***** But I have found two more issues:
>> ***** 1)* How do I level the white keys on this unit?
>> ***** 2)* The high G# does not decay properly like the other keys.
>> ********* It almost acts like it has the sustain pedal down all the
>> ********* time.* So it keeps sustaining while the other keys decay
>> ********* and taper off as they should.* It seems like it's some
>> ********* sort of RC time constant, so I will probe, and check
>> ********* the components around this key, and compare them to it's
>> ********* neighboring keys.

> ******* Ok, issue #2 has disappeared for some reason, after I cleaned
> and did some in-circuit impedance checking.* After checking the
> keys again, the G# decays properly now.
> ******* I also found out how to level the keys.* There is a small
> plastic box on each key, and a corresponding metal finger for
> each key, with a rubber stop on the top and bottom.* This controls
> the key dip, and the key leveling when at rest.
> ******* I could shim each key, but I don't think it's worth my
> time, since I think the sound and play-ability of this keyboard
> is not exactly my cup of tea.* It's kind of like an analog
> clavi-chord, with some vibrato, but it's rather limited, with only
> the basic clav sound, and a basic electric piano voice.
> ******* So I will likely put this unit up on Ebay.* I'm sure
> a collector of old Italian keyboards will buy it!* Definitely
> a historical, and rare unit!

Ok, I'm going to have to replace ALL of the original
key contact springs with 0.052" guitar string.

Why? The original contact spring metal is SUPER
thin and skinny, so much so, that even on the springs
that are not broken, most of them have formed a little
kink at the point which they contact the "key ON" bar,
which makes the contact very intermittent and unsure.
This affects the volume of the attack of the note, which
ends up being too quiet (or sometimes completely dead) on the keys
that have the original springs.

This is to be expected on a keyboard made sometime in the
70's, but even if I had been successful in finding new contact
springs identical to the originals (I thankfully wasn't!), I still think
the 0.052" guitar string would perform better, because the
increased stiffness reduces the latency between the "key OFF" bar (which
charges each capacitor), and the "key ON" bar (for discharge).

To be continued.....


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