"minimalist bias supply/preamp" conversion for Wurlitzer Pianos

[Filmosound 621]

hey folks. 

if your Wurlitzer Amp is broken or gone    and you want to get a signal out of your
Wurlitzer Piano and into your Computer or any other amp outside of your Piano, there are at least to possibilities.

Nr. 1 is for the DIY guys out there, it keeps the original voltage on the reed bar but
needs no working amp to get the signal out of the Piano:

https://viva-analog.com/wurlitzer-270-passive-conversion/

Nr. 2 is what I learned about today, a cheap plug-in solution to convert the Piano
to "passive" useage without the original amp and voltage but with the help of a 9 volt battery, check this:

https://borishelectronics.com/products/wurlitzer-200b-amplifier-kit-200-200a-206-206a-214-custom


perfect idea, perfect solution, I might get one of these for my dead 207 Teacher Piano.

 



Edith has altered the thread title as per recommendation from member velo-hobo.
thank you.

[velo-hobo]

I've installed a Borish 200B for client - they wanted it put into a 140B tho, which, aside the need to fab a custom hardware solution with zero support from the vendor, we both determined we didn't care for the sound of the stock lowpass/DC blocking filter circuit. As I've not auditioned one with a 200-series piano, I can't be sure if that's just how the amp sounds generally speaking, or if the fact that it was a 140-series model made any difference.

Anyway, I changed out the wima film cap for a different value to raise the filter cutoff frequency and I think it made a significant improvement to the sound. Fortunately it is fairly easy to tweak this component value, as it's a through-hole part and not SMD like pretty much every other part on the Borish preamp board.

In considering the options for this client, before choosing the Borish we also looked at that viva-analog post, but the info shared was a bit unclear to me and the long string of ALL-CAPS discussion in the comments was hurting my brain to try to follow.

For my part, I can't call this approach a "passive" conversion - a bias voltage is necessarily applied to the pickup, else it does not produce any electrical signal on the output whatsoever. There's no such thing as a passive Wurlitzer EP, because it is unlike a guitar or passive Rhodes that produces signal via electromagnetic induction. My preference is to refer to these types of amp alternatives as a "minimalist bias supply/preamp"