Author Topic: Disconnecting speakers vs. amplifier damage on a 200A  (Read 175 times)

Offline Eleven

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Disconnecting speakers vs. amplifier damage on a 200A
« on: August 03, 2021, 10:28:43 AM »
I’m using the aux jack on the Wurli to an external amp so effects can be used. This is a stay at home piano. The external amp is set to a relatively low volume therefore the internal speakers wash out the full effect of the effects, even with the piano volume down.

I could change the aux jack to one that bypasses the internal speakers when a cord is plugged in but am under the impression that amplifiers should not be run without a load (ie. Speakers) connected or severe amp damage will occur. Would this be true with the small Wurli amp? If so what is the most economical work around?

Thanks…Rich

Offline Jenzz

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Re: Disconnecting speakers vs. amplifier damage on a 200A
« Reply #1 on: August 03, 2021, 02:49:44 PM »
Hi .-)

Just plug a plain TS plug into the Phones jack. This cuts off the internal speakers and automatically connects an internal load resistor to the amp's output (see schematic or open the piano, the resistor is located on a small soldering post directly at the Phones jack).

Jenzz
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Offline Eleven

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Re: Disconnecting speakers vs. amplifier damage on a 200A
« Reply #2 on: August 04, 2021, 08:21:36 AM »
Hi Jenzz, appreciate your help! When I use the HP out jack to connect to the amp I get a loud hum similar to a bad ground. The hum is there regardless of what the trim pot is set to. I can’t check for hum through my phones because they all have mini ends or are Bluetooth. I guess that would be the next step in searching for the problem so I’ll need to get an adapter. I recently gutted the Wurli to inspect, clean, lube and adjust the action, and use contact cleaner on the pots, trims, and jacks. The piano has very little play time on it however it has been in storage for 20 years. All the wiring looks solid.

Rich

Offline Jenzz

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Re: Disconnecting speakers vs. amplifier damage on a 200A
« Reply #3 on: August 04, 2021, 09:36:00 AM »
Hi .-)

Allways use a Line-iso box to connect a Wurlitzer to an Amp, regardless of using the AUX or the Phones jack, otherwise grounding problems can occur. It is essential to have Amp ground an Piano ground separated (via the transformer inside the Line-iso box)

Palmer PLI-01 is a good example

Please note that the ground / sleeve contact of the Phones jack is not identical to the piano ground !
There is a 470 ohm resistor between ground and the sleeve contact for current limiting.
When using a line-iso box, this resistror doesn't matter.

Jenzz
Rhodes tech in Germany
www.tasteundtechnik.de
www.spontaneousstorytelling.net

VintageVibe 64 ACL + DOD FX25B, EHX SmallStone, Tone City Sweet Cream, Pearl FG-01

Adams Solist 3.1 Vibraphone

Offline Eleven

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Re: Disconnecting speakers vs. amplifier damage on a 200A
« Reply #4 on: August 04, 2021, 11:12:24 AM »
I wasn’t aware of that- thanks! I did find an adapter for the phones and found the jack and trim work perfectly with no hum. I’ll set out to find the product you suggested. I’ve heard the item mentioned here before thinking it only applied to the 200.

Thanks again…Rich