The Electric Piano Forum

General => The Wurlitzer Electric Piano => Topic started by: Abraham on February 25, 2021, 06:16:56 AM

Title: 200a cheap amp replacement
Post by: Abraham on February 25, 2021, 06:16:56 AM
Sorry but I couldn’t justify myself spending $400 plus shipping on a wurlitzer replacement amp... You can find TDA based amp boards on Aliexpress for cents doing pretty much the same job with power enough to drive those little speakers... you don’t even use the amp for recording, so why not?

I mean, I’m not criticizing such prices, it’s nice to have a direct replacement if you can afford such investment. Also, I understand design and production of such implies costs beyond my knowledge and they have a limited market to make it profitable. Just to make clear, I’m not saying those amps are overpriced, I’m just saying I can’t afford one.

So, did anyone try such DIY alternatives? I know about the “free wurli” project, but it’s from years ago. Build cost estimation was 120€ then, I think nowadays we could do it cheaper, I could be wrong though.

Title: Re: 200a cheap amp replacement
Post by: drpepper on February 25, 2021, 07:51:06 AM
Just out of interest what is wrong with the current amp?
If you consider your wurli as an investment you might deprecate the value more than you save going cheap.
Title: Re: 200a cheap amp replacement
Post by: Abraham on February 25, 2021, 08:59:07 AM
Current amp has some nasty crossover distortion, my tech couldn’t find the problem so it’s still there. Line out is just fine, only speakers and phones are distorted. I usually plug any guitar amp or powered speakers to line out and it plays just fine. I’d go with original amp since it doesn’t affect recording, but I’d like to play the instrument standalone as intended, just out of those speakers. A properly refurbished original amp will do just fine (and keep the instrument 100% original).
Title: Re: 200a cheap amp replacement
Post by: pianotuner steveo on February 25, 2021, 02:15:27 PM
Don't forget that part of the uniqueness of the original Wurlitzer amp is the roughly 150vdc that it creates for the reed bar. A generic amp will not do this. The Wurli is not passive like a Rhodes.
Title: Re: 200a cheap amp replacement
Post by: Jenzz on February 26, 2021, 05:53:55 AM
Current amp has some nasty crossover distortion, my tech couldn’t find the problem so it’s still there.

Hi .-)

Always check for proper bias. If its too low, you will get this crossover distortion.

Jenzz
Title: Re: 200a cheap amp replacement
Post by: Abraham on March 08, 2021, 12:51:54 PM
First thing first, disclaimer: My “knowledge” on electronics is more than basic so I won’t pretend I can even understand how this works, but I’ll try my best to explain:

This piano was sold as “non working condition”. It was cheap, and later inspection revealed its action looked quite new and barely used, so I think I scored a good deal.

As soon as I had this delivered at my door I couldn’t help myself but to inspect the insides and get my clumsy hands dirty... I noticed this blown fuse, and it was Friday night so I couldn’t source a replacement until Monday... so I just replaced it with a thin wire and it suddenly came back to life... for a while though. I know (and I knew then) I should’ve stop right there till Monday, but I was so excited that I couldn’t stop playing and I didn’t, so I ended up with a loud pop, some smoke and a blown power amp transistor. Fuses are there for a reason. Blown fuses are blown for a reason. I know, please don’t tell me about it...

According to my tech, it was this Motorola 142349 voltage regulator that was damaged, fuse wasn’t there to protect, boom! Broken wurly.

He couldn’t find a proper replacement, so he had to replace it with some newer “somewhat equivalent” part (I will edit and include some pictures later). 3 pins instead of 14, I think we’re missing something there, but he’s the tech not me, and he keeps insisting this part serves its purpose. He also replaced this blown power amp transistor (I can’t recall if just one or both), apparently with a matching part this time. And he also replaced an electrolytic capacitor he didn’t like for some reason.

Ta-da! The amp now works. Kind of. I didn’t had the time to notice if crossover distortion was there at the beginning, so I don’t know if any of this replacements could be the cause for this malfunction.

And it’s been like this for a decade. Distortion is just present through speakers or phones, line out is “fine”. We’ll address this later, I know there’s room for improvement.

But this is mainly used as a playing instrument, now that I have time to actually play, and it’s something I’d like to fix.

I know mouser now stocks a direct replacement part for this 14 pin voltage regulator and maybe I could start there and try.

Also, I recently got myself another original amp + preamp I still have to test. I’ll keep you posted.

Title: Re: 200a cheap amp replacement
Post by: cinnanon on March 08, 2021, 01:44:33 PM
I'd just get a Retrolinear or VV amp and forget about it. Way more reliable. Those original amps are an antiquated design anyway.