one more Wurlitzer 200 question...

[Milkmansound]

...before I make a decision regarding mine.

Basically - I have serious noise, weak signal... its just a mess. I am wondering if I should completely replace every component on the PCB, part the damn thing out - or maybe just bite the bullet and get the redesigned amp from Vintage Vibe (like this one seen on ebay)

its been in my grandparents basement for a few months while I went back and forth on what to do with it. Already I am stuck with a 220V transformer in it because of the morons at Morelock's. If I do rebuild the amp I will either have to find a new transformer for it or put another one in somewhere.

oh, the question: If I do replace every part on the PCB, is that going to help? Are all of the modern parts going to change the sound for the better? I assume it will be a lot cleaner sounding - but what I am not sure of is if the noise is generated by poor design, or by shifting in values and tolerances.

 

[BradAvenson]

I designed a tube amp to replce the original. It has a few bugs, but if you are interested in building a replacement, this is a cool sounding one. If you build it there are a few things you need to change, but this is the basic circuit:
http://www.avensonaudio.com/tech/Wurlitzer/schematic%20rev-A.jpg

You can get rid of the BJT follower if you use a higher value pot than came stock.

You need more RC filtering for the reedbar voltage. I ditched the feedback around the transformer and just used a DI transformer for the output.

If you have any other questions feel free to ask.

 

[Milkmansound]

wow - that looks really simple!

you have built this sucessfully? Do you have a layout for it as well?

also, I can not tell if something is cut off from the top of the schematic.

I have a few impedance matching (little IMP I think they are called) transformers hanging around that I never use - maybe this is a good way to make use of them and get the wurly back in action at the same time.

yes - please let me know what changes are necessary! What value do I change that pots to?

also - would it run ok at half voltage or should I deal with my transformer too?

thanks

 

[BradAvenson]

No, nothing is cut off at the top, its just the b+ rail. I used a voltage doubler to get 225 volts for the b+, but you could run it lower at like 120 for less headroom (not really a big deal) and less voltage on the reedbar. I would just replace the transformer and power supply with a scheme like the G9 project. It will help the hums, ect from the reed bar. That way you can skip the doubler and my heater supply.

You want to add at least 2 RC (maybe more) stages from the b+ to the 499k resistor that feeds the reedbar. Any hum on the reedbar is amplified just like the signal.

As far as replacing the pot, use a 100k so it doesn't load the first tube stage. Then you can leave out the follower.

I actually have some boards, but they don't have any of these changes, so its a bit cubersome to use. I bet you could breadboard it just as easy.

I'll see if I can draw something up tommorrow.

 

[enthalpystudios]

this is really cool... I have a 200a that has intermittent (mostly on loud notes) distortion and bad clipping.... Always figured I'd either need to get a scope, which I finally got, or replace everything.... this sounds way better!

going to go look at this schem for about 2 hours and then give up ;]

billy

 

[Milkmansound]

yeah man - that would be awesome if you could draw something up for this!

I can build... but as far as designing tube gear I do not trust myself at all!

are the tubes just something like a 12AX7? I even have some lying around...

if the boards can be modded I could do that...

also - what are RC stages?

does the amp still do tremolo?

thanks - this is definitely an exciting prospect for a near dead instrument.

enthalpystudios: mine is the 200 - not the A revision. They are slightly different in that the 200A has a seperate PSU near the reeds, and a lot of design revision to get rid of the noise. I wonder if the reed bar is essentially the same and if this amp would fit in both. I imagine it would. I always thought that the distortion on the 200A was because of the fuses in the audio path - I do not remember where I heard that from. I have worked on the 200A before, and it was a lot more responsive to repair than my 200 is.

 

[BradAvenson]

OK, here is a new scheme for the replacement amp.
http://www.avensonaudio.com/tech/Wurlitzer/wurlypreamp.pdf

The tremolo circuit is an adaptation of the ESP project:
http://sound.westhost.com/project29.htm

The tube stages are a very simple, fenderish design. I used a 12au7 because you don't need too much gain.

The amp needs a 12V regulated DC heater. This also powers the tremolo.

It also needs a very clean B+ supply of around 170v to 250v or so. I think the Wurly sounds a bit better with a higher reedbar voltage, but don't take my word for it. The original circuit had 170V.

You can adjust R7 for the right amount of gain, the preamp really only needs 15 db, but there is much more than that.

The output transformer can be any stepdown say 6:1 to like 12:1. I think I used a 6:1 DI bo transformer.

You might make R19 and R20 a bit bigger for more filtering, or add more stages.

I think it works right, but I haven't tested the circuit as drawn.

 

[Milkmansound]

so this just acts as a kind of DI essentially - not a power amp?

 

[BradAvenson]

Right, I didn't bother to hook up the speakers because I didn't have any in the student models I had. If you want to add a speaker output, maybe the LM1875?
http://cache.national.com/ds/LM/LM1875.pdf

You can also take an unbalanced out before the transformer to run to an amp ect.

 

[Milkmansound]

that would work I suppose. I usually do not use the speakers either since one of mine is torn. Also, I could take them all out and make room for either another transformer or just keep the weight down.

schematics downloaded... I will try and throw something together in the next few weeks if I am not too busy.

thanks a lot for posting that and being on hand to answer my questions!

 

[enthalpystudios]

that sounds awesome to me.. thanks brad!

i actually tore my speakers out the day i got it (which was a bout a week before I had any clue what it was)

i was just thinking "this thing probably would be cooler through an old fender"

a friend of my mom's when I had just graduated high school gave it to me.... I had heard the sound of them, but didnt really know what they were.....

that was cool though, a free 200a!

thanks again for the schemo!


billy

 

[Milkmansound]

well the speakers can actually be nice if you just want to sit down and write some music and not use anything but the piano...

first I am going to build this preamp, then explore the amp, then make a decision if I want to lose the speakers. It would be nice to bypass them for live playing though and use an amp.

 

[BradAvenson]

If you don't need to listen loud, you could probably use the unregulated heater DC supply to drive the lm1875. With like 15v you should be able to drive the speakers loud enough. Just use the single supply schemo in the datasheet. Oh and a good heatsink.

 

[Milkmansound]

I can probably just sink it onto the huge metal shield that basically is the wurly (need one of those plastic insulating do-hikeys though)

as for the LM1875 - yeah, the thing in the datasheet looks perfect. I can even throw a regulator into the supply for that thing. I will toss one onto my next order if I do not have something like that left over from my TV/stereo days.

its just got to be loud enough so I can hear over the noise of playing the thing

 

[BradAvenson]

OK I finally put together all my Wurly service info. The file might have some redundant stuff, but hopefully everything is there somewhere.

http://avensonaudio.com/tech/Wurlitzer/Wurlitzer%20200-200a%20service%20info.pdf


And here are some schematics for the 140 series stuff:
http://avensonaudio.com/tech/Wurlitzer/Wurlitzer%20140%20schematics.pdf

 

[Flundran]

Have anyone tried to build this Wurlitzer tubeamp from Avenson Audio yet? Any reflections on it?

My wurly is in need of a new amp, this sounds like a cool project.

/F

 

[BradAvenson]

I have. :grin:

The layout is kinda important, but it should be pretty quiet if you are carefull. (first PCB's I made had a silly layout error that added like 20 db more noise to the signal than it should have.) You might think about replacing the power transformer all together, but you can use it with the design as is.

I just sold my 200 with the tube mod and the guy was really happy with the sound. I am thinking about a new version that has the tremolo and a tube amp to drive the speakers in my teacher model.

 

[Flundran]

Hi Brad!

Thanks for your reply. I have actuallly thought about replacing the power-transformer, since it's 110V primary and I need 230V. I have used a step-down trafo for it so far. Is there a PCB-layout available for the amp? Maybe even PCB's for purchase? (I don't have a etchingmachine yet..)

If you recieved an email from me eariler, you might reply to that instead.


/F

 

[klydolph]

Thanks for all the good info on the Wurlitzers. I bought a very nice 200A in an evilbay auction some years ago, complete with pedal, original carrying trunk, that little chair to sit on and the note-holder thing on top. Very nice and complete. But I had Fedex ship it from US to Norway. Never again!!! When it got here the whole thing had been beaten like hell. The carrying case was in pieces. The metal hinges and latches were twisted. The piano itself had scrapes and bruces. And the electronics didn't work. After searching for the fault I found the PCB was broken in the middle. The break was not visible from the upside but several traces underneath it were broken. After fixing that the speakers were buzzing like hell so I had to change them too.
It almost seemed as Fedex had put the whole shabang into a big canon and fired it into a brick wall.

kly

 

[wmtunate]

OK, here is a new scheme for the replacement amp.
http://www.avensonaudio.com/tech/Wurlitzer/wurlypreamp.pdf

The tremolo circuit is an adaptation of the ESP project:
http://sound.westhost.com/project29.htm

I've built and installed this tube circuit in my 206A and have been using it for almost 2 years now, but until this point I never wired up the tremolo bypass switch.  I've just been turning the depth down and living with the slight trem with the pot down fully.  I just tried wiring up the bypass this morning and I'm getting a huge pop when I open the switch and turn off the trem.  Is there a better place to put the switch to disable the oscillator?  On the ESP circuit, the oscillator is disabled by grounding the non-inverting pin of the first opamp stage, essentially shorting across R5 (on that schematic), but that's on a bipolar supply.  Can I accomplish the same thing by wiring the switch in parallel with R11 on Brad's circuit?