146 Student Model Mods

[VintageSoul]

Hey all, first off, before I get flamed, I know that there was a post on here about a year ago about a guy doing something similar to his 146.  To me it looked like the thread was dead, so I wanted to ask my question in a new thread.

OK, that's out of the way, I recently picked up a Wurlitzer 146 Student Model EP.  The insides are actually in REALLY good shape.  The amp looks as clean as the day it was wired, the key bushings are surprisingly in tact, etc.  However, part of THAT wurli sound that everyone wants is the vibrato (i know it's actually a tremolo, but in all the schematics, etc, Wurlitzer calls it a vibrato). I've done much research and know that the 146 has the 140-B amp installed which DOES include the vibrato circuit, light bulb and LDR. 

My question is this, would i simply purchase a 100k linear pot and wire it to the control plug going to the amp?  See the attached schematic of the vibrato control.  It looks to me that if i just ran a wire from pins 2 and 5, to a vibrato pot, this should be able to control the vibrato.  I just wanted to get some advice from those smarter than me before tearing into this.

Thanks,
Rich

[velo-hobo]

Hey, I had posted last year on the 140B thread you mention - turns out I am actually (very slowly) working on a 146 for a friend right now which involved adding a vibrato control.  I don't have my notes from that project in front of me right now but you're pretty much on the right track.

Basically you need pull out the student switch and associated wiring and add a control pot for the vibrato as indicated in the 140B schematic.  Because the vibrato circuit is so old (component values may have drifted etc) it may need some work to get it tuned and functioning properly, but the first step is installing a pot.  You can do this with clip leads to do a quick check.

And actually you don't even need the pot to check the functionality of the vibrato, you can just put a jumper across the contacts that the pot would connect to - vibrato should go full on if the oscillator circuit is working.

Can't recall whether I used the spec'd 100k linear pot or something else - will check on that later when I can get to my workbench.

[VintageSoul]

Perfect... now, at this point I'm going to sound REALLY juvenile in my electrical abilities (and I am)... been a sax player my entire life and am really getting into these old boards... anyway, here goes.  I see three posts on the linear pots and know that there are only the 2 pins on the connector.  How would I solder in the linear pot?  See? I told you it was a dumb question!

[velo-hobo]

Not a dumb question - in this case you're using the pot as a variable resistor, so you only need the center lug (which is the wiper) and one of the outer lugs.

The choice of which outer lug to use depends on how you want the pot to behave with regard to rotational orientation  (Clockwise vs Counterclockwise for on/up) - double check with a clip lead/etc. before you solder.

Looking at the schematic, you can see that Pin 5 goes to the center lug/wiper and Pin 2 goes to the outer lug, but functionally in this case I don't think it really matters.

[VintageSoul]

Thanks so much!  Now, I know this is a bit of a deeper repair, but do you have any knowledge on converting the speaker out to an aux out for amp / DI usage?  That's really the only other mod I'm looking at right at this moment.

[velo-hobo]

Yeah, I typically do that to all the 140-series pianos that I work on, they can sound absolutely phenomenal through a good amp.

You can just buy the outboard box or the internal mod kit from Vintage Vibe, though lately I've taken to using their circuit design as the basis for aux out filters of my own construction.  I found that I usually had to tune the output level of their units by swapping out a resistor and it uses only a handful of parts anyhow.  It's like $2 worth of stuff, couple of caps, couple of resistors and a terminal strip.  If you make an outboard unit in a project box you can even get away with doing point-to-point wiring between the two 1/4" jacks, it's that simple.

There are probably a bunch of different ways to do it, though I can maybe post a schematic and some photos of my approach if I have time at some point.

[VintageSoul]

Very cool, if you get time, please post the info... I did forget that they had those for sale.  And I'm a cheap-skate anyway. It pains me to buy something for $32 that I can make for $2.  But of course, I know their quality is amazing.

[velo-hobo]

Ok, so I looked at the 146 that I'm working on - turns out I used a 50k linear pot for the vibrato control.  I think I initially tried the spec'd 100k linear and the adjustment was too crude - no vibrato til about halfway/two-thirds and then very difficult to dial in the desired amount.

Pretty sure I tried a 25k also but that wasn't enough to kill the vibrato when all the way down.  100k log taper might be the way to go, though my local supplier didn't have one in stock and the 50k seems to work fine for me.

I'm attaching a schematic I threw together and some photos of my aux out filter approach.  I have to give credit to Vintage Vibe for the basic circuit design, though the one I purchased from them came with a 100k resistor on the input side which I found to allow too hot of a signal.

I experimented and found 470k to work nicely, but you might investigate on your own to see what works best for you.  The cap that goes from there to the jack tip is for DC blocking, I believe, and the components that connect from signal to ground are essentially a filter for noise and undesirable high frequencies (similar to a tone control on a guitar, but non-adjustable).

The terminal strip is bolted into a pre-existing hole in the chassis.

[VintageSoul]

MANY thanks for adding this!  Did you get the terminal strip online or locally?  Also, did you just use the current speaker out jack that was already in place?

[velo-hobo]

I got the terminal strips from an electronics store that was closing years ago.   RatShack sells a cheaply-made version but they break easily.  It might be possible to locate a source for higher quality parts but I haven't looked yet.

Also, pretty sure I just used the existing 1/4" jack in this case since it's a simple guitar-style jack and that's all that's required.  If the jack was questionable I'd put in a new one.

If you want to make an outboard filter, simply put this circuit in a project box between two 1/4" jacks.  If you're careful and handy with the soldering pencil, you don't even need the terminal strip.  Output side is the same as drawn, input side takes signal from the jack tip, ground from the ring.

[VintageSoul]

Great!  OK, one more question, for now.  What's the voltage on the .033uF Mylar Cap?

[velo-hobo]

Not sure - it's probably not critical anyhow, it's basically a tone control on an instrument-level signal.  Certainly, it doesn't need to be gigantic, but you can't go wrong with too large a rating.  A ceramic cap would work too, I used the film cap because I had some lying around already.

Note that the 35V electrolytic is what was on the VV kit that I am essentially copying so I just stuck with that.  I'm not an electrical engineer and their circuit works well so I left it as is (other than the resistor mod that I did to tame the signal level).

As I said before, there are probably a bunch of other ways to do it (I can recall seeing at least one or two mentioned here or on the yahoo Wurly group), so don't take this as the gospel.  I just know it works for me!

Also I can't stress enough that the credit for the basic circuit design is due to Vintage Vibe.  I've learned a ton from what they've shared with the community - in combination with this forum, it's been critical in developing my own understanding of how these instruments work and what they require in order to function at their best.

[VintageSoul]

Agreed! VV has done amazing work in getting the old Vintage keys that we all know and love back to playing condition.  Thankful to them and people like you who are willing to help those who aren't as experienced.

[VintageSoul]

Oops... meant to write this post in this thread...

Just got some time to work on the keyboard last night.  Got the vibrato pot installed in the cheek block where the "Self / Ensemble" switch once resided.  The vibrato sounds great.  Very happy there!  However, I think adding the vibrato to the sound alerted my ears to just how much hum is coming out of the speaker (assuming it's the AC running along side the audio wires in the control harness to the bulb on the cheek block.)  Having said that, I know that VV sells their LED mod for $36 + SH... in your opinion, is it worth just purchasing this mod from them, or is there a much cheaper way of doing this?  Does anyone have the schematics on a DIY solution? Thanks.

[bcatchings]

Hey folks, so I tried the line out setup shown in this thread and while it does work I still have a mean hum coming from the line out. Any thoughts?

[VintageSoul]

I believe the issue stems from a few things.  I've watched a few videos from Vintage Vibe and done some reading and it appears that the amp in the 140 series is a bit noisy to begin with, then, you have the fact that the old shielded audio cables break down over time AND are run along with AC cables in the wiring harness, and yeah, it makes for a pretty noisy environment.  Having said that, I've gigged with mine several times and the hum is not something that's been too overbearing / a complaint of sound guys, etc. so there may be a louder hum in yours than in mine, in which case something like this might help... http://www.vintagevibe.com/shop/wurlitzer-electric-piano-140-b-wiring-harness-complete-with-l-e-d-mod/

[Max Brink]

There's a better way to do the output: use a shielded instrument cable and run the signal from the wiper to the 1/4" output jack.

When it comes to noise the incandescent light bulb adding noise to the circuit is mostly myth. Although in theory the LED mod makes logical sense the noise that is added from the AC bulbs is very minimal as long as everything is grounded correctly.

I have never had to replace ALL the cabling in any Wurlitzer. If they wiring is that far gone there's a lot more to be said about the condition of the Wurlitzer than just firing from the hip and replacing the whole thing.

The best thing you can do for noise in any Wurlitzer pre-200A is add the 200A shielding. That and making sure that all your ground connections are correct. This should eliminate a vast majority of unwanted noise in most situations.

[VintageSoul]

Thanks for clearing that up Max, It's always great hearing from the real-world techs that bring clarity to the giant mass of information that's out there.  When you say 200A shielding, are you talking about adding a hum shield like what's on the 200A's?

[Max Brink]

Correct. The shielding that I was referring to is the pickup reed bar shielding. It's a must-have for any 140 or 200 that does not have the shielding. You may need a Dremel tool to modify them for a 140 series.


Also to clarify on the 1/4" output when I say "from the wiper" make your life easy and run just a 6" instrument cable from the point on the bottom of the amp board rather than a 2' cable on the pot's wiper...

[bcatchings]

Thanks for the responses guys. Yeah I have replaced my entire wiring harness. Everything is pretty nicely shielded and whatnot and when I play it through the onboard speaker it sounds fine. It's just when I run it from the line out that I get the hum.

I assume that when gigging with the line out the sound guy is running you through a DI with at least a decent transformer and probably lifting the ground too. And if that's what I have to do to get it cleaned up I can accept that but it kind of baffles me that there isn't a better way to do this. Can you not come off one of the legs of one of these transistors before the signal goes to the power section of the circuit and just send that out?

Either way, going to keep looking for my DI to see if a transformer and a ground lift fixes my line out noise.

[Alan Lenhoff]

Correct. The shielding that I was referring to is the pickup reed bar shielding. It's a must-have for any 140 or 200 that does not have the shielding.

Full disclosure:  I'm not a tech, and the 140B I own is the only one I've ever worked on. So, I hesitate to question Max, who may have extensive experience with them...

But my understanding is that the 140/145/146 series models have no need for additional reed shielding. The whole case is a shield.  The top is metal, and the interior of the case is covered with electrostatic shielding paint.  My 140B, after rebuilding the amp with new electrolytic caps, low noise transistors and wire resistors, is very quiet without any mods, new wiring harnesses, etc. I thought the point of adding reed shields to the 200 series was to overcome the hum introduced by going to a plastic top.

Is there something I'm missing here?

Alan

[Max Brink]

That is correct that the 140 series' lid serves a shielding function. And because of this it's important to insure that there is good continuity between the ground scheme and the lid...

The shielding that I am talking about is the same as the shielding that was introduced on the 200A and is much closer to the pickups. It goes underneath the damper assembly and although the function is the same as the shielding lid it is much more effective because of its closer proximity to the pickup rails. They are available by Retro Linear, Ken Rich, or VV (although there may be a minimum order quantity depending on the dealer).

[pianotuner steveo]

I am confused about the 10k resistor in the schematic above. What is that for?? Why is it going across the signal like that?

[sean]

Mr. O,

The 10K resistor and the 470K resistor act together as a voltage divider.  They make the signal that reaches the headphones much smaller in amplitude than the signal that would be pumped into the speakers.

Sean

[pianotuner steveo]

Thanks,  I was confused.

As I have said many times, my expertise lies in the piano portion, not the electronics.