140B Modifications (Vibrato, Student Removal, etc)

[bcatchings]

Hey folks,

This is my first post to the forum.  I own a handful of different EPs and have recently started restoring, servicing and modifying them. 

I am currently working on a 1962 Wurlitzer 140B Student Model - the solid state version.  I've got it tuned, voiced and pretty much back in working order; however, this model does not include vibrato.  The cheek block has the original lamp, a speaker/headphone switch, an ensemble/self switch and a volume knob.  Ideally I'd like to have either an LED, speaker on/off, vibrato blend and volume or an LED, speaker on/off, vibrato speed, vibrato blend and volume.  I am sure I've seen this done, the problem is I don't know if it's been done by adding a vibrato circuit or by simply tapping into an existing vibrato circuit on this board that is not in use because of the student/ensemble switch.  I believe in the case of at least the variable vibrato the vibrato circuit has been replaced with a third party piece like the VariVib or something else.

Have any of you done this before? Can you point me in the right direction or maybe just clear up whether or not this model actually has a vibrato circuit?

All the best,
Ben

[bcatchings]

After finding a much better version of the service manual, I've determined that the small gold rectangular box in the photo is in fact the LDR. That leads me to believe that this amplifier does in fact have a vibrato circuit.  So I guess now the question has become how do I replace the ensemble/self switch with a potentiometer that controls the vibrato circuit?

Ben

[pianotuner steveo]

Im confused by the student/ ensemble switch...are you sure this is not a 146?

That would make more sense. The amp pictured is a 140 series amp, but usually the student models ( that end with a 6) are the only models with that switch.

[bcatchings]

Hey thanks for the reply.  I thought that the 140B was the student model of the solid state 140 and the 146 was the student model of the tube 145 - either way the control block and the harness seems to have been the only real difference. 

I actually figured it out with this 140 model specific service manual I found.  I cut out the ensemble/self and speaker/headphone switches for the moment, I cut out the 180K resistor at the terminal strip, jumpered the first two tabs on the terminal strip, cut out the lamp at the cheek block, installed a LED and a resistor (grounded the negative side to the volume pot and ran the positive to the grey wire from the lamp in the 4 pin harness), ran the red wire from the lamp to the shield in the 4 pin harness.  Then I jumpered pins 3 and 6 on the inside of the chassis at the 9 pin harness (after realizing I was getting no sound from the speaker), moved the metal pins from 3 and 6 on the harness to the open holes on 2 and 5, then I ran pin 2 to lug 1 and pin 5 to lug 2 on a 100k linear pot that controls the vibrato.

So this gives me an LED, a vibrato pot and a volume pot on the cheek which is pretty close to where I want to be.  I plan to replace the speaker on/off switch, exchange the phono output on the chassis for a 1/4 inch output and probably add a grounded power plug too.

So my next questions would be: How do I make the vibrato pot blend better (it kinda comes all the way in around halfway around the pot) and how do I add a vibrato speed pot to the circuit?  I think I'm going to look at how they do it on a Fender Bandmaster.  The vibrato circuit is at least similar with the LDR and whatnot and it has a speed pot.  There's got to be a way to drop another pot in this circuit.

Your thoughts?

Ben

[velo-hobo]

Looks like you've been digging pretty deep!

In a 140B, R5, R6 and R7 are the main resistors which govern the vibrato circuit.

I have had very good results replacing R6 with a 25k linear pot (wired as a variable resistor) in series with a 1.8k resistor.   R6 is the one that is closest to the foreground and furthest to the left in your photo, between the first two big brown/red caps.  (btw, unless the piano sounds really really great as is, I recommend replacing all the electrolytic caps on the board)

I also replaced R5 (18k) with a 22k resistor, it seemed to dial in the speed range for me.   The range and quality is almost as impressive as the expensive aftermarket vibrato mods.

I put the extra pot where the headphone jack was.  I also modded the wiring harness to accommodate the new wires, but you don't really have to go that far.  I was refurbishing the piano in question for the purpose of selling it, so I wanted it to be seamless.

You may have to play around with the specific component values, as the resistor-capacitor network here is somewhat finely tuned; it will stop functioning if you exceed certain limits.  I suggest playing around with different resistors and alligator clips to find the best choice for your tastes.

Also, regarding the blend (depth) pot, I think it is pretty typical for the effect to be quite subtle or non-existent until halfway up or more.  This is the case with all my wurlitzers and many tube guitar amps I have had as well.

[velo-hobo]

Also, this is a whole other thought I had about the 140B vibrato circuit, but here goes -

Since the LDR/bulb assembly determines the rate, intensity and contour of the vibrato, one could possibly devise a different, more modern means of controlling the bulb, so you could have a tremendous range of frequency, wave shape, or even alternate/asymmetric wave patterns!

One could potentially get some pretty wild delay/echo or synthy sounds out of a 140b this way.

[bcatchings]

Okay that's awesome - gonna try the variable speed stuff in the next day or so.  That's much much simpler than what I'd imagined.  I was out looking up variable frequency oscillator ICs and that sort of thing.  From what I found that would have been more like the modern options you were talking about - which I agree may be pretty interesting.  Speaking of modern would replacing the bulb in the LDR with an LED change the quality of the vibrato? I plan to leave it alone since it works but I'm curious.

As for the electrolytics, I'll probably have to replace them at some point but believe it or not this thing sounds absolutely incredible.  It's so smooth and round sounding.  I'm holding out as long as possible out of fear that it would end up sounding bright or brittle in comparison.

Thank you for all of that by the way.  Left to my own devices I almost always choose the most difficult option possible.

[pianotuner steveo]

Just for future reference. ALL Wurlitzer models that end in a 6 are student models.  I THINK that a 145 is basically a tube version of the 140B. The 145 is one of the few models I have not worked on, but I believe the piano portion is the same as the 140.

[bcatchings]

Ah, I see. This would be called a 146 then but the amp actually says 140B.  So I imagine the only difference in the two is the cheek block and the harness.  I found this in the service manual.  It would appear that most of the differences are tube vs solid-state, transistor type, speaker size and power.  Whatever it's called, it sounds great with the vibrato running.

[velo-hobo]

I would leave the incandescent and LDR assembly intact unless you really want to monkey with vibrato quality.  I think a big part of the contour or character of the pulsation has to do with the way the bulb lights up and dims.  An LED could behave differently than an incandescent in this way, though how it did would depend on the particular diode and power supply.  If you want to mess around with it, try putting together a whole new assembly and set the old one aside in case you want to put it back in.

Also consider that maybe the LDR is most sensitive to a certain range of wavelengths, and going to an LED could alter the response characteristics in that way too.

I have to agree about the electrolytics too, I have a few 140B pianos around right now - the one I mentioned earlier needed the whole board rebuilt as it was having a bunch of electrical issues, but I have another one that is dead stock and it is louder and more aggressive/full-sounding.  I plan on keeping that one and mostly leaving it alone until I encounter problems.

One thing to consider is you could always just replace a few caps at a time, like just the vibrato caps, and keep the old ones around, intact and labeled so you could put them back in if you weren't happy with the new ones.   In my experience sometimes just rebuilding the vibrato section will really make a big difference in the intensity of the effect, and it's a cheap way to bring some life into an ailing piano.

[bcatchings]

I had a hell of a time finding this but I determined that the pins in the molex connector are the same or similar to some molex pins used in pinball machines so I ordered some from Great Plains Electronics.  I'm going to fill out the connector on my harness (currently there are only 5 of the 9 possible pins), replace the pins I relocated for the vibrato and reinstall the speaker/headphone switch as a speaker on/off switch, and use the final two unused pins to build the vibrato speed into my harness.

[velo-hobo]

Cool, good find, would you mind posting the manufacturer part number for those pins?

I live near a big electronic distributor and all the molex-type pins they have are of a different type.  I had to harvest some pins out of a beat-up 206 that I picked up for $10 (it was missing the harps, reeds and all the electronics.  Still good for action parts and random bits though)

[bcatchings]

I may or may not have gotten this right. We'll see when they arrive but as they were only 8 cents a piece I won't be out much. Anyway, I ordered these two: 08-50-0134 & 08-52-0072.

[kenrichsoundservices]

The reason why your vibrato jumps on and becomes full blast halfway up the pot rotation is because you're using a linear taper pot rather than an audio taper pot. Now, if you want truly linear vibrato speed change then you need the 140B VariVibe system that Warneck Research and myself developed exclusively for 140B pianos.  Installation is very straight ahead. It's 3 wire hook up and a harness. It will give you true linear vibrato from 1Hz to 15Hz.

http://kenrichsounds.com/ed_roth_vid.html

http://kenrichsounds.com/zak_rae.html

The sound isn't great on these videos, but they give you an idea of the quality of the product, with feedback from a couple of incredible players, Ed Roth and Zak Rae.

This product isn't listed in the www.kenrichsounds.com/shop online store because we generally just install these in our workshop. You would easily have the skills to do this yourself though.

E-mail me if you're interested.

info@kenrichsounds.com

Ken

[bcatchings]

Thank you, Ken.  I truly admire your work. That is indeed what's going on with the vibrato blend pot.  I thought there may be something wrong because the schematic called for a linear pot but that would explain why a poorly operating vibrato blend is accepted as the norm with these things.

I've seen all of your videos already (I want a Clav with a whammy bar some kind of bad - that is truly brilliant) and the VariVibe is undeniably cool.  If I had the money, or if you guys sold empty PCBs, I would own one.

I will be posting pictures of my work soon - it turns out I'm not the best painter in the world so I've been taking my time with it but I am nearing the end of the project.

[VintageSoul]

Hello... I just happened on to a Wurli 146 as well and am curious as to how this all worked out for you. 

[VintageSoul]

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]

So I just brought my 140B back from the dead yesterday. I had a short in the wiring harness that I'd given up on finding for a while and now that I'm back up and running I've started toying with some modifications again. At the moment I'm experimenting with what I believe to be the most important of the mods I'd like to do. I've always wanted to add a line out so I can use other amps, effects and some other outboard gear that I run regularly.

I'd tried this in the past and even got advice about it but never really got it working correctly. In writing this post I dug through some of my old notes and found that the resistors I was recommended were different values (1k and 18k to be exact) but in messing with it yesterday I put a 470 ohm resistor across the tip and sleeve of the new line out jack. I ran a wire from the tip of the speaker output jack to a 47k ohm resistor and to the line out jack's tip. Then I ran a wire from the sleeve of the line out to the chassis ground.

So this sort of works except for the massive hum I get if it doesn't go through a ground lifted DI (pain in the ass) or into an old combo amp that I'm guessing doesn't have grounded input jacks (not the safest amplifier I own).

I've been eyeing the VVibe line out pod (which at $36 seems pretty reasonable... and tempting) but I can see what's on the board and know I have all of it laying around so I'd love to just figure it out instead. Either way it appears to be similar with the exception of two caps. I'm pretty sure the NP cap is a bit of tuning for the output signal and I'm assuming that the electrolytic is what I'm missing to filter out this horrific hum. Anyone have some insight as to the configuration and value of those two caps or do you imagine this noise problem should be solved differently?

Any advice or suggestions for those caps? Anyone done this on a 140B at the preamp stage instead of coming off the speaker?

Found this http://ep-forum.com/smf/index.php?topic=7712.msg39633#msg39633 after writing all that... Velo-Hobo for the win June of 2013.

[Max Brink]

For a line out from the preamp stage you can pull the signal directly from the wiper of the volume pot. I run a 6" shielded instrument cable from the bottom of the amp board directly out to the 1/4" jack.

[bcatchings]

No kidding? That's what you were talking about in the other thread? By the way, sorry to everyone else for all the cross-thread discussion. I'll give that a shot before I try the DI.

[bcatchings]

Wow Max. Huge difference. I pulled the internal cabling for the volume pot that was running along the chassis right next to all the power wiring, reran it out of the way of the power, and cleaned the terminals on the harness connector. Then I ran a wire from the same spot on the board as the wiper to the line out and grounded it. So much better. I mean there's the tiny hum you would expect to be present but it is infinitely more useable.

[Max Brink]

Yep. The DI mod that they sell and the LED aren't the way that I would do things...

[bcatchings]

Alright... here's a weird one for you then. What if I wanted to put in a secondary input for a guitar or another keyboard so I could plug straight into the 140B's amp and run BOTH a Clav or Synth or something like that AND also play the Wurli? Another benefit I imagined would be recording that beautiful vibrato on another instrument.

I already tried changing the phono plug on the back to a 1/4 jack and running the tip and sleeve to the tip and sleeve of the Wurli's input jack. The result is underwhelming with a guitar (and I'm sure that it's largely because the amp isn't voiced for a guitar). And I'm guessing that anything else with multiple inputs I need an input cap (the value of which I'm uncertain) and a resistor for this second input. I'm also thinking that instead of piggybacking on the wurli jack I need to wire this secondary jack into the same spots as the wurli jack. What I'm not sure about is whether or not that would change the fact that when the secondary was plugged in I had no sound from the wurli. Not even a lower signal... just guitar.

Am I on the right track with this or have any of you tried something similar?

[Max Brink]

You will need to have it setup so that the amplifier is seeing the right impedance for whatever input you would like. Phono inputs are different from Aux. inputs and Instrument inputs. It's not something that I have performed before so it's beyond my scope of knowledge what you would need to do specifically... The other two cents that I would add, though, are that Wurlitzer's amplifier has a fixed EQ curve that may not be what you are looking for in a guitar amplifier. Even after doing all your homework to get the input working with the amplifier who knows if you'll be very pleased with the tone...

[pianotuner steveo]

I would not plug in other nstruments to that little amp and little speaker. You are better off taking an output from the Wurlitzer and going into a larger amp.