Stand-alone true pitch shifting vibrato for guitar

[sluckey]

Ever since I restored the Maggie M10-A, I've been intrigued with the pitch shifting vibrato idea. A few months back FYL posted some info on a Wurlitzer organ vibrato circuit. That got me thinking, "What's going on with the old Hammond organ vibratos?" I've seen many of the small vibrato units on eBay for cheap! Maybe it could be converted to guitar use.

Well, it's actually pretty easy to convert them for guitar use. Here's my project...

          (Click on the pic for more info)

[Fresh_Start]

Good morning Steve!  That's a great project, and your presentations are all very thorough.  I should check back on your website more often.

Cheers,

Chip

[Geezer]

Really sweet, Steve!

Comments on the sound?

[tubeswell]

But does it sound as interesting as it looks? (And what do all those bottles do? Any chance of a schematic?)

[sluckey]

Comments on the sound?

Ha! I'll try. Have you ever heard a Magnatone? This is very very similar, but since the Hammond uses three shifting stages (Maggies use only one or two)the sound is fuller than the Maggie and even comes close to a chorus pedal when set right. There's an almost liquid or fluid sound when set to very slow and strong. And fast sounds kinda psychedelic. Set it to medium speed and strength and it sounds really good on Clapton's middle guitar part on Badge. It does suck some of the twang out of a guitar though.

I can't really describe how this sounds, but it works better on clean guitar. I can almost hear (imagine) some of your stuff thru this vibrator. I don't even own a mic, but I may be able to do a line level patch into my computer and record something. I'll let you know if I come up with some sound bytes.

[sluckey]

But does it sound as interesting as it looks? (And what do all those bottles do? Any chance of a schematic?)

The sound is the best part. One bottle is an input/output buffer to get the guitar signal high enough to drive the vibrator unit. Two bottles are the actual phase shift modulator. One more bottle is the LFO and driver, similar to a Fender trem osc/driver.

Look again at the web page. Near the top you'll see a pdf with the actual Hammond AO-41 and AO-47 schematics and a therory of operation. At the bottom of the page is my usual Visio drawn schematic and layout for my as built circuit in pdf format.

[Willabe]

That was George playin the bridge part (thru a Leslie), payin back Clapton for playin on the Beatles White,"While my Guitar Gently Weeps".

     Brad     

[phsyconoodler]

That is one nicely done project! You are a true craftsman!

 That drill press has seen some mile,with all the surface rust,eh?

 I built a very simple pitch-shifting vibrato in my V-Verb amps,no where near as complicated as the Hammond and likely not as nice sounding.
 

[tubenit]

Sluckey,

I was hoping you'd share some info on that project. I got to hand it to you, you are a MASTER at these projects and documenting them for the benefit of others.

My hat is off to you!  That looks like a fabulously successful project. Bravo!

The one time we met and jammed, I remember you showing me the riff for Badge so it gives me a good mental picture of what this thing probably sounds like with you playing thru it.
 :icon_thumright:

THANKS so much for sharing it! You sure come up with some innovative approaches and they always look incredibly well done.

Best regards, Tubenit

[sluckey]

That drill press has seen some mile,with all the surface rust,eh?

Sure looks that way. Actually, the gulfcoast is just a rusty place to live. I could go down to the bay and pick up a bucket of oil for a lube job.   

[Willabe]

sluckey,

What is that Trany in the cathode circuit? I'm thinkin, it's part of whats wobblin the cathodes? But why a trany, for isolation from the LFO? From the text, is this trany being used as some kind of LC low pass, or has freq. got nothing to do with it?    :icon_scratch:    Got any idea's of what could be swapped in as a sub.? Hopfully something could be bought off the shelf? Maybe 3 seperate units? I'd like to do this build too. I love this/these's kinds of FX.

    Thanks,    Brad    

[SoundmasterG]

That was George playin the bridge part (thru a Leslie), payin back Clapton for playin on the Beatles White,"While my Guitar Gently Weeps".

     Brad     

Sorry to say, but that isn't true. George played the rhythm guitar part, while Clapton didn't play on the song at all until the Leslie part came in. Clapton is playing the leslie part and the solo. There have been quite a few interviews over the years where Harrison alludes to this song and Clapton's playing on it.

Greg

[sluckey]

The tranny is not a standard transformer. It's a saturable reactor. This unit has three mounted on a common frame. I don't know how it's made or if there is an affordable COTS unit available. Why not just get the right part to begin with? The entire Hammond vibrato unit (AO-41 or AO-47) is still very affordable on eBay. You guys just don't need to get into a bidding war though!  

The saturable reactor is the key to this circuit. Without it, you got nothing. You can read the theory of operation to see how it works it's magic in the modulator circuit. Here's basically how it works...

Don't think of this as a transformer that's gonna step up or down some ac voltage. Instead, think of it as a device that the primary winding is going to control the impedance of the secondary winding. When current flows thru the primary in one direction, the secondary impedance will be high Z. When primary current reverses directions, the secondary impedance will be low Z. Now make that primary voltage a very smooth, low frequency sine wave and the secondary impedance will smoothly change from a low impedance to a high impedance at the frequency of the sine wave. This secondary is connected such that it switches (actually blends) the plate signal and cathode signal together and passes it on to the next stage. Using the input signal as a reference, the cathode signal will have zero phase shift while the plate signal will have 180 degrees phase shift. The varying impedance of the secondary smoothly blends the 0 and 180 signals together such that the resultant signal has a smoothly varying phase shift. This change in phase causes a change in frequency of the resultant signal.

There's a lot more going on with saturable reactors. Most of it seems like magic.

BTW, I've seen a circuit that uses analog optocouplers to do the same thing as this saturable reactor does.

[Willabe]

I seem to remember reading the opposite, but I very well could be wrong. Still a great song!      


    Thanks,    Brad    

[Willabe]

sluckey,

Thanks. Do you remember where you saw the roach schemo?

      Brad      

[sluckey]

Yes, it was on my computer screen. Can't find it now though. It 'may' have been posted by FYL back in September. Just can't remember.

[tubeswell]

Saturable Reactors aye? Are they known by any other names? I have to locate one. What about the soundbyte(s)?

[sluckey]

That's the most common name. They're used in AC voltage regulators, synchro data to azimuth pulse data converters (don't ask). Usually associated with so called magnetic amplifiers. These are the smallest ones I've ever seen.

No sound bytes yet. Maybe over the holidays.

Here's a schematic symbol...

[DummyLoad]

niiiice!   :glasses9:

[rafe]

Very impressive as usual

[PRR]

> Saturable Reactors aye? Are they known by any other names? I have to locate one.

Saturable Inductors were hot-poop from 1957 to 1962, and then vanished from the face of the earth.

I'm overstating. Stuff like that was around in 1930s and even 1890s. They lingered past the 1970s, though by that point transistors had taken over many of their jobs.

Each one is designed FOR the job it must do. There were no general-purpose saturable reactors.

Buy the old Hammond. Wire just about like Hammond did or with Sluckey's mods. He added an input booster (organ signal is hotter than guitar signal), and a similar but more-adjustable wobbler (from Fender).

He tried an additional post-boost and removed it. _I_ suspect no post-boost is needed at all; take the last L-C phase network to 250K level pot and out. Loss through the three shifty stage is about 0.4, you want to make-up plus a little more, put a gain of 5 in front. The original Hammond V3(123) post-boost stage is suitable as guitar pre-boost. That makes the same tube-count and 98% the same parts as Hammond AO-47. Just re-wire the post-boost as a pre-boost and then dolly-up the oscillator. (This does mean using 7247 or changing to 12AX7+12AU7.)

He also omitted the dry/wet mixer, which may be interesting to put back in.

> I've seen a circuit that uses analog optocouplers to do the same thing as this saturable reactor does.

The circuit is very general. You can use photoresistors, varistors. or FETs as the variable resistance. The FET variant is VERY popular in some circles.

[Willabe]

sluckey,

I was looking around your site, you do very nice,very neat work!

I went on flea- bay, and found an AO-41, but the guys got it packaged with some other stuff (that I dont need) and wants $99.

WWW and this guy is 20 mins. down the road from me.    Can you belive it? No e-mail address listed either.    So.....  I'll have to wait for someone else to put one up for sale.

       Thanks,      Brad     

[Jack_Hester]

This is a really beautiful job.  I'm overwhelmed by the projects that you guys create.  But, I'll have to take my time and build in bits.  Hope to live up to the standards that you and your peers provide. 

Jack

[sluckey]

I went on flea- bay, and found an AO-41, but the guys got it packaged with some other stuff (that I dont need) and wants $99.

That guy has had that 'deal' running since early October when I started watching. No one's gonna pay that for those units. Just be patient. Your deal will come along. I won't be bidding against you either. Every one I've seen sell during the past 2 months has gone for under $15. Many sellers just call these preamps. Here's a good search string that will pick up most, if not all, of the AO-41s and 47s.

                  hammond (preamp,vibrato,ao-41,ao41,ao-47,ao47)

[Willabe]

Thanks sluckey.

     Brad     

[Jack_Hester]

Saturable Inductors were hot-poop from 1957 to 1962, and then vanished from the face of the earth.

I'm overstating. Stuff like that was around in 1930s and even 1890s. They lingered past the 1970s, though by that point transistors had taken over many of their jobs.

Each one is designed FOR the job it must do. There were no general-purpose saturable reactors.

Probably not practical to build, but some info that might help someone do so:

www.toshiba.com/taec/components/Generic/M2.pdf

That being said, we don't necessarily build because it's practical.

Also, a short thread from a another unrelated site:

http://www.antiqueradios.com/forums/viewtopic.php?t=35055&view=next&sid=e4ecdbeb0abdd7928ddb43b0ab418424

Jack

[sluckey]

Here are a couple short, poor quality sound clips. The chain is Taylor T5--Warbler--Stuffed Vox--line in at builtin soundcard in computer. The soundcard really loads the amps preamp output and causes a distorted sound. This stuff sounds much cleaner/better without the soundcard connection, but I still don't have a mic. Maybe in a few days...

http://home.comcast.net/~seluckey/amps/warbler/warbler1.mp3
http://home.comcast.net/~seluckey/amps/warbler/warbler2.mp3

This is my first attempt. I used Jet Audio to record. Don't have a clue what I'm really doing. Hopefully this will give you sense of the sounds the Warbler makes. I didn't try any over the top psychedelic sounds. And listen to the Warbler, not my fingers!   

[SoundmasterG]

I seem to remember reading the opposite, but I very well could be wrong. Still a great song!      


    Thanks,    Brad    

Here's a quick thing I found on wikipedia, but I do remember a proper intreview about it that I saw in years past. It is an awesome song....one of my favorites from Cream!

Greg

http://en.wikipedia.org/wiki/Badge_(song)

[Willabe]

slucky,

Sounds great! Very rich, thick, round, and smooth. I'm gonna build one. Just gotta get my hands on one of those saturable reactors. It might not fill a room as well as a real Leslie, but then it sure does'nt weigh as much or take up as much spaceon stage.     How well does it fill a room? I'd bet pretty darn good. I have a EH, 2 tube pedal thats called the Wiggler (?). It's multi vib/trem/chourse thing, sounds pretty good but I dont think it sounds as good as your Warbler build. Hopefully I'll be able to A/B them for my self some day soon.

I do have a ?.....   Of the two (41,47) one has one end of SR grounded, and the other has one end of the SR biased up to 150vdc and no ground. Also, I see that one is (the other end of the SR) plate feed and the other is feed from the cathode. Whats up with this? Why did they do two different ways? Noise,  better function of the effect? Also IIRC you built yours to go in an FX loop, but if any one wanted to use the Warbler in front, do you think it would be usefull to wire up that last unused gain stage as a CF?  

     Thanks,   Brad                

[Willabe]

Thanks for the link SoundmasterG. The sound of the guitar on the bridge has always cut me deep.

Take a listen to slucky's Warbler in action, sounds good huh? Man I've got to build one. Thats one of my favorite type of FX.   

[sluckey]

I do have a ?.....   Of the two (41,47) one has one end of SR grounded, and the other has one end of the SR biased up to 150vdc and no ground. Also, I see that one is (the other end of the SR) plate feed and the other is feed from the cathode. Whats up with this? Why did they do two different ways? Noise,  better function of the effect?

I think it's just a normal progression of the circuit. Maybe it was a cost cutting idea (one less tube) or maybe the 12DW7 was not even around at the time the AO-41 circuit was designed. I've played it with both drivers and didn't notice any difference in sound. The driver is not in the signal path.

I liked the cathode driver better simply because it uses one less tube. The SR is identical in both units though. So if you're gonna totally rebuild, it doesn't matter which unit you get, unless it comes with tubes. I'd lean toward the AO-47 in that case to possibly save having to buy a 12DW7.

Also IIRC you built yours to go in an FX loop, but if any one wanted to use the Warbler in front, do you think it would be usefull to wire up that last unused gain stage as a CF?

My prototype was built on the actual AO-41 chassis, stealing B+ and filaments from another amp. The circuit was left pretty much stock except that I put the fender LFO in it and converted the driver from plate driven to cathode driven like the AO-47. It didn't have enough gain to sit in front of an amp, so I put it between my amp's preamp and power amp (kinda like a passive FX loop). At that point I didn't want to add any more circuitry than absolutely necessary until I was satisfied with the sound effect.

The finished project was intended to be used in front of an amp and included a pre amp and a post amp. The post amp was not needed. I suppose you could convert it to a cathode follower. Might come in handy, especially if you use long cables between the unit and the amp, or want to plug it into a low impedance device like a SS amp.

[Geezer]

Whoa!  :tongue9: LOVE that sound! Much better to my ears than trem (which I never liked).

I'll have to keep my eyes peeled for one of those (after the other guys get theirs, of course!)

G

[PRR]

> one has one end of SR grounded, and the other has one end of the SR biased up to 150vdc and no ground. Also, I see that one is (the other end of the SR) plate feed and the other is feed from the cathode.

Put the two thoughts together. Plate-fed goes up to supply voltage. Cathode-driven goes to ground.

The '41 circuit is sloppy. The large oscillator swing is cut way down, buffered for no reason, then amplified-up again. The plate swing is probably very much like the oscillator swing. Seeing that, the '47 redesign just put the signal to a cathode-follower, saved a bunch of parts.

The back-story may be more complicated. There may be a saturable reactor re-design before the '41 or between '41 and '47, the older SI needed the bigger drive. An improved SI allowed less drive but the tube-works didn't change right away. Recall that unlike guitar amps, church-organs are not SO price-sensitive, the vibrato is the smallest part of a full organ, a few bucks over-spent was not the Big Deal that it would be at Gibson or Kay.

> usefull to wire up that last unused gain stage as a CF?

The output impedance from the R-C-L Y-network is not higher than R115+R114 or 25K. Probably under 20K worst-case, even lower under many conditions. So it can drive a 250K-1Meg output pot and average stage-cable directly. It's really a better source than a guitar, and that works OK.

[Willabe]

I live very close to Lenco Transformer, IIRC Victoria amps has had their tranys made there for a long time, as well as at least a few other boutique builder's. Their an old company (started back in the 40's?). I ran across them yesterday, while doing a search on SR's, to learn more about them. Anyway, their site says that they make SR's, and from slucky's pic's, they look pretty small, so maybe getting a small run say, 25 to 50 would'nt cost very much? Maybe, since all 3 SR's (put togther as 1 unit) are the same, they could make them as just the singles? Get 7/8 sets, might put it in reach. I'd also be interested in trying a 4th stage of phase, like the U-vib has. If they were singles, would be easy to try. When I get my hands on 1, I think I'll bring it over to them and see if they'll give me a quote. If it works out I'd have a few sets to let go to any one who's interested (for my cost only of coarse, no $$$ for me). Might just be dreamin again.

      Thanks,    Brad                      

[billcreller]

 That is a really nice sound!  When ever I hear something unusual like that, I wonder how my steel guitar would sound through it.

[Willabe]

Ahhh, ok, Thanks PRR.

Yeah, why not on a steel guitar? IMO it could/would sound great, even if just on some things. Nice "thickener", sure worth a try.


    Brad            

[sluckey]

I wonder how my steel guitar would sound through it.

I can almost hear a steel crying out Sleepwalk thru a vibrato!   

[tubenit]

Wow!  You're getting some incredibly sweet tones thru the Warbler. Very nice.

With respect, Tubenit

[spacelabstudio]

Wow.  That's cool.

FTR, if anyone ever wants a good, clean recording of their homebrew gear, you can ship (or bring) it to me, in Durham, NC.  Getting to play with our stuff is all the payment I need.

Chris
--
http://spacelabstudio.com/

[topbrent]

Sorry for the spam:  I have a few of these Hammond AO-41 units if anyone is interested.

PM me for info.

[Willabe]

Hey,   I got one!            Looks good, in great shape. It's stamped, A  H-AO-41-1.

Talked with a guy at Lenco, he was very nice. He said there's a good chance they could figure it out with out destroing it. It wont cost any $$$ to do that, and to give me a quote.

He did say might be a problem with using "modern" core matt. because saturation of the core is key for it to function right in the design schem. He also said it's a little different ball game making SR's, that there not as easy to make (if your backwards enginering it), and get them to work right in the design schem. as would be a trans. I'm gonna take it over to see him soon and see what he says. Worth a shot, nothing to loss, can only learn something. Should be interesting.

   Thanks,   Brad          
            

[plexi50]

Steve are you related to Leo? Your info and work quality is amazing!

[sluckey]

You mean Uncle Leo? From Seinfeld?   

[plexi50]

  Yes uncle. I just bought a AO-41 unit on  Ebay. Did you build the board?

I am looking forward to pestering you about any issues i can not figure out. MERRY CHRISTMAS!!!

That warble machine sounds great. The notes and chords ring on and dont decay quickly. I like that

[sluckey]

Yes, I built the board. There's a full size board drill guide on that web page. Just print it out full size and tape to your blank.

Please tell me you didn't pay $99 for that!

[plexi50]

Heck no. I made a best offer and he accepted $50.00. I saw no others on the site and what the heck i have sold a lot of stuff latley on Ebay so im doing pretty good right now. The key is to not go crazy and spend it all. I dont do that. Yeah in the past i have seen them for $20.00

Cool i will print out the template. Does Doug have a blank board that will do?

[sluckey]

Does Doug have a blank board that will do?

Yes. And turrets too.

[sluckey]

***CAUTION***

Hey guys. Before you put a soldering iron on that SR, take a close look. There are a lot of very tiny wires on those terminals. Even the terminals are fragile. If you break a wire, you'll be up s--t creek without a paddle!

[tubeswell]

Wow that sure is pretty sounding!. Many thanks for posting those.

[Dave]

What is Sluckey's homepage?

Dave