warbler-related project

[Willabe]

This was started by member Brinkman in Buy Sell Trade. He's looking to buy saturable reactor coils for a project he want's build. I asked a couple questions, he posted a schematic, needs to be here now;

    Quote from: Brinkman on May 09, 2025, 06:30:12 pm

        ".... I’m looking for 4 more for a warbler-related project I am working on."


    What are you building?

    How many SR's are going to be in it?


"18, see schematic for reference. It will be tubes though, not transistors."

[Willabe]

 I have a Warbler I built and it sounds very good.

But looking at the schematic you posted, I don't understand how this works?

Those SR's come from a Hammond organ, I think the L series? This is where the Warbler comes from. And each SR coil is driven by it's own triode. Even though each gain stage/phase shift stage has it's own triode gain stage, each stage still loses a little gain. You can see the voltage loses looking at Sluckey's schematic. So 18 stages with only 1 drive gain stage would have a huge total loss by the time the signal gets to the output.

Each coil is 1 phase shift stage, so 3 stages of phase shift total. And it's enough to get a very good sounding pitch shift.

In the schematic you posted there's 18 SR coils in series. But their not being driven separately. The way it's wired up, it looks like it's just 1 giant SR coil being driven by only 1 gain stage?

How is this supposed to get more than 1 stage of phase shift?

If the SR coil circuit worked with only 1 triode to drive more than 1 SR coil, Hammond would have done that to save money. 

Have you heard a sound clip of this build? Can you post the sound clip?     

[Willabe]

From Brinkman;

"The measured resistance of the signal winding in both the Hammond SR and Schaller SR is roughly the same, around 40 ohms. The Schaller schematic linked above states the total series resistance as 800 ohms (800/18~=44 ohms each winding) and the Warbler schematic has each signal winding as being 48 ohms.

In the end, the Rotor sound is really just a phaser with 18 all-pass filters and as such they only affect the signal phase. If my understanding is correct, that creates 9 notches in the frequency response when the phase shifted signal is mixed with the dry signal.

The BC109 transistor is fairly high gain, fwiw."

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[Brinkman]

This was the original video I had linked to. Particularly the 1:20 mark to the end.

Thanks for the move.

[Willabe]

...

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[Brinkman]

To my ears it is a very “wet” or “fluid” sounding phaser, perhaps due to the wave shape of the opto-isolator based LFO in conjunction with the BH curve of the SR.

[Willabe]

At 1:25 the sound changes and gets much deeper/thicker. Way more like a Leslie or a Magnatone amp with true pitch shift vibrato.

And a few seconds latter, he shows a different effects unit build?

The Schaller unit(1st FX unit) with the controls all the way up couldn't get that fuller, way more wobble sound.

And there's another large knob on that 2nd unit. What is that?

What is the 2nd build?

[Brinkman]

The signal chain in the video I posted is the following: Strat - Rotorsound - Custom Marshall 50W - M811 - AA Six - DAW.

The M811 is a telefunken mic, the AA Six (the second unit) is an Analog Addicts Series Six tube mic preamp: https://reverb.com/item/19927425-analogue-addicts-uk-1960s-mono-valve-tube-mic-pre-preamp

[Willabe]

To my ears it is a very “wet” or “fluid” sounding phaser, perhaps due to the wave shape of the opto-isolator based LFO in conjunction with the BH curve of the SR.

The old Uni-Vibe (roto vibe) was a 4 stage phase shifter. It used a LDR. And they say that those bulbs heat up/cool down at a different speed. So the wave form that's produced is asymmetrical, it's not even because of turn on/turn off. They say that's a big part of the Uni Vibe's wobble.

I have a Leslie, it was a 2 speed, I bought a multi speed add on that works with an expression pedal, 6 speeds. And I have a (new) Magnatone with pitch shift vibrato and the Warbler I built.

The old Schaller (1st unit) sounds like a phase shifter to me with the controls all the way up.

That 2nd unit, now that sounds much more like real pitch shift vibrato to me. It sounds a lot like my Maggi and the Leslie at middle speeds.

I like it very much! I would play through that, oh yes I would. 

Edit: I got this wrong, there's only 1 unit.

In the sound clips he does not line up the pictures of the FX unit's control settings with the sound track part. And he shows a mic pre that I thought was a different cloned build that was modded to get a much more intense sound.         

[Willabe]

The signal chain in the video I posted is the following: Strat - Rotorsound - Custom Marshall 50W - M811 - AA Six - DAW.

So the 2nd unit he shows is a mic pre?

Well, at ~1:25 that sounds much more like a multi speed Leslie and a Maggie with true pitch shift vibrato. I think it kills a Uni-Vibe!

I don't get how it works, but it sounds great if you like a wobble sound.   

[Willabe]

To my ears it is a very “wet” or “fluid” sounding phaser, perhaps due to the wave shape of the opto-isolator based LFO in conjunction with the BH curve of the SR.

What is BH?

[Rontone]

I've just been going through Merlin's Power Supplies for Tube Amps [2nd Edition] again [its my bedtime book!]

Magnetic Force Field = H
Flux Density = B

From page 14, Section 1.4.3

"Ferromagnetic materials have very non-linear permeability, that is, doubling the magnetic force field H does not necessarily double the flux density B. This can be appreciated by plotting a curve showing how much B is produced as H is varied. This is called the BH curve of the material, and a working knowledge of its characteristics is useful when dealing with transformers and chokes of all kinds."

[tubeswell]

I also built a stand alone warbler (and agree that only one set of warbler coils is needed to get the thing to work properly). Does freaky sounding vibrato

[Willabe]

I also built a stand alone warbler (and agree that only one set of warbler coils is needed to get the thing to work properly). Does freaky sounding vibrato

Pete listen to the clip in reply #3, at ~ 1:25 it get's a great intense warble!

https://el34world.com/Forum/index.php?topic=32727.msg363339#msg363339

I don't understand how it works with the 18 SR coil series string, but it sounds great turned up.

From Brinkman reply #2;

"In the end, the Rotor sound is really just a phaser with 18 all-pass filters and as such they only affect the signal phase. If my understanding is correct, that creates 9 notches in the frequency response when the phase shifted signal is mixed with the dry signal."

[Brinkman]

What is BH?

https://www.electronics-tutorials.ws/electromagnetism/magnetic-hysteresis.html

Short answer: The LFO current through the SR control winding builds up a magnetic field in each SR twice per cycle (once per + and - peak). The magnetic field in the ferromagnetic core of each SR ramps up through its linear region up to saturation, where the magnetic field cannot increase with an increase in current and back down through its linear region into saturation twice per cycle, commensurate to each peak.

Operation in the linear region only is the principle of operation for mag amps.

[Brinkman]

I originally came across the rotor sound while researching the effects used on this particular track by the German avant-rock band Can:

The effect can be heard on the guitar from 0:12 to 1:30.

The album was recorded over three months, from November 1970 into February 1971. I don’t know what phaser effects where made when and where they were distributed but this particular guitarist was known to have used a Schaller fuzz unit at this same time. The Schaller Rotor Sound is claimed to have been in production by 1969 and into the early 70s.

I’m 85% positive the Rotor Sound is what is being used here but it’s only me ears telling me this. It hasn’t been suggested elsewhere.

[Willabe]

The effect can be heard on the guitar from 0:12 to 1:30.

That is set mildly at best. I can't really hear any difference from that and any other FX type like it.

The strong setting in the clip you posted, now that has it's own sound.

[Willabe]

I found your post on another forum asking about the Schaller, how it works.

Here's the link to it for the guys here;

Requesting help analyzing Phaser schematic | diyAudio

And here's the close up of the Schaller's SR coil. Looks like there's 4 wires coming from it like there should be. looks like 1 wire on each side on top of the insulator 'tab', like on a pot, and the other 2 wires must be on the bottom side of those insulator 'tabs'. With solid wire leads coming off the tabs for connection to the circuit board. Look at the wiring labeling on top of the SR coil.   

[Willabe]

Here's the text from your post from that link to another forum;

"Below is a schematic of a German phaser instrument effects unit from the late 60s/early 70s called “Rotor Sound” and manufactured by Schaller. “Rotor Sound” alludes to the sound produced by a Leslie speaker cabinet. A demonstration of the effect produced by the unit can be heard here.
 
Similar to the vibrato units Hammond made for its organs, the Rotor Sound uses a saturable reactor as part of the effects filter (as seen at the top of the schematic). The effects filter itself is comprised of a 18-rung ladder network of low-pass filters, the series elements of which are the DCR and the inductance of each reactor’s “power” winding and a capacitor to ground as the sole shunt element.
 
Driving the reactor’s control winding is a vactrol-based oscillator (lower middle of schematic).

The saturable reactors in the device are two-winding P14/8 pot core transformers:

Someone else measured these saturable reactors; the power winding (the “in circuit” winding) is 2.2mH with a DCR of 65 ohms. The schematic itself does not denote the inductance; all it states is that the total resistance of the power windings in series is 800 ohms (800/18 =~ 44 ohms each).

What I need help with is understanding how to look at the effects filter. My understanding so far is that when the current through the control winding is low, each rung of the ladder network is a second-order LCR filter. When the current through the control winding is high, the core of the reactors saturate and the inductance in the LCR drops significantly, changing the filters topology into that of a first-order RC filter. However, I feel like this is the wrong way of looking at it as daisy-chaining 18 low pass filters is not going to produce an easily calculated response at a given frequency. Still, I feel like this shifting of topology twice per cycle of the LFO is key to understanding the function of the effect.

I’m asking for insight because I have managed to salvage a couple saturable reactors from some Hammond vibrato units and would like to repurpose them for something closer to the phaser schematic above."

From your 2nd post;

"I’ve been reading about phaser effect pedals and it seems like every pair of filters creates a 180° notch."
 
And the reply;

"My take is the filters are a "T" section all pass filter, (lattice phase equaliser) with up to 180 degrees phase shift per filter, 3240 degrees total.
The saturable reactor changes the coils inductance, so varies the frequency of the phase shift.
When combined with the direct signal, the phase shifted comb filter response sweeps up and down in frequency which varies with the rate of the oscillator."

[Brinkman]

I’m be curious to find out what the inductance of the signal winding on the Hammond unit is. The Schaller SR signal winding is 2.2mH.

[Willabe]

The saturable reactors in the device are two-winding P14/8 pot core transformers:

I found this on 'two-winding P14/8 pot core transformers'.

"The pot core shape is a convenient means of adjusting the ferrite structure to meet the specific requirements of an application. Both high circuit Q and good temperature stability of inductance can be obtained with these cores. Pot cores, when assembled, nearly surround the wound bobbin. This self-shielded geometry isolates the winding from stray magnetic fields or effects from other surrounding circuit elements. Typical applications for pot cores include; differential inductors, power transformers, power inductors, converter and inverter transformers, filters, both broadband and narrow transformers and telecom inductors."

[Willabe]

I’m be curious to find out what the inductance of the signal winding on the Hammond unit is. The Schaller SR signal winding is 2.2mH.

That's the thing, the Hammond SR's might not work in that Schaller circuit.

And getting the right LDR might be a problem.

[Willabe]

Some years back I found a small local transformer winding shop close to my house.

I brought them a Hammond SR coil and they found the correct bobbins for it and gave me a bid to make them. But as with most things I would have needed to buy at least 100 of them. And they didn't have the metal brackets that hold 3 coils together, which didn't bother me.

If you could find a trashed unit then you could have 1 of the SC coils tested and get a bid to have a run made.

And then if you do make a working clone, with a new clear/easy to read schematic and layout drawing, Sluckey was the best at doing this. Then you could try selling kits/partial kits for guys to build a clone. 

You might not make any money, but you could probably sell the extra SR coils. Or you might be able to sell the whole thing, plans/drawings/SR coil source to a company. Like an an amp building company. Maybe Mojo or Weber?   

I might buy enough to make 2 clones if the price was reasonable.

[Brinkman]

I devoted some time to thinking how best to approach the implementation of tubes in this Rotor Sound redesign.

I think I will keep the oscillator circuit from the Hammond/Warbler more or less intact though I would like to incorporate an opto-isolator into it (per the Rotor Sound). I am going to use a bulb and LDRs similar to the ones used in the similar vintage, German-made Schulte “Compact Phaser A”. This should get me in the ballpark.

Another alteration will be to omit the 1K ohm cathode resistor of the “12AU7 half” of the 7427 tube that drives the control winding of the saturable reactor(s). In the Hammond/Warbler schematic, the 1K cathode resistor is in series with the DCR of the SR control winding (260 ohms), putting the total resistance in the ballpark of 1K3 ohms. Adding five more SR will increase the total DCR to around 2K6 ohms; omitting the cathode resistor will drop the total DCR back down to around 1k6 ohms which is much closer to the original 1K3 ohm design center.

Yet another change will be to the signal circuitry, which I’m going to make much closer to the Rotor Sound topology. In place of the two BC109 transistors that drive the wet and dry signal (respectively), I will replace each with a 7427 tube (so three in total including the one in the oscillator). Both 7427 tubes will be wired per Merlin Blencowe’s bootstrapped cathode follower arrangement (see attachment). This will maximize gain and lower the output impedance of the stages, making them behave much more closely to a transistor.

The rest of the circuitry will resemble the Rotor Sound, ie all 18 all-pass filters and a mixer pot to output.

The power supply will be retained from the Warbler.

Thoughts are welcome.