Reducing Ampex 440 wow/flutter on playback

[Gold]

As an aside the reason the 440 was the standard broadcast deck was that despite speed variations over the course of a reel the overall length of the program was exactly right because it is locked by a synchronous motor. 15:00 was always exactly 15:00. When your revenue comes from selling advertising time having a machine like an Otari running slightly slow could cost you a lot of lost revenue.

 

[abbey road d enfer]

I don't see a synchronous motor in the AG440. Unless there's a variant, the schematics I have show a run capacitor (not a start capacitor) that is the mark of an asynchronous motor.
That means there is slippage. The traditional solution for minimizing slippage was oversizing the motor.

 

[Gold]

I don't see a synchronous motor in the AG440. Unless there's a variant, the schematics I have show a run capacitor (not a start capacitor) that is the mark of an asynchronous motor.

Are you sure about that? The Lyrec turntable motor for Neumann lathes uses a run capacitor and it is most definitely a synchronous motor.

 

[abbey road d enfer]

Are you sure about that? The Lyrec turntable motor for Neumann lathes uses a run capacitor and it is most definitely a synchronous motor.

Is it a "run" capacitor or a "start" capacitor?

 

[Gold]

Is it a "run" capacitor or a "start" capacitor?

It's a run or phase capacitor. You can tweak the value to make the motor run more smoothly. The capacitor value depends on the specs of the motor. They came in at least three versions. 220VAC 60Hz and 50Hz. Also 120VAC 60Hz. All use different value run capacitors.

 

[abbey road d enfer]

It's a run or phase capacitor. You can tweak the value to make the motor run more smoothly. The capacitor value depends on the specs of the motor.

So that's an asynchronous motor. Means that it tries to run at the speed of the AC feed but actually slips. If it didn't there would be no torque. In the nominal range of operation, torque is about proportional to slippage, so it's actually some kind of self-regulating process.

 

[Gold]

So that's an asynchronous motor.

Lyrec calls it a Synchronous motor. It says it right on the tear sheet. The capacitor is called a run capacitor in the literature.

Here is a link to some literature on the motor. www.drdub.com/pix_extern/lyrec_sm8-3a.zip

 

[Brian Roth]

Our lathe here at The Mastering Lab has one of those Lyrec motors. I've attached the schematic and the data sheet. It is clearly called a synchronous motor. That cap is referred to as a "phase-shifting condensor" in the data sheet.

My 440 manuals are buried in a box in my garage, but I'm almost certain those decks used the same arrangement (unless they have the servo capstan motor!).

Bri

 

[abbey road d enfer]

The Lyrec motor is a real synchronous type, although a variant. Since synchronous motors are not self starting, they usually need a start capacitor, that disconnects after the motor has reached enough speed. The Lyrec uses an auxiliary asynchronous motor to start.
The Ampex motor is of a different type, with a run capacitor.
In the past there was some confusion; the french called the latter "asynchronous-synchronous".
All modern litt clearly defines the difference:
With start capacitor or auxiliary start-up mechanism=synchronous. With run capacitor=asynchronous.

 

[radardoug]

The Lyrec motor is a real synchronous type, although a variant. Since synchronous motors are not self starting, they usually need a start capacitor, that disconnects after the motor has reached enough speed. The Lyrec uses an auxiliary asynchronous motor to start.
The Ampex motor is of a different type, with a run capacitor.
In the past there was some confusion; the french called the latter "asynchronous-synchronous".
All modern litt clearly defines the difference:
With start capacitor or auxiliary start-up mechanism=synchronous. With run capacitor=asynchronous.

I think you will find the motor is a hysteresis Synchronous motor. The 440C had the option of a servo motor.

 

[Brian Roth]

Interesting comments. One minor quibble....Olde School mechanical alarm clocks used a sync motor that would self-start and didn't have any capacitor. Very small torque, though.

I've asked some other folks who worked at Ampex eons ago for clarification.

Two things now puzzle me.

1. The motors Ampex used for the capstan were quite different from the two spooling motors. I think different capstan motors were required for 60 or 50 Hz.

2. Within a fairly wide range, varying the AC voltage to the machines would not cause a capstan speed variation. To vari-speed the capstan you needed to change the frequency above or below 60 Hz (USA) as fed to the capstan motor. For years predating the 440, Ampex sold an external unit that was essentially an adjustable AC oscillator (tunable above or below 60 Hz...USA models again) followed by a power amplifier which then drove the capstan motor. DIY guys at the studios did their own version using a HP (or other brand) bench oscillator into the input of a audio power amp usually followed by a step-up transformer to reach "117 VAC".

Studer had a similar (?) capstan motor design for the C37/J37 machines. I once had to concoct a similar "oscillator into a power amp" to make a 50 Hz machine run at correct speed in a 60 Hz world.

Bri

PS, the Lyrec motor on our lathe has the wiring for the start motor...but no motor! We get it running by manually "twirling" the platter with power on.

 

[Brian Roth]

I think you will find the motor is a hysteresis Synchronous motor. The 440C had the option of a servo motor.

Indeed! IIRC..... the servo was standard on a 440C, with a sync motor as an available option. I'm pretty sure the servo capstan was an OPTION for later production 440B decks.

Bri

 

[Gold]

I thought a synchronous motor is timed from the line frequency and an asynchronous motor is not. The capstan motor of my Telefunken M15 ( not M15A) tape machine is locked to the line frequency. The Studer A80 is not.

Brian,
The Lyrec start motor is a separate coil in the same housing. It is slow and the coil often burned out. The Start button was always on the frame of the lathe. I think you just have the sleds and not the complete lathe frame. The start motor might still work but no one ever used them. It’s the two position terminal block located to the left at the top of the main terminal block. If you short those the start motor will work, or not.

Edit: Apply line voltage to the two position terminal block to use the Start motor. Not short them.

 

[abbey road d enfer]

I think you will find the motor is a hysteresis Synchronous motor.

Interesting: i didn't think about this option.

 

[abbey road d enfer]

The motors Ampex used for the capstan were quite different from the two spooling motors.

Indeed. Spool motors must be capable of delivering torque all over the speed range, so they are clealy the basic induction type.

I think different capstan motors were required for 60 or 50 Hz.

There would be either a different capstan diameter or a different number of poles.

Within a fairly wide range, varying the AC voltage to the machines would not cause a capstan speed variation. To vari-speed the capstan you needed to change the frequency above or below 60 Hz (USA) as fed to the capstan motor.

Both induction, asynchronous and synchronous motors have a direct dependance on AC frequency. Asynchronous operate across a very wide speed range, though.

Studer had a similar (?) capstan motor design for the C37/J37 machines. I once had to concoct a similar "oscillator into a power amp" to make a 50 Hz machine run at correct speed in a 60 Hz world.

I made in 1975 at Barclay Studios, for vari-speeding the Hammond C3.

 

[Brian Roth]

Brian,
The Lyrec start motor is a separate coil in the same housing. It is slow and the coil often burned out. The Start button was always on the frame of the lathe. I think you just have the sleds and not the complete lathe frame. The start motor might still work but no one ever used them. It’s the two position terminal block located to the left at the top of the main terminal block. If you short those the start motor will work, or not.

I always thought that start motor was "outboard" from the main Lyrec motor. It seems to say that in the data sheet I posted. The schemo I posted seems to show it was an independent motor, with its own motor cap. But I never saw a brand-new Lyrec. So, it's all new to me! <g>

The rotary motor control switch on our's looked like an ancient relic. Select 78, 45, 33 speed with a momentary spring release "start" position at one end. It was flaky, so I replaced it with a HEFTY DPDT "center off" toggle with only 33 and 45 as speed choices. The original rotary switch still sits on a panel so it has that Vintage Look! lol

I say...."That rotary is one reason the cutting system sounds so good!" LOL!

Bri

 

[Brian Roth]

I made in 1975 at Barclay Studios, for vari-speeding the Hammond C3.

Now a Hammond organ was a different sort of beast. To "start" one motor coupled into the tone wheel box, then the sync motor would lock speed/pitch after releasing the momentary start switch. That sync motor indeed require a "helper" to reach correct speed. What would you call that sync motor...sync or async? A GIANT alarm clock motor?

Too long since I looked, did the "run" motor have a a capacitor in the circuit?

Just trying to learn something new every day!! <g>

Bri

 

[abbey road d enfer]

The rotary motor control switch on our's looked like an ancient relic. Select 78, 45, 33 speed with a momentary spring release "start" position at one end.

Don't you think this "momentary spring release "start" position" would be the starter motor switch?

 

[Brian Roth]

Don't you think this "momentary spring release "start" position" would be the starter motor switch?

Indeed! The wiring went to two wires "hanging in the breeze" down at the Lyrec motor, which led me to ASSume there was once an external helper motor.

Paul said that there was Yet Another set of windings inside the Lyrec to "start" vs an external helper motor. Perhaps Paul has a later model Lyrec.

Bri

 

[abbey road d enfer]

Now a Hammond organ was a different sort of beast. To "start" one motor coupled into the tone wheel box, then the sync motor would lock speed/pitch after releasing the momentary start switch.

Not too different than the Lyrec. The Hammond tone gen can hardly be started manually, though.

That sync motor indeed require a "helper" to reach correct speed. What would you call that sync motor...sync or async? A GIANT alarm clock motor?

The service manual states "A shaded pole induction motor is used for starting the generator".
The "run" motor is clearly identified: "the synchronous motor can supply power only at synchronous speed,"

Too long since I looked, did the "run" motor have a a capacitor in the circuit?

I don't remember either, but the wiring diagram does not show a separate run cap. It is probably integrated in the motor housing.