Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on January 03, 2015, 04:10:56 am

Title: How work an Hammond Vibrato Scanner ?
Post by: kagliostro on January 03, 2015, 04:10:56 am

I just discovered that esist such an item

(http://www.hammondclub.nl/db/upload/cache/image_resized/600x513/SCANNER_INSIDE.jpg)

looking to the structure I can think to it as a multiple variable capacitor on which the rotation of the rotor move the rotable plates from a group of  fixed plates to one other, doing this the capacity reached from one single capacitor increases till his max and then decreases tin his min

but also if about it I'm near sure, I don't understand the function on the whole circuit (that I've not seen)

the page that I've found didn't help me much as it is in dutch and trying to translate it with an online translator didn't help much

http://www.hammondclub.nl/nl/menu/Hammond/De_Hammond_Encyclopedie/A-K_series/B_series/New_B-3_Series/De_Uitdaging_2 (http://www.hammondclub.nl/nl/menu/Hammond/De_Hammond_Encyclopedie/A-K_series/B_series/New_B-3_Series/De_Uitdaging_2)

Thanks

K

Title: Re: How work an Hammond Vibrato Scanner ?
Post by: HotBluePlates on January 03, 2015, 09:06:10 am

Note that the fully-assembled scanner has brass stators all the way around, and not at a portion of the scanner, as shown in your picture.

Start reading here (http://nshos.com/HAMMOND9.htm) and through the pages which follow. Hopefully the online translator works better on English.

Quickly:
The center rotor of the scanner does work on the principle of capacitance, but not to vary the circuit. Instead, it is a capacitive connection to the circuit attached to the plate momentarily aligned with the rotor plates. The rotor spins at a constant speed and is sequentially stepping through each stator connection in turn.

If you look at the stator (the non-moving plates at the edge of the scanner), all are the same size and shape. Therefore, the capacitance that results from the rotor being aligned with any one set of plates is the same as for all the other plates.

Additional pages on that site which flesh out the Scanner Vibrato explanation are here (http://nshos.com/VIBRATO6.htm).

Title: Re: How work an Hammond Vibrato Scanner ?
Post by: kagliostro on January 03, 2015, 10:12:49 am

Thasks HotBluePlates

I'll read the link you attached with interest

Franco

Title: Re: How work an Hammond Vibrato Scanner ?
Post by: PRR on January 03, 2015, 09:28:53 pm

It looks like a capacitor, and is; but it is easier to think of it as a "switch".

There is a filter/phaseshift unit with 18 or 27 outputs. The scanner selects one of those outputs at a time. But we keep it spinning so it sequences through all outputs.

An actual switch would click and glitch. Instead this has a super high impedance recovery amplifier which will pass wide-range audio through very small capacitors, such as the rotor capacitance.

Title: Re: How work an Hammond Vibrato Scanner ?
Post by: kagliostro on January 04, 2015, 02:38:04 am

Thanks PRR


this is a simple way to explain a complicate thing


Franco