Hammond Organ, is it safe

[Mad collector]

Good morning
I have just purchased a Hammond Organ
On inspecting the plug I see the mains Lead is just twin core
In order to get the organ pat tested does it need to be earthed
I see the mains lead goes into a mains transformer
I need to know the organ is safe before I start playing it
Any suggestions please
Sharon

 

[Lucien Nunes]

OK, so long as it is actually Class II that's wrapped up. Otherwise, treat it as a historic item and pay good attention to its maintenance. Do not ignore warning signs of electrical faults. I run a lot of vintage gear and some of it definitely does not meet current standards by a very large margin. It can be safe so long as one understands its limitations and handles it wisely.

Yes, I do seem to have one of the later T-series, up in Bedford. If that sounds vague, I have over 40 electric organs in three different locations and they are not static, they arrive, some leave or are stripped for parts. Its purpose in the collection is to compare and contrast with the Compton CL72. When I am next there I will have a look at its electrical safety aspects and maybe play a few tunes on it.

 

[Mad collector]

Hi Lucien
Just a thought as you have a T102
Last week we moved the organ from East Yorkshire to Hayle in Cornwall
We moved it on its back in a trailer
When we connected it and I checked it over
Both keyboards play ok
However, when I move the pedal drawbar we get a most horrendous noise from the organ speaker
The more I move the drawbar out the louder the noise is
The pedals play ok
Any ideas what the problem could be?

 

[Lucien Nunes]

What kind of noise? Roaring / crackling / humming / whining etc?
How does its level compare with the notes that play?
Most likely a connector has been disturbed by the move. I will take a look at the service manual and pin that down a bit more closely.

I recall that in the T-series, the pedals use electronic dividers instead of sourcing the tones directly from the generators. This means that there is a wider variety of possible faults, it is not simply a question of routing generator pitches through key contacts and drawbars to the matching transformer.

 

[Mad collector]

It's buzzing noise that gets louder the more I pullout the drawbar

 

[DPG]

It's buzzing noise that gets louder the more I pullout the drawbar

Maybe be an earth lead has pulled free?

 

[Lucien Nunes]

For buzzing that is certainly a possibility but we should call it signal ground instead of earth

 

[DPG]

For buzzing that is certainly a possibility but we should call it signal ground instead of earth

A fair point. In my defence I was trying to keep things simple.

 

[Mad collector]

Someone coming to look at the organ tomorrow, it seems he's been fixing Hammond Organs for about 150 years, he's no youngster lol

 

[Lucien Nunes]

I was just looking at the circuit. I suggest beginning by looking at the connections from pedal divider board to pedal mute tab and its associated wiring, as these lie between the keying diodes on the divider board (which aren't controlling the buzz) and the drawbar (which is). I would begin by linking divider board pin 1 (output) to pin 9 (ground) and seeing if that clears the buzz partially or completely. Then we can move forwards or backwards depending on the result.

Do you have a multimeter?

E2A Ah I see you have found someone to do this, hope it goes well. Also ignore previous incorrect reference to pin 6!

 

[Mad collector]

Yes I have an AVO model 8

 

[Lucien Nunes]

Hmm, well if you want to have a look at your own risk, try my suggestion, pedal div board link pins 1 & 9.
And/or confirm what effect the pedal mute tab has on the buzz.
Make sure the pedal div board can see ground properly, it might pass signal in the absense of a solid ground connection due to paths through the footage switch etc.
Service manual is available here https://medias.audiofanzine.com/files/hammond-xtp-series-service-manual-478272.pdf
It is missing a few pages and parts of it are specific to the XTP but the circuits for the cabinet T's are there.
P29/30 of the PDF shows the pedal divider schematic, 31 the PCB, 33 & 38 the wiring from divider to the pedal drawbar

 

[DPG]

I can't stop picturing the Viz comic strip 'Captain Morgan and his Hammond Organ'

 

[Lucien Nunes]

It's always possible to drag the tone of a thread downwards.

Actually the organ (the instrument) has always had a problem with its name. I'm sure there would be much less tittering in the back row if it were called the 'omniphone' or 'aerochord' or really anything but organ. Perhaps the piano could be renamed the plonker, to distract attention.

 

[DPG]

It's always possible to drag the tone of a thread downwards.

Actually the organ (the instrument) has always had a problem with its name. I'm sure there would be much less tittering in the back row if it were called the 'omniphone' or 'aerochord' or really anything but organ. Perhaps the piano could be renamed the plonker, to distract attention.

Omniphone - I like that.

 

[Lucien Nunes]

If you listen to some good orchestral-style playing on a big multi-genre civic organ, and in this domain there is no finer example than Richard Hills at the Southampton Guildhall Compton, you will get a sense of how apt the 'omni' is. Try these little samples from this instrument:

http://www.ssfweb.co.uk/silverst/The_Dancing_Years.mp3

http://www.ssfweb.co.uk/silverst/In_Malaga-1.mp3

http://www.ssfweb.co.uk/silverst/March_Heroique.mp3

And to return towards the original subject of the Hammond, this one features the Melotone electrostatic tone generator which is incorporated into the pipe organ.

http://www.ssfweb.co.uk/silverst/The_Girl_from_Corsica.mp3

The men at Compton who designed this had tried electromagnetic generators as used in the Hammond, ran into some of the same limitations as Hammond, and developed the more versatile electrostatic system instead that sounded more convincingly like a pipe organ. However, Hammond did a much better job of selling his invention and and although his tone generators didn't sound quite like a pipe organ (in fact there was a lawsuit in which it was questioned whether the Hammond instrument was, in fact, an organ) their signature sound was promoted, caught on and became a legend of its own.