[HAM] Percussion & Matching Transformer

[Jordan Kersten]

Thank you so much for your help, I do have a small core transformer and I also have the percussion switch that fits under the "B" preset key that I am going to install.  Is there somewhere online I can find these Service Manuals and Diagrams? 




----------------------------------------
> From: thermionic27609 at earthlink.net
> Date: Thu, 10 Jan 2008 21:38:47 -0500
> To: hammond at zeni.net
> Subject: Re: [HAM] Percussion & Matching Transformer
> 
> Jordan,
> 
> If you want to make your organ precisely like a 3-series organ, you  
> have to add the 3.9M resistor (R1), a 1M resistor (R2), and a 470pF  
> capacitor (C1) in parallel with the 1M resistor. It's all there in  
> the service manual. Just compare the 2-series and 3-series wiring  
> diagrams. There's a picture that shows you exactly where the  
> additional components go.
> 
> Also, the Preset Percussion Switch under the Upper B preset key in 3- 
> series organs guarantees that R1 (3.9M) is shorted when presets other  
> than B are selected. If Percussion was left On with Percussion Volume  
> at Normal, the volume of the Upper Manual would be reduced on ALL  
> presets. (In other words, there are TWO switches that short R1  
> restore full manual volume; a switch in the percussion switch  
> assembly shorts it at certain settings, and the switch under the B  
> preset shorts it when any other preset is pushed down.) This switch  
> under the preset key is not present in organs before the 3-series,  
> and retrofitting one could be a bit tricky.
> 
> Or, like Scott says, you can leave out the two resistors and the  
> capacitor, and your percussion will work fine. These components have  
> nothing to do with the triggering, harmonics, etc... You'll just end  
> up with one shielded cable from the percussion switch that doesn't  
> connect to anything and doesn't need to.
> 
> David
> 
> On Jan 10, 2008, at 8:54 PM, Jordan Kersten wrote:
> 
>>
>>
>> Thank you for that detailed explanation, it was exactly what I was  
>> looking for.  I only have one last question: If I have a B2 with an  
>> AO-10 D, E, F or G, then my matching transformer is the same that  
>> is in a 3-series organ and the only mod I would have to make is to  
>> add the 3.9M resistor for the percussion circuit?
>>
>>
>>
>> ----------------------------------------
>>> From: thermionic27609 at earthlink.net
>>> Date: Thu, 10 Jan 2008 16:36:38 -0500
>>> To: hammond at zeni.net
>>> Subject: Re: [HAM] Percussion & Matching Transformer
>>>
>>>
>>> Jordan,
>>>
>>> The answer is a bit complicated, so bear with me.
>>>
>>> Page 2-25 of the Hammond service manual reads that the early 2-series
>>> organs used "small core transformers" with AO-10 preamplifiers with
>>> codes A,  B, and C.
>>>
>>> The later 2-series organs with AO-10s D, E, F, and G (plus all 3-
>>> series organs) used "revised small-core transformers with smaller
>>> stack and greater number of turns."
>>>
>>> The manual says these matching transformers types are not
>>> interchangeable, but your mileage may vary. The two groups of AO-10s
>>> do have somewhat different input circuits.
>>>
>>> The modifications to the matching transformer wiring to make it like
>>> a 3-series organ aren't too complicated, though you may need more
>>> solder terminals. What these resistors do is to lower the volume of
>>> the entire upper manual at certain percussion settings. Some people
>>> don't like this effect and jumper the 3.9M resistor permanently out
>>> of circuit to maintain full volume on the upper manual at all times.
>>> You might also want to add the special preset switch under the B
>>> preset key, present in 3-series organs, but not in 2-series models.
>>>
>>> One effect you have to deduce from the wiring is that the cable
>>> capacitance of the wiring used to short the 3.9M resistor becomes
>>> significant due to the high value of the resistor. My calculations
>>> indicate it should be about 400pF, and the effect is that the volume
>>> is reduced less at higher frequencies since this cable capacitance
>>> bypasses the 3.9M resistor. My theory is that the 470pF cap across
>>> the 1M resistor is there to compensate for this cable capacitance,
>>> and you could tune this 470pF value to taste, especially based on the
>>> capacitance of the cable you have running from the percussion switch
>>> to the matching transformer assembly. Lower capacitance cable might
>>> make a smaller capacitor of 220pF-330pF useful.
>>>
>>> Bottom line: your percussion circuits will work just fine without the
>>> extra resistors and capacitor. It all depends on whether you want it
>>> to work exactly as Hammond designed it for the 3-series organs.
>>>
>>> David A.
>>>
>>> On Jan 10, 2008, at 3:48 PM, Jordan Kersten wrote:
>>>
>>>>
>>>> Does anyone know exactly what the difference between a B2 and B3
>>>> matching transformer is?  I know that the B3's have some sort of a
>>>> resistor that has to do with percussion volume, and the B2's
>>>> wouldn't have this.  Are the transformers themselves the same? Can
>>>> you modify a B2's transformer with the percussion circuitry it
>>>> needs? Or would you have to replace the B2 transformer with a B3-
>>>> style one?  I am converting a B2 to a B3.  I now have tracked down
>>>> the plate with percussion tabs, the AO-28 preamp, smooth drawbars
>>>> and even a newer style vibrato line box.  I have herd that they
>>>> have different transformers.  Can anyone comment on this?
>>>>
>>>>
>>>> -Jordan-
>>>
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>>
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> 
> 
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