[sdiy] TH XR2206 VCO tune pot

[Derek Holzer]

Actually it's the main tune pot I want to change, it's too wide. 
Recommendations?
D.

Tom Bugs wrote:
> Yep - try changing it to 4M7 (I like it at 3M3 but I hear what you're 
> saying)
> xb
> 
> Derek Holzer wrote:
>> If you look at the schematic:
>>
>> http://www.bugbrand.co.uk/docs/TH_XR2206VCO_BugPCB.PDF
>>
>> You'll see that the fine tune and main tune are essentially the same: 
>> 100K pots between V+ and V-. The only difference is that the wiper of 
>> the fine tune goes through a 3M3 resistor, and the main tune goes 
>> through a 100K. They are both summed after that. That's the part I'm 
>> trying to understand.
>>
>> D.
>>
>> Scott Gravenhorst wrote:
>>> Derek Holzer <derek at umatic.nl> wrote:
>>>> Hi Scott,
>>>>
>>>> thanks for your reply. I did think of this, but since the range of 
>>>> another pot in the schemo is restricted by following it with a 
>>>> larger resistor, rather than putting resistors between V+/V- and the 
>>>> pot, I thought that I would try to understand how that worked.
>>>>
>>>> best!
>>>> Derek
>>>
>>> I can understand how that could modify one end of the range, but not 
>>> both.  I'll be interested to
>>> hear how that works.
>>>
>>>> Scott Gravenhorst wrote:
>>>>
>>>>> You can restrict the range of the pot this way:
>>>>>
>>>>>      v+
>>>>>      |
>>>>>      |
>>>>>      Ra
>>>>>      |                                                 
>>>>> |                                            P
>>>>>      O<----- ...
>>>>>      T
>>>>>      |
>>>>>      |
>>>>>      Rb
>>>>>      |
>>>>>      |                                       V-    Where POT is the 
>>>>> original tuning pot and Ra and Rb are resistors you will add.  The
>>>>> values of these resistors will have to be trimmed or calculated by 
>>>>> you.  If Ra and Rb
>>>>> are the same resistance as the pot, then the new range will begin 
>>>>> at about a third of
>>>>> where it was without Ra and Rb and it will end about 1/3 before it 
>>>>> gets to the end.  I
>>>>> can't guess what frequencies this will give...  Ra and Rb can also 
>>>>> be trimmers so that
>>>>> you can adjust the exact range you get.
>>>> -- 
>>>> ::: derek holzer ::: http://blog.myspace.com/macumbista ::: 
>>>> http://www.vimeo.com/macumbista :::
>>>> ---Oblique Strategy # 101:
>>>> "It is simply a matter of work"
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>>>
>>> -- ScottG
>>> ________________________________________________________________________
>>> -- Scott Gravenhorst
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> 
> 

-- 
::: derek holzer ::: http://blog.myspace.com/macumbista ::: 
http://www.vimeo.com/macumbista :::
---Oblique Strategy # 169:
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