[sdiy] 3340 oscillator - current limiting resistor equation is wrong?

[Michael E Caloroso]

FWIW, the Memorymoog voicecard replaced the series resistors with an
onboard (-)5VDC rail.  The pads for the resistors were always on the
voicecard.

Oberheim also elected to use a (-)5VDC rail.

MC

On 11/18/17, Tom Wiltshire <tom at electricdruid.net> wrote:
> Ok, so this is why you choose the next value down, rather than the next
> value up.
>
> Hence 820R not 1K.
>
> Thanks Neil.
>
> Tom
>
> ==================
>        Electric Druid
> Synth & Stompbox DIY
> ==================
>
>> On 18 Nov 2017, at 20:38, Neil Johnson <neil.johnson71 at gmail.com> wrote:
>>
>> Tom,
>>
>> If you read the datasheet carefully you see that all the resistor is
>> doing is limiting the current for the internal zener diode.  So the
>> actual current is not that critical, it just needs to be enough to
>> bias the diode into its zener region.  The equation in the datasheet
>> suggest this needs to be at least 8mA, more (but not too much) is also
>> ok, but less may lead to problems.
>>
>> I would go with the E12 series explanation.
>>
>> Neil
>>
>> On 18 November 2017 at 17:44, Tom Wiltshire <tom at electricdruid.net> wrote:
>>>
>>>> On 18 Nov 2017, at 16:20, Florian Anwander <fanwander at mnet-online.de>
>>>> wrote:
>>>>
>>>> On 18.11.17 16:17 , Pete Hartman wrote:
>>>>>
>>>>> Could it be as simple as the closest E12 value without going over?
>>>>>
>>>> 1k would be much closer to 975R than 820R
>>>
>>> I agree, and for a current *limiting* resistor, I’d have thought you
>>> wanted a slightly larger value to be on the safe side, rather than a
>>> slightly smaller one.
>>>
>>> So no-one has ever come across this before?! Seems hard to believe.
>>>
>>> I notice both the V3340 and AS3340 data sheets say only “current limiting
>>> resistor required for supplies greater than -6V” without actually
>>> providing any equation or committing themselves to a figure!!
>>>
>>> Tom
>>>
>>> ==================
>>>       Electric Druid
>>> Synth & Stompbox DIY
>>> ==================
>>>
>>>
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>>
>>
>>
>> --
>> http://www.njohnson.co.uk
>
>
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