[sdiy] saw core VCO tuning/scaling (Roland SH-2)

[Adam Inglis]

Magnus, many thanks

The Roland SH-2 SM PDF can be found here..

http://manuals.fdiskc.com/flat/

The VCOs are on page 4

Thanks for your time - I'll see if I can find a pin-out to find this  
"oven-setting resistor"
cheers
Adam


On 19/08/2011, at 4:58 AM, Magnus Danielson wrote:

> Adam,
>
> On 18/08/11 09:23, Adam Inglis wrote:
>
>> I realise this is probably a timeworn query - my apologies to the  
>> veterans.
>>
>> I'm having some trouble with my SH-2 (dual VCO monosynth 1979):
>> I've had it up on the bench a couple of times to calibrate VCO 1.  
>> VCO 2
>> comes up sweet.
>> I leave it on for an hour, follow the SM routine ("width", then
>> "linearity" then footages) and think it sounds good, check it with a
>> tuner, but after I put back in the rack it goes out (of tune but also
>> scale width) after an hour - so I guess it is temperature related.
>>
>> The key CVs are spot-on, and the supply voltages seem solid. VCO 2
>> remains fine. Measuring the voltages after the CV summing op-amp  
>> gives
>> equal values between octaves. From that point, I'm not sure what  
>> to look
>> for with my ancient scope and my Fluke - it's current-dependant,  
>> is it not?
>> The expo converters are metal can uA726 - they both run quite warm to
>> touch.
>>
>> I've read Ian Fritz's and Magnus Danielson's info regarding these  
>> type
>> of Electronotes-based VCOs, but if anyone can point me to some
>> troubleshooting articles, that would be most appreciated,
>>
>
> OK, by strange coincidence I have been discussing troubleshooting  
> of uA726 based oscillators today, and then my name even pops up  
> here, and it can't be recent I wrote much about the topic. Ah well.
>
> The uA726 is unique in that it contains an oven. First thing to  
> check is if the oven is running and if the oven setting resistor is  
> properly hooked up. There can be other sources of this instability.
>
> I haven't checked the SH-2 schematic, but if someone toss me the  
> link to a good schematic I might help a little more.
>
> Cheers,
> Magnus
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