[sdiy] Potting ARP VCOs, was: VCO reference voltages

[cheater cheater]

I guess it's even better if you stick all the sensitive parts, and the
heater, to that piece of metal?

D.

On Sun, Apr 18, 2010 at 19:02, Jean-Pierre Desrochers
<jpdesroc at oricom.ca> wrote:
> One cool way to avoid potting a complete module
> (unable to repair it in the future ...) is to put some
> kind  of a metalic box with cover all around the grouped  sensitive parts
> with
> a heater or a temp controled oven. this way everything stay temp stabilised
> and is repairable in the future..
>
> Just my 2 cents.
> J-Pierre
>
> ----- Original Message ----- From: "thx1138" <thx1138 at earthlink.net>
> To: <rob at emulatorarchive.com>; "SDIY List" <synth-diy at dropmix.xs4all.nl>
> Sent: Sunday, April 18, 2010 10:55 AM
> Subject: Re: [sdiy] Potting ARP VCOs, was: VCO reference voltages
>
>
>> On 4/17/10 3:31 PM, "rob at emulatorarchive.com" <rob at emulatorarchive.com>
>> wrote:
>>
>>> Hi,
>>> In the non-potted ARP 2600 VCO I found that the integrator capacitor and
>>> HFT resistor were sensitive to temperature, possibly also other
>>> components. Of course the transistor pair and tempco were...! The
>>> transistor pair being 2 transistors, at best glued together, is very
>>> sensitive, and not "buried" in a 8 pin DIL "matched transistor pair".
>>>
>>> So I simply potted the complete VCO core, using the same layout as the
>>> 4027-1 but with 2x 5pin SIP plugs/sockets.
>>> Modern thermal potting compound is very good. A very simple test is to
>>> blow over your VCO and see if its frequency changes.
>>> With a potted module it does not and there is lots of thermal mass.
>>>
>>> Whether its worth potting other modules is a mute point.
>>> For frequency accuracy like the E-mu Systems VCC  - yes.
>>> For VCF's I really don't think so.
>>> I do plan to build future Roland VCO's with a potted core.
>>> Just the matched pair and tempco.
>>>
>>> Regards
>>> Rob
>>> www.amsynths.co.uk
>>>
>>>
>>> thx1138 wrote:
>>>>>
>>>>> Hi Rob! Very interesting. I have read your page on the ARP VCO - very,
>>>>> very cool! You mention that "the VCO core has a number of temperature
>>>>> sensitive components as well as the transistor pair; the integerator
>>>>> capacitor and a few resistors". What were those resistors? Why did
>>>>> they need to be potted with the transistors?
>>>
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at dropmix.xs4all.nl
>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>
>> Hi Rob,
>>
>> The reason we potted several of the VCF - UAF was to stabilize the Filter
>> trackin when we turned up the Q and it became an oscillator. We wanted it
>> to
>> be able to track like an osc as well as possible.
>>
>> Regards,
>>
>> Terry
>>
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