[sdiy] Prophet 5 scale problem

[Adam Inglis]

At great expense an original Burr-Brown DAC has been obtained, and it has fixed the problem completely.

Thanks to those who helped.

cheers
AI
> On 17 Nov 2016, at 5:09 PM, rsdio at audiobanshee.com wrote:
> 
> A properly-designed adaptor board with a different parallel DAC should work, but I wouldn't recommend it as a beginner design project. Shifting voltages, converting current to voltage (if necessary), adjusting timing and polarity of controls signals could get very messy if the timing isn't just right. Today's parts are faster, though, so it's not impossible.
> 
> Roman Sowa's suggestion is solid, assuming that someone has already designed such an adapter board for the Prophet 5 and we know it works. It could be as simple as ordering the kit and putting it together.
> 
> Brian
> 
> 
> On Nov 16, 2016, at 4:29 PM, Adam Inglis <21pointy at tpg.com.au> wrote:
>> The DAC from Taiwan turned out to be a dud. Grrr..
>> 
>> Before I take Peter up on his gracious offer, can I just ask the list, has anyone here dropped a different DAC in to a Prophet, and done the attendant mods? Is it straightforward? This is out of my sphere of experience.
>> 
>> I note in the data sheet the COB version has a +/-10 volt output, whereas the stock CSB is 0 - +10 volts, is that a problem?
>> 
>> many thanks 
>> 
>> Adam
>> 
>> 
>>> On 17 Oct 2016, at 9:29 PM, Ullrich Peter <Peter.Ullrich at kapsch.net> wrote:
>>> 
>>> Hi!
>>> 
>>> I have 8 unused (NOS) DAC71-COB-V that I don't need.
>>> They have never been used - so they should be OK.
>>> Stored on antistatic foam for years.
>>> 
>>> 10€ per piece + postage 4.90€
>>> 
>>> Datasheet: https://www.usbid.com/datasheets/dsid/166157.pdf
>>> 
>>> This is the version with the voltage output where the service manual says that
>>> You should bypass the external opamp.
>>> 
>>> COB is the version with the 10k feedback resistor instead of the 5k resistor.
>>> According to the diagram on page 3 it should be possible to connect another 10k resistor in parallel 
>>> to the internal 10k resistor (mount this resistor between pins 17 and 21)  so that you get the same 
>>> output level as with the CSB-version.
>>> 
>>> Ciao
>>> Peter
>>> 
>>> -----Ursprüngliche Nachricht-----
>>> Von: Synth-diy [mailto:synth-diy-bounces at dropmix.xs4all.nl] Im Auftrag von Roman Sowa
>>> Gesendet: Montag, 17. Oktober 2016 11:13
>>> An: synth-diy at dropmix.xs4all.nl
>>> Betreff: Re: [sdiy] Prophet 5 scale problem
>>> 
>>> At that price I would go for DAC8820 and adapter PCB.
>>> 
>>> Roman
>>> 
>>> W dniu 2016-10-17 o 01:07, Adam Inglis pisze:
>>>> This guys page would suggest that a faulty DAC is a possibility:
>>>> 
>>>> http://www.mindburner.co.uk/synth/prophet5_DAC%20Information.html
>>>> 
>>>> Looks like these sell for around 60 - 100 $
>>>> 
>>>> I’m starting to think this could be the problem. Going through the VCO scale trim procedure as per the manual shows each VCO can be tuned manually, but as soon as the computer re-calculates the bias, they go out again.
>>>> 
>>>> AI
>