[sdiy] as3340 PW/tuning issue

ColinMuirDorward colindorward at gmail.com
Sun Dec 22 00:10:58 CET 2019


Thanks, Doug.
Is it true that this problem didn't manifest with the original CEM3340?
Colin

On Sat, Dec 21, 2019, 3:08 PM Doug Terrebonne, <dougt55 at yahoo.com> wrote:

> I just tried as AS3340 in my JP-6 and changing the PW does affect the
> pitch (mostly noticeable in the higher octaves). The autotune can
> compensate for it though (adjust PW, hit Tune button).
>
> Doug
> synthparts.com
>
> On Thursday, December 19, 2019, 3:12:35 PM PST, ColinMuirDorward <
> colindorward at gmail.com> wrote:
>
>
> Out of curiosity, does anyone have an mks80 rev4 and/or Jupiter 6 they
> could test for this problem?
>
> My brother sold his mks80 rev4 already, but claims the pitch error was
> quite bad in his unit.
>
> In the next model, the rev5, Roland apparently switched the 3340 for a
> proprietary VCO chip.
>
> Colin
>
>
> On Thu, Dec 19, 2019 at 3:48 PM Tom Wiltshire <tom at electricdruid.net>
> wrote:
>
> My own view of it is that if you want cheap, you buy the Alfa AS3340. If
> you want original and can afford it, you buy the CEM3340 G. The V3340 falls
> somewhere in the middle and therefore doesn’t offer a unique selling point
> for DIYers.
>
> Coolaudio don’t care, since Behringer needs tons of ‘em! ;)
>
> Tom
>
> On 19 Dec 2019, at 13:53, ColinMuirDorward <colindorward at gmail.com> wrote:
>
> I didn't see a lot of discussion on this topic include the v3340. Not sure
> if people had already collected the CEM and AS versions by the time the Vs
> came out, or what, but the coolaudios don't seem to be on as many work
> benches.
> I just checked a neutron and no surprise that I could not find any pitch
> error there.
> I have a lot of as3340s, so when my next prototype comes in, I could check
> for error variation between chips.
>
> Colin
>
> On Thu, Dec 19, 2019 at 10:01 AM Tom Wiltshire <tom at electricdruid.net>
> wrote:
>
> A quick test on my Pro-One doesn’t reveal any tuning problem. I routed the
> LFO to PW on oscillator A, then listened to Oscillator A’s ramp wave alone
> (so no beating to confuse things) and couldn’t hear any difference, even
> with maximum mod depth and maximum LFO rate. Checking the output on the
> oscilloscope showed no pitch variation either.
>
> That said, there’s some evidence Sequential *did* select 3340s. The ones
> regarded as “not good enough” were used for LFO duties, and if you check
> the PCBs you’ll see paint blobs on those ones. I’ve never seen anything
> documenting what the tests were though. Maybe they just built the things
> and swapped out any that caused a problem, put a blob on them, and then
> used them later where it wouldn’t matter.
>
> A more interesting test which I might get to later would be an A/B/C
> comparison on my 3340 test board between CEM3340 G, AS3340, and V3340.
> Despite having all three chips on the shelf, I’ve never actually done this.
>
> Tom
>
> ==================
>        Electric Druid
> Synth & Stompbox DIY
> ==================
>
> On 19 Dec 2019, at 12:06, Mattias Rickardsson <mr at analogue.org> wrote:
>
> I remember talking to Dieter Doepfer about this back in the day... Ah,
> here it is:
>
> /mr
>
>
>
> At 17:52 2003-02-02, Dieter Doepfer wrote:
> > > -----Ursprüngliche Nachricht-----
> > > Von: Mattias Rickardsson
> > > Gesendet am: Mittwoch, 29. Januar 2003 11:10
> > > An: hardware at doepfer.de; technik at doepfer.de
> > > Betreff: A-111 problem? (PW affects Frequency)
> > >
> > > Hi,
> > > I have a problem with several of my A-111 High-End VCOs:
> > >
> > > The pulsewidth (both PW knob and PWM input+knob) affects the frequency
> > > of the oscillator. I.e., when turning the PW knob or PWM modulating
> with
> > > a slow LFO, the frequency makes a clearly audible change.
> > >...
> >
> >Dear Mattias,
> >I forward your inquiry to our A-111 specialist Matthias Marass
> >(mailto:keyboards at doepfer.de). He is responsible
> >for the final tests and repairs
> >of the A-111. He will answer you directly.
>
> At 15:36 2003-06-11, Döpfer Musikelektronik - Keyboardservice wrote:
> Dear Mr. Rickardsson,
>
> the influence of the external and internal PW
> control voltage to the oscillator frequency is a
> problem of nearly 80..90% of the CEM3340 we ever
> used. Unfortunately there is no chance to repair
> this problem. The only way would be a strict
> selection of the CEM3340 circuits.
> ...
> Best regards,
> Matthias Marass
> keyboards at doepfer.de
>
>
>
>
>
> Den tors 19 dec. 2019 10:42Oakley Sound via Synth-diy <
> synth-diy at synth-diy.org> skrev:
>
>  > ... "So as a conclusion the goal is to have on pin3 as close as
> possible to -5V and the PWM to tune error will not manifest itself."
>
> I did not find this to be the case since I always run any 3340 circuit
> from a precision 5V reference. The solution for me was to get the
> CEM3340 rev G. The CEM3340 has the detune too, it's just that it is
> quite small. I can't remember exactly, but I think it's in the region of
> +/-1 cent. It would almost certainly be there on the SH-101.
>
> Alfa's solution is to use the newer AS3340-HYB. The other thing to do is
> make your own triangle or saw to pulse wave convertor from an op-amp or
> comparator external to the chip.
>
> When repairing an OB-Sx I found that the AS3340 did not work well as a
> sub for the original CEM3340. Even with the various resistor changes
> required to get the AS3340 to work properly, the VCOs in last three
> voice card positions on the motherboard displayed a very audible pitch
> instability at pulse widths at less than 45%. Clearly, there was some
> layout issue but although I tried all sorts of things (including bus bar
> 0V and liberal dousing of capacitance) it wouldn't solve the problem.
> Again, the solution was to replace all the VCOs with CEM3340 G.
>
> Tony
>
> www.oakleysound.com
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