[sdiy] as3340 PW/tuning issue

Doug Terrebonne dougt55 at yahoo.com
Sun Dec 22 00:08:21 CET 2019

 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).

    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. 


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! ;)

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.

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.
       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:

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.detechnik 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.


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