[sdiy] as3340 PW/tuning issue
ColinMuirDorward
colindorward at gmail.com
Sun Dec 29 02:17:57 CET 2019
Thanks for chiming in, Alex. Interesting to hear of the possibility of a
future revision.
I wonder if this is a good place to cast my vote (again!) for a
through-zero 3340?
Jay, I think you're right, but on the other hand, using the chip means I
don't need to source tempcos or matched transistors.
Colin
On Sat, Dec 28, 2019 at 3:13 PM Jay Schwichtenberg <jschwich53 at comcast.net>
wrote:
> My personal thought is that for just a VCO I'd go with a classic design.
> To me these chips are more appropriate for something like a stand alone
> keyboard or poly synth. Using them as a regular VCO usually requires you to
> normalize the output waveforms bias and level, typically with additional
> op-amps. By the time you add that circuitry you're getting close to the
> number of chips you have in a classic VCO and a PCB of about the same size.
>
> I was wondering if you add the -5V regulator, set the PWM to some optimal
> value and then used an external PWM circuit off the saw wave whether or not
> that would either eliminate or considerably reduce the problem of
> PWM/frequency issues?
>
> Jay S.
> On 12/28/2019 2:47 AM, Aa Bb wrote:
>
> (From ALFA RPAR AS)
> Dear Sir's
>
> We've noticed discussion on DIY forum's about AS3340 PWM issues.
> It looks several opinions exist and some of them are partly close to
> reality. We
> wanted to provide some information about these question.
>
> 1.1 First important moment - all 3340 incarnations have influence
> PWM on
> frequency (linear influence and spike at 50%). They differ in character
> and level.
> For better understanding curve - Freq.dev./ Pwm level must be
> build an analyzed.
> Example of such curve for AS3340-HYB is provided in datasheet :
> http://www.alfarzpp.lv/eng/sc/AS3340-HYB.php
>
> 1.2 Main source of such influence - very fast switching of
> comparator output (pin 4). But also
> some other minor effect exist. High slew rate makes problems for internal
> circuitry (high current spikes
> on different internal nets ) and also, if layout is made not so good, on
> negative supply (pin 3).
> Almost identical schematics of these comparator, for better
> understanding, is provided
> in AS3340-HYB datasheet:
> http://www.alfarzpp.lv/eng/sc/AS3340-HYB.php
>
> 1.3 Different solutions may be used in different situations and
> requirements.
> 1.3.1 Old builds repair.
> In old builds situation is "as is" and it is almost impossible to
> change anything. For such case
> we offer - AS3340-HYB - solution witch almost totaly excludes PWM
> influence on frequency (in
> comparison with all other 3340 variants !!!).
> Main idea - DIP module is based on AS3345F (QFN) and is
> pin-to-pin compatible with 3340.
> Comparator, similar to the one inside of AS3340 is made on separate
> transistors/resistors. Internal
> comparator is turned OFF. So, high slew-rate current spikes in these
> solution are flowing through
> "external" comparator and it's influence on AS3340 is minimized.
> Certainly, for better immunity, output current minimization, better
> to decrease output current
> by increasing load resistor till 51k or more (depends from application).
> So, for such case, - our opinion - use AS3340-HYB.
>
> 1.3.2 For new designs.
> Several variants , moments:
> 1.3.2.1 If You use PWM - "protect" pin3 from pin 4 - layout,
> bypass capacitor.
> 1.3.2.2 Try to decrease slew rate of comparator output:
> - increase load resistor (it will decrease comparator output
> current)
> - connect pin 5 and pin pin 4 with MegaOhm resistor and add to pin
> 4 capacitor.
> But linear influence PWM on frequency still remains.
>
> 1.3.2.3 Use AS3340-HYB - witch it the best in these moment.
>
> We just tried to explain "mechanism" of problem. Other schematic
> tricks can be used.
>
> We hope, in some time, new revision of AS3340A will be available.
>
> ALFA RPAR AS
> Alex Zaslavsky
> alfa at alfarzpp.lv
> http://www.alfarzpp.lv/eng/sc/application.php
>
> On Sun, 22 Dec 2019 at 01:17, Doug Terrebonne via Synth-diy <
> synth-diy at synth-diy.org> wrote:
>
>> Yes, the original rev F CEM3340s in the JP-6 don't have this issue.
>>
>> Doug
>> synthparts.com
>>
>> On Saturday, December 21, 2019, 3:11:12 PM PST, ColinMuirDorward <
>> colindorward at gmail.com> wrote:
>>
>>
>> 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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