[sdiy] as3340 PW/tuning issue
Quincas Moreira
quincas at gmail.com
Sun Dec 29 02:49:39 CET 2019
Colin, put it in a through hole breakout board and call it a day ;)
On Sat, Dec 28, 2019 at 7:21 PM ColinMuirDorward <colindorward at gmail.com>
wrote:
> 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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>>
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--
[image: QMA]
Quincas Moreira
Director | QMA
mobile: 5534988825
site: quincasmoreira.com
email: quincas at gmail.com
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