[sdiy] as3340 PW/tuning issue

ColinMuirDorward colindorward at gmail.com
Sun Dec 29 02:58:22 CET 2019


Quincas, do you mean to put the tempco and transistors in a breakout?
I guess it was more to do with the cost of sourcing those parts. I priced
it out and just buying the 3340 was less expensive (at the time). But
moving forward, I'd like to try your solution. Got any photos to share?
Cheers,
Colin

On Sat, Dec 28, 2019 at 5:49 PM Quincas Moreira <quincas at gmail.com> wrote:

> 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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>
>
> --
> [image: QMA]
>
> Quincas Moreira
> Director | QMA
> mobile:  5534988825
> site:  quincasmoreira.com
> email:  quincas at gmail.com
>
>

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