[sdiy] as3340 PW/tuning issue

Quincas Moreira quincas at gmail.com
Sun Dec 29 17:42:43 CET 2019


Colin, I mean put the SMD 3340 in oine of those adaptor boards for
prototyping, essentially making it through hole. Here's an example I found
in a quick search :
https://protosupplies.com/product/pcb-smd-sop-28-ssop-28-to-dip-adapter5-pack/

On Sat, Dec 28, 2019 at 7:58 PM ColinMuirDorward <colindorward at gmail.com>
wrote:

> 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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> https://www.instagram.com/colinmuirdorward/
> -
> <https://www.instagram.com/colinmuirdorward/>
> https://www.instagram.com/ssdp_synthesis/
>


-- 
[image: QMA]

Quincas Moreira
Director | QMA
mobile:  5534988825
site:  quincasmoreira.com
email:  quincas at gmail.com
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