[sdiy] as3340 PW/tuning issue
Jay Schwichtenberg
jschwich53 at comcast.net
Sun Dec 29 00:09:45 CET 2019
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 <mailto: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 <mailto: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 <http://synthparts.com>
>
> On Saturday, December 21, 2019, 3:11:12 PM PST, ColinMuirDorward
> <colindorward at gmail.com <mailto: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
> <mailto: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 <http://synthparts.com>
>
> On Thursday, December 19, 2019, 3:12:35 PM PST,
> ColinMuirDorward <colindorward at gmail.com
> <mailto: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 <mailto: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 <mailto: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 <mailto: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 <mailto: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
>>> <mailto:hardware at doepfer.de>; technik at doepfer.de
>>> <mailto: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 <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 <mailto:keyboards at doepfer.de>
>>>
>>>
>>>
>>>
>>>
>>> Den tors 19 dec. 2019 10:42Oakley Sound via
>>> Synth-diy <synth-diy at synth-diy.org
>>> <mailto: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 <http://www.oakleysound.com/>
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at synth-diy.org
>>> <mailto:Synth-diy at synth-diy.org>
>>> http://synth-diy.org/mailman/listinfo/synth-diy
>>>
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>
>>> http://synth-diy.org/mailman/listinfo/synth-diy
>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>
>> http://synth-diy.org/mailman/listinfo/synth-diy
>>
>>
>>
>> --
>> https://www.instagram.com/colinmuirdorward/
>> -
>> <https://www.instagram.com/colinmuirdorward/>
>> https://www.instagram.com/ssdp_synthesis/
>
>
>
> --
> https://www.instagram.com/colinmuirdorward/
> -
> <https://www.instagram.com/colinmuirdorward/>
> https://www.instagram.com/ssdp_synthesis/
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>
> http://synth-diy.org/mailman/listinfo/synth-diy
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>
> http://synth-diy.org/mailman/listinfo/synth-diy
>
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at synth-diy.org
> http://synth-diy.org/mailman/listinfo/synth-diy
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20191228/b1a1ab05/attachment.htm>
More information about the Synth-diy
mailing list