[sdiy] BODE Frequency Shifter

[atsushi maeda]

Thanks so much, David G Dixon


I am very grateful for the very detailed explanation.
I checked the phase difference one by one and went.
In the process, I confirmed a very suspicious fact.
It is a mistake of mounting parts.
It was due to misreading of the numerical value of CAP.
As a result, the circuit operated normally as a result of replacing the 
part.
We succeeded in obtaining a phase difference of 90 degrees at all 
frequency points.
Thank you very much.


Atsushi Maeda

On 2018/11/01 3:43, David G Dixon wrote:
> Here's my two cents on Dome filters, which I call 90-degree phase
> displacement networks...
>
> If you have built a 90D PDN with 10 or 12 allpass stages, all individually
> tuned with trimmers, then you should have no problem tuning each one.  Just
> achieve a perfectly circular Lissajous figure between the fed sine and the
> stage output on each one at the desired frequency, and then the whole thing
> should give you a 90-degree (+/- 1 or 2 degrees) difference between the two
> cascades over the designed range of frequencies.  You should be able to feed
> a slow frequency-swept sine wave to the filter and see a more or less
> perfectly circular Lissajous figure between the two cascades over the entire
> range.  However, the phase shift will be dramatically different once you
> exceed the frequency range, on either end.
>
> At least, that's my experience.  I built a 12-stage (6 x 6) filter for a
> range of 15 to 15000 Hz using QuadNet, and it worked perfectly.  I did it
> two ways:
>
> 1) The first one was with all different monolithic ceramic cap values
> selected to give the proper frequencies with a resistance of about 32k, and
> I used 27k fixed resistors and 10k trimpots and tuned each one individually.
>
> 2) The second one was with 102, 103 and 104 film caps (4 of each) and I used
> pairs of 1% resistors to get as close to the required time constants as
> possible.  For example, for the frequency of 1340Hz, given a 103 (10nF) cap,
> the required R is 11875 ohms (the cap values were selected to keep the
> resistances mostly between 10k and 100k).  This can be obtained with an
> 11.8k resistor and a 75R resistor, both standard 1% values.  (My biggest
> resistance error was 0.013%.)  I bought a small pile of 102, 103 and 104
> film caps, and I made a simple triple relaxation oscillator with 10k, 100k
> and 1M resistors that should generate outputs of 455Hz for 104, 103 and 102
> caps, respectively.  Then I tested all the caps in my collection and
> separated them into bins depending based on 4-Hz ranges.  Hence, all the
> caps that gave between 453 and 457Hz went into one bin, between 458 and 462
> in another, and between 448 and 452 into a third.  Any that were outside of
> those ranges were excluded (there weren't that many -- I find that caps are
> generally closer to their stated values than the spec would lead you to
> believe).  I didn't select the resistors, since my design suggested that 1
> or 2% tolerance on the RC value wouldn't make a significant difference to
> the performance of the PDN.  It worked well (in that it gave a more or less
> perfectly circular Lissajous figure between 15 and 15000 Hz) and required no
> trimming whatsoever.  No trimmers means a much simpler layout and quicker
> build.  Testing the caps went quickly, since I could do three at a time (one
> of each value), and so within a half hour I could generate enough caps for
> half a dozen 90D-PDN circuits.  My spreadsheet analysis suggested that the
> PDN would work equally well if all of the caps had the same tolerance.  In
> other words, if all the caps were 1% low or 1% high, the PDN would work just
> as well as if they were all perfect.
>
> Not sure if any of this helps, but that's my experience.  I've done similar
> thinking on all parts of my frequency shifter so that there are no trimmers
> at all and it works very well, with little if any carrier bleed.  The key
> thing is to AC-couple all of the inputs to the multipliers, since the
> majority of carrier bleed is from DC levels on the various signals.
>
>
>> -----Original Message-----
>> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On
>> Behalf Of Dave
>> Sent: Wednesday, October 31, 2018 7:02 AM
>> To: synth-diy at synth-diy.org; atsushi maeda
>> Subject: Re: [sdiy] BODE Frequency Shifter
>>
>>
>>
>> On October 30, 2018 3:45:25 AM PDT, atsushi maeda
>> <shine32 at kr.tcp-ip.or.jp> wrote:
>>
>>> The current problem occurred when adjusting DOME Filter.
>>> It may be adjusted so as to have a phase difference of 90
>> degrees at 40
>>> Hz, 170 Hz, 725 Hz, 3080 Hz, 13090 Hz, but if I adjusted it to 90
>>> degrees phase difference at 13090 Hz, the phase difference
>> will be 90
>>> degrees at other frequencies It will not be.
>>> No matter how many times you try to adjust it, it will not change.
>>> Is my understanding wrong?
>> Please post your measurements.  How large are the errors?
>>
>> -Dave
>>
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>