Freq. Independent Phase Shifter
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From: Jan Panteltje on 10 May 2010 15:38 On a sunny day (Mon, 10 May 2010 12:32:38 -0700) it happened Joerg <invalid(a)invalid.invalid> wrote in <84r5apFvq9U3(a)mid.individual.net>: >Jan Panteltje wrote: >> On a sunny day (Mon, 10 May 2010 09:19:56 -0700) it happened Joerg >> <invalid(a)invalid.invalid> wrote in <84qq1hFobmU1(a)mid.individual.net>: >> >>> Bill Murphy wrote: >>>> I am using a commercial stereo amp to output continuous wave test >>>> signals in the low audio range, up to about 2KHz. However, I need a >>>> third channel with a 120 degree phase shift. Is there a circuit that >>>> will do this evenly across this entire frequency range? >>>> >>>> Is it possible to do same using an off-the-shelf transformer and >>>> current subtraction? >>>> >>>> Any advice would be appreciated. >>>> >>> Paul's suggestion with multi-channel sound cards is a good one. But keep >>> in mind that phase shifts in the very low range (tens of Hertzes) can be >>> iffy on some cards, output cap tolerances and all that. Unless you want >>> to go in there with a solder iron. >> >> It is too much, all you need is 3 EPROMS, a 4040 counter, and a 4046 PLL as VCO, >> add a pot to set the frequency. >> Add 3 R2R networks, or 3 cheap DACS. >> I have made one variable sine wave generator like that in the long ago past. >> Milliwats, and in a small box. >> Mine had auto sweep too, so I could test filters. >> Just an integrator and a FF, and 2 comparators added. >> 256 point 8 bits sinewaves. >> After al this is s.e.d. not 'alt.pc.sales' or whatever. >> > >It all depends. When you do this for a living you need to weigh the time >it takes to whip this up against the cost and installation time of a >multi-channel sound card. When you are retired, different thing. But >many of us aren't there yet. Well, if that takes so much time, say more then 2 hours, I think you need more time to go shopping or order the soundcard thing. Plus put it in a PC, plus write the soft, plus it is not real time adjustable with a pot, plus it is not GREEN, it sucks power, plus well it is all so obvious. Who knows, you may not reach your pension... may as well build it now!
From: John Larkin on 10 May 2010 15:55 On Sun, 9 May 2010 16:22:00 -0700, "Joel Koltner" <zapwireDASHgroups(a)yahoo.com> wrote: >"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message >news:03geu592n811uiilhhh4teqone5bf6k2l1(a)4ax.com... >> If you wanted a 12-bit binary counter to make a sine wave at 1 MHz, >> you'd have to clock it at 4 GHz. But a DDS accumulator clocked at 4 >> MHz can easily make a 1 MHz sine wave. > >...although you'll need rather more filtering on the output in the later case! > Beats buying a 12-bit, 4 GHz dac! [1] A 4:1 ratio, half of Nyquist, doesn't require heroic filtering. Above there the filter cost increases without limit as you approach 2:1. John [1] which actually exists
From: Paul Keinanen on 10 May 2010 16:09 On Mon, 10 May 2010 09:19:56 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Bill Murphy wrote: >> I am using a commercial stereo amp to output continuous wave test >> signals in the low audio range, up to about 2KHz. However, I need a >> third channel with a 120 degree phase shift. Is there a circuit that >> will do this evenly across this entire frequency range? >> >> Is it possible to do same using an off-the-shelf transformer and >> current subtraction? >> >> Any advice would be appreciated. >> > >Paul's suggestion with multi-channel sound cards is a good one. But keep >in mind that phase shifts in the very low range (tens of Hertzes) can be >iffy on some cards, Some manufacturers make 4-6 channel codecs suitable for sound cards and home theater systems. These are typically specifies for frequencies above 3 Hz. How low does a typical COTS stereo amplifier go ? While the amplitude response may be bad, why would the phase shift characteristics suffer from this ? >output cap tolerances and all that. The cap tolerances would indeed cause problems. >Unless you want >to go in there with a solder iron. For low production run devices, it would be perfectly feasible to use production measurements and software to compensate for the capacitor variations. In discussing, which is the "best" way of implementing something, you always must consider the expected size of the production run. It is quite different to design a one off product or design a product for 100, 10,000 or 1,000,000 unit production / year, each requiring a different approach.
From: Joerg on 10 May 2010 16:57 Jan Panteltje wrote: > On a sunny day (Mon, 10 May 2010 12:32:38 -0700) it happened Joerg > <invalid(a)invalid.invalid> wrote in <84r5apFvq9U3(a)mid.individual.net>: > >> Jan Panteltje wrote: >>> On a sunny day (Mon, 10 May 2010 09:19:56 -0700) it happened Joerg >>> <invalid(a)invalid.invalid> wrote in <84qq1hFobmU1(a)mid.individual.net>: >>> >>>> Bill Murphy wrote: >>>>> I am using a commercial stereo amp to output continuous wave test >>>>> signals in the low audio range, up to about 2KHz. However, I need a >>>>> third channel with a 120 degree phase shift. Is there a circuit that >>>>> will do this evenly across this entire frequency range? >>>>> >>>>> Is it possible to do same using an off-the-shelf transformer and >>>>> current subtraction? >>>>> >>>>> Any advice would be appreciated. >>>>> >>>> Paul's suggestion with multi-channel sound cards is a good one. But keep >>>> in mind that phase shifts in the very low range (tens of Hertzes) can be >>>> iffy on some cards, output cap tolerances and all that. Unless you want >>>> to go in there with a solder iron. >>> It is too much, all you need is 3 EPROMS, a 4040 counter, and a 4046 PLL as VCO, >>> add a pot to set the frequency. >>> Add 3 R2R networks, or 3 cheap DACS. >>> I have made one variable sine wave generator like that in the long ago past. >>> Milliwats, and in a small box. >>> Mine had auto sweep too, so I could test filters. >>> Just an integrator and a FF, and 2 comparators added. >>> 256 point 8 bits sinewaves. >>> After al this is s.e.d. not 'alt.pc.sales' or whatever. >>> >> It all depends. When you do this for a living you need to weigh the time >> it takes to whip this up against the cost and installation time of a >> multi-channel sound card. When you are retired, different thing. But >> many of us aren't there yet. > > Well, if that takes so much time, say more then 2 hours, I think you > need more time to go shopping or order the soundcard thing. > Plus put it in a PC, plus write the soft, plus it is not real time adjustable > with a pot, plus it is not GREEN, it sucks power, plus well it is all so obvious. > Who knows, you may not reach your pension... may as well build it now! > Hint: One can load revolving wave tables into a sound card :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Bill Murphy on 10 May 2010 17:17
On Mon, 10 May 2010 06:59:03 +0300, Paul Keinanen <keinanen(a)sci.fi> wrote: >Since the OP only needed frequencies up to 2 kHz and was using COTS >amplifiers, a cheap dedicated computer running a multiple (4-6) >channel sound card running at 8-48 kHz sampling frequency would do the >trick. > What about a single card with 4.1 or 5.1 outputs? Either way, how would I generate the three 120 degree offset channels in software? Thank you for your reply. Bill Murphy |