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From: «Leo» on 26 Mar 2010 11:23 I want to make a circuit that takes a guitar input signal, and then outputs a signal with fundamental and 2nd order harmonic with the same level (or arbitrary levels, I want to amplify the two components at will). I figured that there are various ways to do this, but I'm trying to do it all analog if possible (since it usually produces more pleasant sounds). Plus there are already commercial digital octave doublers, and the ones that are analog come as ring modulators (they add more components to the signal). The frequency range is 20hz-20khz at worst, the available DC source is 9V. I'm trying to get the 2nd order harmonic by taking the input signal through a emitter follower stage, biased so the amplification is sufficiently non-linear to produce 2nd order harmonic distortion (and a little 3rd). Then to isolate the 2nd harmonic, I thought of inverting the input through another signal path and then adding the two signals, and hope that the fundamental frequency cancels out. While trying to do this in spice, I realized that I'm going to have to have some kind of AGC so the two signals hace the same component of the fundamental. Designing the AGC has been rather complicated so far. So the idea that i had is getting a little bit complicated. Any help or new ideas would be appreciated.
From: Rich Webb on 26 Mar 2010 11:48 On Fri, 26 Mar 2010 08:23:12 -0700 (PDT), �Leo� <leo2100(a)gmail.com> wrote: >I want to make a circuit that takes a guitar input signal, and then >outputs a signal with fundamental and 2nd order harmonic with the same >level (or arbitrary levels, I want to amplify the two components at >will). A phase-locked loop. The CD4046 plus a divide by N is the classic "PLL 101" approach. TI has a pretty good app note on this and there are tons of "phase locked loop" examples on the 'net. -- Rich Webb Norfolk, VA
From: Jim Thompson on 26 Mar 2010 11:52 On Fri, 26 Mar 2010 11:48:30 -0400, Rich Webb <bbew.ar(a)mapson.nozirev.ten> wrote: >On Fri, 26 Mar 2010 08:23:12 -0700 (PDT), �Leo� <leo2100(a)gmail.com> >wrote: > >>I want to make a circuit that takes a guitar input signal, and then >>outputs a signal with fundamental and 2nd order harmonic with the same >>level (or arbitrary levels, I want to amplify the two components at >>will). > >A phase-locked loop. The CD4046 plus a divide by N is the classic "PLL >101" approach. TI has a pretty good app note on this and there are tons >of "phase locked loop" examples on the 'net. Not one that can track changing music input. But perhaps you could make an analog squaring circuit to double the input frequency. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy
From: Tim Wescott on 26 Mar 2010 12:11 �Leo� wrote: > I want to make a circuit that takes a guitar input signal, and then > outputs a signal with fundamental and 2nd order harmonic with the same > level (or arbitrary levels, I want to amplify the two components at > will). > > I figured that there are various ways to do this, but I'm trying to do > it all analog if possible (since it usually produces more pleasant > sounds). Plus there are already commercial digital octave doublers, > and the ones that are analog come as ring modulators (they add more > components to the signal). The frequency range is 20hz-20khz at worst, > the available DC source is 9V. > > I'm trying to get the 2nd order harmonic by taking the input signal > through a emitter follower stage, biased so the amplification is > sufficiently non-linear to produce 2nd order harmonic distortion (and > a little 3rd). Then to isolate the 2nd harmonic, I thought of > inverting the input through another signal path and then adding the > two signals, and hope that the fundamental frequency cancels out. > While trying to do this in spice, I realized that I'm going to have to > have some kind of AGC so the two signals hace the same component of > the fundamental. Designing the AGC has been rather complicated so far. > So the idea that i had is getting a little bit complicated. > > Any help or new ideas would be appreciated. Whatever you do will, I think, give you tremendous distortion but may not make the thing sound a higher tone -- I suspect that at best you'll take out the fundamental, but leave the odd-order harmonics. Nay-saying aside, a squaring circuit would be the first thing to try -- my knee jerk reaction would be to use an analog multiplier (goodness those things are expensive now!) with both inputs connected to your signal. Perhaps a _really fast_ AGC on _one_ channel, so that the output envelope is proportional to the input. If that doesn't work, I'd try a phase shift network like the old-style "phasing" single-sideband receivers used -- this is a set of all-pass filters that shift phases in both channels such that the resultant phase is 90 degrees apart. You'd have a much better chance of getting rid of the DC bias on the output, and possibly of getting rid of the odd-order effects. But all-pass filters tend to have nasty effects on audio quality*, so even if it sounds better one way, it may not be worth it. * I'm told. Personally, I have a tin ear. I think it's because they're not minimum phase, which is also the 'real' problem with much of the DSP that gets done. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
From: Rich Webb on 26 Mar 2010 12:42
On Fri, 26 Mar 2010 08:52:17 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Fri, 26 Mar 2010 11:48:30 -0400, Rich Webb ><bbew.ar(a)mapson.nozirev.ten> wrote: > >>On Fri, 26 Mar 2010 08:23:12 -0700 (PDT), �Leo� <leo2100(a)gmail.com> >>wrote: >> >>>I want to make a circuit that takes a guitar input signal, and then >>>outputs a signal with fundamental and 2nd order harmonic with the same >>>level (or arbitrary levels, I want to amplify the two components at >>>will). >> >>A phase-locked loop. The CD4046 plus a divide by N is the classic "PLL >>101" approach. TI has a pretty good app note on this and there are tons >>of "phase locked loop" examples on the 'net. > >Not one that can track changing music input. True enough. I assumed he was looking for a tuning gizmo rather than a real-time doublers. -- Rich Webb Norfolk, VA |