Very low distortion
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From: John Larkin on 19 May 2010 19:53 On Wed, 19 May 2010 18:00:01 -0500, "Tim Williams" <tmoranwms(a)charter.net> wrote: >"whit3rd" <whit3rd(a)gmail.com> wrote in message >news:8ddff6a1-fd6c-4186-9bef-99347114cda2(a)b21g2000vbh.googlegroups.com... >> Self-heating is completely nonnegligible >> at low frequencies, and the best resistors aren't specified for their >> thermocouple voltages AT ALL. Resistors will make second-harmonic >> distortion. > >Tektronix called this effect "thermals", although that was regarding >transistor self-heating specifically. > >Curiously, this effect has been recognized since the vacuum tube days. >Wonder if that's due to plate/grid heating, exapnding and distorting the >electrode structure. There is a "cathode interface" mechanism in oxide-coated cathodes that causes some loss of gain at low frequencies. Old Tek scopes sometimes have networks to compensate. Transistor scopes often had thermal hooks that had to be equalized too. John
From: Jan Panteltje on 20 May 2010 06:21 On a sunny day (Thu, 20 May 2010 09:30:47 +1000) it happened David Eather <eather(a)tpg.com.au> wrote in <ocOdneqgH5856WnWnZ2dnUVZ_u-dnZ2d(a)giganews.com>: >On 18/05/2010 4:28 AM, Mike wrote: >> Vladimir Vassilevsky<nospam(a)nowhere.com> wrote: >>> Would it be possible to make a cascaded amp to boost >>> the open loop gain and improve distortion? >>> >>> Vladimir Vassilevsky >>> DSP and Mixed Signal Design Consultant >>> http://www.abvolt.com >> >> Yes. See AN67, Linear Technology Magazine Circuit Collection, Volume III >> >> An Ultrapure Oscillator By Dale Eagar. >> >> Http://cds.linear.com/docs/Application%20Note/an67f.pdf >> >> Article starts on page 62 >> >> Schematic is Figure 96 on page 65 > >This is just my curiosity.. > >Having a look at this circuit they are using an lt1228 OTA for amplitude >control. Does anyone have any experience in using a light dependent >resistor in this role and what sort of distortion did they experience? I have seen LDRs used as volume control in the old TV studio audio mixer, no distortion to speak of (tube age). the LDR was driven normal bulb with a DC from the fader. There was some drift IIRC, as bulbs age.. No cracking noises moving the faders! Nice solution.
From: George Herold on 20 May 2010 08:16 On May 19, 7:30 pm, David Eather <eat...(a)tpg.com.au> wrote: > On 18/05/2010 4:28 AM, Mike wrote: > > > > > > > Vladimir Vassilevsky<nos...(a)nowhere.com> wrote: > >> Would it be possible to make a cascaded amp to boost > >> the open loop gain and improve distortion? > > >> Vladimir Vassilevsky > >> DSP and Mixed Signal Design Consultant > >>http://www.abvolt.com > > > Yes. See AN67, Linear Technology Magazine Circuit Collection, Volume III > > > An Ultrapure Oscillator By Dale Eagar. > > > Http://cds.linear.com/docs/Application%20Note/an67f.pdf > > > Article starts on page 62 > > > Schematic is Figure 96 on page 65 > > This is just my curiosity.. > > Having a look at this circuit they are using an lt1228 OTA for amplitude > control. Ahh, thanks for the 'hint' I was a bit confused how the gain control was accomplished. >Does anyone have any experience in using a light dependent > resistor in this role and what sort of distortion did they experience? I assume you've seen AN43 by J. Williams, he beats on the Wien bridge oscillator at the end of the app note. The last circuit of which uses an LDR. George H. - Hide quoted text - > > - Show quoted text -
From: David Eather on 20 May 2010 20:04
On 20/05/2010 10:16 PM, George Herold wrote: > On May 19, 7:30 pm, David Eather<eat...(a)tpg.com.au> wrote: >> On 18/05/2010 4:28 AM, Mike wrote: >> >> >> >> >> >>> Vladimir Vassilevsky<nos...(a)nowhere.com> wrote: >>>> Would it be possible to make a cascaded amp to boost >>>> the open loop gain and improve distortion? >> >>>> Vladimir Vassilevsky >>>> DSP and Mixed Signal Design Consultant >>>> http://www.abvolt.com >> >>> Yes. See AN67, Linear Technology Magazine Circuit Collection, Volume III >> >>> An Ultrapure Oscillator By Dale Eagar. >> >>> Http://cds.linear.com/docs/Application%20Note/an67f.pdf >> >>> Article starts on page 62 >> >>> Schematic is Figure 96 on page 65 >> >> This is just my curiosity.. >> >> Having a look at this circuit they are using an lt1228 OTA for amplitude >> control. > > Ahh, thanks for the 'hint' I was a bit confused how the gain control > was accomplished. > >> Does anyone have any experience in using a light dependent >> resistor in this role and what sort of distortion did they experience? > > I assume you've seen AN43 by J. Williams, No, but that won't be true in a minute. he beats on the Wien bridge > oscillator at the end of the app note. The last circuit of which uses > an LDR. > > George H. > > - Hide quoted text - >> >> - Show quoted text - > |