On Sat, 04 Jul 2015 16:30:24 -0400, bitrex <bitrex@de.lete.earthlink.net> wrote:>So as a hobby project I'm thinking of building a tiny little theremin >using some of those Soviet subminiature pentodes that are really cheap >on eBay. Unfortunately, it seems that the most complicated part of the >project would be the frequency mixers, as I don't think they really made >subminiature heptodes and a "proper" mixer would probably require two tubes. > >I'm thinking about going solid state for the mixers in the first >iteration at least...since the RF is so low I could probably just use a >dual opamp with sufficient GBW. There was this article but of course >all the links to the schematics are broken: > >http://electronicdesign.com/analog/make-frequency-mixer-op-amps > >Can anyone suggest an opamp mixer topology for the low 100s of kHz?Any tube will mix: diode, triode, pentode, CRT, PMT. Armstrong didn't need any fancy-pants megagrid tubes when he invented the superhet: https://www.google.com/patents/US1342885?dq=armstrong+1920&hl=en&sa=X&ei=LlSYVfrkLNPcoATEo47YDw&ved=0CE8Q6AEwBw A PMT would make an optical superhet. LO one of the dynodes.
Opamp frequency mixer
Started by ●July 4, 2015
Reply by ●July 4, 20152015-07-04
Reply by ●July 4, 20152015-07-04
On Sat, 04 Jul 2015 17:40:34 -0400, bitrex <bitrex@de.lete.earthlink.net> wrote:>On 7/4/2015 5:06 PM, Jim Thompson wrote: >> On Sat, 04 Jul 2015 13:53:15 -0700, Joerg <news@analogconsultants.com> >> wrote: >> >>> On 2015-07-04 1:30 PM, bitrex wrote: >> >> [snip] >> >>>> >>>> Can anyone suggest an opamp mixer topology for the low 100s of kHz? >>> >>> >>> If it absolutely has to be semiconductors I'd use the MC1496. >> >> I'd go with the MC1494... if you can get it. It has the level >> shifting built-in... quite adequate for audio, and immensely eases the >> pain of doing your own level-shifting. >> >> ...Jim Thompson >> > > >Also, I have about a hundred LM13700s I picked up dirt cheap in the DIP >package somewhere around here in a box ;)That's always the best solution ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●July 4, 20152015-07-04
On 7/4/2015 5:53 PM, John Larkin wrote:> On Sat, 04 Jul 2015 16:30:24 -0400, bitrex > <bitrex@de.lete.earthlink.net> wrote: > >> So as a hobby project I'm thinking of building a tiny little theremin >> using some of those Soviet subminiature pentodes that are really cheap >> on eBay. Unfortunately, it seems that the most complicated part of the >> project would be the frequency mixers, as I don't think they really made >> subminiature heptodes and a "proper" mixer would probably require two tubes. >> >> I'm thinking about going solid state for the mixers in the first >> iteration at least...since the RF is so low I could probably just use a >> dual opamp with sufficient GBW. There was this article but of course >> all the links to the schematics are broken: >> >> http://electronicdesign.com/analog/make-frequency-mixer-op-amps >> >> Can anyone suggest an opamp mixer topology for the low 100s of kHz? > > Any tube will mix: diode, triode, pentode, CRT, PMT. Armstrong didn't > need any fancy-pants megagrid tubes when he invented the superhet: > > https://www.google.com/patents/US1342885?dq=armstrong+1920&hl=en&sa=X&ei=LlSYVfrkLNPcoATEo47YDw&ved=0CE8Q6AEwBw >Armstrong was an amazing guy--he invented the oscillator! Also the superhet, the superregen, FM radio, and many other things. One of my technical heroes. Chees Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 4, 20152015-07-04
On Sat, 04 Jul 2015 18:23:12 -0400, Phil Hobbs <hobbs@electrooptical.net> wrote:>On 7/4/2015 5:53 PM, John Larkin wrote: >> On Sat, 04 Jul 2015 16:30:24 -0400, bitrex >> <bitrex@de.lete.earthlink.net> wrote: >> >>> So as a hobby project I'm thinking of building a tiny little theremin >>> using some of those Soviet subminiature pentodes that are really cheap >>> on eBay. Unfortunately, it seems that the most complicated part of the >>> project would be the frequency mixers, as I don't think they really made >>> subminiature heptodes and a "proper" mixer would probably require two tubes. >>> >>> I'm thinking about going solid state for the mixers in the first >>> iteration at least...since the RF is so low I could probably just use a >>> dual opamp with sufficient GBW. There was this article but of course >>> all the links to the schematics are broken: >>> >>> http://electronicdesign.com/analog/make-frequency-mixer-op-amps >>> >>> Can anyone suggest an opamp mixer topology for the low 100s of kHz? >> >> Any tube will mix: diode, triode, pentode, CRT, PMT. Armstrong didn't >> need any fancy-pants megagrid tubes when he invented the superhet: >> >> https://www.google.com/patents/US1342885?dq=armstrong+1920&hl=en&sa=X&ei=LlSYVfrkLNPcoATEo47YDw&ved=0CE8Q6AEwBw >> >Armstrong was an amazing guy--he invented the oscillator! > >Also the superhet, the superregen, FM radio, and many other things. > >One of my technical heroes. > >Chees > >Phil HobbsI'm just finishing this one http://www.amazon.com/Much-ADO-about-Almost-Nothing/dp/0615139957/ref=sr_1_1?ie=UTF8&qid=1436049038&sr=8-1&keywords=much+ado+almost+nothing which is pretty cool. It's amazing what a jerk DeForest was, and how crazy Tesla was. And how many great inventors died poor. Hans invented the 555 chip, which makes the few glaring errors in this book all the more strange.
Reply by ●July 4, 20152015-07-04
On 7/4/2015 6:23 PM, Phil Hobbs wrote:> On 7/4/2015 5:53 PM, John Larkin wrote: >> On Sat, 04 Jul 2015 16:30:24 -0400, bitrex >> <bitrex@de.lete.earthlink.net> wrote: >> >>> So as a hobby project I'm thinking of building a tiny little theremin >>> using some of those Soviet subminiature pentodes that are really cheap >>> on eBay. Unfortunately, it seems that the most complicated part of the >>> project would be the frequency mixers, as I don't think they really made >>> subminiature heptodes and a "proper" mixer would probably require two tubes. >>> >>> I'm thinking about going solid state for the mixers in the first >>> iteration at least...since the RF is so low I could probably just use a >>> dual opamp with sufficient GBW. There was this article but of course >>> all the links to the schematics are broken: >>> >>> http://electronicdesign.com/analog/make-frequency-mixer-op-amps >>> >>> Can anyone suggest an opamp mixer topology for the low 100s of kHz? >> >> Any tube will mix: diode, triode, pentode, CRT, PMT. Armstrong didn't >> need any fancy-pants megagrid tubes when he invented the superhet: >> >> https://www.google.com/patents/US1342885?dq=armstrong+1920&hl=en&sa=X&ei=LlSYVfrkLNPcoATEo47YDw&ved=0CE8Q6AEwBw >> > Armstrong was an amazing guy--he invented the oscillator! > > Also the superhet, the superregen, FM radio, and many other things. > > One of my technical heroes. > > Chees > > Phil Hobbs > >I've read about the story of Armstrong and it's very sad. I often found myself wondering why, at some point, someone didn't urge him to cut his losses, come to some kind of settlement with Sarnoff and RCA, and then just walk away. It would have been far better for his health in the long run. What good is pride if the end result is a 12 story swan dive off a hotel balcony?
Reply by ●July 4, 20152015-07-04
On 7/4/2015 5:40 PM, Joerg wrote:> On 2015-07-04 2:24 PM, Tim Wescott wrote: >> On Sat, 04 Jul 2015 16:30:24 -0400, bitrex wrote: >> >>> So as a hobby project I'm thinking of building a tiny little theremin >>> using some of those Soviet subminiature pentodes that are really cheap >>> on eBay. Unfortunately, it seems that the most complicated part of the >>> project would be the frequency mixers, as I don't think they really made >>> subminiature heptodes and a "proper" mixer would probably require two >>> tubes. >>> >>> I'm thinking about going solid state for the mixers in the first >>> iteration at least...since the RF is so low I could probably just use a >>> dual opamp with sufficient GBW. There was this article but of course >>> all the links to the schematics are broken: >>> >>> http://electronicdesign.com/analog/make-frequency-mixer-op-amps >>> >>> Can anyone suggest an opamp mixer topology for the low 100s of kHz? >> >> I second the thought of using a MC1496 or MC1494 if you're going to use >> semiconductors. The NE612 may also suit, but you'd need level shifting. >> >> But you don't do tube projects unless you're planning on using an excess >> of parts. See if you can find a pre-1964 ARRL Handbook and look through >> it for mixers, or do a search on "tube mixer circuits" -- there's a lot >> more ways to do it than with heptodes, that's for sure. >> > > With tubes it doesn't have to end up in excess, except for power > consumption, of course. When I was a kid I built a receiver that could > demodulate AM as well as SSB. It contained only two tube stages and very > few other parts. > > >> You could make a 180 degree shifter and summer by making an appropriate >> transformer (probably at least mildly resonant at good toob impedances) >> from signal A, with the secondary center-tapped and fed with signal B. >> Feed a pair of triodes with the transformer outputs, and poof! you have a >> single balanced mixer. >> > > For 180 degree shifting all you need is one triode as a follower. Make > the anode resistor the same as the cathode resistor. Then the anode > carries the 180 degree signal.Only problem then is that the two outputs have wildly differing output impedances, which could be a problem...
Reply by ●July 4, 20152015-07-04
>It would have been far better for his health in the long run. �What good >is pride if the end result is a 12 story swan dive off a hotel balcony?I'm not a big fan of pride in general, but it's easy to get fixated on your own rights. Cheers Phil Hobbs
Reply by ●July 4, 20152015-07-04
On 7/4/2015 7:45 PM, Phil Hobbs wrote:>> It would have been far better for his health in the long run. What good >> is pride if the end result is a 12 story swan dive off a hotel balcony? > > I'm not a big fan of pride in general, but it's easy to get fixated on your own rights. > > Cheers > > Phil Hobbs >Yeah, I could see that. For my part, sometimes knowing when to fold 'em has kept me fairly sane these past 30 something years.
Reply by ●July 4, 20152015-07-04
On 7/4/2015 10:23 PM, bitrex wrote:> On 7/4/2015 7:45 PM, Phil Hobbs wrote: >>> It would have been far better for his health in the long run. What good >>> is pride if the end result is a 12 story swan dive off a hotel balcony? >> >> I'm not a big fan of pride in general, but it's easy to get fixated on >> your own rights. >> >> Cheers >> >> Phil Hobbs >> > > Yeah, I could see that. For my part, sometimes knowing when to fold 'em > has kept me fairly sane these past 30 something years.You and me both, brother. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 5, 20152015-07-05
On 4.7.15 23:30, bitrex wrote:> So as a hobby project I'm thinking of building a tiny little theremin > using some of those Soviet subminiature pentodes that are really cheap > on eBay. Unfortunately, it seems that the most complicated part of the > project would be the frequency mixers, as I don't think they really made > subminiature heptodes and a "proper" mixer would probably require two > tubes. > > I'm thinking about going solid state for the mixers in the first > iteration at least...since the RF is so low I could probably just use a > dual opamp with sufficient GBW. There was this article but of course > all the links to the schematics are broken: > > http://electronicdesign.com/analog/make-frequency-mixer-op-amps > > Can anyone suggest an opamp mixer topology for the low 100s of kHz?Forget tubes or opamps. The semiconductor solution is called a Gilbert cell (Google for it). With unsorted transistors from the same batch, you will get a far better mixer than with tubes. Do not forget the low-pass filter after mixing. In the Theremin case, you do not even need fight with the dynamic range in the same way as radio receiver designers do. <nag> You should eject the idea of using tubes at all. A couple of FETs will get a far better thing. If you need the dull glow of heaters and associated show, use one or some tubes with only heaters. </nag> -- -TV
