On 2015-07-06, bitrex <bitrex@de.lete.earthlink.net> wrote:> On 7/5/2015 12:39 PM, Clifford Heath wrote:> Unfortunately, however, it seems like the MC1494, 1496, LM3046, and so > on are all non-stock just about everywhere.Farnell has several thousand MC1496 and LM3046 but not in DIP -- umop apisdn
Opamp frequency mixer
Started by ●July 4, 2015
Reply by ●July 6, 20152015-07-06
Reply by ●July 6, 20152015-07-06
On Sunday, July 5, 2015 at 5:02:52 PM UTC-7, Phil Hobbs wrote:> On 7/5/2015 6:26 PM, whit3rd wrote:[about high-speed OTAs]> > They do: TI's OPA861, for example. They just have such opaque > > datasheets and descriptions, that it's hard to recognize the > > face under the greasepaint and red nose. > > > > <http://www.ti.com/lit/ds/sbos338g/sbos338g.pdf> > > The OPA861 isn't an OTA, despite the name--it's intended as an improved > BJT. It lacks differential inputs, for a start. TI rented the name for > a completely different device, drat them.If you mirror a second current output for an OTA, with opposite polarity (so it sinks when the 'main' output sources), and then connect that second output to one of the OTA differential inputs, you get a 'diamond transistor', which is what the OPA861 is. A bipolar transistor has transconductance; an OTA has transconductance, too, but accepts input bias above AND below the "emitter" voltage (i.e. the "emitter" is actually the second of the differential inputs, but with nonneglligible current draw). IMHO, they should have used more connection pins and brought out all the functions.
Reply by ●July 6, 20152015-07-06
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?Our sites are currently under maintenance. Please try back later. We apologize for any inconvenience. "PENTON"
Reply by ●July 6, 20152015-07-06
On Sunday, July 5, 2015 at 10:00:16 PM UTC+2, John Larkin wrote:> On Sat, 04 Jul 2015 19:27:27 -0400, bitrex > <bitrex@de.lete.earthlink.net> wrote: > >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:<snip>> >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? > > A lot of creative inventor types are bipolar and compulsive and a > little schitzoid. Not survival traits. Business types and sociopaths > and evil VCs often take advantage of them.Some inventors are weird, but then again, so are some of the general population. The inventors I've known - and I've known a few - have mostly been regular people. The one bipolar inventor I know did quite well in business, but his particular venture capitalist seems to be a nice guy. -- Bill Sloman, Sydney
Reply by ●July 6, 20152015-07-06
On 7/6/2015 2:16 AM, piglet wrote:> On 05/07/2015 22:58, Phil Hobbs wrote: >>> Which design was that? I can't imagine modulating filament power at low >>> audio frequencies could be very great for it...O_o >> >> No kidding. Running a tube in the cathode-emission-limited condition >> is for a good time, not a long time. (Rectifiers are an exception.) >> >> Cheers >> >> Phil Hobbs >> > > No cathode. Directly heated, the thermal TC of a cathode would respond > far too slowly to volume hand movement. > > pigletIf it's using an oxide-coated or thoriated filament, the same issue applies. If it's plain tungsten, the emission will be much less, but the filament is far more rugged. 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 6, 20152015-07-06
On Saturday, July 4, 2015 at 5:51:41 PM UTC-4, Bill Sloman wrote:> On Saturday, July 4, 2015 at 11:24:21 PM UTC+2, 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. > > Anything the MC1496 can do, the AD633 can do more painlessly. The AD834 and AD835 can do it a lot faster. > > -- > Bill Sloman, SydneyHe doesn't need anything complicated for this little hobby app, an analog switch mixer is adequate, LO selects one of two signals 180o out.
Reply by ●July 6, 20152015-07-06
On 06/07/2015 15:46, Phil Hobbs wrote:> > If it's using an oxide-coated or thoriated filament, the same issue > applies. If it's plain tungsten, the emission will be much less, but > the filament is far more rugged. > > Cheers > > Phil Hobbs >Yes, the UX-120 was developed in 1924 and went on sale 1925 and did use the still very new thoriated filament. Important as it was intended for power work and battery powered so emission efficiency is important. Still think it is a delightfully simple and crazy way of making a voltage vartiable volume control. piglet
Reply by ●July 6, 20152015-07-06
On Sun, 5 Jul 2015 14:58:29 -0700 (PDT), Phil Hobbs <pcdhobbs@gmail.com> wrote:>>Which design was that? I can't imagine modulating filament power at low >>audio frequencies could be very great for it...O_o > >No kidding. Running a tube in the cathode-emission-limited condition is for a good time, not a long time. (Rectifiers are an exception.) > >Cheers > >Phil HobbsA 1B3 makes a nice 30 kilovolt amplifier. Input is filament voltage. Bandwidth is a bit limiting. I used to charge oil caps this way when I was a kid, neon sign transformer and a 1B3. A flashlight battery and a wirewound pot, with a long insulated shaft and a knob, was the control mechanism. Somehow I'm still alive.
Reply by ●July 6, 20152015-07-06
On Monday, July 6, 2015 at 4:48:24 PM UTC+2, bloggs.fred...@gmail.com wrote:> On Saturday, July 4, 2015 at 5:51:41 PM UTC-4, Bill Sloman wrote: > > On Saturday, July 4, 2015 at 11:24:21 PM UTC+2, 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. > > > > Anything the MC1496 can do, the AD633 can do more painlessly. The AD834 and AD835 can do it a lot faster. > > He doesn't need anything complicated for this little hobby app, an analog switch mixer is adequate, LO selects one of two signals 180o out.None of those devices is any more complicated than the MC1496, and they all do much the same job. My memory of the MC1496 was that is was bit harder to get it to do the job than it is with more recent chips. -- Bill Sloman, Sydney
Reply by ●July 6, 20152015-07-06
On 7/6/2015 12:34 PM, Bill Sloman wrote:> On Monday, July 6, 2015 at 4:48:24 PM UTC+2, bloggs.fred...@gmail.com wrote: >> On Saturday, July 4, 2015 at 5:51:41 PM UTC-4, Bill Sloman wrote: >>> On Saturday, July 4, 2015 at 11:24:21 PM UTC+2, 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. >>> >>> Anything the MC1496 can do, the AD633 can do more painlessly. The AD834 and AD835 can do it a lot faster. >> >> He doesn't need anything complicated for this little hobby app, an analog switch mixer is adequate, LO selects one of two signals 180o out. > > None of those devices is any more complicated than the MC1496, and they all do much the same job. My memory of the MC1496 was that is was bit harder to get it to do the job than it is with more recent chips. >The output of the 1496 is the voltage difference between the two pairs of collectors, neither of which is near ground in general. For AC use, as in a superhet, you just AC-couple to the IF, but at DC it's a bit less convenient. Last time I used a 1496 for real, I used a flying capacitor output stage to fix that. It had a CD74HC4352 to switch the cap between three 1496es and the output. Worked great. 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
