Opamp frequency mixer

bitrex · Jul 6, 2015

On 7/5/2015 12:39 PM, Clifford Heath wrote:

On 06/07/15 02:22, Clifford Heath wrote:
On 05/07/15 07:06, 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:
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.

If you can't get MC1494 but can arrange one bipolar drive signal, you
can make the rest of a Gilbert cell very easily using the matched
transistors in a LM3046, which are readily available, cheap and
sufficiently retro. You even get a spare transistor you could use for
the phase splitter.

Forgot to mention, the Ft of the LM3046 is circa 350MHz, so no problem
operating at HF. And there's always the rather faster and more expensive
HFA3101 if you need to operate up to 1GHz . But the LM3046 is one of
my jelly-beans for discrete stuff up to 50MHz. It can go higher, but
it's less trouble to design using faster transistors.

Unfortunately, however, it seems like the MC1494, 1496, LM3046, and so
on are all non-stock just about everywhere.

bitrex · Jul 6, 2015

On 7/5/2015 12:39 PM, Clifford Heath wrote:

On 06/07/15 02:22, Clifford Heath wrote:
On 05/07/15 07:06, 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:
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.

If you can't get MC1494 but can arrange one bipolar drive signal, you
can make the rest of a Gilbert cell very easily using the matched
transistors in a LM3046, which are readily available, cheap and
sufficiently retro. You even get a spare transistor you could use for
the phase splitter.

Forgot to mention, the Ft of the LM3046 is circa 350MHz, so no problem
operating at HF. And there's always the rather faster and more expensive
HFA3101 if you need to operate up to 1GHz . But the LM3046 is one of
my jelly-beans for discrete stuff up to 50MHz. It can go higher, but
it's less trouble to design using faster transistors.

If you feel like showing me an example of the kind of circuit you have
in mind, that would be great... ;-)

Jasen Betts · Jul 6, 2015

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

Clifford Heath · Jul 6, 2015

On 06/07/15 12:18, bitrex wrote:

On 7/5/2015 12:39 PM, Clifford Heath wrote:
On 06/07/15 02:22, Clifford Heath wrote:
On 05/07/15 07:06, 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:
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.

If you can't get MC1494 but can arrange one bipolar drive signal, you
can make the rest of a Gilbert cell very easily using the matched
transistors in a LM3046, which are readily available, cheap and
sufficiently retro. You even get a spare transistor you could use for
the phase splitter.

Forgot to mention, the Ft of the LM3046 is circa 350MHz, so no problem
operating at HF. And there's always the rather faster and more expensive
HFA3101 if you need to operate up to 1GHz . But the LM3046 is one of
my jelly-beans for discrete stuff up to 50MHz. It can go higher, but
it's less trouble to design using faster transistors.

Unfortunately, however, it seems like the MC1494, 1496, LM3046, and so
on are all non-stock just about everywhere.

LM3046 is available in heaps of places, and used in lots of designs so
is likely to be manufactured for some time. Use the SMT versions. I was
thinking of a circuit like this one. The input transformer does the
phase splitting and provides the low impedance you need. You can ground
either of the other inputs for single-ended, and ignore either of the
outputs:

<https://www.dropbox.com/s/bvql4eii5w3g33n/LM3046%20mixer.pdf?dl=0>

No need to sign in or sign up to Dropbox, just cancel on through to the PDF.

Clifford Heath.

whit3rd · Jul 6, 2015

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.

Robert Baer · Jul 6, 2015

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"

Bill Sloman · Jul 6, 2015

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

Jul 6, 2015

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, Sydney

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.

Bill Sloman · Jul 6, 2015

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

Phil Hobbs · Jul 6, 2015

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...

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.

piglet

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

--
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

piglet · Jul 6, 2015

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

John Larkin · Jul 6, 2015

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...

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

A 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.

Phil Hobbs · Jul 7, 2015

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

bitrex · Jul 7, 2015

On 7/5/2015 7:16 PM, Clifford Heath wrote:

On 06/07/15 12:18, bitrex wrote:
On 7/5/2015 12:39 PM, Clifford Heath wrote:
On 06/07/15 02:22, Clifford Heath wrote:
On 05/07/15 07:06, 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:
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.

If you can't get MC1494 but can arrange one bipolar drive signal, you
can make the rest of a Gilbert cell very easily using the matched
transistors in a LM3046, which are readily available, cheap and
sufficiently retro. You even get a spare transistor you could use for
the phase splitter.

Forgot to mention, the Ft of the LM3046 is circa 350MHz, so no problem
operating at HF. And there's always the rather faster and more expensive
HFA3101 if you need to operate up to 1GHz . But the LM3046 is one of
my jelly-beans for discrete stuff up to 50MHz. It can go higher, but
it's less trouble to design using faster transistors.

Unfortunately, however, it seems like the MC1494, 1496, LM3046, and so
on are all non-stock just about everywhere.

LM3046 is available in heaps of places, and used in lots of designs so
is likely to be manufactured for some time. Use the SMT versions. I was
thinking of a circuit like this one. The input transformer does the
phase splitting and provides the low impedance you need. You can ground
either of the other inputs for single-ended, and ignore either of the
outputs:

https://www.dropbox.com/s/bvql4eii5w3g33n/LM3046%20mixer.pdf?dl=0

No need to sign in or sign up to Dropbox, just cancel on through to the PDF.

Clifford Heath.

Thanks!

Phil Hobbs · Jul 7, 2015

Arrow even has them in DIP but hurry, they are EOL'd and they've only
got about 10,000 of them

I already bought four tubes of them, so Arrow's are safe for now.

Cheers

Phil Hobbs

Joerg · Jul 7, 2015

On 2015-07-05 9:44 PM, Phil Hobbs wrote:

Digikey shows 6000-odd of the MC1496 in stock. http://www.digikey.com/product-detail/en/MC1496DR2G/MC1496DR2GOSCT-ND/1139685?WT.z_cid=ref_octopart_dkc_buynow&site=us

Arrow even has them in DIP but hurry, they are EOL'd and they've only
got about 10,000 of them

http://components.arrow.com/part/detail/40219439S7075697N1952?region=na&utm_source=FindChips&utm_medium=invListing&utm_campaign=FC2015

Of course, they may not be retro enough for this project because they
don't come in a glass package and nothing glows.

--
Regards, Joerg

http://www.analogconsultants.com/

Tim Williams · Jul 7, 2015

"Joerg" <news@analogconsultants.com> wrote in message
news:d0285kFmdegU1@mid.individual.net...

Arrow even has them in DIP but hurry, they are EOL'd and they've only
got about 10,000 of them

http://components.arrow.com/part/detail/40219439S7075697N1952?region=na&utm_source=FindChips&utm_medium=invListing&utm_campaign=FC2015

Of course, they may not be retro enough for this project because they
don't come in a glass package and nothing glows.

Check Richardson's stock, maybe they have some that glow! :^)

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com

Opamp frequency mixer

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