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'[EE:] General Opamp questions'
2004\08\10@092258 by Josh Koffman

face picon face
Hi all. Few questions about opamps. If I see a circuit running off a
split power supply, but the negative voltage is only used for the
opamps, can I redesign it using single power supply opamps such as the
TLC272? If I must use a split power supply, would something like the
http://focus.ti.com/docs/prod/folders/print/pt5062.html from TI
(+5Vin, -15+15Vout) be a bad idea due to switching noise? This is for
audio purposes.

Also still looking for balanced microphone receiver/preamp schematic.

Thanks!
Josh
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2004\08\10@095131 by Spehro Pefhany

picon face
At 09:22 AM 8/10/2004 -0400, you wrote:
>Hi all. Few questions about opamps. If I see a circuit running off a
>split power supply, but the negative voltage is only used for the
>opamps, can I redesign it using single power supply opamps such as the
>TLC272?

"Single supply" generally means that input common mode range and the
output range extend to the negative supply rail and close to the negative
rail respectively. It may be possible to *redesign* the circuit
so that it uses single supply (or rail-to-rail) op-amps, but it will
usually be more than a simple substitution of parts. If you have to
ask, the answer is probably "no".

>If I must use a split power supply, would something like the
>http://focus.ti.com/docs/prod/folders/print/pt5062.html from TI
>(+5Vin, -15+15Vout) be a bad idea due to switching noise? This is for
>audio purposes.

You should not have a problem with *audible* switching noise, since
that part operates at 650kHz, however if you use a very wideband
op-amp as used for "professional" audio, you might end up with some
high frequency noise finding its way through the circuit if you are
not careful with layout, bypassing and filtering. Sometimes a relatively
crummy part like a TLC272 (unity gain bandwidth only 2.2MHz typ.) will
be more stable and cause less problems.

That power supply part should work fine if you don't mind the $16
cost. Note that +/-15V will definitely fry a TLC272, though. +/-8 maximum
(16V total). I suggest at least a 0805 ferrite bead series then a 1uF ceramic
cap to ground on each output, with careful attention paid to layout to
keep the 650kHz noise under control.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spam_OUTspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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2004\08\10@095543 by Russell McMahon

face
flavicon
face
> Hi all. Few questions about opamps. If I see a circuit running off a
> split power supply, but the negative voltage is only used for the
> opamps, can I redesign it using single power supply opamps such as the
> TLC272?

Yes. But redesign is definitely the word. Single supply amps come in many
flavours. A few have their own internal power supply generators so they can
genuinely go rail to rail on input and output but many/most have some
limitations. As long as you observe data sheet requirements you'll be OK.
These include input allowable range and common mode range, output range. And
more.

> If I must use a split power supply, would something like the
> http://focus.ti.com/docs/prod/folders/print/pt5062.html from TI
> (+5Vin, -15+15Vout) be a bad idea due to switching noise? This is for
> audio purposes.

Switching power supplies always make life harder in low noise circuits but
are almost always able to be used with due care except in leading edge/
marginal applications that already push other componentry to it's limits.

A single supply conversion is liable to be less troublesome IF you can do it
while still achieving general requirements.



       RM

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2004\08\10@104401 by Josh Koffman

face picon face
Ok, thanks for the advice Spehro and Russell. I should have mentioned
a few things. First off, there really isn't _A_ circuit I'm trying to
modify. I've found a couple of examples of mixers using dual rail
opamps. My main problem is I'm not really skilled enough in analog to
start calculating the values I need to give the correct gains.
Actually, I'm not even sure what the correct gains are supposed to be.
I was hoping to find a balanced, low impedence mic preamp schematic
that I could use to take the mic signals to line level. Then I could
use an opamp to combine them all with a small amount of gain to
overcome the losses in the mixer itself. So, my choice of parts is
entirely open.

The design I'm looking at right now
http://www.mitedu.freeserve.co.uk/Circuits/Audio/6ipmix.htm doesn't
list the part number for the opamp, but it does list the gains he
used. So...if I chose another opamp, then calculated the values out to
get the correct gains, my circuit should end up functionally
equivalent to his, just not using a split power supply. Any
suggestions on a good part to use. I'd like to keep this surface
mount, and compact as well.

Another problem I'm having is locating logarithmic potentiometers for
this project. The schematic mentioned above uses 10K pots. I'm trying
to keep this as compact as possible though, and most of what I've been
able to find are either linear slides, or large panel mount. This is
mostly a set once and forget it (for the most part) mixer, so I don't
need really big controls. Having to carry a screwdriver around would
be a drag, though I can't even find small PCB log pots. Any ideas? Or
would using a linear taper be a horrible thing? I know I'd sacrifice
some controlability, but will it be really bad?

As an aside, I'd like to stay away from the DC-DC convertor if
possible. It's kind of large, and I'm worried about it's switching
frequency either spilling into audio or affecting my ADC and DAC
somehow. I know it shouldn't, but I'm paranoid.

Thanks!

Josh
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On Wed, 11 Aug 2004 01:55:52 +1200, Russell McMahon
<.....apptechKILLspamspam@spam@paradise.net.nz> wrote:
> Yes. But redesign is definitely the word. Single supply amps come in many
> flavours. A few have their own internal power supply generators so they can
> genuinely go rail to rail on input and output but many/most have some
> limitations. As long as you observe data sheet requirements you'll be OK.
> These include input allowable range and common mode range, output range. And
> more.

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2004\08\10@105822 by Charles Linquist

flavicon
face
There are two basic problems with single supplies in low-level, low-noise
audio circuits that
MAY be an issue, depending on how you are using them.

First, you must use coupling capacitors at the input and output, since both
will be at approximately
half the supply voltage.  Capacitors can add their own distortion unless
very good types (polystyrene)
are used. Also, you have to wait for the capacitors to charge before you can
pass a signal through the amp.
This can cause a big THUMP! during turn on/off.

Secondly, since you are biasing up the input with the supply, you should be
careful to bypass that bias
voltage, otherwise you will couple power supply noise right into the input.
Avoid the tendency to just
use two resistors to set the bias level.  Use three resistors and a
capacitor. Connect two of the resistors
as a voltage divider with the capacitor from the junction to GND, and the
third resistor from that junction
to the input of the op-amp.

Charles Linquist


{Original Message removed}

2004\08\10@121610 by Bob Blick

face picon face
> Also still looking for balanced microphone receiver/preamp schematic.
>
Hi Josh,

Depending on the results you're trying to achieve, there are lots of ways
to get there. Actually, there are always many ways there :-)

It's easy to design a balanced input preamp, but hard to design one that
is quiet. That's why the really expensive consoles use input transformers
typically of the 600:10000 ohm variety. You get perfect balancing and also
voltage gain. An added benefit is the ability to add DC for phantom power,
no capacitors needed. So it becomes very simple, except good transformers
are big and expensive.

If your requirements are more basic, you might consider just building an
unbalanced input. You can hook a balanced mic to it, you'll just not have
the luxury of 300 foot noiseless cables.

Cheerful regards,

Bob

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2004\08\10@131920 by Josh Koffman

face picon face
Well, my goal here isn't exactly studio quality. I'm making an addon
to my portable ADC for live recording. It will take a line level
signal from the mixer, and one or two mic level signals from room
mics. A bit of noise in the preamp will likely be drowned out by noise
elsewhere in the system. I'm not going to be mastering albums on this
thing.

I think I've mostly gotten my head around how to make a simple opamp
mixer that sums up some line level signals. The ideal situation would
be to now have a balanced line receiver/preamp module that bumps the
level up to match the line inputs. Then I just do the opamp summing
mixer and I'm good to go.

I've been shunning transformers for a few reasons. First, they can be
large, and I'm trying to keep this super small. Then again, opamps and
support components take up space too. However, the only transformers I
can find at Digikey are about $20-25 each. That's a little pricey,
plus they aren't small. And they don't even meet the 600:10000 ohm
spec. Radio Shack used to sell little balanced to unbalanced
convertors, I could check to see if they still do, then gut them,
though that doesn't seem a really clean solution.

In the schematic I linked to earlier, he has an unbalanced input
stage. I know it would be easier to just take that, but I just keep
feeling it's somewhat of a cop out. It'll work fine for dynamic mics,
but I'm worried what would happen if I try to connect a condensor or
something to the XLR in. No, I won't be feeding it phantom power, but
some of the mics are wired so that shorting the cold and ground
together screws them up. Analog even makes a balanced line receiver
for audio, but of course it requires split power supplies.

Josh
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On Tue, 10 Aug 2004 09:15:26 -0700, Bob Blick <bblickspamKILLspamsonic.net> wrote:
{Quote hidden}

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2004\08\10@165747 by Jinx

face picon face
> As an aside, I'd like to stay away from the DC-DC convertor if
> possible. It's kind of large, and I'm worried about it's switching
> frequency either spilling into audio or affecting my ADC and DAC
> somehow. I know it shouldn't, but I'm paranoid.

You don't need 9W do you, just a sniff of -ve for the opamps ? If so,
why not make your own split supply, with a MAX232 for example
to get +/- 8, or an ICL7660 / 555 / PIC pins / whatever to make -5

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2004\08\10@171448 by Jinx

face picon face
> though I can't even find small PCB log pots. Any ideas?

I've never tried and measured (spreadsheet ?) this but it's said
if you put a fixed R in parallel across the end terminals of a linear
taper it approximates a log taper

BTW, this might be useful for something

http://www.mindspring.com/~clist/PotGraph.html

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2004\08\10@214911 by Rich

picon face
----- Original Message -----
From: "Josh Koffman" <.....joshybearKILLspamspam.....GMAIL.COM>
To: <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU>
Sent: Tuesday, August 10, 2004 9:22 AM
Subject: [EE:] General Opamp questions


> Hi all. Few questions about opamps. If I see a circuit running off a
> split power supply, but the negative voltage is only used for the
> opamps, can I redesign it using single power supply opamps such as the
> TLC272? If I must use a split power supply, would something like the
> http://focus.ti.com/docs/prod/folders/print/pt5062.html from TI
> (+5Vin, -15+15Vout) be a bad idea due to switching noise? This is for
> audio purposes.
>
Josh:
You can use a different op amp that does not require a bipolar supply. While
I don't recommend the LM124 for your audio application, it is an example of
an op amp that can run on a single ended supply.  It has pnp transistors in
the input that are ground referenced due to the pnp biasing requirement.  I
don't know of a particular low noise audio op amp that is similarly
configured.  Perhaps you can search it out.  If memory serves me correctly,
the LM386 has been used in audio applications and has a relatively good
spec.  Since I do not know what your noise budget looks like I cannot
recommend any chip. However, I believe that low noise audio circuits are
best configured with low noise discrete components at low voltage and low
current configurations and very stable clean power supply,  rather than with
op amps.The Johnson noise (popcorn noise) cannot be eliminated if bipolar
transistors are used, and field effect devices are much more sensitive to
thermal environment.  The low power biasing considerations are well
considered in that respect.  I would be interested in seeing your design
criteria including your error budget/noise budget. I hope this is some small
help to you.  Good Luck.

{Quote hidden}

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2004\08\10@215325 by Rich

picon face
Hi Josh:
I looked at the mixer design.  I was surprised that the pots were log taper
and not audio taper pots.  Audio taper are abundantly available.  I
apologize if I missed something but what exactly do you want to accomplish?

{Original Message removed}

2004\08\10@215949 by Rich

picon face
Josh:
Have you considered a +/- 5 volt operation using a +5 to -5 converter to get
the negative rail?

{Original Message removed}

2004\08\10@220612 by Josh Koffman

face picon face
Well I feel like an idiot for forgetting that trick. And that website
is great! I think that with a 10K pot, if I use a 1.2K resistor, I
come pretty close to a log curve. BTW, for other users of this page,
if you want a fractional K value (ie 1.2K), you need to flip down to
ohms and put in 1200.

Thanks Jinx!

Josh
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completely foolproof is to underestimate the ingenuity of complete
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On Wed, 11 Aug 2004 09:16:04 +1200, Jinx <joecolquittspamspam_OUTclear.net.nz> wrote:
> > though I can't even find small PCB log pots. Any ideas?
>
> I've never tried and measured (spreadsheet ?) this but it's said
> if you put a fixed R in parallel across the end terminals of a linear
> taper it approximates a log taper
>
> BTW, this might be useful for something
>
> http://www.mindspring.com/~clist/PotGraph.html

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2004\08\10@222930 by Josh Koffman

face picon face
Well, the short answer is...uh, I don't know. Like I said...analog
isn't my thing. Here's what I'm thinking though.

First off, this will be used to record live shows. The result isn't
going to be released as an album or anything, so I can tolerate some
noise, as long as it isn't distracting. Chances are the sound boards
I'll be hooking into in the clubs will be so old and abused, they will
have tons of noise to begin with.

Second, I'm reconsidering my single rail only requirements. If I go
with an ICL7660 type inverter, I could use an INA103 as the balanced
to unbalanced convertor, then use a regular opamp to boost the level
up. Then again, looking at things again, the ICL7660 will likely
oscillate right in the audio frequency range, and the INA103 wants a
minimum supply of +-9V.

Man this is tough! Any ideas? I wonder what they use in portable electronics.

Josh
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On Tue, 10 Aug 2004 21:50:08 -0400, Rich <@spam@rgrazia1KILLspamspamrochester.rr.com> wrote:
{Quote hidden}

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2004\08\10@223139 by Josh Koffman

face picon face
Personally, I want to mix basically a line level and a microphone
level signal together. The circuit will be duplicated to get a stereo
mix. The design that I linked to wasn't mine, just something I found
during numerous web searches. Will I notice the difference in using a
log pot vs an audio one? Basically the pot will be used to balance the
two sources at the beginning, then left alone the rest of the time.

Josh
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On Tue, 10 Aug 2004 21:54:26 -0400, Rich <KILLspamrgrazia1KILLspamspamrochester.rr.com> wrote:
> Hi Josh:
> I looked at the mixer design.  I was surprised that the pots were log taper
> and not audio taper pots.  Audio taper are abundantly available.  I
> apologize if I missed something but what exactly do you want to accomplish?

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2004\08\10@224628 by Kelly Kohls

picon face
Josh,

>If I go with an ICL7660 type inverter, I could use an INA103 as the
balanced
>to unbalanced convertor, then use a regular opamp to boost the level
>up.

Have a look at the Analog Devices SSM2142 and SSM2143 for the balanced to
unbalanced conversions.  I've used these in an audio project and they seem
to work well.

Kelly Kohls, N5TLE
Dallas, Texas
There never enough time to do it right, but plenty of time to do it over.

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2004\08\10@225703 by Josh Koffman

face picon face
Hi Kelly, haven't seen you in a while! Thanks for the tip. Years back
I ordered samples, I might have to try and find them again. They don't
spec a minimum supply voltage, just a maximum of +-18V. What did you
run them at?

Thanks,

Josh
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On Tue, 10 Aug 2004 21:47:22 -0500, Kelly Kohls <RemoveMEkkohlsTakeThisOuTspamprodigy.net> wrote:
> Have a look at the Analog Devices SSM2142 and SSM2143 for the balanced to
> unbalanced conversions.  I've used these in an audio project and they seem
> to work well.

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2004\08\10@231828 by Kelly Kohls

picon face
Josh,

>Hi Kelly, haven't seen you in a while!

I've been in lurk mode.

>They don't spec a minimum supply voltage, just a maximum of +-18V. What did
you
>run them at?

+/-15V.  I used them in conjunction with the TI PGA2310 audio volume control
device.  The combined devices provided a simple way to convert a balanced
signal to unbalanced, digitally control the level and convert the signal
back to balanced.  I also discovered that an additional op amp on the output
of the PGA2310 helped prevent annoying pops when the level was changed.

Hope this helps.

Kelly Kohls, N5TLE
Dallas, Texas
There never enough time to do it right, but plenty of time to do it over.

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2004\08\11@040522 by Nigel Orr

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pic microcontroller discussion list <> wrote:
> mixer that sums up some line level signals. The ideal situation would
> be to now have a balanced line receiver/preamp module that bumps the
> level up to match the line inputs. Then I just do the opamp summing
> mixer and I'm good to go.

Have a look at the Analog Devices SSM2016/SSM2017 (one of those part
numbers should be right, IIRC).  They're not cheap, but I've used them in
the past for quick and easy balanced inputs and outputs.  If you're not
experienced in opamp design and this is a one-off, I'd recommend them
highly.

Nigel
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2004\08\11@045823 by David Duffy

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face
Nigel Orr wrote:

>pic microcontroller discussion list <> wrote:
>
>
>>mixer that sums up some line level signals. The ideal situation would
>>be to now have a balanced line receiver/preamp module that bumps the
>>level up to match the line inputs. Then I just do the opamp summing
>>mixer and I'm good to go.
>>
>>
>
>Have a look at the Analog Devices SSM2016/SSM2017 (one of those part
>numbers should be right, IIRC).  They're not cheap, but I've used them in
>the past for quick and easy balanced inputs and outputs.  If you're not
>experienced in opamp design and this is a one-off, I'd recommend them
>highly.
>
>

I've not heard of the SSM2016 but the SSM2017 *is* discontinued.
Burr Brown makes the INA217 (IIRC) as a drop-in replacement.
And yes, yery easy to get going. The datasheet has all you'll need.
David...

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2004\08\11@061244 by Nigel Orr

flavicon
face
David Duffy wrote:
> Nigel Orr wrote:
>> pic microcontroller discussion list <> wrote:
>>
>>> would be to now have a balanced line receiver/preamp module that
>>> bumps the level up to match the line inputs. Then I just do the
>>
>> Have a look at the Analog Devices SSM2016/SSM2017 (one of those part
>
> I've not heard of the SSM2016 but the SSM2017 *is* discontinued.

A couple of web searches suggest it is/was another audio preamp- I can't
get a datasheet, so I presume that it's gone too.  It's been a few years
since I last used the 2017 (at least 5 years), it's a shame it's been
ditched.

> Burr Brown makes the INA217 (IIRC) as a drop-in replacement.

That's good news, thanks.

Nigel
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2004\08\11@063804 by Russell McMahon

face
flavicon
face
I'm sure that a solution using integrated balanced front end amplifiers, as
many people suggest, is a low development and construction pain route, but
it is unlikley to be as cheap as less integrtaed alternatives. There are
vast numbers of op-amp based differential amplifier solutions out there. An
utterly superb place to look for application notes for all things analog is
Linear technolgies app note library.

Publications generally

       http://www.linear.com/pub/

Application notes

   http://www.linear.com/pub/doc_group.html?pub_type=app

_____________________________________________

Misc app notes of variable usefulness


Analog Devices SSM2135 dual single supply audio opamp
Available digikey. Not overly cheap.
Some good ideas in data sheet though.


http://www.analog.com/UploadedFiles/Data_Sheets/527742802SSM2135_0.pdf

AD AN115 - balanced low noise microphone amplifier design.
Cheating again !!!! :-)
Sounds to be exactly what you want EXECPT not single supply as shown.

   http://www.datasheetarchive.com/cgi-bin/q.php?pi=2261


http://212.57.231.17/datasheetarchive/Datasheets/AnalogDevices/DS5634.pdf

_____________________________________________

Large number of audio amplifier ccts
Most (?all) the below came via here)

       http://www.discovercircuits.com/A/a-audioamp.htm

Low noise balanced microphone preamp - split supply

       http://sound.westhost.com/project66.htm


Totally OTT FEt preamp just for interesty - +/-24v !

       http://www.borbelyaudio.com/index32.htm


How the professionals do it.
They cheat ! :-) - INA163 front end !!!

       http://www.rane.com/pdf/ms1bsch.pdf

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2004\08\11@082054 by Olin Lathrop

face picon face
Rich wrote:
> I looked at the mixer design.  I was surprised that the pots were log
> taper and not audio taper pots.

I thought audio taper WAS log taper.  The point is to have a fixed rotation
angle of the pot change the loudness by a percieved fixed amount.  Since
human sound perception is logarithmic, in the olde phashioned days before
digital processing, volume control knobs had a logarithmic profile.  Maybe
"audio" taper has some deviation from logarithmic at the high or low end
(human perception is MOSTLY logarithmic), but even if that is the case, I
expect there won't be a huge distinction for hobby projects.


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2004\08\11@100754 by Josh Koffman

face picon face
Good links Russell. I'm now looking at the SSM2135 datasheet. Looks
nice, plus good example circuits. Of course, Digikey wants USD$5 each!
I'll see if I can get some samples.  On page 11 of the datasheet, they
show a balanced line receiver. I believe they're using 1/2 of an
SSM2135 to generate a 2V signal to bias one of the other 2135s. Since
they are so expensive, would it work if I used an external voltage
reference chip rather than one of the 2135s?

I had seen the link page you mentioned as well. They also have a small
mixer page, which is where I got the 6 channel mixer link I posted
yesterday. If I go with the 2135s for balanced line receivers, plus
then use more for mic preamps, I only have to find a single opamp to
act as the final slight boost amp in that circuit. I'm looking at the
TLC272 (only because I have some on hand), but I'm open to
suggestions.

Thanks!

Josh
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On Wed, 11 Aug 2004 22:38:02 +1200, Russell McMahon
<spamBeGoneapptechspamBeGonespamparadise.net.nz> wrote:
{Quote hidden}

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2004\08\11@123341 by Brian Aase

picon face
Portable mixers use anything from a single differential-input opamp,
to circuits with discrete transistors followed by opamps, to chips
like the INA103/INA163/TI2017 (can't exactly remember that last
number, it's a replacement for the SSM2017).  It all depends on
the level of performance they want, and how much money they
plan to charge.  The first option I mentioned ought to work for
you, but it will have more residual noise than the fancier circuits.

If you want to contact me offlist, I can send you a copy of a
Famous Microphone Mixer Company's product schematic,
but I suspect you may be put off by the complexity.  My suggestion
is to start with the simplest possible design, and see if it's
performance is good enough for your intended purpose.

Brian Aase

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2004\08\11@124212 by Brian Aase

picon face
Ideally, yes it is.  But (almost) all commonly used potentiometers that claim
"audio taper" actually use a piecewise linear approximation that is just
tolerably close to logarithmic over a few (maybe four) decades at best.
Looking at the published curves from Alps, Noble, Panasonic, etc.
visually suggests that only two segments are generally used.

The last time I actually saw a true, guaranteed logarithmic-taper pot was
back in the days of Allen-Bradley, and they charged a bundle for the things!

Brian Aase

> I thought audio taper WAS log taper.  The point is to have a fixed rotation
> angle of the pot change the loudness by a percieved fixed amount.  Since
> human sound perception is logarithmic, in the olde phashioned days before
> digital processing, volume control knobs had a logarithmic profile.  Maybe
> "audio" taper has some deviation from logarithmic at the high or low end
> (human perception is MOSTLY logarithmic), but even if that is the case, I
> expect there won't be a huge distinction for hobby projects.

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2004\08\11@154951 by Dwayne Reid

flavicon
face
At 08:27 PM 8/10/2004, Josh Koffman wrote:

>Second, I'm reconsidering my single rail only requirements. If I go
>with an ICL7660 type inverter,

Hi there, Josh.

I've been following this discussion but didn't get a chance to respond 'til
now.

1) pots: Digi-key part numbers

P2G1103-ND POT 10K OHM 12MM VERT MET BUSHING
P2T3103-ND POT 10K OHM 12MM HORZ MET BUSHING

These are nice and small and are PC mount.  You can cut the shafts down to
whatever size you need.

2) bipolar supply: you don't really need one but it does make things easier
if you have a negative rail.  If you really do have to stick with a single
supply rail, create an artificial ground with a voltage divider followed by
a buffer.  This means that all your inputs and outputs have to be
capacitively coupled.  While this is not a problem for the output, it *is*
a problem for balanced inputs: you have to ensure that the capacitors are
matched or the CMRR goes out the window at low frequencies.  I've got a
couple of boards that do this and it is a *pain* matching all those caps.

If you don't mind my asking - why not just use 2- 9v batteries?  Or, if
current consumption is a problem, 2- 9V battery packs built from AA cells.

The lowest noise op-amp I've used to date is the LT1028.  But it's a
current hog and runs warm from a bipolar 12V supply.

3) Microphone pre-amp chips: an old favorite is the ssm2017 from Analog
Devices.  This part was discontinued but one of the disti reps told me
recently that Analog Devices was going to bring it back because of customer
demand.  It is available from places like America II right now but you pay
a premium from those guys.  However, if you need only a few, that is by far
the most cost effective easy solution.

dwayne

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2004\08\12@094831 by Rich

picon face
You could be correct , Olin.  I have never actually graphed rotation versus
resistance on all of the pots.  I am aware, however, that pots specified as
log taper, log log taper, linear taper and audio taper are available.  I
have never personally substituted a log taper for an audio taper pot.
Although I am aware that humans do hear in discrete levels of change I did
not know that it is in exact logarithmic increments.  Thank you for your
clarification.  I am always learning something from the list.  It's Great.



{Original Message removed}

2004\08\14@015355 by Paul Hutchinson

picon face
> -----Original Message-----
> [RemoveMEPICLISTspamTakeThisOuTMITVMA.MIT.EDU]On Behalf Of Olin Lathrop
> Sent: Wednesday, August 11, 2004 8:21 AM
>
> I thought audio taper WAS log taper.  The point is to have a fixed
rotation
<snip>

Yes audio taper is a log taper but, it is one of two available log tapers.
The 50% rotation point could be at 10% or 90% of full resistance.

IIRC, the Variable Resistive Components Institute standard, names the audio
taper as logarithmic and the other as reverse logarithmic. So, when a pot is
specified as just logarithmic it should be audio taper. Reverse logarithmic
pots were often used for contrast controls on scopes.

Paul

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2004\08\14@021125 by Jinx

face picon face
> Reverse logarithmic pots were often used for contrast controls
> on scopes

And log-antilog pots as amplifier balance controls, often with
a loudness tap

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2004\08\14@031219 by Rich

picon face
Thank you for the clarification, Paul.
----- Original Message -----
From: "Paul Hutchinson" <paullhutchinsonEraseMEspam.....YAHOO.COM>
To: <EraseMEPICLISTspamMITVMA.MIT.EDU>
Sent: Saturday, August 14, 2004 1:54 AM
Subject: Re: [EE:] General Opamp questions


> > {Original Message removed}

2004\08\16@132635 by dr. Imre Bartfai

flavicon
face
Hi,

for single supply audio apps I recommend NE5532 (obsolete) or its
successor LM833. Works great!

Imre


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On Tue, 10 Aug 2004, Rich wrote:

> Josh:
> Have you considered a +/- 5 volt operation using a +5 to -5 converter to get
> the negative rail?
>
> {Original Message removed}

2004\08\23@194421 by EBoggs

picon face
In a message dated 8/10/2004 10:03:54 PM Eastern Daylight Time,
RemoveMErgrazia1EraseMEspamEraseMEROCHESTER.RR.COM writes:
> Hi all. Few questions about opamps. If I see a circuit running off a
> split power supply, but the negative voltage is only used for the
> opamps, can I redesign it using single power supply opamps such as the
> TLC272? If I must use a split power supply, would something like the
> http://focus.ti.com/docs/prod/folders/print/pt5062.html from TI
> (+5Vin, -15+15Vout) be a bad idea due to switching noise? This is for
> audio purposes.
Can you use the +/- 12vdc from a max232 chip. I was going to try it myself.
Not much
drive current.


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2004\08\23@225505 by Rich

picon face
This was not said by Rich.  I sometimes also get confused by replies to a
posted message.  Rich suggested an op amp similar to the LM324 which is nice
because it has PNP input transistors, which, therefore, can be ground
referenced.  A couple of zeners (with low ESR capacitors) can split a single
ended supply because they do have a low impedance.  But there is a great
variety of solutions to that problem.


{Original Message removed}

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