Question on pre design for Kevin A. (or anyone else)

[Guest]

Archived from groups: rec.audio.pro (More info?)

What would be the most cost/performance effective way today
using electronics to achieve continuous trim for multiple
pre channels using a single control and having tight
tracking? Ganged, rotary switched resistors not of interest.


Thanks,

Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

"Bob Cain" <arcane@arcanemethods.com> wrote in message
news:d50nll02a35@enews4.newsguy.com...
>
> What would be the most cost/performance effective way today
> using electronics to achieve continuous trim for multiple
> pre channels using a single control and having tight
> tracking? Ganged, rotary switched resistors not of interest.
>
>
>

parallel VCAs (voltage controlled amplifier)

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

TimPerry wrote:
> "Bob Cain" <arcane@arcanemethods.com> wrote in message
> news:d50nll02a35@enews4.newsguy.com...
>
>>What would be the most cost/performance effective way today
>>using electronics to achieve continuous trim for multiple
>>pre channels using a single control and having tight
>>tracking? Ganged, rotary switched resistors not of interest.
>>
>>
>>
>
>
> parallel VCAs (voltage controlled amplifier)

Got a part number that you think would not introduce too
much noise or distortion in the front end of a pre? It's
pretty much got to be the first gain stage.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

Bob Cain wrote:

> What would be the most cost/performance effective way today
> using electronics to achieve continuous trim for multiple
> pre channels using a single control and having tight
> tracking? Ganged, rotary switched resistors not of interest.

Give a real world application.

IME multiple mics are never matched *that* tightly, and their usage
isn't matched *that* tightly.

This is a recording forum right - all fine level setting is deferred
to the mix, right?

In SR - well it's meatball surgery so existing analog pots with all
their warts, still get the job done. Besides, you also have the faders
for fine settings.

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

Bob Cain wrote:
> What would be the most cost/performance effective way today
> using electronics to achieve continuous trim for multiple
> pre channels using a single control and having tight
> tracking? Ganged, rotary switched resistors not of interest.
>

I am having difficulty understanding the question exactly. It seems that
you are asking about many ganged channels, all having their gains
adjusted at once.

If continuous really mean continuous, then there is only one practical
solution, that is VCA (voltage controlled amplifiers).

If finite step size is allowed, then using digital i.c. gain pots is an
option. That is, there are chips that have digital lines to control
their internal tapped resisters. The digital lines are just fed to all
pots.

http/www.analog.com/digital_pots.html

http/www.maxim-ic.com/appnotes.cfm/appnote_number/3484

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http/www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

In article <d50nll02a35@enews4.newsguy.com> arcane@arcanemethods.com writes:

> What would be the most cost/performance effective way today
> using electronics to achieve continuous trim for multiple
> pre channels using a single control and having tight
> tracking? Ganged, rotary switched resistors not of interest.

I'm not Kevin, thank goodness, but how about digitally controlled
attenuators? The steps are quantized, but you should be able to get
ones with fine enough resolution to seem continuous.

--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

Bob Cain wrote:
>
> What would be the most cost/performance effective way today using
> electronics to achieve continuous trim for multiple pre channels using a
> single control and having tight tracking? Ganged, rotary switched
> resistors not of interest.

Bob, what would be the point of this?

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

Bob Cain wrote:
> TimPerry wrote:
>> "Bob Cain" <arcane@arcanemethods.com> wrote in message
>> news:d50nll02a35@enews4.newsguy.com...
>>
>>> What would be the most cost/performance effective way today
>>> using electronics to achieve continuous trim for multiple
>>> pre channels using a single control and having tight
>>> tracking? Ganged, rotary switched resistors not of interest.
>>>
>>>
>>>
>>
>>
>> parallel VCAs (voltage controlled amplifier)
>
> Got a part number that you think would not introduce too
> much noise or distortion in the front end of a pre? It's
> pretty much got to be the first gain stage.
>

Your probably going to have to have some gain first, to use any standard
parts.

There is a very low noise VCA, its the AD602, we use it in ultrsound as
a time swept amplifier.

http/www.analog.com/en/prod/0,2877,AD602,00.html

It has a low impedance, so it would require at least an emitter follower
buffer to interface to a mic directly. Its distortion is well, I don't
know. Look it up.


Kevin Aylward
informationEXTRACT@anasoft.co.uk
http/www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

In article <d526dc12nk3@enews1.newsguy.com> arcane@arcanemethods.com writes:

> Got a part number that you think would not introduce too
> much noise or distortion in the front end of a pre? It's
> pretty much got to be the first gain stage.

This has been the problem in the past. Maybe it's better now. The
reason why most sound cards and many didigtal recorders don't have
input level controls is that adding a digitally controlled attenuator
would add a couple of dB of noise. Since they're in a spec war, nobody
wanted to publish a noise specification higher than it had to be even
though controlling the sensitivity of the input would be a great
convenience to the users who understand how to use such a control.



--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

In article <2YGdneQWVMQpX-nfRVn-1g@comcast.com> arnyk@hotpop.com writes:

> Give a real world application.
>
> IME multiple mics are never matched *that* tightly, and their usage
> isn't matched *that* tightly.

I can see this as a preamp for a multi-channel mic setup such as a 5.1
array, Holophone, Soundfield or that ATMOS (commercial products)
system that has an overall level control.


--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

Mike Rivers wrote:
> In article <2YGdneQWVMQpX-nfRVn-1g@comcast.com> arnyk@hotpop.com writes:
>
>
>> Give a real world application.
>>
>> IME multiple mics are never matched *that* tightly, and their usage
>> isn't matched *that* tightly.
>
>
> I can see this as a preamp for a multi-channel mic setup such as a 5.1
> array, Holophone, Soundfield or that ATMOS (commercial products)
> system that has an overall level control.


Bingo.

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

Arny Krueger wrote:
> Bob Cain wrote:
>
>
>>What would be the most cost/performance effective way today
>>using electronics to achieve continuous trim for multiple
>>pre channels using a single control and having tight
>>tracking? Ganged, rotary switched resistors not of interest.
>
>
> Give a real world application.

Ambisonic mic. In general, multiple capsules in an array to
capture and encode directional information.

> IME multiple mics are never matched *that* tightly, and their usage
> isn't matched *that* tightly.

The bane of Ambisonics but it works pretty well anyway. I
just don't want gains wandering relative to each other when
setting the overall record level of an array. If they do,
the encoding logic is all screwed up. I can compensate for
fixed differences in capsules to a large extent with
measurment based DSP but not for gains wandering with
respect to each other in use.

> This is a recording forum right - all fine level setting is deferred
> to the mix, right?

Not in this case. It's all about amplitude differences
among the channels so changing the overall gain should
introduce very little systematic error.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

Kurt Albershardt wrote:
> Mike Rivers wrote:
>>
>> I can see this as a preamp for a multi-channel mic setup such as a 5.1
>> array, Holophone, Soundfield or that ATMOS (commercial products)
>> system that has an overall level control.
>
>
>
> Bingo.

Indeed.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

"Bob Cain"
>
> What would be the most cost/performance effective way today using
> electronics to achieve continuous trim for multiple pre channels using a
> single control and having tight tracking? Ganged, rotary switched
> resistors not of interest.
>


** Is this for a mic-preamp ??

Real application or some asinine hypothetical ??




............ Phil

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

Phil Allison wrote:
> "Bob Cain"
>
>>What would be the most cost/performance effective way today using
>>electronics to achieve continuous trim for multiple pre channels using a
>>single control and having tight tracking? Ganged, rotary switched
>>resistors not of interest.
>>
>
>
>
> ** Is this for a mic-preamp ??

Yes.

>
> Real application or some asinine hypothetical ??

Real. The only box capable of it today is the Metric Halo
2882 and it's overkill for my app.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

Kevin Aylward wrote:

> Your probably going to have to have some gain first, to use any standard
> parts.
>
> There is a very low noise VCA, its the AD602, we use it in ultrsound as
> a time swept amplifier.
>
> http/www.analog.com/en/prod/0,2877,AD602,00.html
>
> It has a low impedance, so it would require at least an emitter follower
> buffer to interface to a mic directly. Its distortion is well, I don't
> know. Look it up.

Looks great! +/-.3dB gain accuracy should be fine. .1%
distortion (if that's what -60 dBc means) ain't wonderful
but I can live with that better than noise which is only 1.4
nV/rootHz.

0-40 dB gain is good enough if it's going into a converter
with 20 or so real bits. Gonna get some.


Many Thanks,

Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

Bob Cain <arcane@arcanemethods.com> wrote in
news:d5269002nk3@enews1.newsguy.com:

>
>
> Phil Allison wrote:
>> "Bob Cain"
>>
>>>What would be the most cost/performance effective way today
>>>using electronics to achieve continuous trim for multiple pre
>>>channels using a single control and having tight tracking?
>>>Ganged, rotary switched resistors not of interest.
>>>
>>
>>
>>
>> ** Is this for a mic-preamp ??
>
> Yes.
>
>>
>> Real application or some asinine hypothetical ??
>
> Real. The only box capable of it today is the Metric Halo
> 2882 and it's overkill for my app.
>
>
> Bob

How many simultaneous channels? You might consider a light
dependent resistor in the feedback path of an op-amp, controlled
by the brightness of a LED.

--
Bob Quintal

PA is y I've altered my email address.

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

Bob Quintal wrote:
> Bob Cain <arcane@arcanemethods.com> wrote in
> news:d5269002nk3@enews1.newsguy.com:
>
>
>>
>>Phil Allison wrote:
>>
>>>"Bob Cain"
>>>
>>>
>>>>What would be the most cost/performance effective way today
>>>>using electronics to achieve continuous trim for multiple pre
>>>>channels using a single control and having tight tracking?
>>>>Ganged, rotary switched resistors not of interest.
>>>>
>>>
>>>
>>>
>>>** Is this for a mic-preamp ??
>>
>>Yes.
>>
>>
>>> Real application or some asinine hypothetical ??
>>
>>Real. The only box capable of it today is the Metric Halo
>>2882 and it's overkill for my app.
>>
>>
>>Bob
>
>
> How many simultaneous channels?

Four.

> You might consider a light
> dependent resistor in the feedback path of an op-amp, controlled
> by the brightness of a LED.

Hmmm, that's a new idea! (At least for this app.) Any idea
how well such devices track? I'll look into it but I'll bet
that noise will be a signifigant problem; noise from the
light source as well as from the device itself. Definitely
worth an investigation, though, because it's so darned simple.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

Bob Cain wrote:

> What would be the most cost/performance effective way today
> using electronics to achieve continuous trim for multiple
> pre channels using a single control and having tight
> tracking? Ganged, rotary switched resistors not of interest.

If you can live with 1dB steps TI's PGA2500. Rather a good mic amp in
its own right. Gain is controlled by an SPI interface.

Graham

 

[Guest]

Archived from groups: rec.audio.pro (More info?)

On Sat, 30 Apr 2005 12:52:22 -0700, Bob Cain
<arcane@arcanemethods.com> wrote:

>
>What would be the most cost/performance effective way today
>using electronics to achieve continuous trim for multiple
>pre channels using a single control and having tight
>tracking? Ganged, rotary switched resistors not of interest.

There's the (lamp or LED)/CDS photocell combination such as the
Vactrol brand name or cheap surplus ones such as this:

http/www.goldmine-elec-products.com/prodinfo.asp?number=G15396&variation=&aitem=1&mitem=1

Running a control current through each LED of several such units
and using the photocell resistance in the preamp feedback circuit for
each channel would 'work', but I understand CDS photocells don't have
very consistent light-resistance characteristics from one unit to the
next (I wonder if they're temperature-sensitive as well). So, use a
12-bit A/D to read the control voltage (from a front-panel gain
potentiometer), and use a microcontroller to generate several outputs,
each calibrated for its particular LED/photocell combination.
Calibration is not something one wants to do in production, but
since you've already put a microprocessor in there, have a path from
the micro to the pre inputs, so it injects a known level signal, and
then measure each output in 1dB steps over the whole gain range of
each preamp, writing each LED current value to FLASH memory (you DID
pick a chip that can write FLASH under program control, didn't you?).
Values between 1dB steps (from that 12-bit word from the front-panel
control) can be interpolated by the processor.
A pushbutton, perhaps on the back panel, would initiate
calibration.

It appears you want this for production


If you want a pure analog solution, there's the idea of the
front-panel knob adjusting vanes between small lamps or LED's and
photocells, sort of a multichannel Morley volume pedal behind a front
panel. But that could have 'issues', it might need manual calibration.


>Thanks,
>
>Bob

-----
http/mindspring.com/~benbradley