Audio Attenuator

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Chris M. White

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Jun 8, 2021, 4:29:52 PMJun 8
to
Hi guys,

I have an old vintage HP audio osciallator which I want to use for
some experimentation to get more practice in electronics. Its output
is continually variable between 4 and 20 volts. Problem is, for some
experiments I have in mind, I need it to output only between 1mV and
10mV. The oscailator's output impedance is 600 ohms it states.
Can anyone suggest a simple passive attenuator I could build from
easily available components which would give me this much lower output
please?
thanks!

Phil Hobbs

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Jun 9, 2021, 4:06:52 AMJun 9
to
A bit more detail would be useful.

However, something like a resistive voltage divider will probably be a
good place to start.


10k
GEN 0----RRRRR----*----0 OUT
|
R
R 10 ohms
R
|
|
GND

To get down to 1 mV, you can hang a pot on the output. Figuring out
just how to do that would be a step forward.

Cheers

Phil Hobbs

Jasen Betts

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Jun 9, 2021, 4:30:47 AMJun 9
to
a simple resistive divider will give a fixed ratio reduction in
amplitude, unfortunately that won't cover the whole 10:1 range you
want as your input only has 5:1 adjustment.

You could use a potentiometer to make an adjustable attenuator and get
a variable reduction that way.


--
Jasen.

Chris M. White

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Jun 9, 2021, 11:24:08 AMJun 9
to
On Wed, 9 Jun 2021 04:06:44 -0400, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:

>Chris M. White wrote:
>> Hi guys,
>>
>> I have an old vintage HP audio osciallator which I want to use for
>> some experimentation to get more practice in electronics. Its output
>> is continually variable between 4 and 20 volts. Problem is, for some
>> experiments I have in mind, I need it to output only between 1mV and
>> 10mV. The oscailator's output impedance is 600 ohms it states.
>> Can anyone suggest a simple passive attenuator I could build from
>> easily available components which would give me this much lower output
>> please?
>> thanks!
>>
>
>A bit more detail would be useful.

I'm happy to oblige. Anything specific?

>
>However, something like a resistive voltage divider will probably be a
>good place to start.
>
>
> 10k
>GEN 0----RRRRR----*----0 OUT
> |
> R
> R 10 ohms
> R
> |
> |
> GND
>
>To get down to 1 mV, you can hang a pot on the output. Figuring out
>just how to do that would be a step forward.

What's the problem in that? Seems simple enough to my simple mind!

Phil Hobbs

unread,
Jun 9, 2021, 11:37:09 AMJun 9
to
On 6/9/21 11:24 AM, Chris M. White wrote:
> On Wed, 9 Jun 2021 04:06:44 -0400, Phil Hobbs
> <pcdhSpamM...@electrooptical.net> wrote:
>
>> Chris M. White wrote:
>>> Hi guys,
>>>
>>> I have an old vintage HP audio osciallator which I want to use for
>>> some experimentation to get more practice in electronics. Its output
>>> is continually variable between 4 and 20 volts. Problem is, for some
>>> experiments I have in mind, I need it to output only between 1mV and
>>> 10mV. The oscailator's output impedance is 600 ohms it states.
>>> Can anyone suggest a simple passive attenuator I could build from
>>> easily available components which would give me this much lower output
>>> please?
>>> thanks!
>>>
>>
>> A bit more detail would be useful.
>
> I'm happy to oblige. Anything specific?

What's the load? Any DC involved?
>
>>
>> However, something like a resistive voltage divider will probably be a
>> good place to start.
>>
>>
>> 10k
>> GEN 0----RRRRR----*----0 OUT
>> |
>> R
>> R 10 ohms
>> R
>> |
>> |
>> GND
>>
>> To get down to 1 mV, you can hang a pot on the output. Figuring out
>> just how to do that would be a step forward.
>
> What's the problem in that? Seems simple enough to my simple mind!
>

Well, if you understand pots, you understand voltage dividers already.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
https://hobbs-eo.com

Phil Allison

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Jun 9, 2021, 8:24:02 PMJun 9
to
Chris M. White wrote:
-----------------------------
>
> >A bit more detail would be useful.
> I'm happy to oblige. Anything specific?

** What old HP have you got?

Sure it has not been modified to get only 4-20V out ?
Seems weird otherwise.


..... Phil

Chris M. White

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Jun 10, 2021, 5:34:53 PMJun 10
to
On Wed, 9 Jun 2021 11:37:00 -0400, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:

>On 6/9/21 11:24 AM, Chris M. White wrote:
>> On Wed, 9 Jun 2021 04:06:44 -0400, Phil Hobbs
>> <pcdhSpamM...@electrooptical.net> wrote:
>>
>>> Chris M. White wrote:
>>>> Hi guys,
>>>>
>>>> I have an old vintage HP audio osciallator which I want to use for
>>>> some experimentation to get more practice in electronics. Its output
>>>> is continually variable between 4 and 20 volts. Problem is, for some
>>>> experiments I have in mind, I need it to output only between 1mV and
>>>> 10mV. The oscailator's output impedance is 600 ohms it states.
>>>> Can anyone suggest a simple passive attenuator I could build from
>>>> easily available components which would give me this much lower output
>>>> please?
>>>> thanks!
>>>>
>>>
>>> A bit more detail would be useful.
>>
>> I'm happy to oblige. Anything specific?
>
>What's the load? Any DC involved?

No DC and very high impedance load (> 1M ohm)


>>
>>>
>>> However, something like a resistive voltage divider will probably be a
>>> good place to start.
>>>
>>>
>>> 10k
>>> GEN 0----RRRRR----*----0 OUT
>>> |
>>> R
>>> R 10 ohms
>>> R
>>> |
>>> |
>>> GND
>>>
>>> To get down to 1 mV, you can hang a pot on the output. Figuring out
>>> just how to do that would be a step forward.
>>
>> What's the problem in that? Seems simple enough to my simple mind!
>>
>
>Well, if you understand pots, you understand voltage dividers already.

My main concern was not to draw too much from the already quite high
impedance (600 ohms) of the source generator. Did you allow for that
in the values you came up with?
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