My new digital FM tuner puts out too strong a signal compared to my
other inputs (TV and CD). I want to install a dual potentiometer
between the tuner and preamp to reduce the volume. What is the best
value pot to use for this. I have ordered 50K, 100K, 250K and 500K from
Mouser (the pots are cheap - the shipping is not).


---MIKE---
In the White Mountains of New Hampshire
(44° 15' N - Elevation 1580')

On Sat, 3 May 2008 13:00:52 -0400, (---MIKE---)
wrote:

My new digital FM tuner puts out too strong a signal compared to my
other inputs (TV and CD). I want to install a dual potentiometer
between the tuner and preamp to reduce the volume. What is the best
value pot to use for this. I have ordered 50K, 100K, 250K and 500K from
Mouser (the pots are cheap - the shipping is not).


IIRC, 50K should work OK.


---MIKE---
In the White Mountains of New Hampshire
(44° 15' N - Elevation 1580')
--
Mark Lloyd
http://notstupid.laughingsquid.com

"So far as I can remember, there is not one word
in the Gospels in praise of intelligence."
--Bertrand Russell

---MIKE--- wrote:
My new digital FM tuner puts out too strong a signal compared to my
other inputs (TV and CD). I want to install a dual potentiometer
between the tuner and preamp to reduce the volume. What is the best
value pot to use for this. I have ordered 50K, 100K, 250K and 500K
from Mouser (the pots are cheap - the shipping is not).


Hint: If there are three terminals that connect to the innards of the pot,
short two adjacent ones together (center and either side).

This prevents a full open circuit when the wiper inside makes a poor contact
or hits a bump.

HeyBub wrote:

---MIKE--- wrote:

My new digital FM tuner puts out too strong a signal compared to my
other inputs (TV and CD). I want to install a dual potentiometer
between the tuner and preamp to reduce the volume. What is the best
value pot to use for this. I have ordered 50K, 100K, 250K and 500K
from Mouser (the pots are cheap - the shipping is not).



Hint: If there are three terminals that connect to the innards of the pot,
short two adjacent ones together (center and either side).

This prevents a full open circuit when the wiper inside makes a poor contact
or hits a bump.



That would only work if he puts the pots in SERIES with the signals and
inputs.

I think he's more likely to use them as potentiometers, in which case
your offering won't work.

Peace,

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.98*10^14 fathoms per fortnight.

On Sat, 3 May 2008 15:34:20 -0500, "HeyBub"
wrote:

---MIKE--- wrote:
My new digital FM tuner puts out too strong a signal compared to my
other inputs (TV and CD). I want to install a dual potentiometer
between the tuner and preamp to reduce the volume. What is the best
value pot to use for this. I have ordered 50K, 100K, 250K and 500K
from Mouser (the pots are cheap - the shipping is not).


Hint: If there are three terminals that connect to the innards of the pot,
short two adjacent ones together (center and either side).

This prevents a full open circuit when the wiper inside makes a poor contact
or hits a bump.


I've seen a lot of audio wiring diagrams, and that's not the way it's
done. IIRC you connect the fixed resistor across the source and the
wiper of the pot to the load. The source never has less than 50 ohms
across it.
--
Mark Lloyd
http://notstupid.laughingsquid.com

"So far as I can remember, there is not one word
in the Gospels in praise of intelligence."
--Bertrand Russell

On Sat, 03 May 2008 17:03:15 -0500, Mark Lloyd
wrote:

On Sat, 3 May 2008 15:34:20 -0500, "HeyBub"
wrote:

---MIKE--- wrote:
My new digital FM tuner puts out too strong a signal compared to my
other inputs (TV and CD). I want to install a dual potentiometer
between the tuner and preamp to reduce the volume. What is the best
value pot to use for this. I have ordered 50K, 100K, 250K and 500K
from Mouser (the pots are cheap - the shipping is not).


Hint: If there are three terminals that connect to the innards of the pot,
short two adjacent ones together (center and either side).

This prevents a full open circuit when the wiper inside makes a poor contact
or hits a bump.


I've seen a lot of audio wiring diagrams, and that's not the way it's
done. IIRC you connect the fixed resistor across the source and the
wiper of the pot to the load. The source never has less than 50 ohms
across it.

Sorry, for the messup. That was it's never greater than 50K ohms.
--
Mark Lloyd
http://notstupid.laughingsquid.com

"So far as I can remember, there is not one word
in the Gospels in praise of intelligence."
--Bertrand Russell

---MIKE--- wrote:
My new digital FM tuner puts out too strong a signal compared to my
other inputs (TV and CD). I want to install a dual potentiometer
between the tuner and preamp to reduce the volume. What is the best
value pot to use for this. I have ordered 50K, 100K, 250K and 500K from
Mouser (the pots are cheap - the shipping is not).


---MIKE---
In the White Mountains of New Hampshire
(44° 15' N - Elevation 1580')

You cannot get an effective result using a simple potentiometer. You are
attempting to attenuate a signal that involves voltage, current and a
frequency range without denigrating it. It requires more that simple
series resistance. You can buy audio frequency filters that are designed
for that purpose, to correct a mismatched input, they are not expensive,
although more than just the cost of a pot. Try one of your local
hobby/electronics stores. Failing that, try to obtain a circuit diagram
for your FM tuner and try playing with the front-end AGC. If you don't
have an adjustable AGC, then that is the part of the circuit that would
be more suited to adding a pot, or preferably and tunable RC network.

Regards

Mack

My new digital FM tuner puts out too strong a signal compared to my
other inputs (TV and CD). I want to install a dual potentiometer
between the tuner and preamp to reduce the volume. What is the best
value pot to use for this. I have ordered 50K, 100K, 250K and 500K from
Mouser (the pots are cheap - the shipping is not).

I would have ordered 1K, 5K, 10K, 25K, 50K

A more elegant look is to order an inline attenuator. They cost way more
than some pots and are not adjustable, but you won't see dangling wires.

peter wrote:
My new digital FM tuner puts out too strong a signal compared to my
other inputs (TV and CD). I want to install a dual potentiometer
between the tuner and preamp to reduce the volume. What is the best
value pot to use for this. I have ordered 50K, 100K, 250K and 500K from
Mouser (the pots are cheap - the shipping is not).

I would have ordered 1K, 5K, 10K, 25K, 50K

A more elegant look is to order an inline attenuator. They cost way more
than some pots and are not adjustable, but you won't see dangling wires.

Actually, with today's solid state
equipment, it usually means lower
impedance.
So, IMO, without knowing any details, I
would grab a 5K or 10K and because
it is audio, one with an audio taper.
However, if you have a 50K, use it. Wire
the fixed resistor (ends) across the
output of the tuner. Then wire the low
fixed
side (ground) and the wiper to the input
of the amp. It should work fine. I've
done this at our local access TV studio
for a tuner that plays over text. It's only
mono, but it's the same idea.

Mike,

Mack's advice is entirely incorrect.

Using pots as simple voltage dividers is an absolutely correct design
approach. The size of the pot ultimately is dictated by home much
attenuation you need as well as the impedance of the source (your tuner
output) and the load (your amplifier input) which are likely to be around
the industry standard of 47K ohms.

I would start with the 50K ohm pot which is just about perfect for this
impedance. Shunt the top end of the pot from the Line out to ground such
that the pot therefore has the total signal voltage appearing across it. Use
the wiper (the center contact) as your divided output, and this will be the
attenuated signal. As the wiper approaches the top end of the pot, you will
see the up to the maximum line out voltage, and conversely, as you turn the
pot towards the grounded end you will see further attenuation. Chose the
setting to match your other audio inputs.

Obviously you will need to do this the same on both on the left and right
channels.

Do not, under any circumstances, play with the tuner's AGC as "Mack the
Knife" suggests. This is not in any way whatsoever related to the audio
output of the tuner. This AGC gain control is used to adjust the RF
amplifiers to compensate for external signal level differences arriving at
the antenna, and is not in any way used to control audio output.

Nor is is there any reason to buy "an audio filer". This is not a filtering
issue whatsoever, since filters are for modifying frequency response. You do
not want to alter frequency response.

I am a graduate electrical engineer with EE degrees and 37 years of
experience in hardware design. You were on the correct track to begin with
by buying the pots. All you have to do is wire them up.

Smarty


"Mack the Knife" wrote in message
...
---MIKE--- wrote:
My new digital FM tuner puts out too strong a signal compared to my
other inputs (TV and CD). I want to install a dual potentiometer
between the tuner and preamp to reduce the volume. What is the best
value pot to use for this. I have ordered 50K, 100K, 250K and 500K from
Mouser (the pots are cheap - the shipping is not).


---MIKE---
In the White Mountains of New Hampshire
(44° 15' NO - Elevation 1580')

You cannot get an effective result using a simple potentiometer. You are
attempting to attenuate a signal that involves voltage, current and a
frequency range without denigrating it. It requires more that simple
series resistance. You can buy audio frequency filters that are designed
for that purpose, to correct a mismatched input, they are not expensive,
although more than just the cost of a pot. Try one of your local
hobby/electronics stores. Failing that, try to obtain a circuit diagram
for your FM tuner and try playing with the front-end ARC. If you don't
have an adjustable AGC, then that is the part of the circuit that would be
more suited to adding a pot, or preferably and tunable RC network.

Regards

Mack

On 5/3/2008 9:46 PM Mack the Knife spake thus:

---MIKE--- wrote:

My new digital FM tuner puts out too strong a signal compared to my
other inputs (TV and CD). I want to install a dual potentiometer
between the tuner and preamp to reduce the volume. What is the best
value pot to use for this. I have ordered 50K, 100K, 250K and 500K from
Mouser (the pots are cheap - the shipping is not).

You cannot get an effective result using a simple potentiometer. You are
attempting to attenuate a signal that involves voltage, current and a
frequency range without denigrating it. It requires more that simple
series resistance. You can buy audio frequency filters that are designed
for that purpose, to correct a mismatched input, they are not expensive,
although more than just the cost of a pot. Try one of your local
hobby/electronics stores. Failing that, try to obtain a circuit diagram
for your FM tuner and try playing with the front-end AGC. If you don't
have an adjustable AGC, then that is the part of the circuit that would
be more suited to adding a pot, or preferably and tunable RC network.

With all due respect, you're just plain wrong, and this is from
empirical evidence (I've done exactly what the OP is asking about,
between the line-out output from one receiver into the line-in input to
another, and it works just fine).

Besides, just look at the circuit diagram for a receiver, and you'll see
exactly what's been suggested--a simple potentiometer--between
preamplifier stages.


--
The best argument against democracy is a five-minute
conversation with the average voter.

- Attributed to Winston Churchill

Smarty, Thanks for your learned and commonsense reply. I have on order
in addition to the 50K, 100K, 250K, & 500K pots, a 5K and 10K. I will
experiment between the 10K (recommended by some) and the 50K to see what
works the best, I have also sent emails to Sangean (the maker of the
tuner) asking their opinion. I'm not holding my breath waiting for an
answer from them!


---MIKE---
In the White Mountains of New Hampshire
(44° 15' N - Elevation 1580')

Glad to help Mike. If your amp has a very low input impedance (which it
shouldn't) and falls well below the 47K ohm "standard" which is commonly
used, then you may find that the other pots will work better in the sense
that a larger fraction of their rotational range will be useful. The pot is
merely a voltage divider, and, as such, divides a ratio determined in part
by the input impedance of your amplifier input. You can experiment and see
which one works best, but any of the pots, once set, will do exactly the
same voltage division to give you the attenuation your are looking for.

Similarly, a pot with an "audio taper" rather than a "linear taper" will
make the adjustment in sound 'volume' more proportional, since the ear
perceives sound volume logarithmically and a linear pot seems to have an
unnaturally slow response when rotated. Even so, the ultimate voltage
division is still all that matters to get you the attenuation you are
looking for. Therefore any of them should work, but some will seem much more
fussy to set.

Good luck!

Smarty



"---MIKE---" wrote in message
...
Smarty, Thanks for your learned and commonsense reply. I have on order
in addition to the 50K, 100K, 250K, & 500K pots, a 5K and 10K. I will
experiment between the 10K (recommended by some) and the 50K to see what
works the best, I have also sent emails to Sangean (the maker of the
tuner) asking their opinion. I'm not holding my breath waiting for an
answer from them!


---MIKE---
In the White Mountains of New Hampshire
(44° 15' N - Elevation 1580')

On May 4, 10:22*am, Art Todesco wrote:
peter wrote:
My new digital FM tuner puts out too strong a signal compared to my
other inputs (TV and CD). *I want to install a dual potentiometer
between the tuner and preamp to reduce the volume. *What is the best
value pot to use for this. *I have ordered 50K, 100K, 250K and 500K from
Mouser (the pots are cheap - the shipping is not).

I would have ordered 1K, 5K, 10K, 25K, 50K

A more elegant look is to order an inline attenuator. They cost way more
than some pots and are not adjustable, but you won't see dangling wires.

Actually, with today's solid state
equipment, it usually means lower
impedance.
So, IMO, without knowing any details, I
would grab a 5K or 10K and because
it is audio, one with an audio taper.
* However, if you have a 50K, use it. *Wire
the fixed resistor (ends) across the
output of the tuner. *Then wire the low
fixed
side (ground) and the wiper to the input
of the amp. *It should work fine. *I've
done this at our local access TV studio
for a tuner that plays over text. *It's only
mono, but it's the same idea.

Depends on the impedance/s of the output of the sound source and the
input to the amplifier. The impedance of a so called 'line input'
connection bewteen out put of a tuner and input of amplifier could be
as low as 600 ohms!
Since the OP doesn not define really define 'too strong' it may be
wise to assume a reduction of around 6 to 12 db. And then jigger up a
resistor arrangement to reduce the audio voltages to achieve that sort
of reduction (one quarter the voltage for example will give power
reduction of about 16 times or roughly 12 db.) A 1k pot might be a
good starting point. Since it will presumably be rarely adjusted once
in place the type of taper etc. may not, unlike a regular volume
control that can be varied easily to the desired listening level, be
critical at all.

On May 4, 10:22*am, Art Todesco wrote:
peter wrote:
My new digital FM tuner puts out too strong a signal compared to my
other inputs (TV and CD). *I want to install a dual potentiometer
between the tuner and preamp to reduce the volume. *What is the best
value pot to use for this. *I have ordered 50K, 100K, 250K and 500K from
Mouser (the pots are cheap - the shipping is not).

I would have ordered 1K, 5K, 10K, 25K, 50K

A more elegant look is to order an inline attenuator. They cost way more
than some pots and are not adjustable, but you won't see dangling wires.

Actually, with today's solid state
equipment, it usually means lower
impedance.
So, IMO, without knowing any details, I
would grab a 5K or 10K and because
it is audio, one with an audio taper.
* However, if you have a 50K, use it. *Wire
the fixed resistor (ends) across the
output of the tuner. *Then wire the low
fixed
side (ground) and the wiper to the input
of the amp. *It should work fine. *I've
done this at our local access TV studio
for a tuner that plays over text. *It's only
mono, but it's the same idea.

BTW is thi mono or stereo? Or multi audio channel?

Terry asked:

BTW is thi mono or stereo? Or multi
audio channel?

This is two channel stereo. I have ordered dual pots and I am aware of
a potential tracking problem. I have had suggestions ranging from 1K to
50K so I am still unsure about the best value. I will probably start
with 10K


---MIKE---
In the White Mountains of New Hampshire
(44° 15' N - Elevation 1580')

From: (---MIKE---)
Terry asked:
BTW is thi mono or stereo? Or multi
*audio channel?
--------
This is two channel stereo. I have ordered dual pots and I am aware of a
potential tracking problem. I have had suggestions ranging from 1K to
50K so I am still unsure about the best value. I will probably start
with 10K
************************************---MIKE---
In the White Mountains of New Hampshire
(44° 15' N - Elevation 1580')
-----------------------
I had a similar situation a few years back with an office stereo sound
system and purchased a stereo attenuator from mcm electronics - it wires
in easliy - worked like a charm.

Roy Q.T. ~ US/NCU ~ E.E. Technician
[have tools, will travel]