# Parallel resistor in line level output

#### batata004

##### Member
I have a MONO LINE LEVEL OUTPUT and I want to share it with 2 devices (which will received the LINE LEVEL OUTPUT and use it for whatever reason). In one of those devices I need to use a 10K potentiometer in order to control the signal level that goes to one of those devices. See my drawing below, please.

My question is: does this 10k potentiometer affects the signal on device 1? I mean, will the signal get lower OR lose any bass? I am asking this, because as I am seeing, the potentiometer that was added is in parallel between + and -, so I think it should affect a little bit device 1 but I am not sure because I am pretty sure that devices 1 and 2 have high input impedance, so maybe this 10k resistor would not affect (less than 1%). But what do you think?

#### DonH56

##### Master Contributor
Technical Expert
Forum Donor
It depends on how strong (low impedance) the output of the source and the input impedance of the two devices. It will probably work OK, but 10k strikes me as a little low since you may not know any of that, so I would probably use a 50k or 100k.

#### MaxwellsEq

##### Addicted to Fun and Learning
My question is: does this 10k potentiometer affects the signal on device 1?
This is one of these "it might" situations.

Really, to answer the question, we'd need to know the output impedance of the driving device (and how high and stiff its voltage rails are). We'd need to know the impedance of the cables or how long they are, and we'd need to know the input impedance of the two devices.

You probably won't break anything, so you could build it and take some measurements.

#### Speedskater

##### Major Contributor
If the components are modern solid state units, the output impedance probably under a fer hundred Ohms (but some receivers have higher impedances).
The input impedance is probably in the neighborhood of of 10,000 Ohms.
The impedance and length of the connecting coax cables don't enter into the equation.

#### DonH56

##### Master Contributor
Technical Expert
Forum Donor
Yah, I expect a SS output would be in the 100-1000 ohm range, tubes on the high end of that and maybe above. For short cables they won't matter (I took a look at that but am too busy/lazy to look up the article, see my sig). 10k was the minimum suggested load for preamps for many years, and still is for the couple I checked, so the other input in parallel with 10k means a load less than that. Knowing nothing else, I'd get a 100k log or audio taper pot and call it done.

#### Speedskater

##### Major Contributor
On second thought:
The cable attached to the output of the 10k Ohm pot, needs to be short.

#### MaxwellsEq

##### Addicted to Fun and Learning
On second thought:
The cable attached to the output of the 10k Ohm pot, needs to be short.
That's what I thought - depending on impedances, there's a risk that this could by like a worst-case "passive preamp". It probably would be OK, but better to keep the wires short, just in case...

#### LTig

##### Master Contributor
Forum Donor
On second thought:
The cable attached to the output of the 10k Ohm pot, needs to be short.
Yep, and even more important with a 50k or 100k pot. Better have it directly at the input of device 2.

#### DonH56

##### Master Contributor
Technical Expert
Forum Donor
If the volume is near 0 so most of the 100k is to the load, and say there is 10' of regular coax around 30 pF/ft, that gives a corner around 1/(2*pi*100k*10*30pF) = 5.3 kHz. A 5' cable would yield around 10.6 kHz, and of course at higher volume the impact is less. E.g. a 5' cable at half volume, with 50k resistance, yields around 21 kHz.

OP

#### batata004

##### Member
Hello my friends, you are so smart and kind to provide details about your suggestion! I feel sorry that I didnt explain it right: the source of my signal is a smartphone (I believe most smartphones have a source impedance of up to 1000 ohm) and the destination are two PAN8610 mini amplifieres, each one connected to a speaker.

According to everything you said, I should use a 100k ohm instead of a 10k ohm right? I thought that using a too high resistor (pot) there would be very little current to drive the destination... I believed that because the source voltage is probably no more than 2V (line level), then using a 100k ohm, the current would be veeeeeery low...

So as I understood, I will have a better audio using 100k ohm, correct?

#### DonH56

##### Master Contributor
Technical Expert
Forum Donor
PAM8610? This? https://www.diodes.com/assets/Datasheets/products_inactive_data/PAM8610.pdf -- not recommended for new designs.

No input impedance in the datasheet I could see, and the fixed divider values refer to Table 1 that I could not find (maybe missed it). It does have on-chip volume control, using an external voltage you could provide using a pot from the supply, so maybe do that instead?

As for adding a volume control, there's no way to say the effect on the sound and best value to use without knowing at least (a) the input impedance of the amplifier and (b) length (and type) of cable after the control. If you are putting the control right next to the amp, then 100k is probably OK. If you have long cable after the control before the amp, then 10k or 20k might be better. All that really matters in this case is the voltage, since the amplifier's input should draw very little current, the capacitance set by the length of cable and amplifier's input capacitance (also unknown), and amplifier input impedance.

With too little knowledge, I would assume a short cable (1 m or less) from control to amp, and just try 20k to see how it works.

OP

#### batata004

##### Member
Thank you so much. One final question: why most of you guys told me I must have a very small cable after the potentiometer? A big cable would introduce a few ohms/capacitance, but why would that cause problems after the potentiometer and not before?

#### MaxwellsEq

##### Addicted to Fun and Learning
Thank you so much. One final question: why most of you guys told me I must have a very small cable after the potentiometer? A big cable would introduce a few ohms/capacitance, but why would that cause problems after the potentiometer and not before?
As I think a few people have pointed out, it may not be an issue.

As the discussion has continued, the consensus has been not to go with a 10k potentiometer, but perhaps a 100k with a taper. It's worth then thinking of this impedance as a potential divider with the load. The load is made up of the input impedance of downwind device and the impedance of the cable connecting your potentiometer to your load. The capacitance of the cable can then produce a low-pass filter that reduces the treble frequencies. @DonH56 in post https://audiosciencereview.com/foru...istor-in-line-level-output.41770/post-1478151 did the mathematics showing that the shorter the cable, the higher the frequency where this becomes a problem (i.e. 5.3k and 10.6k are not good, but 21k should be OK). As he pointed out - it's probably not a problem with sensible cable lengths, but it's generally considered good practice to minimise the cable after a "passive pre" for peace of mind!

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