Hi all
Firstly I am a complete newbie to all of this audio/elect. engineering. So apologies in advance if I seem confused, and thank you for any input or responses! Its my first foray into DIYAUDIO but I have learned a lot already. As I spend time on a classic car board being helped and helping others, I know how much value your help offers. I also ask you to be simple in your answers. I don't know the jargon beyond the very basics.
I am asking about Balance and Fade potentiometer controls for a very specific use case as a controller for stereo line level output from a BT receiving, splitting it to 4 channel, LF, RF, LR, RR in order to send it to a 4 channel simple 50W RMS amp. Before even diving into the idea of designing and building something, I would like to better understand some of the varying positions I have read about in my research of this subject.
Why? I want to be able to change the sound stage in my car while driving rather than via DSP presets on an expensive and big overly powerful amp. I am adding modern audio to a classic car (keeping a 'vintage' Blaupunkt head unit with cassette player. I am not looking to build a crazy system, just a 4 channel amp, better speakers and a BT ATX HD receiver. The BT receiver has no controller for the volume, it outputs stereo, not 4 channel, and has no balance and fader control.
Call me old fashioned but it’s nice to be able to make adjustments to fade/balance based on who is in the car and what music is playing. Since I can’t seem to find a line level fader/balance controller to buy, I figure why not try to build it.
In my research to date, I understand there are linear and taper pots, 10K and 100K recommendations for resistance, using non-Pot resistors methods, etc. All of which makes sense sort of, but I am left with some very basic questions…
For Example:
Stereo volume: 2 gang taper pot with inputs on left resistor track lugs and output on wipers for left and right volume.
Balance: dual gang linear pot gang linear pot with inputs on wiper lugs and output on both resistor track lugs. 4 signals out.
Fader: 4 gang linear pot (one per channel) with LF and RF inputs on left resistor track lugs and the LR and RR inputs on right resistor track lugs, outputs on wipers.
If this all makes sense and if would work, then here are my follow up questions…
I can solder wires and things together, get them mechanically mounted and working, but designing much more than the above is way above my pay grade!
Thanks for any input.
Firstly I am a complete newbie to all of this audio/elect. engineering. So apologies in advance if I seem confused, and thank you for any input or responses! Its my first foray into DIYAUDIO but I have learned a lot already. As I spend time on a classic car board being helped and helping others, I know how much value your help offers. I also ask you to be simple in your answers. I don't know the jargon beyond the very basics.
I am asking about Balance and Fade potentiometer controls for a very specific use case as a controller for stereo line level output from a BT receiving, splitting it to 4 channel, LF, RF, LR, RR in order to send it to a 4 channel simple 50W RMS amp. Before even diving into the idea of designing and building something, I would like to better understand some of the varying positions I have read about in my research of this subject.
Why? I want to be able to change the sound stage in my car while driving rather than via DSP presets on an expensive and big overly powerful amp. I am adding modern audio to a classic car (keeping a 'vintage' Blaupunkt head unit with cassette player. I am not looking to build a crazy system, just a 4 channel amp, better speakers and a BT ATX HD receiver. The BT receiver has no controller for the volume, it outputs stereo, not 4 channel, and has no balance and fader control.
Call me old fashioned but it’s nice to be able to make adjustments to fade/balance based on who is in the car and what music is playing. Since I can’t seem to find a line level fader/balance controller to buy, I figure why not try to build it.
In my research to date, I understand there are linear and taper pots, 10K and 100K recommendations for resistance, using non-Pot resistors methods, etc. All of which makes sense sort of, but I am left with some very basic questions…
- Is there an actual balance pot, one designed specifically for balance or fade or both combined? Not just a regular liner or taper POT? I have not yet found one online
- I understand the difference between linear and taper pots, is it correct that linear would be preferred or required for balance/fade functions?
- Is there a significant loss of signal quality if one uses a regular linear pot with say the left channel of a stereo signal into the wiper and the resistor track lugs as output for left front and left back channels? If so, why? This goes to my question of using a standard pot for balance. Is a taper pot more appropriate
- Can I simply arrange pots in a circuit such that volume, balance and fade are strung together to make the 4 outputs I need?
For Example:
Stereo volume: 2 gang taper pot with inputs on left resistor track lugs and output on wipers for left and right volume.
Balance: dual gang linear pot gang linear pot with inputs on wiper lugs and output on both resistor track lugs. 4 signals out.
Fader: 4 gang linear pot (one per channel) with LF and RF inputs on left resistor track lugs and the LR and RR inputs on right resistor track lugs, outputs on wipers.
If this all makes sense and if would work, then here are my follow up questions…
- Would this sound like crap?
- What would the input levels need to be for the output to be usable?
- What total resistance pots would be best, 10k, 100k, other?
I can solder wires and things together, get them mechanically mounted and working, but designing much more than the above is way above my pay grade!
Thanks for any input.
What you ask makes sense. But the 'simple' path wants special pots. The most direct path may be to get the factory radio out of a 1970s Cadillac and extract its faders. Much later, and this stuff was reduced to an integrated circuit. Similar to LM1035, but that's not it, and after 2 days of headbanging and even de-boxing my attic library, I can't find chips or docs.
Not any more. Older gear used a dual section pot with half of each track a short circuit, but in opposite directions.
This had no insertion loss at the center setting. Now with gain cheap, a single pot with wiper grounded can serve
as a balance control, provided there are series resistors in each line, to act as a voltage divider. This has insertion loss.
Linear is used for balance. Linear works because only small balance adjustments are typically needed.
Wiper is for the output with most volume control circuits, preferably into a high impedance.
Normally around 10k, except for tubes.
You need to read this:
https://sound-au.com/pots.htm
Thank you for the responses. Very helpful. Again as a total non-elect engineer, I am trying to understand a bit more about two parts of the discussion.
Two notes: interesting that insertion loss is called insertion loss. I would have expected to to be something like circuit length loss or just circuit loss - the loss caused by the length and complexity of the circuit componentry. Then again, maybe I have that wrong in concept as well?
Also in the balance example in the article, 100K pots are used. Again I see this a lot in what i read, 10K v. 100K... What happens if you use 20K or 50K, I assume the best pot resistance value should be relevant to the source value of the line ins?
I recently talked to an acquaintance who is an electronics engineer - but mostly a programmer. He is fairly young and basically echoed that no-one really does this anymore in analog. Just use a microprocessor of some sort and write some code.
Again - thanks for the info, all very interesting and leading to more questions.
The article you linked to was basically clear to me, reinforcing particularly that regularly available balance pots are not available, but a more complicated setup can be used with additional resistors to create the right 'profile' of the signal attenuation (maybe not the right word) of the output of a standard linear pot. Here's where I fall down... I am trying to understand how the resistors before the pot on the input side affect the curve of the output of the pot. I would think a single resistor would be constant in its resistance to the input signal before it reaches the pot and not have any effect? Also, if a linear tape is desired for balance controls, why affect the taper with a resister previous to make a better balance control as indicated in the article? Lastly, I still expect that when a dual gang, with reversed setups for use in balance control - that the center position will always yield partial signal for both sides, only by rotating full to one side do you get a full signal - not an issue except maybe downstream when trying to set the gain for on an amp input. Do you configure the amp for the max possible input or the 'balanced' input? I assume max to avoid clipping etc. but then wonder about losing potential volume on output. Maybe I am over thinking all of this.
Two notes: interesting that insertion loss is called insertion loss. I would have expected to to be something like circuit length loss or just circuit loss - the loss caused by the length and complexity of the circuit componentry. Then again, maybe I have that wrong in concept as well?
Also in the balance example in the article, 100K pots are used. Again I see this a lot in what i read, 10K v. 100K... What happens if you use 20K or 50K, I assume the best pot resistance value should be relevant to the source value of the line ins?
I recently talked to an acquaintance who is an electronics engineer - but mostly a programmer. He is fairly young and basically echoed that no-one really does this anymore in analog. Just use a microprocessor of some sort and write some code.
Again - thanks for the info, all very interesting and leading to more questions.
The use of a series resistor before the linear pot results in a nonlinear attenuation curve,
depending on the relative values of the resistor and pot. This circuit functions as a (variable)
voltage divider, sometimes called an L-pad.
The best analog audio equipment uses switched (low signal relays or rotary switch) metal film resistors,
and can have any taper desired by proper choice of resistor values. TVs and common consumer
gear of course use cheap solutions and are not focused on sound quality.
In general, lower resistor and pot values are better, due to lower noise and higher bandwidth.
depending on the relative values of the resistor and pot. This circuit functions as a (variable)
voltage divider, sometimes called an L-pad.
The best analog audio equipment uses switched (low signal relays or rotary switch) metal film resistors,
and can have any taper desired by proper choice of resistor values. TVs and common consumer
gear of course use cheap solutions and are not focused on sound quality.
In general, lower resistor and pot values are better, due to lower noise and higher bandwidth.
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