Actually, Bell described one decibel (one-tenth of a Bel) as the smallest change in volume a human can detect (steady state tone, no hearing defects). Bell was an audiologist. His initial interest in electricity was not to revolutionize world-wide communications; he was working on a hearing aid.

ak

bell is logarithmic scale yes? so increase 1bell = increase by 10? increase db by 1 increase db by 100?

 

Right. A trained listener with steady tones in a laboratory environment clocked humans at 1.1% of the voltage ratio.
Now, try that in front of a guitar amplifier with real music containing a peak to average ratio of ten to one, with two channels containing different information. Have you ever thought to yourself, "I should tell Paul McCartney to turn his volume knob up by 1%?"


We're trying not to dump it all on you at once. (You probably won't be doing anything so special that temperature tracking will be important in the first year.)

Now for some theory. Electric guitars often contain volume and tone controls in the range of 250,000 ohms, so guitar amplifiers are high impedance inputs, like 680,000 ohms. If your music supply has an impedance of less than 68,000 ohms, the guitar amplifier will believe that's just fine.

The other end is the music supply. Earphone outputs are usually designed to drive something way less than 100 ohms, so you can protect the music source with anything from 100 ohms to...68,000 ohms. Don't go to the 68,000 ohm end. It tends to pick up noise. I'm going with MrChips in the 100 ohm to 1000 ohm range.

any thoughts on my last two numbered points in post #1? viz:

5 I assume that part of the goal of having these resistors in the circuit is to protect the input circuitry (from shorting the stereo chanels) not just to protect the destination amp from being overpowered by the doubled voltage of the input signal. If so couldnt you put a diode in place of R3? Or maybe since we are dealing with AC(?) the diode wouldnt pass the other half of the signal. If so would this problem be insoluable, ncessiating the use of the resisotor(s)? Either way i dont want to ruin the audio amplifier in my smart phone!!

6 Does the summing box need to be shielded?

 

any thoughts on my last two numbered points in post #1? viz:

5 I assume that part of the goal of having these resistors in the circuit is to protect the input circuitry (from shorting the stereo chanels) not just to protect the destination amp from being overpowered by the doubled voltage of the input signal. If so couldnt you put a diode in place of R3? Or maybe since we are dealing with AC(?) the diode wouldnt pass the other half of the signal. If so would this problem be insoluable, ncessiating the use of the resisotor(s)? Either way i dont want to ruin the audio amplifier in my smart phone!!

6 Does the summing box need to be shielded?

got to get back to my shift. dam

 

A diode has no place in this circuit.
You can probably get away without shielding because you are going to follow instructions and stay down between 100 ohms and 1000 ohms so this circuit doesn't pick up a lot of noise.

 

A diode has no place in this circuit.

okay but why?
is that because of what i said. it would presumably block the current from signal wire to ground, thus eliminating possibility of shorting the two channels of the phones amp.

 

You can probably get away without shielding because you are going to follow instructions and stay down between 100 ohms and 1000 ohms so this circuit doesn't pick up a lot of noise.

yes i am going to follow instructions.
could you please tell me why the low resistance values will limit the noise. or just point me in the right direction so i can learn the answer myself.

 

just point me in the right direction

OK. The right direction is to start a new Thread.
A 3 resistor audio mixer is about as simple as a switch and a light bulb, but that question received half a dozen good responses. Now you want to ask about why a diode doesn't work like a resistor and how impedance and noise are related.
New Thread.

 

that question received half a dozen good responses.
New Thread.

Yes and I acknowledged/ replied to/ thanked everyone of them. What's your point exactly?

 

Now you want to ask about why a diode doesn't work like a resistor and how impedance and noise are related.
New Thread.

Ok I will start a new thread already. I was and remain unaware of what protocol I have broken. But I'll start a new thread.

I am only trying to learn by asking questions. I'm not ashamed of how dumb they are or how basic they are.

Thx for yr patience #12. I appreciate it. Always do, even if I cop what can only be described as your irascibility. I will never be rude back to you though.

 

What you have done is expand the range of your question into different areas that can use attention all their own.
How to connect a hand held audio source to a guitar amplifier? Three resistors. Very practical.
How noise and impedance interact? Why a diode is not the right thing? You just changed from practical application to theory. You need different people to go down that road. If you ask those questions separately, you will get a new crowd of people who are attuned to those aspects.

 

What you have done is expand the range of your question into different areas that can use attention all their own.
How to connect a hand held audio source to a guitar amplifier? Three resistors. Very practical.
How noise and impedance interact? Why a diode is not the right thing? You just changed from practical application to theory. You need different people to go down that road. If you ask those questions separately, you will get a new crowd of people who are attuned to those aspects.

Yes I see now. Thanks for the explanation. I'll be careful about that in the future. Thx #12

 

guitar amplifiers are high impedance inputs, like 680,000 ohms.

Oops. I slipped a digit. Fender guitar amplifiers use 68k for input impedance resistors...not 680K, but that's where I got the number. I just forgot how many zeros.
My bad.
The principles remain the same. Keep your input driver impedance below 6.8K ohms to avoid some very significant signal loss caused by the design of the tiny mixing network you seem to be building.

 

A 3 resistor audio mixer is about as simple as a switch and a light bulb

haha no its not methinks (see your post at # 32) joke joyce

 

Oops. I slipped a digit. Fender guitar amplifiers use 68k for input impedance resistors...not 680K, but that's where I got the number. I just forgot how many zeros.
My bad.
The principles remain the same. Keep your input driver impedance below 6.8K ohms to avoid some very significant signal loss caused by the design of the tiny mixing network you seem to be building.

thanks #12.

it will be cool to be able to do away with the coax link. but that for another thread hehe i will darken your doorway with this one day.

 

@Mellisa_K
There is a software solution to your problem as well. You can flip the phase of one channel and then simply ignore the ground pin on your output cable. Imply connect L and R or your output to the amplifier's input.

An audio editing tool (possibly even iPhone app) can flip one channel (see Studio One)

 

I have successfully completed this project and I just wanted to share my success with the people who helped me in this Thread.

As a reminder, Figure 1, below, shows the problem I wanted help with:

Figure 2, below, shows the solution (values of R1, R2 and R3) and Figure 3 shows the first stage wiring inside the cover of the half-inch male jack that goes into the guitar amplifier mono female input jack. The three resistors have been soldered into the the vacant space that will be the inside of the mono jack. (Note I have used a stereo jack - it was the only one I could find - and I shorted the two "live" lugs)

Figure 4, below, shows the other end of the coaxial lead which is a pre-wired stereo jack which fits into the female jack of the smart phone.

Figure 5, below shows the finally wired version of the mono jack shown in Figure 3, after the coax cable has been wired in and after R3 has been earthed and R1 and R2 have been covered with heat-shrink tubing to insulate them from the earthing lugs, framing of the jack

Figure 6, below, shows the final outcome. I can hear music!!

The final stereo to mono coax lead works very well. It doesnt appear to hum at the mono jack when I touch it. And i am definitely getting both channels through the guitar amp.

This is my first completed project. I'm very proud of it - especially my soldering. I still have the irrigation timer on the go, https://forum.allaboutcircuits.com/threads/relay-switching-circuit.133857/ , and plans to build a proximity capacitance switch for my disabled uncle. [Delays caused by workload earning a living :-( ]

Thankyou to all those who helped in this thread (in order of appearance):
@#12
@AlbertHall
@dendad
@AnalogKid
@MrChips
@Alec_t
@GopherT

You are all very kind and very knowledgeable!

 

Excellent! The sense of accomplishment doesn't come often enough, I love seeing the success.

 

OUTSTANDING.

ak

 

Yes I know what you mean! I love DIY. such a sense of satisfaction and self efficacy that comes from DIY cannot be beaten