Howdy,
Does anyone know of a Y-adapter which combines stereo to mono and rematches impedance? Please point me ...
I found it... thanks. Having read it, I thought that was for maintaining L&R signals when going to a mono signal, which is not an issue, i.e., an online computer is getting the internet signal and passing it to the transmitter via USB DA interface. This is because using the internet as a STL is the most affordable way to do remotes
The Y-connector works, but of course it doubles the signal. Therefore in my case the only issue is doubling ... so are you saying I still need to put a 47k-ohm resistor inline with each (L&R stereo) output (2 resistors). Since the L&R signals are combined with no other issues, then a single 94k-ohm resistor should work inline with the final mono ... right?
Ken,
If I follow you the USB DA means USB Digital Audio adapter. Correct? If so doesn't it have RCA jacks for the stereo audio output? Maybe the audio could be mixed to mono via software.
The linked thread was about how to produce mono audio from two stereo (L and R) lines by mixing the two without shorting the L and R signals so stereo is preserved on the two lines. For example, here I do this for feeding both the AM transmitter (my old Ramsey with a single mono input) and the FM transmitter in stereo. Both transmitters have internal audio level adjustments so no external attenuation is needed.
The attenuation can be changed by changing the resistor which goes from the junction of the two line resistors to ground. Smaller R gives more attenuation.
Neil
Hi Neil ...
"If I follow you the USB DA means USB Digital Audio adapter. Correct?"
Not exactly, but you're on the right track. It means Digital/Analog converter.
"The linked thread was about how to produce mono audio from two stereo (L and R) lines by mixing the two without shorting the L and R signals so stereo is preserved on the two lines. For example, here I do this for feeding both the AM transmitter (my old Ramsey with a single mono input) and the FM transmitter in stereo. Both transmitters have internal audio level adjustments so no external attenuation is needed.
The attenuation can be changed by changing the resistor which goes from the junction of the two line resistors to ground. Smaller R gives more attenuation."
Preserving the stereo isn't important in this case. I can attenuate the signal with a single resistor once the L&R signals have been combined, can't I?
Ken,
OK, now I think I am up to speed on this. Since you don't need to preserve the stereo then you could just connect the two lines together BUT I DON'T RECOMMEND THIS because it is possible if the D/A converter circuit has low output impedance it could be damaged or this could create distortion.
If it were mine and me doing this I would construct the Y adapter to provide isolation as well as attenuation. You could replace the output resistor (the one from the line series resistors junction to ground) with a pot and adjust it to suite your needs. The mixer/attenuator output comes off the pot wiper. I like to keep resistances rather low to reduce noise pickup and reduce loading effects. 22k to 47k line series Rs and a 10k to 20k pot should be a good starting point. Using a pot eliminates the need for calculations based on sometimes unknown data such as line levels and impedances.
I had a similar problem when I was recently computer capturing some old reel to reel audio. The Sony recorder had very "hot" line levels so I used two pots to knock the L and R down (one for each). Adjustment was easy and the results were good with no calculations involved.
Neil
Neil has it right. Consumer audio sources typically have a low source impedance of less than 100 ohms and are intended to drive a high impedance load, typically 10k or higher. Since the load to source impedance ratio is 100:1 or higher, the load does not affect the voltage level of the audio waveform significantly and does not draw much current from the source.
If the L and R sources are connected directly together, each will greatly load the other and much higher currents will flow between the two sources, especially when one is at 0 voltage and the other is at a max peak. This will load down the drivers way beyond the intended design levels. Distortion is the likely result. Damage to the drivers is unlikely because they should be designed to handle a dead short.
As an aside, the standard consumer audio nominal line voltage is:
Consumer Line Level = 0.316227766 Vrms = 0.447213595 Vpeak = -10 dBv
FWIW, here's the best article and circuit solution I've see so far, and the one I'll build today.:
http://www.rane.com/note109.html
Ken,
The circuit in Figure 1 shorts the two sleeves together.
A computer sound card output uses the tip for one channel and the sleeve for the other channel. The circuit in Figure 2 should work but I don't see the need for 1% resistors. 5% or 10% resistors are OK and the nearest standard value to 475 ohms is 470 ohms.
Let us know how it turns out.
Neil
Thanks for the heads-up ... however, I don't use computer sound cards (if I did I would probably go with Metric Halo). My interfaces and converters are FireWire (32 channels), the sound comes from a recording snake from my analog board.
Yeah, resister values shouldn't be that critical. I'm hoping to get to an electronic supply store on the mainland next week. I need a few germanium diodes and a belt/tire kit for a Nakamichi deck too, so I have to be careful in those kinds of stores ... I could spend the better part of a day wandering around and spend too much moolah 😉
Thanks again ...
need a few germanium diodes
Good luck finding those at Rat Shack!
Fortunately for Ken, there are some older RS stores on the mainland that still have some components in the back of the store - I think they are HOPING the parts will get shoplifted 🙂
There is also a Frys store in Renton that has a surprising array of components.
Not like to old days though, when we had Allied, Lafayette and Heathkit stores in Seattle...
I've found MCM Electronics to be a good source. They accept credit card payment and ship fast.
Yes, gone are the days when Radio Shack was the place to go for a good variety of parts.
Also consider Jameco Electronics
They really helped me with the 13.56mHz transmitter
Why i said good luck was Rat Shack discontinued germanium diodes years ago. All they have is silicon.