The Internet is littered with the corpses of questions like mine, but since I bought my mono audio amp (BOB-11044) from Sparkfun, I thought it best to go straight to the brains what built it.
I’m looking for best practices/guidelines for bridging stereo output into mono, so that both left and right channels are cleanly fed into the amplifier. I’ve seen solutions that use resistors and solutions that use capacitors, and I’m sure there are advantages to either. Ultimately what I’m trying to ensure is that my audio source does not think there is a “bad” short (thereby turning off the audio) and provides a clean (or as clean as possible) signal regardless of whether the source is a stereo headphone jack or a stereo line-out.
Thanks for the info, Mark. You can tell I’m a novice, and your comment reminded me I need to read the datasheet. I should make that my mantra.
For posterity and everyone else: I also learned that what I was looking for is a summing circuit, and not knowing/using that as a keyword has probably muddied the waters a bit. :oops:
It seems that everything I’ve been reading, including MikeGrusin’s comment on the product description page https://www.sparkfun.com/products/11044 … 871f000000 implies that I should connect either L or R into the BOB’s + in pin, but not both. Not without summing the Left and Right, somehow. Several sources referred to Why Not Wye, which recommends adding a 10k ohm resistor to each channel before connecting them to each other. I’m going to give that a shot.
jer-el:
:oops: …and let me amend my mistake above. Not 10k ohm resistors. Between 470 and 1k ohms seems to be the commonly suggested value.
Doesn't matter in this case. Your resistors will tie to a DC blocking cap which is in series with a 150k resistor. Even 10k is small compared to that. In fact I'd prefer 5k - 10k if the source is a line level output. If the source was meant to driver "speakers" then lower values are OK.
BTW is the source singled end ? As in a signal and a ground. Not differential, as in signal+ and signal- ? Whatis your source, it may make a difference in how the other wires (not mentioned so far) are treated.
Hi Mee_n_Mac. I’m learning a lot here, which is great. The source is a 3.5mm stereo headphone jack as found on a phone/mp3 player. So single-ended tip (left), ring (right) and sleeve (ground) if my understanding is correct.
Since your outputs were intended to drive headphones, it really doesn’t matter what the summing resistances are so long as they’re > 200 ohms. You almost can’t go wrong (famous last words).
