tech question - doc, bob, someone...

OneRoomStudios

OneRoomStudios

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So I'm going to build a little portable mono preamp, but I'd like it to double to a stereo output. If I have a single Vout, how do I wire it to a stereo wire so it will double? If that doesn't make sense, let me know. Thanks,

-Peter
 
can't get true stereo out of a mono preamp... you can split the signal at the output... but that's not stereo... just two identical mono signals... and you could more easily accomplish that at your patch bay
 
MOFO Pro said:
can't get true stereo out of a mono preamp... you can split the signal at the output... but that's not stereo... just two identical mono signals... and you could more easily accomplish that at your patch bay
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I realize it's not true stereo, but it's better than sound only coming from the left side. The patch bay idea won't work since this is a portable preamp and I won't be taking my patch bay with me. Like I said, I just want to "double" the singal, or send it to both channels, so it will be "stereo" but not really...


Anyone know how to do that?
 
OneRoomStudios said:
I realize it's not true stereo, but it's better than sound only coming from the left side. The patch bay idea won't work since this is a portable preamp and I won't be taking my patch bay with me. Like I said, I just want to "double" the singal, or send it to both channels, so it will be "stereo" but not really...


Anyone know how to do that?
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Dunno what pre you're building, but most designs can drive more than one load, so just wire it to two outputs, or a tip-ring of a TRS, whatever.
 
mshilarious said:
Dunno what pre you're building, but most designs can drive more than one load, so just wire it to two outputs, or a tip-ring of a TRS, whatever.
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I concur. Just attach Vout to each stereo input. If there are separate L and R line ins, just make or buy a Y adapter with the appropriate connectors.
 
Thanks guys, so could I basically just wire both the L and R of the stereo direct to the single Vout? Or is there some reason I need a Y adaptor?

Also, it's based around an INA217 like the last one I made, do you think it would be ok to replace the 8 Ohm res (equivalent to R6 in the TI data sheet diagram) with a 10 Ohm and the 1.6K pot (R7) with a 5K pot? The 8 Ohm controls the amount of gain, so replacing it with a 10 should just lower the maximum gain slightly right? And the 1.6K pot along with the R6 controls the minimum gain, so a larger value there wouldn't hurt anything right?

Thanks a lot for the help, I really appreciate it!
 
OneArmedStud....err...One....oh whatever....

I used a 10 ohm resister and a 10k pot. Works perfectly fine.
You should be able to use a 1 to 2 breakout cable for two mono signals. This will lower the output by small audible amount however. These kinds of cables are sold by RadioShack or Parts Express. Its quicker than adding more circuitry to your box although the additional circuit is pretty simple.
I use my Mackie VLZ for monitoring. If you plug a mono signal into the left input, both left and right playback the same signal. Thats handy when monitoring what your recording.
As for mono tracks, Sonar has a button that lets the track simulate dual mono for stereo plugins. Most likely other sequencers do also.
Have fun with your project and....make music!

Bob
 
Bob's Mods said:
Its quicker than adding more circuitry to your box although the additional circuit is pretty simple.
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I already have a nice gold plated sony stereo cable that I was planning to use as the output though (I was going to hardwire it). If I just connect both the L and R parts of the stereo cable to the output of the preamp, will it give me signal in both channels or is there more to it? Thanks again BTW,

Peter
 
I would think the best way to do it would be add a unity gain output buffer, so you dont lose any signal on the channels. A simple way to do it would be to use an opamp with a negative feedback loop, and probably 2 10k resistors.
 
OneRoomStudios said:
Thanks guys, so could I basically just wire both the L and R of the stereo direct to the single Vout? Or is there some reason I need a Y adaptor?
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Whatever cables/hardware works is fine. I didn't (and don't) know what you were going to plug it in to.

Also, it's based around an INA217 like the last one I made, do you think it would be ok to replace the 8 Ohm res (equivalent to R6 in the TI data sheet diagram) with a 10 Ohm and the 1.6K pot (R7) with a 5K pot? The 8 Ohm controls the amount of gain, so replacing it with a 10 should just lower the maximum gain slightly right? And the 1.6K pot along with the R6 controls the minimum gain, so a larger value there wouldn't hurt anything right?

Thanks a lot for the help, I really appreciate it!
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That should work fine.
jjmanton2 said:
I would think the best way to do it would be add a unity gain output buffer, so you dont lose any signal on the channels. A simple way to do it would be to use an opamp with a negative feedback loop, and probably 2 10k resistors.
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This wouldn't be a bad idea, but if you're just going to connect it to the usual 600 ohm line inputs, it's probably not necessary. I think it should be able to source enough current to drive them.
 
Many times, company component catalogs contain sample circuits. The TI catalog had a simple audio distribution circuit. If you have access to manufacturer component catalogs, specifically one for opamps, I'm sure you'll find diagrams for such circuits.

Bob
 
Bob's Mods said:
Many times, company component catalogs contain sample circuits. The TI catalog had a simple audio distribution circuit. If you have access to manufacturer component catalogs, specifically one for opamps, I'm sure you'll find diagrams for such circuits.

Bob
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The datasheet circuit for for the INA217 is what I based this pre on. It didn't have any info on the mono to stereo wiring though....



And thanks to everyone for getting back to me and aswering my annoying questions :)
 
by the way, i built 5 of these pre's that are in the INA217 specs. Use good caps and resistors, and they work excellent. Plus TI sent me the 217 and the opamps for free as samples :). I think the total cost for 5 was like 37 dollars with 1 amp power supply, so i could make a lot more, lol.
 
OneRoom,

You might want sift through some online PDF's of various opamps at company websites such as Fairchild, TI, Burr-Brown, THAT, Motorola and others. Check 072 and 082 opamp types. You'll surely find sample circuits for an audio distribution network. Peace o' cake.

Bob
 
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