PC recording monitor questions...

[GibsonGM]

Ok, another place I'm a "noob" in!       Stereo.

I want to take the phones output from my PC speakers, and the phones out from my Digitech pedal,  and run them to a magic box.  These outputs are stereo.  The magic box will contain TWO LM386 headphone amplifiers which will output at a stereo jack for my monitoring phones.

My little 'thought problem' is as follows:   should one mix the Lefts and the Rights thru say, 1K resistors, then apply them to the 386?  So BOTH Lefts are on one channel, and BOTH rights on the other?   If I did this, I'm picturing a volume pot on at least one of them after the summing R...

OR, should each complete phone out be 'summed' into mono, again via 1k resistors, and then sent to their own "L" and "R" channel, respectively, in mono?  Then each side has its own volume pot on the input. 

This is so I can multitrack a little better, BTW.  Leaving one phone off stinks     Sound quality isn't a big issue as long as it's AM or better.  Basically working with the "Headbanger Headphone amp" schematic.

Any thoughts?  Thanks.

[Quackzed]

i'd go with the first way, left pc speaker out mixed with left pedal out via 2 1k resistors to 'left' 386,same with rights for right 386.
i'd think the pedals volume would be good enought to mix the 2 sources to desired balance...with a stereo 386 volume for adjusting volume of both...

[GibsonGM]

Thanks, Quackzed, sounds like the plan.  Just need something easy to mix the signals - had thought about doing a summer w/an opamp, but why waste the chip?

[pappasmurfsharem]

Thanks, Quackzed, sounds like the plan.  Just need something easy to mix the signals - had thought about doing a summer w/an opamp, but why waste the chip?

If you won't have stereo inputs why bother? Just tie tip and ring together on a single 386 output

[GibsonGM]

Yup, that's were it landed, mostly.  Wasn't sure if the 386 could "handle"  summing.  Seems that it can.   
You can't just "tie the tabs together', tho - that will make the sound card 'see' a shorted output = BAD for sound card.  Not always, but it could fry something, so it's not advised.  I placed a 1K resistor in series with both L and R, tied the ends of the resistors to the 386 input.   This gives the sound card a "load", if you will.....sounds fine.

One neat thing, tho - if you sum the stereo into mono with the two, 1K resistors at the 386 input, that's fine....but if you add a 50K level pot, you can't add much more resistance or the 386 collapses into instability.  IDK why, must be that darn input impedance thing again, ha ha.   This must be why some designs call for a 50 ohm pot (as if we have THOSE kicking around.....).   

I ended up just leaving the input alone (no input "trim" level control) and added a vol. pot to the output instead.    All is good.

[pappasmurfsharem]

Yup, that's were it landed, mostly.  Wasn't sure if the 386 could "handle"  summing.  Seems that it can.    
You can't just "tie the tabs together', tho - that will make the sound card 'see' a shorted output = BAD for sound card.  Not always, but it could fry something, so it's not advised.  I placed a 1K resistor in series with both L and R, tied the ends of the resistors to the 386 input.   This gives the sound card a "load", if you will.....sounds fine.

One neat thing, tho - if you sum the stereo into mono with the two, 1K resistors at the 386 input, that's fine....but if you add a 50K level pot, you can't add much more resistance or the 386 collapses into instability.  IDK why, must be that darn input impedance thing again, ha ha.   This must be why some designs call for a 50 ohm pot (as if we have THOSE kicking around.....).  

I ended up just leaving the input alone (no input "trim" level control) and added a vol. pot to the output instead.    All is good.

Not sure what your talking about. As far as the sound card is concerned it would see two separate inputs left and right.

Your running into the line in I imagine?

Edit: wait are you running the output from the PC this box? You said "PC speaker out" I assumed you just meant the input to a set of speakers. Do you really mean stereo PC out?

What is the purpose of the digitech pedal? What is the signal chain vs what you are trying to accomplish?

[GibsonGM]

The Digitech is a USB device, basically an amp simulator to get your signal into the PC.  You can connect a mic to it and mic your own amp, too (why I need headphones....).

I need to monitor the signal, like you would out of a mixer.  So I'm taking the headphone output from the PC and mixing it with the headphone out of the Digitech pedal.   This avoids latency issues - which can be very aggravating!  You do NOT want to listen to your own signal AND playback when you're recording as there is a delay that will make you insane.    Only other option is playing games to hear the playback and yourself, such as leaving one headphone off, etc.....not good if you're mic'ing your amp.

So there's a need to mix 2 stereo signals.   If one were to make a stereo signal mono, you can't just short them together and apply them to headphones - you need some resistors - not complicated.   

What I was asking is whether it's best to do each input to a headphone amp as mono, or keep them stereo and 'layer them' on each other.


       

[boppy100]

A TDA2822m makes a nice little stereo/headphone amp and should work well in this situation.  300mw, 9V into 32R.  Just 8-10 parts plus the 1K resistors and 5-50K dual volume pot.  Renegadrian has a nice vero in the Layouts Gallery.

[pappasmurfsharem]

The Digitech is a USB device, basically an amp simulator to get your signal into the PC.  You can connect a mic to it and mic your own amp, too (why I need headphones....).

I need to monitor the signal, like you would out of a mixer.  So I'm taking the headphone output from the PC and mixing it with the headphone out of the Digitech pedal.   This avoids latency issues - which can be very aggravating!  You do NOT want to listen to your own signal AND playback when you're recording as there is a delay that will make you insane.    Only other option is playing games to hear the playback and yourself, such as leaving one headphone off, etc.....not good if you're mic'ing your amp.

So there's a need to mix 2 stereo signals.   If one were to make a stereo signal mono, you can't just short them together and apply them to headphones - you need some resistors - not complicated.   

What I was asking is whether it's best to do each input to a headphone amp as mono, or keep them stereo and 'layer them' on each other.


       

Is the processing done in the PC or on the digitech? What model is it?

[mth5044]

A TDA2822m makes a nice little stereo/headphone amp and should work well in this situation.  300mw, 9V into 32R.  Just 8-10 parts plus the 1K resistors and 5-50K dual volume pot.  Renegadrian has a nice vero in the Layouts Gallery.

Thanks for this - I didn't know this chip existed. Available at Tayda for $0.26.

[GibsonGM]

Thanks, Boppy - yes, there are some more 'elegant' ways to do this, but this is supposed to be right out of the junk box, y'know...stuff I have lying around, and we all have 386's!    It's working out fine - I did one side last night, and it sounds good.   

Pappasmurf - I have an RP350 - I just use it to get my guitar from the outside world into the PC, and I record using Audacity (free).  You can set the RP up to be very clean, just a box to pass thru, or set up patches.   Pretty handy for home recording, I think.   

I'm probably making this sound more complicated than it is - just need to hear the output of the PC (drums and bass, for ex.) at the same time I hear the signal going INTO the PC from the pedal.   This will work fine.         

[Kipper4]

I'm aware you want a diy solution but an audio interface ( digitech maybe one) offers a good solution.
For daw. Have you tried Reaper? It's a fully featured daw. With a longish trial period and very impressive price point.

[pappasmurfsharem]

Thanks, Boppy - yes, there are some more 'elegant' ways to do this, but this is supposed to be right out of the junk box, y'know...stuff I have lying around, and we all have 386's!    It's working out fine - I did one side last night, and it sounds good.    

Pappasmurf - I have an RP350 - I just use it to get my guitar from the outside world into the PC, and I record using Audacity (free).  You can set the RP up to be very clean, just a box to pass thru, or set up patches.   Pretty handy for home recording, I think.    

I'm probably making this sound more complicated than it is - just need to hear the output of the PC (drums and bass, for ex.) at the same time I hear the signal going INTO the PC from the pedal.   This will work fine.        

The RP350 is technically an audio interface. You should be able to use ASIO drivers and output the effected signal through the headphones build into the unit with minimal latency

From the manual

8. USB Port
The USB port is for connecting the RP350 to a computer and serves two purposes: (1) for use
with the downloadable X-Edit™ Editor/Librarian software, and (2) for streaming audio to and
from the computer. The RP350 will stream 2 channels up and 2 channels down from the computer
at 44.1kHz, 16 and 24 bit. A utility panel in the Editor/Librarian controls the direct/playback
mix and USB record level with any recording software the RP350 is connected to. Knobs
2 and 3 also control the direct/playback mix and USB record level when USB is connected and
the Pickup Row is selected.

Now if the few MS delay is what it bothering you.

Then you could also just not use the USB from the RP350.

Plug the Headphone output into the Line-In on the back of the PC then plug your speakers into the normal speaker out.

Set audacity to record off the line in and also set your windows config to "Listen" on the line input.

[Kipper4]

If you were to use a unity gain summing/mixer amp and output headphone from rp and speaker headphones out to summing/mixer then you could monitor both by phones as long as you don't use the daw monitor for the rp350 channel you should be good to go.

The rp has two in/ two out USB

http://2fecf431b6f093853a80-bc95634e606bab3d0a267a5a7901c44d.r9.cf2.rackcdn.com/product_documents/documents/56_1289414637/RP350_Manual18-0436V-A_original.pdf

[GibsonGM]

Cool, thanks.  I'm passively mixing and using the 386's, currently, which seems to work fine.   There are probably 10 ways to do this, and several better than what I'm doing, ha ha!