Split outputs, how?

Joecool85 · February 03, 2006, 08:09:15 AM

Ok, I'm building an amp, but because of space limitations its just going to be a power amp with a volume control. So, I'll be making a large EQ/preamp pedal to run in front of it. Its going to be a 3 band tone stack into a LPB-1. Is it possible to split the output into two 1/4" jacks and run two separate amps? Can I just split it or is it like inputs where you have to add some resistors and stuff?

Joecool85 · February 03, 2006, 11:33:26 AM

Well, brian said it should be ok. anyone here have any experience with it?

Mark Hammer · February 03, 2006, 11:53:50 AM

Ideally, you want the separate outputs to be noninteractive. So, whatever you send output A to should have no impact on output B (or C if you choose to go beyond 2).

Okay, now imagine that you simply have two output jacks coming off the output of your circuit, and each of those goes to an input pot somewhere else. If destination A has a 25k pot on its input jack, and destination B has a 100k pot on its input jack, then the output of the EQ/preamp pedal is going to "see" two parallel resistances on its output, right? The circuit doesn't actually recognize what our eyes do. We may think its two separate destinations, but all the preamp knows is the combined parallel loads.

Consequently, you'll need to provide isolated outputs that create a kind of "electronic firewall" between the output jacks such that whatever weirdness you do to output A will have absolutely no impact on output B. In this way the two things you send the signal to will be able to operate to the best of their individual capacity.

Check on www.muzique.com for some sample splitter/buffer circuits. You can also look in the appnotes for the TL074 for some ideas too.

Joecool85 · February 03, 2006, 01:14:15 PM

So, it sounds like my plan of splitting the signal and going to two totally separate amps shouldn't be a problem.

twabelljr · February 04, 2006, 05:34:16 PM

Are you taking pictures as this build progresses? I've read a few threads with info and ?'s about your goal. Sounds very interesting. Would make a cool photoessay.

Joecool85 · February 04, 2006, 07:00:17 PM

Yeah, I'm still gathering parts and stuff. My PCBs from chipamp.com should be in later this week, then I just need to grab a transformer, a potentiometer, a switch, and some time to put it all together. It should be a beastly little unit. You should see the massive heatsink I'm using! Brian said it should be big enough for 2 or 3 lm3886s, so if I want to upgrade later I can use the same heatsink. I'm also going to be using a 330va 25+25 toroidal so it will be big enough to power 2 lm3886s if I do upgrade later.

d95err · February 05, 2006, 11:45:52 AM

Quote from: Joecool85 on February 03, 2006, 01:14:15 PM
So, it sounds like my plan of splitting the signal and going to two totally separate amps shouldn't be a problem.

When going to two separate amps, there is a fairly big chance you may get ground loops that cause a lot of hum. To avoid this, you need to isolate one of the outputs from the ground of the other output. There are various ways to do this.

Here's an opamp based splitter (ignore the A/B/Y switching and just use both outputs like the schematic in the upper right corner):
http://www.geofex.com/FX_images/oaspltr.gif

Joecool85 · February 05, 2006, 12:02:42 PM

Really? I don't see it being a problem. I was just reading earlier that hendrix and a bunch of other guys use to just use a simple Y splitter!

KMS · February 05, 2006, 12:09:12 PM

Look at the schemo on GEO like d95er said. There is PCB for it on GGG.

I also made a PCB for the 2001 A/B/Y version from GEO which allows up to 8 outputs and a direct out if you should need more spiting in the future. MY PCB has no switching vias. It is set up for splitting only.

I am currently only using 6 outputs and just did not solder the transformers and other parts for the outputs on the board. I do all my switching in the mixer. The PCP works great....a little tight fitting but it works.

You could use it and only populate two outputs which would allow you to expand in the future if needed.

Just right click, go to properties and copy the url into your address bar for the large image.

Edit: Got to this link and then go to page 3 and get the full size PCB http://aronnelson.com/gallery/Schematics-etc

Joecool85 · February 05, 2006, 12:16:32 PM

Eh...are you sure I have to do something that complicated? If that ends up being the case I will probably just have one output for now. I really don't want to add more stuff to my preamp.

KMS · February 05, 2006, 12:17:10 PM

Quote from: Joecool85 on February 05, 2006, 12:02:42 PM
Really? I don't see it being a problem. I was just reading earlier that hendrix and a bunch of other guys use to just use a simple Y splitter!

You can do that...it will work but you could have problems with hum depending on the ground voltage difference of the things you are sending the split signal to. Also as you change the volume from one split signal, the volume of the other split signal will change inversely automatically if you do not isolate the signals.

So any time you adjust the volume of one side of the split, you will have to make counter adjustments back and forth from each split until you get the mix you want. Use the isolated splitter and enjoy some easy mixing.

petemoore · February 05, 2006, 12:18:54 PM

There is an instant a 20$ solution.
A Stompbox in shrink wrap plastic, with two output jacks...very quick/cheep.
You can get a chorus or Flange [IIRC] with stereo outputs at this price range.

Joecool85 · February 07, 2006, 02:49:33 PM

How about this?

http://www.musiciansfriend.com/product/Guitar/Effects?sku=150501

If I was to turn down the rate and depth would it basically bypass the chorus effect?

d95err · February 07, 2006, 03:09:30 PM

Quote from: Joecool85 on February 07, 2006, 02:49:33 PM
How about this?

http://www.musiciansfriend.com/product/Guitar/Effects?sku=150501

If I was to turn down the rate and depth would it basically bypass the chorus effect?

You can keep it in bypass mode, and it will send the input to both outputs. It should work a lot better than a Y-cord, but there is still a small risk of ground loops.

If you do run two amps, by all means try the chorus, it will be spectacular! I've only used it once live when there happened to be a spare amp available, and I remember peoples jaws dropping the first time I switched on the chorus...

Joecool85 · February 07, 2006, 03:33:45 PM

I'll have to pick one up and see how I like it. For now the 2nd amp would just be a Dean Markley K20 while the main amp is a 50w lm3886 based amp I'm working on. I was going to use the K20 as a monitor. But then my brother pointed out that its not really necessary to have a monitor for guitar, just throw your stage rig behind you. So, I might build another 50w amp (since I have the parts for two anyway) and put them next to each other for a killer chorus effect.

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Split outputs, how?