[johnnyb3]

(trying again after mis-posting to Portable Amps forum)

Hi,

Complete noob here, but I've tried to read up on stuff before posting here, so apologies if I didn't do enough homework.

My situation is this: I have an electric piano with a preamp that brings it up to line level. I'd like to build a little mixing headphone amp so that I can either play the piano straight or mix it with an audio signal. I'd also like the option of a mono mix, because there are some play-along CDs that have the piano track entirely in one channel, and you're supposed to play along with the other channel with bass and drums. Hope that makes sense. Anyway.

My plan is to use a cmoy-type design together with a really crude passive line mixer (just a couple of series resistors on each side); after that in the signal I plan to add another such mixer that I can switch in and out to take it down to mono and then split back out to both sides of the output.

My obvious question is whether this whole idea is cockamamie! Aside from that, any advice about the type/quality of switch that should be used in the audio path? Is the Cmoy design reasonable one for such a project

Thanks in advance for any and all advice -- great forum.

John

 

[rds]

What I'd do is have two pots - one for each source. This way you can adjust each source volume independently. You also will not need a switch and you can get each source volumes just right.

 

[Bilavideo]

You can use a Cmoy as a preamp. What you can't do is run speakers off of it. For that, you'd need a bigger amp.

 

[johnnyb3]

rds -- Thanks. I will at least have a volume control on the piano, so maybe I can get away without pots. As for the switches, what I'd like to do is have the capability to mix everything to mono or not. I can't see how to do that without a switch. The problem is that I'd like to play along with a stereo recording or with 1 side of a stereo recording, and in the latter case, I think it would be annoying to have the rhythm track only in one ear.

Bilavideo -- Thanks for pointing that out. I know that this is only a headphone solution.

Best,

John

 

[johnnyb3]

Hi, rds,

The more I think about it, the more I like the idea of using pots. Would a (modified to account for one input being in mono) simple thing like the following be appropriate:

Simple mixer

Thanks!

John

 

[rds]

Hi John,

Yes, what that circuit is showing is exactly what I was suggesting.

If input 2 can be mono or stereo you could have a switch that connects right and left at input 2. So the switch can be open for stereo input and closed for mono.

 

[johnnyb3]

Quote:

Originally Posted by rds /img/forum/go_quote.gif Hi John, Yes, what that circuit is showing is exactly what I was suggesting. If input 2 can be mono or stereo you could have a switch that connects right and left at input 2. So the switch can be open for stereo input and closed for mono.

OK, thanks! Actually, input 2 will always be mono; in fact I'll just be using a 1/4" mono jack. Where I want switching is to have the option of either mixing input 2 with both sides of input 1 (retaining stereo) or mixing all three signals to mono. (This would also allow it to function as a regular ol' audio cmoy.) If you have a specific suggestion for the best way to do that, I'd appreciate it; I was going to do the simplest possible thing and employ an even simpler mixer -- no pots -- that I can switch into the circuit. I'm wondering whether I need a super-expensive switch with precious-metal contacts or whether that's not so critical.

Thanks again!

John

 

[rds]

Quote:

Originally Posted by johnnyb3 /img/forum/go_quote.gif Where I want switching is to have the option of either mixing input 2 with both sides of input 1 (retaining stereo) or mixing all three signals to mono. (This would also allow it to function as a regular ol' audio cmoy.)

I don't know what you mean by "mixing all three signals to mono". Do you mean that both stereo channels of input 1 and the mono input 2 will go either to the left or right only?
In that case I don't understand your following comment that then it will operate like a regular cmoy.

 

[johnnyb3]

Quote:

Originally Posted by rds /img/forum/go_quote.gif I don't know what you mean by "mixing all three signals to mono". Do you mean that both stereo channels of input 1 and the mono input 2 will go either to the left or right only? In that case I don't understand your following comment that then it will operate like a regular cmoy.

Sorry, that was very unclear.

I would like the capability of either (a) keeping input 1 stereo and mixing input 2 into both sides of it or (b) mixing both sides of input 1 and input down to mono and then sending that signal to both sides of the stereo output. I think that option (a) with input 2 open should look like an unmodified audio amplifier.

I hope that made more sense...

 

[Billyk]

How about this, not diy but $49.00 from Dale Pro Audio

 

[johnnyb3]

Quote:

Originally Posted by Billyk /img/forum/go_quote.gif How about this, not diy but $49.00 from Dale Pro Audio

Thanks -- that looks pretty good. There's a similar product from Behringer, but I see their build quality and reliability slagged everywhere. I figured I could make a better-quality product for about the same $$. Are you familiar with this product, or with Samson stuff in general?

Thanks,

John

 

[Billyk]

I use them, but lightly so I cannot state the reliability. They are pretty much set up and left alone. I use them to mix a lavaliere mic and a ceiling mic for interview rooms. I works well for this and the price fits my budget.

 

[johnnyb3]

Good info, thanks!

 

[rds]

I think you'll be more happy with your own gear. Plus you can fix it if something goes wrong.
Plus one you build yourself will almost certainly be far better quality than the mixer shown above.

To achieve the goals you mentioned I think you want 2 switches. One between the left and right input 2 and one between the left and right output.

 

[johnnyb3]

Thanks, rds. Those were my thoughts, and I was looking for an excuse to try a DIY solution anyway.

Your suggestion of two switches would be a lot simpler to implement. That had occurred to me, and I shied away from it only because I couldn't imagine wanting one mono and the other stereo. But down the line, who knows? Maybe it will turn out to be useful.

You've been a great help!

John