[Quake120]

Keep in mind these are purely hypothetical and I haven't considered trying them nor will I probably ever. Don't criticize if they are outlandish

What if you used a variable resistor as the 5K resistor on the output? Could you tune it just so you could eliminate the noise but not much of the signal?
Another idea with a variable resistor is a CMoy you could dial in the gain on by changing the resistance where one of the signal path resistors would go.

What if you soldered a bunch of sockets (4?) for dual op-amp chips and put a switch in between them all so you could switch between chips for instance if you had one chip that sounded 'fast' you could use it for rock, a warmer sounding chip could be used for classical, etc...

I'm just trying to get a feel for how drastically you could really modify a cMoy

 

[ashmedai]

Better to only add the noise resistor if it's necessary (and it usually isn't). Any crap you add in the signal path, even if it's just being bridged through a "0 ohm" resistor...it's crap, and it's undesirable if you can avoid it.

I thought about the gain thing too...but it's really a huge pain that's likely to leave you with unbalanced channels or an unstable circuit or other such fun. IMO again not worth the trouble when you can just hardwire it. A switch of some sort might be fun if you want variable gain, i.e. presets rather than analog variation.

Normal practice on a CMoy is often to use a socket for the ICs. It doesn't harm anything, lets you swap stuff around...and keeps youf rom soldering vulnerable ICs on your first time with a rod in your hand.

 

[elliot42]

I like the idea of switchable opamps without having to pull ICs in and out of a socket, but you'd need a pretty chunky switch if you have to switch between 4 sets of 8 pins. Maybe you only have to change a few of the opamp pins to enable/disable them, not sure.

Cool idea though

 

[Quake120]

Hmm...I wonder if you could wire in all of the op-amps in parallel and just use the switch for the power to each op-amp. To prevent input/output voltage going where you don't want, I think you'd have to use an OR diode or something. I don't understand electronics well enough to know how to set that one up

I really think ashmedai's suggestion of having a switch with a few different statically set gains would be cool. I want to try it all. Headphones and electronics are VERY expensive hobbies!

 

[ashmedai]

I *think* you can get resistor blocks with dip switches on them or something like that. I haven't seen one in ages, but I haven't looked very hard. Also the one I saw most recently was the size of a toaster...or was that one a capacitor block? I forget. I think I need sleep. Could probably use a dip block to control the bugger either way, though.

To the extent of my understanding, you can use a potentiometer for a gain resistor by: 1) never ever adjust it while the circuit is on, 2) add a resistor in series so it goes between say 1k-11k instead of 0k-10k. But I can't imagine wanting more than about 3, maybe 4 gain settings...and it's faster to flip between 'em with presets like an analog radio.

In theory, the op-amp thing should work vis the basic rules for analyzing op-amp circuits, assuming of course that anything applied to the pins is within normal safe parameters (I doubt this would be a problem for any sane combination of parts you would want to choose). Can't think of anything really wrong with this idea other than the usual "don't add crap to audio circuits that you don't have to" rule.

It might be interesting to rig up such a device for meets to demonstrate different op-amps easily. It could be hard to fit in the traditional mint tin, though. The gain selection would make for good synergy, e.g. so people can try their own phones on it. It would at least be interesting to make just to find out how it works...if nothing else, the CMoy basis should keep it as a relatively cheap diversion.

 

[elliot42]

Well I think I'll be building a cmoy tomorrow (haven't made one before) but the only opamp I can get locally is the OPA2134. There are others available, but none from tangent's suggested list. I'll try the switchable gain most definately, and try the switchable opamp (might get an extra cheap chip or two to test the idea).

I'm pretty sure I have some dip switches in my parts bin, and a multi-pole rotary switch, but it's pretty big and clunky and would rather not use it. I have no idea if the opamp part will work, but I'll do some reading and see how it goes tomorrow.

 

[diredesire]

You can easily put a gain resistor in parallel with the default to lower the gain. For instance, you could have
10k/1k

then put a 10k (via switch) in parallel with the other 10k so when you flip the switch you get 5K. 2 switches (one for each channel).

You could do the same thing with a matched (resistor) rotary switch, but IMO it's more trouble than it's worth. Yes, you can build the Moy with all these features, but tuning it to every song/album you listen to is just a little bit too much work for me.

Edit: like has been said, don't lose sight of the idea that we want to listen to music.

 

[Quake120]

Quote:

Originally Posted by diredesire /img/forum/go_quote.gif Yes, you can build the Moy with all these features, but tuning it to every song/album you listen to is just a little bit too much work for me. Edit: like has been said, don't lose sight of the idea that we want to listen to music.

Of course

Remember, these were all hypothetical. I don't think I'd actually do any of these other than maybe the gain switch to accommodate different pairs of headphones.

elliot42, post pics of your build when you are done! I'm curious to see what you come up with