2nd input on an amp

ryno · « **on:** 7 Jul 2005, 11:10 pm »

I'm in the group buy for the UCD amp, with no building experience, and one thing I would like to include is two inputs. One from a stereo pre, and the second from a HT pre. A switch on the back would be fine, but using the 12v remote line from the HT pre to switch to the second input would be great. Is something like this possible?
Thanks, Ryan

ryno · « **Reply #1 on:** 19 Jul 2005, 03:22 am »

Any idea where I could post to get an idea.
Ryan

mgalusha · « **Reply #2 on:** 19 Jul 2005, 03:27 am »

Ryan,

It's entirely possible. You could just use a DPDT relay with a 12V coil to switch between the inputs. Of course this ads another set of contacts to the signal path but that is true with any switch. A relay such as this is very inexpensive, probably less than $10.00, certianly less than $20.00.

Mike

Bingenito · « **Reply #3 on:** 19 Jul 2005, 03:28 am »

I know nothing about the UCD build but if your Stereo Pre does HT pass through you should not need to mod the UCD design.

Go preout for L&R to the stereo pre and stereo pre to your UCD amp inputs. As long as I am understanding your objective that should work.

ryno · « **Reply #4 on:** 19 Jul 2005, 12:31 pm »

Thanks Mike, any idea where I could find one of these switches?
I'm looking at this rather than a bypass on the preamp so I'm not limited to pre's with a bypass, plus, I won't have to flip a switch, the signal will do that. If I ever decide to build a pre, I won't have to include an input switch, so I really won't be adding an additional switch, just moving it to the amp.
Ryan

JoshK · « **Reply #5 on:** 19 Jul 2005, 03:06 pm »

Relays are easy to come by, mouser, digikey, et al will carry them. You want one with a 12V coil and the current rating should be high enough for the incoming signal.

ss397 · « **Reply #6 on:** 19 Jul 2005, 03:06 pm »

i would like to put a 2 position switch on my amp as well. i would like my HT and 2ch. sources to stay seperate and switch at the amp. my preamp does not have ht bypass.

mgalusha · « **Reply #7 on:** 20 Jul 2005, 01:58 am »

Ryan,

As Josh mentioned, relays are very easy to come by. Since you are only sending a very small signal through it, almost all of them will have suffcient current capability.

You can get one at your local Radio Shack. Part number 275-249. It's $5.29 and according to their site all of them within a 10 mile radius of here had them in stock, so you should have no problem finding one.

You will also need some type of connector to connect the relay to the 12V lead from your HT pre. The connector will connect to the relay coil. I strongly suggest NOT using an RCA connector for this purpose, as this will prevent you from accidentally plugging the trigger lead into an input jack.

Below is a quick & dirty schematic of how this could be wired up. Note the "amp" blocks are just a generic IC module symbol.

ryno · « **Reply #8 on:** 20 Jul 2005, 04:41 am »

Thanks again Mike
That's perfect, I appreciate the effort. My HT pre uses a 1/8 mini jack for the turn on signal, I'm sure the shack has input jacks for that.
thanks, Ryan