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-   -   bi-amping with sonic impact t amp/using sonic impact amp for headphones (http://www.diyaudio.com/forums/class-d/73891-bi-amping-sonic-impact-t-amp-using-sonic-impact-amp-headphones.html)

jon_m 12th February 2006 02:33 PM

bi-amping with sonic impact t amp/using sonic impact amp for headphones
 
I've got 1 sonic impact t amp and a 13.8V/6A psu. Was thinking of getting another to use for bi-amping - I've heard that there may be issues with biamping with these amps, though, so if this is likely to cause problems I'd be grateful if someone could warn me ;) The plan would be to use one amp to drive the high frequency of my left (mission 733i) speaker with the left channel and low frequency with the right, and do the same with the right speaker...

Also, I've got a QED speaker switch which includes a headphone socket - I've connected the t amp to the switch and the switch to my speakers. However, the headphone socket does not seem to be working - when I connect 1 channel to the t amp (no matter which) it sounds fine, when I connect both left and right channel's there's a constant hiss on my headphones whatever the volume the amp is set to. I gather than this may be to do with the way the amp is earthed - I've found some imfo here (http://www.diyaudio.com/forums/showt...944&highlight=) where it says that "you cannot tie the two speaker grounds together which means rewiring the headphone cable."
If anyone has suggestions about where I could find an idiot's guide to doing this that, would also be very much appreciated...

TIA; looks like a nice forum you;ve got here :)

Jon

Pano 13th February 2006 09:59 PM

The Sonic is a bridged amp (see the FAQ/Wiki) so you can not connect outputs together or to ground. If your missions have a common earth between sections, it won't work with a T-amp.

I don't reccomend the T-amps for most headphone use. Same common ground problem plus a host of others.

A good opamp based headphone amp would be a much better choice.

jon_m 14th February 2006 11:21 AM

Thanks - interesting wiki. It does sound like using this as a headphone amp is more hassle than it's worth...

In terms of biamping, does the issue re. grounding mean that this is likely to pose a problem as well then?

One other thing I noticed in the wiki info - you're advised "Do not use conventional, common-negative speaker selector boxes or L-pads with a bridged amplifier.
Fully differential speaker selectors or L-pads must be used to prevent ganging of the negative
terminals." I'm using my sonic impact amp with a speaker switch at the mo (playing as I type) and have been for a couple of weeks. No obvious problems - does that mean it's working OK, or is this something I should unplug now :o

Thanks,

Jon

Pano 16th February 2006 10:16 AM

Quote:

Originally posted by jon_m
No obvious problems - does that mean it's working OK, or is this something I should unplug now

If it's working, then no worries! A switch with a common ground (earth) would send the amp into fits straight away. I used to have one of those....


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