XTant 603x

[Dr Zeus]

Wow, This is quite the advanced amplifier for me to work on. This is only the second XTant I've now seen, but the first one was the "Stop sign" off-shored edition. This one is genuine. In working with it, I get a reminder of how difficult it was in working with JL Audio amplifiers.



When I got it, the amp would barely power up; causing my 10A supply to trip/drop down to 8v from 13.5v. I found a shorted IRF9530 at Q26 so I unsolered it from the board. The amp now powers up.



Im having a tough time realizing what all these jumpers, knobs, wheels, and pots are meant for. The instruction manual is pretty useless at detailing the amp's agenda and I just keep scratching my head.




The bad part about this amp currently is that it doesnt play anything correctly out of any speaker terminal. When applying a generated sin wave, here is what my scope shows up at 1v/Div:

[Dr Zeus]

This amp has a total of 11 small blue pots, 3 large blue pots, about ~20 jumpers, and 7 SIP modules.

I'm getting ~+-40vDC rail voltage referencing amplifier's ground, although I'm sure it would be almost exactly +-40vDC from center tap.

The opamps are getting +-17vDC at the power pins


Where is the center tap on this amplifier? i think I found it under the 20w pair of resistors.

[Perry Babin]

I'm not entirely sure what all of the blue pots are for but here's a relatively educated guess.

The ones with the knobs are the gains.

The ones connected to the TL431 regulators are the bias pots.

The ones near the large white film capacitors marked 1k63 are the DC offset pots.

The ones near the SIP resistor networks are used to null the balanced inputs. This is purely a guess. I've never needed to determine what they do.

The pot marked gate threshold, obviously sets the gate threshold. Set the gate off for now.

[Dr Zeus]

Cool that helps a bunch. Luckily I didnt turn too many of these so they're just fine the way they are I imagine.

I'm not sure what all these jumpers are for, but I set the jumpers to disable front and rear balanced line input and the amp works just fine on all 5 speaker terminal outputs.

I believe the final fixation for this amplifier will be to replace all the IRF9530s. Can I use IRF9540s? I have a bunch of them.


How do I set the "Threshold Noise Gate" pot?

[Dr Zeus]

I just looked up the difference in comparison of the IRF9530 and IRF9540. Seems the 9540 is rated for alomost 2x the amperage but other things look equal.. Hmm... I wonder if that could be a good reliable upgrade for this amp? The power output of this amp is only ~150wRMS on the subwoofer channel. It could probably use a little more.

Edit: Looking again, this amp has six of each, IRF530 and IRF9530, so I wold be looking at moving these to IRF540/IRF9540 if possible.

[Perry Babin]

The 540/9540 is what I've used and had no problems with them.

The threshold pot isn't important unless you're using the noise gate when the amp is installed.

[Therum]

Originally Posted by Dr Zeus

The power output of this amp is only ~150wRMS on the subwoofer channel. It could probably use a little more.

Yes into 4ohms. @ 2 ohms its 300w

[Dr Zeus]

Thats like so-so by today's world ratings. That might be enough for 2 10" woofers or a single DVC woofer. Since I put 9540/540 in place of the 9530/530 hopefully the amp will be stronger, or at least more stable under higher loads.

[Therum]

I suppose. I guess it depends upon what you are looking for. Also keep in mind that the number of voice coils does not dictate nor indicate power handling. Its possible it will be somewhat more stable at higher power levels however my experience with the 603 has been that its power supply cannot maintain rail voltage thus was the contributing factor in limiting its power output. I think its output section with the 530's is well capable of delivering the power its was designed to deliver. Yea, the 540's are rated higher but the power supply is still incapable of delivering any more power.

[807tubenut]

Iv got one of these on the shelf, it's a parts amp if you need it.