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jbrooke 23rd September 2008 12:48 AM

Orion 275 XTR noise
When I run this amp on the bench using a battery, it works great. When it's powered by the car, I get terrible alternator whine and general noise.

The same RCAs, power and ground have no problem on any other amp, so the problem seems to be internal to this amp.

I doubt there's a schematic available, but if anybody knows of one, I would like to see it. Also, any suggestions would be appreciated. Since its pretty old and recently bought used, I suppose I should go through and replace the caps and transistors...what else is commonly replaced on a rebuild?

Unfortunately, I don't have access to a scope right now so I'm kinda shooting in the dark. I've built and repaired headphone amps, but never car amps...thought I would query the experts here.

Also any experience here with the older Rockford Fosgate 360.6 amps? It looks like a nicely built amp, but before I go through the trouble installing it, any opinions on it for an SQ install...particulary compnent quality and simplicity of design/ease of repair?

Thanks in advance!

Clipped 23rd September 2008 06:26 PM

resolder the rca connectors that are on the board...not only the connection to the board, but the actual outer barrel ground joint to the frame of the connector both inside and outside.

id go over the pot joints (no pun intended) one more time too, make sure the irons hot.

and if its a pioneer headunit your using, ground the rca cable shield to the radio chassis.

pioneers have a way of blowing the rca outputs when you unplug them without turning off the radio first.

jbrooke 24th September 2008 02:02 AM

Thanks for the tips. I finally got the amp all apart, resoldered the points you suggested along with some other large solder points.

There are four 1000uF 25V caps near the rca jacks that have some white powder around the solder points -- I don't know if its corrosion or leached electrolyte. Also there are two large 3300uF 35V caps that are a bit bulged at the top. I'll go ahead and replace all the electrolytic caps, as I know they have a limited useful life.

Are the FETs, transistors, and IC's normally replaced as needed, or replaced en masse on a typical rebuild?

Clipped 24th September 2008 04:38 AM

if you can find Elna RJH series caps, they have low ESR and are rated for 105 degrees.

usually all the outputs should be replaced for each set per channel...

eg:in a 225hcca there are 3 + 3 for each channel, if 1 in the set of 3 are damaged, id replace all in that not sure of the part number of the xtr 275.

the Digital reference and SX series used 2n6488/ can use BD909/910 for replacement also the BD911/912...the 911/912 have a higher voltage rating, and no it wont increase the power using a higher rating.

the 2n6488/91 are rated at 75 watts each, the BD are rated at 90 watts each.
for the power supply fets id replace with IRF3205, recommended by Perry in the past, and verified by me replacing all the fets in four 2150sx amps and almost all other amps ive repaired.

check the resistors going to the +/- legs of the opamps too, when they go it will cause the amp to put out DC if they fail.

if you have a big 1-2 ohm 50 watt resistor install it 'inline' with the positive batt wire, measure the voltage across the resistor (one lead on each end) and divide the ohm of the resistor by the voltage reading across the resistor, this will tell you the idle current shouldnt be any higher than 2-3 amps....

if it is higher then you more than likely have a bad output or fet somewhere...then you would know whether to change any of them.

also a good idea to check the vertical drive transistors, these can be really misleading when diagnosing a blown orion...and will probably be the last set of semi's you check, after checking the outputs and fets.

so check if there is any DC on the outputs (no more than .050) then check the idle current...if alls good, you probably dont need to change any of those semi's or check them.

oh yeah, and check the rectifying diodes.

jbrooke 24th September 2008 07:07 AM

Great information -- thank you very much!

The 275 does indeed use 2n6488/91, and the recommended replacement part number for the ps fets is much appreciated -- I was having a hard time sourcing direct replacements through mouser or digikey based on the imprinted code.

I'll post results of my testing and reparations when they're done in case somebody else can get some use out of what I'm learning here. Thanks, Clipped, for the assistance!

While I'm ordering up parts, are there any other upgrades often done to Orion amps? In my experience with headphone amps, it was always fun trying different tubes and opamps to get slightly different colors to the sound...though that's much easier to observe with headphones.

Clipped 24th September 2008 04:36 PM

the 225 hcca uses jfets in the soft start/muting circuit...but its a totally different design from the xtr275.

when the soft start/muting circuit malfunctions, you will get very little to almost no output.

the first two letters for the jfets are 2N**** i cant remember the whole part number. but you can identify them because the square pad on the pcb is on the other leg, theyre the little semi round transistors and shoud only be a couple of them if they use the same design in the xtr series.

the 225 hcca responds to capacitor value change (the big vertical ones), but the 2150sx and 250 hcca does not...the highest i went with the values were 1200, 1800, 2200...each step made the bass tighter, but that isnt neccesarily a good thing for fullrange sound

I tried the elna RE3 2200uf caps and didnt like them...made the amp sound fuzzy.

just over the weekend i discovered something i always thought was voodoo - rca cables, i have a really picky customer... that was complaining about the sound stage dropping.

turns out he bought some 4 element microphone cable from somewhere and had them make rca cables out of we tried 4 different types of cable and each type had a different sound characteristic to them...

we tried

1.four element microphone cable
2.shielded coaxial with stranded core - copper
3.non shielded coaxial with solid core - silver/copper mix
4.typical chinese rca cable with no shielding and stranded core

and they all sounded different...the head unit was a denon z-1 alpha one proccessor from the detail was there.

may not have heard the difference with a cheap unit.

Perry Babin 24th September 2008 06:33 PM

When you resoldered the connections on the RCA jacks, did you find any that appeared to be loose (the pin fell to the side when the solder melted)?

With no RCAs plugged into the amp, do you read ~0 ohms between the shield of the input RCA jacks and the non-bridging speaker terminals on the amp?

jbrooke 24th September 2008 07:15 PM

2N5639 is the part number on this board.

jbrooke 24th September 2008 09:41 PM

No -- the pcb pads at the RCA solder points showed no sign of significant stress...I didn't notice any pin movement when I resoldered, but I had a metal rca plug plugged into the jack to stabilize it as well as act as a heatsink. I also used a fairly precise soldering station with the heat just high enough to re-flow the solder, so it set pretty quickly. I'll inspect the integrity of the jack in more detail.

I did read out continuity between the poles of the rca jack, but not resistance between the shield and the speaker terminals -- I'll measure that when I get home this evening.

jbrooke 25th September 2008 08:43 PM

Measuring from RCA shields to non-bridging speaker terminals (R+, L- as specified by the installation manual), I get:

0.3 ohm to R+
~500 ohm to L-

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