SX-950, Phono Rumble

Clmrt

Clmrt

Just thrilled.
So I detailed an SX-950 and she's a beaut. Looks really nice in ambient lighting, and every input sounds great except for phono 1 / phono 2. There's a rumble about -15db below the signal. Records are reproduced faithfully but the rumble is obviously not supposed to be there.

Anyone have any ideas? It's the same rumble in phono 1 and 2, so something in the pre amp stage after the inputs / switch?

I can solder, but I have no SM. I do have a VM.

(BTW, this thing does sound nice and the 85w is audibly "stiffer" thru the Advents. Headroom is apparent immediately vs my 2220B.)
 
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Marantz has a better phono pre built in that cuts a lot of rumble out.
The pioneer is more straight through.
You might have to upgrade turntables with the sx-950.

Clmrt,
You forget that the 2220B is only 20wpc, the sx-950 is 85wpc.
Of course it is going to be stiffer.
 
"Clmrt,
You forget that the 2220B is only 20wpc, the sx-950 is 85wpc.
Of course it is going to be stiffer."

I didn't forget. I was just amazed how readily apparent it was at low level, 65-70db playback.

This isn't spindle rumble. With the TT at rest, theres a very large amount of rumble present, like holding a microphone in the wind. Just for laughs I'll take out the Pro-ject / OM10 and drop in the JVC L-A100 / VSM10.
 
Possible feedback from the vibration of a more powerful bass reponse of the larger amp? Try isolating the turntable and see if it goes away.
 
If the rumble is only in one channel, you have a transistor (or capacitor) in your phono section that is leaking. if in both channels, check for noise in your power supply.

Enjoy,
Rich P
 
Here is a quick, simple test to be used in conjunction with Rich's advice...

Short the phono inputs individually at the back of the receiver. Thus any noise is INTERNAL. Then check for left / right / both ....

Best way is rca shorting plugs... can also have a resistor in them, but in a pinch, you really don't need the resistors on a 950, there's a 3k series and a 68k parallel in there, and then it IS a capacitor coupled input....
 
Thanks, will check. 80% rt channel.

In the meantime I'm using an external TT Pre to the aux, no problems.

Def not TT related.

Thanks again for the suggestions. Looks like a pain to disassemble....
 
Pro-ject / OM10 and JVC L-A100 / VSM10.

All tables work on 2 other receivers. It's not a table problem. With the rat-shack outboard EQ it works great.

I'll think about ripping the board out to see if I can do anything...
 
Well, recently I did a phono preamp (for an AK'er) out of an 838 where the electrolytics were replaced, and the 6 transistors were updated with fairchild low noise transistors. While one channel had shorted out the other "sounded ok", but I did measure an improvement in the noise floor after the new transistors.

The 838 and 950 phono sections use the same transistors, in fact they are BOTH AWF-011 boards.

EW and Dr. audio had different transistors recommended, but the supplier has a minimum order requirement. I have a parts list from mouser for the preamp, and mouser doesn't have a minimum order. You will probably end up paying more for shipping than the parts cost !

Of course you probably don't have the instrumentation to check it out afterwards, except by ear...

The jury is still out on the final results, the recipient got rather busy with personal affairs, and the re- installation is on the back burner. But my instruments and bench receiver/speaker combination were happy with it.

If you d i y it, I don't mind talking you through it here.


EDIT: ONLY the phono board was sent to me, the re-installation means putting the phono board back in the 838...
 
10-4

After I let it run in I'll take it back out and assess the stiuamation.

Thanks for the advice!
 
Clmrt said:
https://www.ued.net/ued/addItems.do?itemCode=PNRAWF-011

~$55 for a NOS / Repaired board?

Can the board be pulled and sent to (insert tech name here)? I'd rather not ship this big 'ol thing.

Thinking out loud.... :scratch2:

It's puncuated by crackles and pops...eep.
Click to expand...

Yes...

Crackles and pops... VERY FAMILIAR.... BTDT... The transistors are breaking down.

See post #11............ :smoke:
 
Which makes me wonder about the integrity of the rest of the unit.

Thanks again. Will advise when disassembly commences.
 
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