Replacing Samson S 3-way Xover Op amps - diyAudio
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Old 14th April 2011, 03:04 AM   #1
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Default Replacing Samson S 3-way Xover Op amps

I have a new Samson S 3-way Xover received as a gift. Unfortunately, it is very noisy. At this noise level I just cannot use it.

I built a line array and purchased several amps around the idea of using an active Xover. Unfortunately, I don't have enough money left for the Marchand units.

Is it worth it to replace the Op amps, and/or other parts in this unit to lower the noise? Is anyone familiar with this unit?
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Old 14th April 2011, 12:32 PM   #2
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How old is it? What kind of noise you get?
Look at input stage - probably there is noisy XLR input.
See resistor values used - they get noisy as their value rise.

You can filter-out that hiss from midrange/woofer outputs by simple passive network.

Opamps? Which opamps do you have there?
Check the OPA2134 - should be fine if you have to replace dual opamps. Check their voltage too (OPA will smoke if powered at something higher than 15v).
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Old 14th April 2011, 01:07 PM   #3
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Default Samson S 3-way

The Samson Xover is currently still selling, although I received it in December. I don't see any model numbers that indicate there were earlier versions etc.

The noise is not from XLR unbalanced cables etc. Balanced or unbalanced, this is transistor white noise. It is not RF, Hum or static. I went through all the cables, avoided AC cords and electrical lines etc. I've heard this noise before--that hiss sound from bad electronics. Remove the unit from the source path, everything sounds fine, insert it, and there it is (the noise).

I've never been in a situation where I have needed to replace parts on a PCB. I have built passive Xovers and other small electronic devices in the past, but not replace. I need an active Xover, and this looks like the least expensive route--modding a noisy one. However, since I have not done this, I am listening to others who might have a better idea as to whether this is a) worth it and b) if anyone has experience with this unit.

I'll take apart the unit today and see if I can tell what op amps are in use. I may be wrong, but I suspect the order of noise removal is first the op amps, then the resistors and capacitors. Am I wrong about that?

Thanks for the help.
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Old 14th April 2011, 02:13 PM   #4
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TL opamps are noisy.
Resistors of greater values are noisy too (higher than 50k).
Then comes the power supply which could be noisy too (switched?).
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Old 14th April 2011, 02:38 PM   #5
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Ok, took it apart.

op amps are 7915A JRC MG025B and 7815A JRC MH012A.

Not sure what the MG and MH numbers signify. The others I think are the model numbers of the op amps.

power supply looks like a simple transformer (10W TOP CHEERS 21/10). 10 watts?

I have a few unused meanwell swithching power supplies around here. If I can figure out what I need, I might be able to replace it.
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Old 14th April 2011, 02:56 PM   #6
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Hmm. Looks like these are voltage regulators. +15 and -15. I cannot find the exact ones, but alldatasheet.com lists a motorola equivalent--I think.

This is about as much as I can figure out.
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Old 14th April 2011, 02:56 PM   #7
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PSU is fine, 7915A/7815A are power supply regulators which are fine too.

You 'll need to find the opamps, they have 8 pins and look like this:
http://wp.hi-fi-insight.com/wp-conte...7AP_Op_Amp.jpg

or this:
http://www.wellgainelectronics.com/i...RCNJM4558S.jpg
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Old 14th April 2011, 05:21 PM   #8
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Ok, I now see how foolish I was.

There would have to be more than two op amps for a 3-way stereo Xover.



I found several 4850 A021F JRC op amps near the outputs on the back. There are some more on a front PCB near the dials and buttons. There are some additional types, but I need a magnifying glass and better lighting to read them--They are very faint.

This is more daunting than I thought. These are very small, and surface mounted. Obviously, this was put together by a machine. The resistors are extremely small.
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