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Koss Esp-9 to ESP-9b Conversion... Help needed with grounding scheme

post #1 of 3
Thread Starter 

Hi There

 

I purchased a set of Koss Esp-9 from E-bay a while ago and have finally got them out of the packing box they went into during a move a while back.

 

They work reasonably well, though I think I will need to give them a decent renovation to get the most from them.  Before I do I thought I would turn my attention to how I am going to drive them.  Ideally I would like to drive them from a decent little digital amplifier module that I have a few of.  But that currently is not possible due to the grounding arrangement of the Esp-9.  The problem can be seen in the schematic below

 

 

You can see in the schematic, the left and right channels of the energiser box share a common ground.  The diagram shows this ground tied to Earth.  Though my multimeter tells me that it is not.  I may be reading the schematic wrong.  I have always hated Earth wiring!  This shared ground for the left and right channels is a problem for a lot of amplifiers as not all can tolerate having their negative terminals connected to a shared ground.  Digital amplifiers certainly don't like it.

 

Now I know from my internet research that the later Koss model the Esp-9b came with an updated energiser box that had a new grounding arrangement.  This was apparently introduced because of compatibility issues with some amplifiers.  The only other difference I have read is someone suggested that separation improved on the later model (possibly linked to grounding differences). I have hunted high and low, but I cannot find a schematic for the Esp-9b anywhere.  But I would like to try and find out what the differences are and document a conversion from 9 to 9b.  It would let me connect more amplifier sources to my headphones and I reckon might be of interest to other Koss Esp-9 owners.

 

I am guessing that Koss would want to solve the grounding problem without altering too much the construction of the energiser box or headphones, so I have made a guestimate as to how they may have separated the grounds....

 

 

Now here is where the help comes in...

 

First things first, can someone with a good knowledge of grounding schemes just check what I have done and tell me if it will function safely.  I am especially interested in whether I need to tie the shared ground to earth or not.  

 

Secondly.  If anyone out there owns a Esp-9B set and a multimeter... any chance that you would be prepared to sketch out the schematic for the Esp-9b?  

post #2 of 3
Thread Starter 
Is it being too impatient to bump this thread? wink.gif
post #3 of 3

That could work but I'd ideally want to see a transformer center tap or something like to set the ground potential.  The ground is much more important in these than other 'stats due to the grounded back stators. 

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