Zanden DAC noise problem

I am looking for advise on how to solve the noise I get at high sound level from the Signature Dac which is connected to the Zanden transport.The dac is feeding an Einstein preamp driving Atma-Sphere M-60 which is powering a pair of ClassicLoudspeakers T3.3 .The sound is wonderful however when I increase the volume beyond my normal listening level there is a hum .All the other sources,Accuphase800/801 and Meridian861V6, into the Einstein are perfectly quiet.I am not in the mood to send the unit back to Japan,done that in 2008,they did a wonderful job but expensive and takes forever.
I have replaced all the tubes both in the power supply and the main unit,NO ,difference.I have also tried different output on the DAC,aes,and the cat cable.The cat5 works best( Have just replaced with Cat 6)I thought mistakenly that the the original Zanden CAT cable was defective,I have sent it for repair to US vendor unfortunately he will not return the cable nor respond to my requests.However good the Zanden equipment is,the technical support is not commensurate with product quality and price.All help will be greatly appreciated.
Ramy, I hear you regarding you not wanting to send the unit to Japan. The cost of round trip shipping alone would cost $800 ( even at Zanden's cost) and yes it takes long time to fix too, as Zanden is a small operation company and I hear most repairs are done by Mr Yamada himself. they are busy building their core equipment and are always developing new ones. They invest very long time to develop a new product and it takes years to roll out a new product.

I sent my transport to Japan last Nov to get the drive and clock replaced and the cost was of course equal to buying say a brand new AMR DAC or equal.

Have you ever talked with Fred Nadal of He is pretty good at diagnosing most issues or it least he may help trouble shoot further. Have you tried to write to Eric Pheils?
Hi Nilthepill,
I had similar experience in 2008 I sent that same DAC to Japan,they did an excellent job at an exorbitant cost.I did contact Eric he is always willing to assist,but his recommendation was change tubes or send to Japan.I had a different suggestion from another audiogoner who has experienced the same problem that it may be a defective choke.I just wish that we could have access to experienced audio electronic technician that had the skills to do minor repairs of overseas manufactured products with no US service and even more important the ability to repair classic electronic components of now defunct companies such as Cello.
Hi Nilthepill,

Great to hear from you. I am glad to hear you still are using your Zanden. You gave me good advice about Zanden...i still have my DAC but have yet to get the Transport.

I have heard there are upgrades available to DAC...have you ever upgraded yours? Was curious what you may know about these upgrades...from vintage 2007. Thanks for any advice!

Have you heard the STahl-Tek Vekian Opus digital?