Hi All,

I have started topic in ZMA of Ways to improve sound quality of the Mystery Amp!. I did mod ZMA in step by step and report the results of sound quality changing. I think that these information is benefit for mod of other pre-amp ,amp, etc also. Then I would like to provide link here. It will be exposed to more readers here rather than just posted in ZMA forum.  If you are interested then you can follow below link.  

https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1409130590

Hi Lord Soth,

Thanks for your cheering. I want to contribute back because I learn a lot from people posting in forum also. It helps us to achieve to our Audiophile goal faster and more money saving.

Yes, I previously though as you. I did tube rolling first.

tube rolling for ZMA. Yes, I have done with Siemens E88CC ($370 for quad), RCA 6L6GC ($380 for quad) and RCA JAN OA3 ($18 for pair).

The sound quality of ZMA with stock tubes is unquestionably superb
. But I need more in lush midrange female vocal, sparkle treble and powerful bass or bass slam.

My first plan is to burn in ZMA with stock tubes for >300 hrs first to know the sound. Then do tube rolling step by step to observe sound quality changing. But ZMA with stock tube's sound is so good that I imagine what if I put Siemens E88CC tubes in, how much is the sound improvement?  
I cannot wait, I change plan to put in Siemens E88CC tubes first 3 days ago. Midrange sound is more lush, both high end and low end extend more, more holograph sound stage. But speed is slower than stock tube.  The fun or PRAT is reduce a little. But overall sound improvement is very satisfy. I replace KT66 with RCA 6L6GC next day. There is more dense sound and more bass. Now speed come back, PRAT is same as stock tube now. But bass is little boated, not well control. Then I put in RCA JAN OA3.
OMG, it is the last jigsaw. RCA JAN OA3 make over all sound dense, coherent and PUNCH SLAM bass!  Boated bass disappear and very well control now.

https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1365130519/975

However after I have experience of Amp Modification. I would say that tube rolling is like fine tuning tonality of sound. And NOS tubes make more delicate sound than current production tubes. But Amp modification affects to DNA of Amp. It is high risk, but the reward is very high also. It can transform your amp to be superb Amp, if it is done successfully. Save a huge money not to buy big brand name!