Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › DIY RA-1 CMOY, SONY XPERIA TL, RF PROBLEMS
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post #1 of 5
Thread Starter 

My Xperia TL, Winamp Pro, FLAC files, sounds pretty good with my Klipsch S4s. I got a DIY RA-1, 18V, CMOY, to drive my T50RPs. Whenever my phone receives data via 4GLTE(Weather Channel, etc), the audio adds hissing and buzzing till the data access ends. This also happens if I switch tracks or turn the screen back on. Is this RF interference? No problem with another FM radio source. I got my kit from Justin at AMPEDUP. It uses the same circuit and board that Fred_Fred sells on EBAY(RA-1,18V,CMOY,DIY) Any ideas about what could be causing this or how to fix it? Thanks,satwilsonhttp://www.ebay.com/itm/CMOY-RA1-18V-Hi-Fi-Headphone-Earphone-amplifier-diy-pcb-printed-circuit-board-/190815146323?pt=AU_Electronics_Audio_Amplifiers&hash=item2c6d781153

Edited by satwilson - 5/30/13 at 3:29am
post #2 of 5

What gain did you use? Pretty please tell me its less than 4, but more than 2. 3 is a good number. 3 is slightly less than pi, and pi is a very good number. If you built an amp with gain of pi (even if rounded to 1 decimal place) you are my hero. 


Do you have access to an oscilloscope? Can you see if the amp is oscillating? If not read on - 


Have you measured the idle current of the circuit? Does it make sense against the datasheets? Oscillating amps frequently draw excessive levels of current with no load. If you cant do that (all you need is a mA meter... not very high tech) read on - 


Do you have access to a "known good" amp to compare against? Does it behave similarly?


If the amp passes all of these tests be happy that your amp isnt acting up and just accept that cell phones emit unusual levels of RF and there is not much you can do about it. If its any consolation cell phones used to be worse. Maybe try a shielded cable. 

post #3 of 5
My DIY ra-1/cmoy also picked up noise from my mobile phone. Changing the gain from 4 to 1 fixed it. In addition, my case is shielded with aluminum tape.
But isn't that kind of noise completely normal?
post #4 of 5
Thread Starter 

Thanks to both of you for your replies. UnknownAX, found your Cmoy components/gain thread and nikongod's comments, etc to be very helpful. Silly me, I imagined my phone and Cmoy would be just plug and play!

post #5 of 5
Thread Starter 

Update, got a Hammond cast aluminum case for the Cmoy and the buzzing is gone and the hum reduced to an acceptable level. BTW, amp was built with resistors for a gain of "4", upgraded caps to 1000uf Nichicon KA(M), FiiO L2 cable. I really like my Xperia TL as a phone and 13MP camera. Now that I have got music happening I am good to go. The S4's are my first IEM's, and even after trying various tips including the Comply's, the comfort level for me was not there. So getting the Cmoy built and working well with my T50RP"s was important. I usually have the Fostex plugged into my NFB-12 desktop setup, which for me is a good pairing. The SQ and power of the Cmoy with the Fostex is acceptable for my first portable setup. After reading reviews here at HF about the new FiiO X3 DAP, the upgrade path is clearly defined, sigh......

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