I'm new to AVS and the forum, I actually found it when troubleshooting my gear and looking for information on Google. I found a thread on this forum: http://www.avsforum.com/t/1375259/emotiva-beware-of-emotiva-issue-resolved/270
. I wanted to share my experience with everyone here with the Emotiva XPA-5 (amplifier) and UMC-200 (pre-amp) and hopefully receive some help or tips in return. So here we go:
Let me start of by mentioning that I live in the Netherlands. Last february I bought a XPA-5 and UMC-200 from Emotiva with some discount, they were on offer since it is factory renewed hardware. I was promised all units are like new but might have some cosmetic damage, furthermore they are tested before being sent out. The testing part is especially important in my case since I live in Europe and already realised any support might become troublesome.
I use the following speakers: front L/R - B&W 601 s2, center - B&W LCR60 s3, Surround L/R Monitor audio radius HD90. All speakers are somewhere around 88 dB spl sensitivity. When I received the XPA and UMC I hooked it all up and I noticed there was a buzz (100 Hz) coming from the speakers. I started troubleshooting and couldn't find what the problem was / is. I use decent interconnects (http://www.ruconnected.nl/18-73-productpagina/interlink-cinch-tulp-1m.jpg
) and don't have any ground loops (I'll explain in more detail in a bit). I disconnected the UMC-200 and focussed my attention on the XPA. I found out that everything is fine when there are just speakers connected, but as soon as there is more than one input (RCA or XLR) in use the buzz becomes audible. I actually still need to verify with the oscilloscope if it is actually not present with only one input in use or not audible. I ruled out the buzz being caused by a ground loop by connecting my iPhone as a pre-amp using a jack to dual RCA cable. One RCA connected equals no buzz, add the second and the buzz is there. The iPhone bit was actually suggested to me by Emotiva and they have been helping me out up untill now (more on their support further on).
After the iPhone test the Emotiva techs themselves were also convinced the buzz is being produced by the XPA itself. This was probably somewhere near the end of february. I then got into a lengthy process with Emotiva tech to try and figure out what is wrong with the amp. A new input board was sent out to me twice. Both times it did not help to replace this board which contains the RCA connectors. It was probably near the end of may when I installed the second input board, so a lot of time went by waiting on Emo tech support and international shipping of the parts. After installing the second input board I was offered an option to return the XPA. This seems fair enough but it doesn't help if I have to pay the return shipping costs ($500! due to the weight of the unit). There was no possibility to get this arranged together with Emotiva in such a way that it would not mean me losing on $500 due to shipping. So I had to decline that offer, I basically had no choice.
Emotiva supplied me with circuit schematics of the boards, which I took to a technician. The guy really knows a lot about amps and was not entirely sure a certain section of the amp boards is designed in the best way to reduce the risk of buzzing or other noise (I can go into more detail for those interested, but I don't think it will add any useful information to this post). Furthermore there are some quite lengthy connections inside the unit for the ground connections, which seems "dangerous", or at least increases the chances that there could be issues. This is due to the placement of the boards inside the "cabinet", it's normally better to minimise the length and consequently the (low frequency) resistance of the ground connections in amp designs. He found out that in some way a 100 Hz signal is being fed back to the input of the amp boards when more than one input is in use. He also told me, and this makes perfect sense, that he had a harder time hearing the buzz because his speakers have a lower sensitivity of around 86 dB. He also tried to place a resistor (10 Ohm) in the ground connection of some interconnects between a pre-amp and the XPA, which made the XPA go into the safe mode. This I actually find strange. Funny thing was, when placing a pure resistive load on the inputs (more than one), there was no buzz at all and the XPA did not go into the safe mode. In the end the only suggestion he had left was to modify one of the input boards and add a voltage divider to each of the inputs. This means the buzz signal which is being fed back to the input is also divided and becomes inaudible, the pre-amp will need to be used with a higher volume setting to reach the same volume level as before.
So in the end it seems I managed (with help) to find a way to get rid of the annoying buzzing, but it would come at a price (I haven't installed any modified input board yet). The gain / volume wouldn't be as high anymore as it could be. So I'm left wondering if I am the only person to experience these issues with the XPA-5 and is there still a defect inside the unit? The power supply boards might have issues (too much ripple voltage on the power to the amp boards?), since it definitely seems linked to power supply due to the frequency (we use 230V 50 Hz here, if you rectify that using semiconductors you will produce 100 Hz). Or is it possible that one or more of the amp boards contain a defect which is feeding the 100 Hz to the inputs?
So I had the XPA and UMC just sitting in a closet for months now, since I really get annoyed by the buzzing and I don't have another amp I can use with the UMC-200. After taking the XPA to the technician I decided to just hook it all up again and try to not be annoyed with the buzz. I then found out that when I turn on the XPA there is a popping sound in all the speakers and then again when turing on the UMC-200. The pop from the XPA is louder than the one from the UMC. I guess I could live with that if it would happen only at turning the stuff on. As it turns out, when I was playing a blu-ray through the playstation 3, there is a pop everytime the audio switches format.. So during all the intro's on blu-rays you get a whole bunch of pops after one another because they are usually in different audio formats. I went through all the connections and in the end had nothing but the subwoofer connected to the UMC-200 (also the XPA was disconnected) and it still popped.
I'm not really sure what I should do now, I guess I will call Emotiva tech about the UMC-200 as well.
A little bit more on the XPA 5; the picture above shows the 5 amp boards at the top and in yellow I drew where the ground connections are that run from the front to the back of the unit, along the input board towards the back of the 5 amp boards. The "true ground" is in the bottom right on the board with the large capacitors. The ground is also connected on the other side of each amp board (I drew that in green for one board) where the power is connected as well to the amp board. Sorry for the Dutch text in the image.
I would appreciate any experiences that people are willing to share or ideas. I would actually also be very much interested in pictures you guys might have taken from the inside of your XPA-5, it would be interesting to see if there are any differences. I'm thinking mostly about the type of wiring used for ground connections that I drew in yellow and green.
To be continued...