Hi, everyone. It's been a long time since I posted. But after 6 or 7 years I have finally completed my surround sound Ugs pre + Mini U.P. Project.
TL;DR: double check your XLR pinouts.
The Project consisted of 4 Ugs stereo pre amps with relay based attenuators pretty much exactly like in the main UGS thread that could be linked and controlled with one acting as a "master" and the others as "slaves". They each have 4 inputs (1 switchable to balanced XLR), balanced XLR and unbal out, 12 volt triggers for power amp on/off and hot/cold bias, and dual mono outboard power supplies.
The power amps are 7 "Mini UGS Power" aka Mini U.P. Monoblocks that have switchable hot/cold bias that in "hot" mode can put out almost 40W class in into 6 ohms (if I remember correctly, definitely 40W into 8 ohms, it's been a while), bal/unbal inputs, and dual mono outboard power supplies.
The designs are nothing different. I pretty much followed exactly what Cheff had done in his threads (Thanks Cheff!) The goal was to build a full surround sound system that had, from source to speakers, zero caps in the signal path. Source is an RME Multiface 2 and the speakers are 3 pairs of PMC TB2+
(I would be using my PMC FB1's for mains, but they won't fit in my bedroom.) Don't have a sub. . .yet.
Anyway, I had "finished" the project around 6/7 years ago, but had never been happy with the performance. The power amps were fine. The preamps however never lived up to expectations. I could never turn them up as loud as I wanted. They would start to get ground hum around 20dB below full and they would start to cause increasingly unmanageable DC speaker offset (like multiple volts.) I spent hours and hours trying to find the problem. It was definitely a ground issue.
So life being what it is, I've just lived with it. For 6 years I've just never turned the preamps above -20dB. Everything works, been watching movies, listening to music, but always known it could be better and always wishing to turn it up just a little bit more.
I had loaned a stereo set of pres and amps to my best buddy when I had finished so he could enjoy the fruits of my labor. About a year ago, I retrieved them back because he said 1 channel had starting humming real bad. I've had them laying around for the past year collecting dust and a couple days ago I finally decided to check them out.
Yup, 1 channel or the preamp humming pretty bad (more than usual). Spent all one night and the next morning dissecting, changing power supplies, checking ground connections, etc.
Checked the pin connections on the XLR connectors. Everything's fine. Check everything again. and again, and again. Check the pins on the XLR connectors. Everything looks good. Start pulling my hair out. Start checking cables. everything is good.
I picked up an XLR cable and looked at the input end. . . .
Unbelievable. I sat there for literally over 15 min saying, "unbelievable" every 30 seconds or so.
I had never noticed, or realized, or thought about it. . . when looking straight on at the input and output ends, pins 1 and 2 on XLR connectors are switched!! I had wired the outputs on all the preamps wrong.
Took me about 30 min to swap pins 1 and 2 on all the outputs on all the preamps.
Now with the preamps turned all the way up, maybe I can hear some hum with my ear against the woofers (my apt is somewhat noisy, it's hard to tell). There is some hiss in the tweeters with an ear against them. Dead silent from more than a foot away.
Speaker offset with preamps full on: rock solid <10mV on all speakers without any additional adjustment. Most around 7-8mV.
And much louder! Normal listening level before was around -30dB for music and -20dB for movies. Now, I'm in the -40dBs and -30dBs. Looks like I gained about 12dB in signal and lost all hum.
The original problem of additional hum in one channel disappeared, must have been a bad connection/solder joint on the output.
Happy Camper!!!!
Sorry for the long post.
TL;DR: double check your XLR pinouts.
The Project consisted of 4 Ugs stereo pre amps with relay based attenuators pretty much exactly like in the main UGS thread that could be linked and controlled with one acting as a "master" and the others as "slaves". They each have 4 inputs (1 switchable to balanced XLR), balanced XLR and unbal out, 12 volt triggers for power amp on/off and hot/cold bias, and dual mono outboard power supplies.
The power amps are 7 "Mini UGS Power" aka Mini U.P. Monoblocks that have switchable hot/cold bias that in "hot" mode can put out almost 40W class in into 6 ohms (if I remember correctly, definitely 40W into 8 ohms, it's been a while), bal/unbal inputs, and dual mono outboard power supplies.
The designs are nothing different. I pretty much followed exactly what Cheff had done in his threads (Thanks Cheff!) The goal was to build a full surround sound system that had, from source to speakers, zero caps in the signal path. Source is an RME Multiface 2 and the speakers are 3 pairs of PMC TB2+
(I would be using my PMC FB1's for mains, but they won't fit in my bedroom.) Don't have a sub. . .yet.
Anyway, I had "finished" the project around 6/7 years ago, but had never been happy with the performance. The power amps were fine. The preamps however never lived up to expectations. I could never turn them up as loud as I wanted. They would start to get ground hum around 20dB below full and they would start to cause increasingly unmanageable DC speaker offset (like multiple volts.) I spent hours and hours trying to find the problem. It was definitely a ground issue.
So life being what it is, I've just lived with it. For 6 years I've just never turned the preamps above -20dB. Everything works, been watching movies, listening to music, but always known it could be better and always wishing to turn it up just a little bit more.
I had loaned a stereo set of pres and amps to my best buddy when I had finished so he could enjoy the fruits of my labor. About a year ago, I retrieved them back because he said 1 channel had starting humming real bad. I've had them laying around for the past year collecting dust and a couple days ago I finally decided to check them out.
Yup, 1 channel or the preamp humming pretty bad (more than usual). Spent all one night and the next morning dissecting, changing power supplies, checking ground connections, etc.
Checked the pin connections on the XLR connectors. Everything's fine. Check everything again. and again, and again. Check the pins on the XLR connectors. Everything looks good. Start pulling my hair out. Start checking cables. everything is good.
I picked up an XLR cable and looked at the input end. . . .
Unbelievable. I sat there for literally over 15 min saying, "unbelievable" every 30 seconds or so.
I had never noticed, or realized, or thought about it. . . when looking straight on at the input and output ends, pins 1 and 2 on XLR connectors are switched!! I had wired the outputs on all the preamps wrong.
Took me about 30 min to swap pins 1 and 2 on all the outputs on all the preamps.
Now with the preamps turned all the way up, maybe I can hear some hum with my ear against the woofers (my apt is somewhat noisy, it's hard to tell). There is some hiss in the tweeters with an ear against them. Dead silent from more than a foot away.
Speaker offset with preamps full on: rock solid <10mV on all speakers without any additional adjustment. Most around 7-8mV.
And much louder! Normal listening level before was around -30dB for music and -20dB for movies. Now, I'm in the -40dBs and -30dBs. Looks like I gained about 12dB in signal and lost all hum.
The original problem of additional hum in one channel disappeared, must have been a bad connection/solder joint on the output.
Happy Camper!!!!
Sorry for the long post.
good and proper rant is always welcome ....... never mind who addressee is
(been there , done exactly that ........
)
I did that fairly recently with my newly built "soundbar" for the TV, which I chose to power with one of the Sure Class D amps. Kept wondering why the sound was so thin... Turns out I wired everything correctly according to the markings on the board, but the + and - of one channel is misprinted on the board!
Frustrating.
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