Help Needed With Self Inflicted WOPL Build Wound....Above My Pay Grade
- Thread starter WWH
- Start date
I dc blocked all my amplifiers...when I discovered my audio generator had some small dc offset. 4.7 uf in series,, and a 220k to gnd at the RCA inputs. Now never a driving source DC problem. Frequency responce really unchanged...down to less than 10 Hz. Always make sure all offset adjustments, are made with NO input at all connected.
First of all the update....As of now she's up and running!!! Happy days..
Now for what happened in hopes of providing any help to others. My dad was an electrician and a DIY guy way before they were called DIY guys. I think they were just called guys...Anyway, whenever we were working on something he always said to go from the simple to complex...No matter how simple so as to eliminate things as you go. What threw me on this problem was coincidence and lack of in depth knowledge...once I shorted that wire and saw smoke and actual damage on that resistor my only thought was any problem had to be from that. I blow a fuse (or worse) working on an old car of mine I have a real good idea of what that can and can't affect. On this, I just didn't know what that one short could lead to. But once all the measurements were checking out and you asked this (and George mentioned checking the preamp, etc.) it made me stop and restart the whole process. The light board was the first thing I unhooked after replacing the resistor as it was involved in the original screw up. No change at that time, so on from there as you all know.
Here's what happened and I have to say this is a new one to me. I went back to eliminate the preamps as a problem. The preamps I have at the moment are both old Sansui receivers so not a sure thing. I tried both and once again got the loud hum from both.... then it happened. Due to limited space the receiver was facing away from me. I moved to turn off the power strip I was using for the preamp instead of getting up to turn of the switch on the front. I bumped the RCA cable. For a split second the hum changed. I moved it some more and the hum varied. My first thought was coming on here and giving this update as my error must have caused some complex issue that affected the output signal to the RCA jacks...etc., etc. However, staying with the very simple to complex theme I realized there was one thing I hadn't changed out the whole time. Something I've never had go bad. Yep, the RCA cable.... I powered down and changed the cable. Holy crap Batman, the hum was gone. It was the same cable I used the first time and the same cable I've always used for a temporary hook up. First time I've had a problem cable....and of course it was now. Damn that Murphy and his law! Thanks again for all the help as I might not have gone back to the beginning not knowing the more technical stuff was checking out. After this I promised myself I would stop letting my one non-working meter bother me....at least for a couple of weeks.
Now for what happened in hopes of providing any help to others. My dad was an electrician and a DIY guy way before they were called DIY guys. I think they were just called guys...Anyway, whenever we were working on something he always said to go from the simple to complex...No matter how simple so as to eliminate things as you go. What threw me on this problem was coincidence and lack of in depth knowledge...once I shorted that wire and saw smoke and actual damage on that resistor my only thought was any problem had to be from that. I blow a fuse (or worse) working on an old car of mine I have a real good idea of what that can and can't affect. On this, I just didn't know what that one short could lead to. But once all the measurements were checking out and you asked this (and George mentioned checking the preamp, etc.) it made me stop and restart the whole process. The light board was the first thing I unhooked after replacing the resistor as it was involved in the original screw up. No change at that time, so on from there as you all know.
Here's what happened and I have to say this is a new one to me. I went back to eliminate the preamps as a problem. The preamps I have at the moment are both old Sansui receivers so not a sure thing. I tried both and once again got the loud hum from both.... then it happened. Due to limited space the receiver was facing away from me. I moved to turn off the power strip I was using for the preamp instead of getting up to turn of the switch on the front. I bumped the RCA cable. For a split second the hum changed. I moved it some more and the hum varied. My first thought was coming on here and giving this update as my error must have caused some complex issue that affected the output signal to the RCA jacks...etc., etc. However, staying with the very simple to complex theme I realized there was one thing I hadn't changed out the whole time. Something I've never had go bad. Yep, the RCA cable.... I powered down and changed the cable. Holy crap Batman, the hum was gone. It was the same cable I used the first time and the same cable I've always used for a temporary hook up. First time I've had a problem cable....and of course it was now. Damn that Murphy and his law! Thanks again for all the help as I might not have gone back to the beginning not knowing the more technical stuff was checking out. After this I promised myself I would stop letting my one non-working meter bother me....at least for a couple of weeks.
Have to wonder if shorting the inputs would be advantageous for checking a amp for DC on the outputs. All the PL2000 preamps come with self shorting RCA's. The shorting feature is enabled on the inputs, but disabled on the outputs by a gap on the ground trace. Convention says to never short the outputs.
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- Halfbiass...Electron Herder and Backass Woof
By definition, a short at the input is Zero Volts, so the output should be Zero volts. Same for both DC couples, and DC blocked amps. I would not short the output of a preamp... no reason to do that. Switched short on Inputs on Preamps do that to reduce crosstalk, if the other inputs have signal on them. Usually no harm is done to the preamp unless something else is wrong with it.
I have a 7000 and an Eight receiver. Neither one has gotten the once over yet, so you have a point. Could have been an issue with both....especially since I haven't used the preamp outputs very much. I did look closer at the RCA cable and found a split that went all the way to the shielding...going to dissect a bit further when I have some time...just out of curiosity.
- Joined
- Jan 14, 2011
- Messages
- 74,968
- Location
- Gillette, Wyo.
- Tagline
- Halfbiass...Electron Herder and Backass Woof
- Joined
- Jan 14, 2011
- Messages
- 74,968
- Location
- Gillette, Wyo.
- Tagline
- Halfbiass...Electron Herder and Backass Woof
I opened the Generator, and made the internal offset adjustment. It was clearly marked. Now its just a few millivolts.
I added the DC block to all my "DC" amplifiers, 4.7uF will not affect Very low bass signals, no audible or sonic difference that I can tell. Amp still flat to 10 Hz. Just belts and suspenders protection.
I added the DC block to all my "DC" amplifiers, 4.7uF will not affect Very low bass signals, no audible or sonic difference that I can tell. Amp still flat to 10 Hz. Just belts and suspenders protection.