Amplifier Distortion, DC-Offset, and You!
- Thread starter EchoWars
- Start date
Finally got around to doing this.
Sansui G-4500; 3.5mV and 7mV
Luxman R-1050; 1mV and 1mV - really low, and I tried over and over to see if I wasn't getting proper contact on the speaker connectors, but I have to conclude, it simply measured very low.
Yamaha CA-1010; 15mV and 38mV. Too high, but it might have other troubles too (meters don't react in the same manner to mono signals).
Sansui G-4500; 3.5mV and 7mV
Luxman R-1050; 1mV and 1mV - really low, and I tried over and over to see if I wasn't getting proper contact on the speaker connectors, but I have to conclude, it simply measured very low.
Yamaha CA-1010; 15mV and 38mV. Too high, but it might have other troubles too (meters don't react in the same manner to mono signals).
Sugardawg34
Active Member
Just tested my SX 1050 and got around 1 or 2 mV....but THEN, after running it for a while, it went into the negatives!!?! like -.8 mV and such. Capacitor problem? I've been suspecting one of the capacitors is drying up because occasionally, the amp will seem to lose power most noticably to the midranges. thay just lose power and start distorting and crackling. So is this a capacitor problem? thanks
EW, I just checked my Sansui QRX 7500 and got the flollowing results.
RF- 5.8-6.2
LF- 5.2-6.6
RR-22.023.7
LR-2.7-3.5
It looks to me like I have one channel that's a potential problem?
My poor Sony STR 7065 is another story.
RC-231-340
LC-189.0-221.3
Now I wish I was a tech for sure. I want to keep the Sony as everyone has "mainstream" receivers and I'd as soon have some of the less popular/well known models. What it does is produce frequency related buzzes & pops (seems to increase in speed as tone control is moved to + side) unless you turn either the high or low filter on. Also you need the treble switch turned off. So I figured the problem is in the treble switch and used some electronic parts cleaner and it helped some but after checking the DC like you suggested I'm pretty sure that no amount of cleaning will make it well. The testing was done with the tone controls in the middle and the filters off. I didn't test it with the treble off & filters on so I think I'll go do that. I'm just curious now to see if it makes any measurable difference.
RF- 5.8-6.2
LF- 5.2-6.6
RR-22.023.7
LR-2.7-3.5
It looks to me like I have one channel that's a potential problem?
My poor Sony STR 7065 is another story.
RC-231-340
LC-189.0-221.3
Now I wish I was a tech for sure. I want to keep the Sony as everyone has "mainstream" receivers and I'd as soon have some of the less popular/well known models. What it does is produce frequency related buzzes & pops (seems to increase in speed as tone control is moved to + side) unless you turn either the high or low filter on. Also you need the treble switch turned off. So I figured the problem is in the treble switch and used some electronic parts cleaner and it helped some but after checking the DC like you suggested I'm pretty sure that no amount of cleaning will make it well. The testing was done with the tone controls in the middle and the filters off. I didn't test it with the treble off & filters on so I think I'll go do that. I'm just curious now to see if it makes any measurable difference.
lorne
Sonic Lizard
Problem?
Really? I guess it could be a problem if it keeps drifting for some reason. As it stands now, I'll bet if it were reduced to approximately the same value as the others, you would not notice the difference. I am eager to read some other opinions more learned than mine, but I don't think that it is worth fussing over. I guess if you have four REALLY good pots you might try adjusting the DC offset.
Now, my AU 307 has values a tad over 100 in both channels, and that IS something to get moving on, and there are is NO DC offset adjustment. There are replacement transistors (unmatched :sigh: ) waiting in the wings. If I get 5 in one channel and 22 in the other, I'll be satisfied.
In the first pages of this thread, there are some quidelines for tolerable tolerances. I carry some fuzzy numbers around in my head, but I will let you look them up in case I misquote them. Still, I think that you are within tolerance. But, if you are striving for symetry and perfection — as they say here — 'Itatakimasu, dozo.' And best of luck too :yes: — Lorne
Really? I guess it could be a problem if it keeps drifting for some reason. As it stands now, I'll bet if it were reduced to approximately the same value as the others, you would not notice the difference. I am eager to read some other opinions more learned than mine, but I don't think that it is worth fussing over. I guess if you have four REALLY good pots you might try adjusting the DC offset.
Now, my AU 307 has values a tad over 100 in both channels, and that IS something to get moving on, and there are is NO DC offset adjustment. There are replacement transistors (unmatched :sigh: ) waiting in the wings. If I get 5 in one channel and 22 in the other, I'll be satisfied.
In the first pages of this thread, there are some quidelines for tolerable tolerances. I carry some fuzzy numbers around in my head, but I will let you look them up in case I misquote them. Still, I think that you are within tolerance. But, if you are striving for symetry and perfection — as they say here — 'Itatakimasu, dozo.' And best of luck too :yes: — Lorne
See post #351 here with regard to reading positive or negative voltages at the output.Sugardawg34 said:
Mike...
The Sony obviously needs attention, but the Sansui, while not perfect, is doing fine. That 22mV reading is still less than half of what most manufacturers say is an 'in-tolerance' reading.
Bobby4244
Active Member
EW, On the 9090db, It was working fine but one ch seemed to be putting out more than the other. So I figured I'd get dangerious and adjust the ofset and bias. Now the protection light stays on flashing red. Any suggestions?
I set the bias and offset to the same specs as the 9090. Is the DB model different?
I set the bias and offset to the same specs as the 9090. Is the DB model different?
Pioneer727
SEMPER FI
Bob the service spec's for the 9090db is diffrent from the 9090 they are not the same horse. The 9090 has more in common with the 8080 then the 9090db
Ron
Ron
Pioneer727
SEMPER FI
Sorry Bob I dont Echo may have them. It looks like you set the bias to high.
Ron
Ron
I have to ask the obvious question...how are you measuring the bias? On both the 9090 and 9090db, the bias is set by removing a fuse and using a meter as a ammeter, jumping across the removed fuse. This is a dangerous procedure unless you know what you are doing...what's more is that we've already been all over the fact that the 9090 and the 9090db are so different that they might as well have been made by a different manufacturer (exaggeration, but I'm trying to hammer home a point here)....why do you suppose you can use a procedure written for the 9090 on the 9090db? The fuses that get removed aren't even the same (F04 and F05 on the 9090db, and F07 and F08 on the 9090). The 9090 is set to 50mA, and the 9090db is set to 30mA, but I have to ask the obvious question again...how did you measure this?
Honestly, I'm hoping all you did was misadjust the offset pot and now the protect is triggered. About the only way the protect would come on when adjusting bias is if you blew it up.
I may ask the mods to remove this thread..there is no freakin' sense in tearing stuff up.
Honestly, I'm hoping all you did was misadjust the offset pot and now the protect is triggered. About the only way the protect would come on when adjusting bias is if you blew it up.
I may ask the mods to remove this thread..there is no freakin' sense in tearing stuff up.
It's either blown up, or you have the offset way out of whack.
You never answered my question about how you went about adjusting the bias?
And if the protection relay won't close because the adjustment is off, you can't use Sansui's procedure to adjust it, because Sansui, in their infinite wisdom (
), has you adjust the offset from the speaker terminals, which is useless if the speaker terminals are disconnected...as they are when the protection relay is open.
You never answered my question about how you went about adjusting the bias?
And if the protection relay won't close because the adjustment is off, you can't use Sansui's procedure to adjust it, because Sansui, in their infinite wisdom (
), has you adjust the offset from the speaker terminals, which is useless if the speaker terminals are disconnected...as they are when the protection relay is open.