gtstallion11228
New Member
ok, On my Sx-880 I have 9mv on my left channel and -19mv on the right. That doesn't sound right? do I have a problem?
Amplifier Distortion, DC-Offset, and You!
- Thread starter EchoWars
- Start date
Sounds just peachy.
Anything less than 10mV is pretty decent. Under 20mV is good. Disregard the sign....it's the total value we are concerned with, regardless of sign.
'+', '-', whatever, as long as it's low.
That Pioneer probably has an adjustment, but from your readings it's not exactly a pressing issue.
Anything less than 10mV is pretty decent. Under 20mV is good. Disregard the sign....it's the total value we are concerned with, regardless of sign.
'+', '-', whatever, as long as it's low.
That Pioneer probably has an adjustment, but from your readings it's not exactly a pressing issue.
gtstallion11228
New Member
ok great. I will leave it be then. I have 2 weeks off from work. Got to love being a school teacher... Plenty Of vacation!!!
AudioGeek
too hip to function
I checked the DCO on this 2250B several months ago and as I recall, it was somewhere in the single digits. But this thread got me thinking to check it again.
Nothing sounds bad yet, but with a 27 year old piece, ya never know when the fun is going to start. :worried:
BTW - Hey Lefty:
:lmao:
I thought all bad/burned out parts went "south"? Never heard of one heading for Phoenix or Boise. They're supposed to go south, SOUTH I say!
Nothing sounds bad yet, but with a 27 year old piece, ya never know when the fun is going to start. :worried:
BTW - Hey Lefty:
:lmao:
I thought all bad/burned out parts went "south"? Never heard of one heading for Phoenix or Boise. They're supposed to go south, SOUTH I say!
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AudioGeek
too hip to function
Marantz 2250B
DC =
L: -6.3 mV
R: -3.6 mV
Looks like everything's still copacetic in Mudville!
Hey EchoWars,
In my service manual:
Q1: I'm getting 49V between 804 & 805, but from the looks of the top of R806, I don't know how I'm going to adjust down to 35V. It's got some weird flat thing on it, and sure doesn't look like any trim pot I've ever seen.(?)
Q2: Does the 49V, which is 40% higher than the 35V spec, going to hurt anything in the long run? Or does it just push the outputs to a higher RMS than the specified 50 w.p.c., so I could be getting something like 70 w.p.c. real-world? As long as I'm getting good offset measurements like I did, should I even worry about it?
Still gotta check the idle current....hope it reads close to 10mV as spec'd!!
DC =
L: -6.3 mV
R: -3.6 mV
Looks like everything's still copacetic in Mudville!
Hey EchoWars,
In my service manual:
Q1: I'm getting 49V between 804 & 805, but from the looks of the top of R806, I don't know how I'm going to adjust down to 35V. It's got some weird flat thing on it, and sure doesn't look like any trim pot I've ever seen.(?)
Q2: Does the 49V, which is 40% higher than the 35V spec, going to hurt anything in the long run? Or does it just push the outputs to a higher RMS than the specified 50 w.p.c., so I could be getting something like 70 w.p.c. real-world? As long as I'm getting good offset measurements like I did, should I even worry about it?
Still gotta check the idle current....hope it reads close to 10mV as spec'd!!
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Can you get a pic? I know some Marantz units used some bizarre pots.
If it is indeed supposed to be 35V and is instead 49V, I'd imagine that there will indeed be some unhappy components in there sooner or later.
This is a regulated voltage, used for gain stages, relay driving, EQ, tuner, etc It won't do a thing for output power, as that is dependant on the large high-current unregulated supply.
The offset is not really a measure of if something is going to blow up or not...like I said, if that supply is really supposed to be 35V and you're pushing 50V, something is wrong and should be addressed ASAP.
00940
H-K all the way
I received my thid H/K A401 today (i should say the 2nd, the last one is still under repair) :
Left channel : 3mV
Right channel : less than 1mV (I don't really trust my multimeter this low, but it's saying 0.7mV)
Not too shabby for a 25 years amp (last one manufactured in 1977).
Left channel : 3mV
Right channel : less than 1mV (I don't really trust my multimeter this low, but it's saying 0.7mV)
Not too shabby for a 25 years amp (last one manufactured in 1977).
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AudioGeek
too hip to function
EW - yer too kind!
I shoulda known that the V-supply to the front-end gain doesn't power the outputs. :bash: What a maroon! :lmao:
And to think that I got a 94% on the resistance matrices test!
Now all I need to do is stick a fork in the toaster to get that crumbly english muffin out, and my day'll be complete....
ZZZT!
I shoulda known that the V-supply to the front-end gain doesn't power the outputs. :bash: What a maroon! :lmao:
And to think that I got a 94% on the resistance matrices test!
Now all I need to do is stick a fork in the toaster to get that crumbly english muffin out, and my day'll be complete....
ZZZT!
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DAGLJAM6
Active Member
I just got back from work and sat down with the pioneer sx650
I found at the goodwill/cancer foundation outlet.
It checks out at : Left- 22.1
Right- 33.4
not to bad for 10.00 and seems decent for my computer room setup. I'll have a go at resetting once I order the repair manual.
-Dave
I found at the goodwill/cancer foundation outlet.
It checks out at : Left- 22.1
Right- 33.4
not to bad for 10.00 and seems decent for my computer room setup. I'll have a go at resetting once I order the repair manual.
-Dave
webbb
Active Member
Luxman R-3055 receiver (got it via audiogon)
Left: 2.6 mV Right: 3.4 mV cold
Left: 0.8 mV Right: 2.1 mV warm
Yamaha CR-620 receiver (got it via eBay)
Left: 8.8 mV Right: 1.4 mV warmed up
I only had made a slight adjustment to the left side
NAD 3140 integrated (had this for 23+ years)
Left: 91 mV Right: 66 mV cold
Left: 83 mV Right: 49 mV warm
Looks like I better deal with the NAD. Anybody know what the adjustment procedure is? There are four trim pots in there but the layout is anything but symmetrical so there is not even a guess as to which one does what. It really looks hand assembled as most of the components are stood on their ends with the long lead bent back around and down. I don't think automation could have placed all that stuff.
Left: 2.6 mV Right: 3.4 mV cold
Left: 0.8 mV Right: 2.1 mV warm
Yamaha CR-620 receiver (got it via eBay)
Left: 8.8 mV Right: 1.4 mV warmed up
I only had made a slight adjustment to the left side
NAD 3140 integrated (had this for 23+ years)
Left: 91 mV Right: 66 mV cold
Left: 83 mV Right: 49 mV warm
Looks like I better deal with the NAD. Anybody know what the adjustment procedure is? There are four trim pots in there but the layout is anything but symmetrical so there is not even a guess as to which one does what. It really looks hand assembled as most of the components are stood on their ends with the long lead bent back around and down. I don't think automation could have placed all that stuff.
The four pots are almost certainly for bias and offset...but telling which is for which would be tricky. I think NAD still sells menuals for all their older gear. If not these guys apparently have one.
If you've had it that long, then apparently it's a keeper for you. No tweak you can do will be as startling an improvement as getting the bias and offset back to factory specs...
If you've had it that long, then apparently it's a keeper for you. No tweak you can do will be as startling an improvement as getting the bias and offset back to factory specs...
cabinover
Dazed and Confused
Echo, if I were to send you a schematic for my Bose amp(which is running about L60mV/R113mV) could you help me to adjust these values back to a reasonable level? There is only 1 pot on each board for bias adj, so it looks like trans swaps. I just adjusted the bias per the manual this morning and that dropped these values a little (it should right?) I just can't imagine how much better it could sound but I'll take it. Thanks, Bob
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On page three here there is a pic of an PNP differential input stage. You should have something like that in your amp (although it could be a NPN stage, but will look almost the same). These are the transistors responsible for keeping distortion and DC offset at a minimum.
If you cannot find them, scan the schematic and post it here. All else fails, sure...I'd look at it...
If you cannot find them, scan the schematic and post it here. All else fails, sure...I'd look at it...