Amplifier Distortion, DC-Offset, and You!
- Thread starter EchoWars
- Start date
Trodder
Member
My Fisher CA-880 that is going to undergo some fixes and enhancements is as follows:
Left A Channel Reading = 37.7mv after 1 minute
Right A Channel Reading = 38.5mv after 1 minute
Both seemed to stabilize after about a minute with no load on the channels. The intial reading when the protection relay kicks it hits 150mv + or - on each than drops rapidly to the specified values and seems to be stable there after only a minute or so.
I will report back with my Nikko -NA-850 (current live system) once I get a change to test that
Left A Channel Reading = 37.7mv after 1 minute
Right A Channel Reading = 38.5mv after 1 minute
Both seemed to stabilize after about a minute with no load on the channels. The intial reading when the protection relay kicks it hits 150mv + or - on each than drops rapidly to the specified values and seems to be stable there after only a minute or so.
I will report back with my Nikko -NA-850 (current live system) once I get a change to test that
KrautNotRice
Well-Known Member
Very helpful thread, thanks to EW for starting it.
I just tested 3 of my amps with multimeter set to 200mv DC:
Yamaha CR-1020 R: 2.5 L: -0.7
Yamaha P2200 R: 21.5 L: 20.1
Teac A-H500 R: 18.1 L: 49 !!!!!!
The craziest thing is that the Teac still sounds AMAZING as is. Just shot out all 3 amps back to back with the same cd and the Teac is fantastic, with the P2200 a close second.
Maybe it's time for a service and it'll be even better?
I just tested 3 of my amps with multimeter set to 200mv DC:
Yamaha CR-1020 R: 2.5 L: -0.7
Yamaha P2200 R: 21.5 L: 20.1
Teac A-H500 R: 18.1 L: 49 !!!!!!
The craziest thing is that the Teac still sounds AMAZING as is. Just shot out all 3 amps back to back with the same cd and the Teac is fantastic, with the P2200 a close second.
Maybe it's time for a service and it'll be even better?
OK, Hi Echowars.
I bet you had NO idea how long THIS thread would go on!
So, 226 pages, WOW!
So I just picked up an Audire Parlando.
Not much out there on the web and I'm still evaluating its functionality, but its working.
I came across your thread at some point and it couldn't be any timelier!
So here's my 2 cents.
This amp takes a Looooong time to stabilize (45min-1 hr) and I may have taken these readings a little prematurely (35 min.)
I measure 29.9-32.2 for my R. channel & -.6/+3 for the L.
The range is due to a slow variation which I assume is it's thermal state stabilizing.
I'm not sure though, The L. channel is the one I was more concerned with as this amp has a bunch of independent heat sinks per channel and there's a lot of variation on the L. channel.
Not too bad considering it was a blind purchase! Leaves me room to tinker, no?
I bet you had NO idea how long THIS thread would go on!
So, 226 pages, WOW!
So I just picked up an Audire Parlando.
Not much out there on the web and I'm still evaluating its functionality, but its working.
I came across your thread at some point and it couldn't be any timelier!
So here's my 2 cents.
This amp takes a Looooong time to stabilize (45min-1 hr) and I may have taken these readings a little prematurely (35 min.)
I measure 29.9-32.2 for my R. channel & -.6/+3 for the L.
The range is due to a slow variation which I assume is it's thermal state stabilizing.
I'm not sure though, The L. channel is the one I was more concerned with as this amp has a bunch of independent heat sinks per channel and there's a lot of variation on the L. channel.
Not too bad considering it was a blind purchase! Leaves me room to tinker, no?
rgbeach
Active Member
Adcom GFA-535II, recently refurbished using kits from Chris Hoppe (https://hoppesbrain.com/), including replacing the power supply board and critical components on both amp boards, notably both pairs of input transistors with closely matched pairs.
R Ch.: 0.2 mVDC
L Ch.: 0.4 mVDC
R Ch.: 0.2 mVDC
L Ch.: 0.4 mVDC
Hello I can here static/distortion in left channel. I read like first 10 pages of this discussion and decided to see how my circa 1994 pioneer vsx 453 receiver faired. DC offset Left 90mv and Right 6mv. I guess I need to find resistors for the left side. I'm very new at this anyone have pics of resistor locations and maybe have a how to/diy of someone doing a similar fix. TIA
bill114
Active Member
bill114
Active Member
thank you!
The Rebel
Active Member
Pioneer SX-1250
Right = 1.1mV
Left = -2.3mV
How bad do I need to worry about the negative reading, and is it something that would be detrimental to mids and tweeters? This receiver has never been re-capped, is very clean inside, and sounds amazing. Is it a candidate for a re-cap, or keep rocking as is? Thanks for the thread Echowars!
Right = 1.1mV
Left = -2.3mV
How bad do I need to worry about the negative reading, and is it something that would be detrimental to mids and tweeters? This receiver has never been re-capped, is very clean inside, and sounds amazing. Is it a candidate for a re-cap, or keep rocking as is? Thanks for the thread Echowars!
Bryston 4B ( original model -could be as much as 40 years old by now) :
R: 14 mV
L: 22 mV
What's interesting about this is I decided to pull it out of service because it was the source of the sticky black goop on the top of the 4B ST mounted about 10" below it. Fortunately (?) the black goop wasn't coming from inside the 4B - but was the residue of the feet -having run real hot for long enough to have MELTED. I had originally walked away from this problem yesterday afternoon (bar system -still played -so....) -but as I thought about it decided to drive down at bar time and replace these two amps -didn't want to have a fire on my conscience. These original model 4B have to be up there with the Crown DC300A when it comes to near indestructibility. But I think this particular 4B is going out to pasture.
R: 14 mV
L: 22 mV
What's interesting about this is I decided to pull it out of service because it was the source of the sticky black goop on the top of the 4B ST mounted about 10" below it. Fortunately (?) the black goop wasn't coming from inside the 4B - but was the residue of the feet -having run real hot for long enough to have MELTED. I had originally walked away from this problem yesterday afternoon (bar system -still played -so....) -but as I thought about it decided to drive down at bar time and replace these two amps -didn't want to have a fire on my conscience. These original model 4B have to be up there with the Crown DC300A when it comes to near indestructibility. But I think this particular 4B is going out to pasture.
bill114
Active Member
NAD 2100. I've owned it for years, bought used. It's been very reliable and has had no repairs done to it (that I know of) other than new protection relays. . Since there is no offset adjust, finally got around to replacing the differential pairs. I also have a 2400 that had a highish reading on one channel (over 60mv) so I sourced original differential pair chips for that amp from B+D.
These only brought offset down to around 35mv so I decided to go the seperate transistor route for the 2100. I matched by Hfe and Vf(Vce) using a transistor tester.
Before:L-56.6 R-71.3
After: L- 4.5 R- 11.9
Research tells me that it's good to also measure Vbe difference in pairs and get that as close to zero as possible but my method yielded pretty good results.
I subbed Fairchild KSC1845FTA for the 2SC3066 chip and Fairchild KSA992FBU for the 2SA1239 chip. Ran the amp for a while after repair and it sounds great.
These only brought offset down to around 35mv so I decided to go the seperate transistor route for the 2100. I matched by Hfe and Vf(Vce) using a transistor tester.
Before:L-56.6 R-71.3
After: L- 4.5 R- 11.9
Research tells me that it's good to also measure Vbe difference in pairs and get that as close to zero as possible but my method yielded pretty good results.
I subbed Fairchild KSC1845FTA for the 2SC3066 chip and Fairchild KSA992FBU for the 2SA1239 chip. Ran the amp for a while after repair and it sounds great.
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