• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Amplifier Distortion, DC-Offset, and You!

Hope I did this right, in reading this enitre thread(ok I scaned the last 10-15 pages) I did not see anyone checking newer equipment. Although my amp is not all that new, I really dont think of it as vintage.

Ok with the pre-amp on, sit to a unused input, volume at zero, my Adcom 545 reads 40 milivolts on the left channel and 26 milivolts on the right channel.

Does this sound ok?

Thanks,
Todd
 
No problems there. It would be nice if it were a little lower, but 50mV is the accepted industry maximum (although Adcom specs for most gear say <15mV, so technically you are probably out of spec).
 
Update: Denon Receiver

fropiler said:
Two decent receivers in two months. no good.

So, what does it mean when you don't hear the "click" sound shortly after power up? Just prior to total meltdown, this unit would intermittantly emit a very loud, short buzz even without volume up. Worked fine otherwise.

Thanks,
Ed
Click to expand...

I recently decided to look into this further, and after letting it sit for four months, it now decides to work!

Not for long though. After about a week, another loud buzz/pop and then silence. This time It was out in the garage so I peeled the cover off and hit the 16 year old (never been serviced or cleaned)dusty circuit boards with compressed air.

Must have been some metallic micro-fiber shorting something out, because it works like a champ now!
 
OK. I recently aquried my second Pioneer SA-9100 and this time I broke down and got myself a service manual. I know I need to adjust the bias and offset (Im getting readings for offset R 45mv L 37mv). The thing is I can't quite figure out the meaning of this one sentence on the alignment page. The're the ones I underlined in red.

I know where terminal no.3 is, but I just can't figure out what it means by terminating it. Does it mean terminate it to "ground" using the 4.7k resistor? I just want to make sure about this before I go any further and risk blowing the thing up :worried:

alignment1a4hi.jpg


And here's the power board schematic just in case.....

alignment29ep.jpg
 
They just want you to ground the input terminal with a 4.7K resistor to eliminate the possibilty of outside influences affecting your measurements. For ballpark adjustment, you can skip it.
 
I checked my 2215B today just for the practice and noticed it fluctuated. W/ the vol off aux selected w/ no input and the speakers disconnected testing at the end of the speaker cables my radio shack DMM 22-718 reads from +5.0 to -4.0 Mv changing to various reading 2 times a second. With such low readings I was happy but am puzzled by the fluctuations, so whatsup??

This must be the longest running post on this site, most likely because it's an easy test anyone can do and it makes you feel like you have at least some control over your equipment.

Show it you care give it the test today.
 
Last edited:
Many amps bounce around a bit...reconnect the speakers and it may reduce the fluctuation, but a lot is simply due to the design of the amp. Some are just a bit more jittery than others.
 
Doh!!

EchoWars said:
You mean...it was working, you decided to do an offset test, and now it's not? Did you by chance short the speaker terminals somehow? Or set your meter to read amps and then connect to the terminals (which would short them)?

Sorry to hear it. Whatever is the matter can be fixed.
Click to expand...

After all this time it just now occured to me. When I had last used the receiver I was also using a friends EQ. In order to use an EQ with this model you need to remove the metal pre-amp JUMPERS on the back and plug in the EQ. I'm not home now, but when I get there I have sneaking suspicion that I will find that I never put the jumpers back in when I returned the EQ.....

What a bone-head!
 
I am doofuss

fropiler said:
After all this time it just now occured to me. When I had last used the receiver I was also using a friends EQ. In order to use an EQ with this model you need to remove the metal pre-amp JUMPERS on the back and plug in the EQ. I'm not home now, but when I get there I have sneaking suspicion that I will find that I never put the jumpers back in when I returned the EQ.....

What a bone-head!
Click to expand...

Hear me roar!

Not a damn thing wrong with my Yamaha RX-1100U Natural Sound Receiver that connecting the preamp to amp section won't take care of.

Not exactly vintage (1987), Nice to have it back though.
 
This is not an advertisement

Trust me when I tell you, You won't find any better than EW. I put him through the test and he won. I stick by him and I swear by him. Nough said? :thmbsp:
 
Using the information I got over in this thread in the Pioneer forum I was able to adjust the DC offset on my SA-9800 from around 55mV and 75mV down to nearly zero. I've just now gotten a chance to do some critical listening and can tell the difference. I can hear the added clarity even with my damaged middle ears, particularly on the Cocteau Twins CD I'm listening to now, with such high-frequency female vocals. Big thumbs up are due to everyone that has helped me out here at AK :thmbsp: -- Foe
 
After clearing the dust and grim bunnies off my Pioneer 737 I discovered that several caps on my power board are leaking. Should I even bother with the DC-offset test with the receiver in this condition?

On a seperate note can someone post pics of the correct setting position of their multimeter for the DC offset test. I have a Sperry DM-4100A if that helps.

Appreciate it.
 
Theres a black glue substance on the board and up the side of 4 caps. Now this thing was grimmy but this is a different black grim and only in the cap areas.
 
If it's hard, like glue, then that's what it is.

I looked at the specs for the Sperry meter. Its best low voltage DC setting is only 2V, so set it to the 2VDC range. Red lead on speaker positive term, black on negative. Read meter...
 
You must log in or register to reply here.
Back
Top Bottom