Amplifier Distortion, DC-Offset, and You!

Recently acquired Sansui AU-9900. Left 6mv right 15mv. That is good enough for me. How often should this be checked?

Jp

 

Sansui 5000. 23.6 - left, 24.2 - right. These were "peak" numbers seen rarely.

 

Hi !

My Harman Kardon HK 3490 gives ok results:

L 25
R 21

I have set trimpots as close as possible to 21.12 as manual stated. Probably I will need to look closer into hardware.

 

Are you confusing bias with DC offset? Be careful if you aren't 100% sure of what you are adjusting. You WILL blow up the output transistors along with other stuff.

 

Yes, I think I might be mixing up the things ! Anyways, I haven`t played with them, simply adjusted to correct values according to the manual as they seemed to drift away.
Now, how could I decrease milivolt values on speaker connectors on HK 3490 ?

 

Well it's been a few months since I recapped my Sherwood S-8910 and here's the DC offset readings as of today; 4.5mV left, 11mV right.

 

My Rotel RB976 (6 channels) range from 4.1mV to 8.4 mV. They are running quiescent currents of about 90mA per channel. It runs slightly warm, but it does sound better than the factory recommendation.

 

Do you need a preamp connected to the amplifier to get a "true" reading, or can this be done with the preamp disconnected?

I check my Rotel RB-980BX after leaving it on for 15 minutes.

L - 1.1mV
R - 8.6mV

 

My Onkyo A-22: left 11.5mV, right 12mV.

 

Sherwood S-7200. Just purchased for $20. Left channel::0.0mv. Right channel: 42mv. When listening (headphones, haven't hooked it to speakers), right channel is "static-y" and distorted.
Also, inadvertently touched two control knobs at the same time and got a lovely hum in the right channel. Be gentle, as I am a newb, but I presume this indicates a ground issue? For the hum, at least?

 

First of all get a manual service .You can find it here : https://elektrotanya.com/sherwood_s-7200_sch.pdf/download.html :After this give look to find the trimmer to set up the DC offset .The left channel seems OK you have to worl to right channel only . Here you can find a lot of advices to proceed...On AK we have the MASTER of Offset...

 

Measure the DC offset at the speaker terminals with everything disconnected and volume at maximum (select a line input if using an integrated amp).

 

Volume at minimum, not maximum .

 

Sony TA-F222ESR
R Channel: 32.5 mV; L Channel: 28.5mV
Both are not good.
I also notice a strange thing. My readings are actually negative. I am sure the connections are correct. Any explanation?

 

I already found answers http://audiokarma.org/forums/index.php?threads/amplifier-distortion-dc-offset-and-you.5634/page-2

EchoWars' excellent explanation!

 

Craig Series 5000 Model # 5504 .

Left 8.0 mv
Right 1.4 mv

 

My newly purchased Sansui AU-D907 (919's Japanese model name)
Was Left 23.5mV, Right 6.5mV
Now Left 2.5mV, Right 2mV after Bias and DC offset adjustment.

 

Sony TA F700ES

Right: 6.5mv
Left: 3mv

Pretty solid!!

 

Yamaha cr 820

R: 11.8
L: 11.6
But I went to measure idling current, and get readings of 0 on both left and right. How can this be or what am I doing wrong? Red to tp1 - black to tp2 - receiver on for 10 mins, speakers off, aux selected, vol at Minimum

 

Purchased an refurbished Sansui 661 from local shop. Decent sound but decided to check the offset after warming it up.
Before: R: 22~28 mV
L: 55~58.5 mV

After adj: R: 2.1 ~ 4.8 mV
L: 0.8 ~ 2.6 mV

I still love the sound of this old SS receiver and my mind says it sounds even better now. EDIT: I listened to the Sansui for hours yesterday. Didn't believe it could sound so much better! Unreal now. THANK YOU Echowars!

Checked an old Kenwood KR-5060 that powers up the kitchen turntable over some vintage Sansui speakers (don't laugh, it's just for making coffee and toast in the mornings). This thing sounds really clean and clear, maybe it's because of decent DC offset?

R: 2.2 mV to 4.5mV
L: -1.9 mV to 2.6 mV


Fisher CA-880 amp (has a Darlington pair and can't find where to adjust it). Still sounds really decent though. Clean.

R: 48.2 mV
L: 52.1 mV

Only with the Sansui does the offset mV swing around and fluctuates a lot even when it is really warmed up but it looks like that's okay. This thread is huge and I've only read up to the first 160 pages or so although I jumped to the end to see what's been happening. Thanks Echo for starting and sharing your knowledge!