Amplifier Distortion, DC-Offset, and You!

komhst

Active Member

• Jul 12, 2015

• #4,101

Accuphase E-450
Left Channel 1.9 mV
Right Channel 2.1 mV

Yamaha RXV-750
Left Channel 8.1 mV
Right Channel 7.8 mV (I didn't measure the center and the surrounds)

 

jriggio

New Member

• Jul 12, 2015

• #4,102

Thanks for this. I just purchased my first older integrated amp: Pioneer SA-9100 and after a friend told be about it, thought I'd run the test before I run the thing. Looks good: 1 mV on Left and 10 mV on the Right.

 

jessbob

Active Member

• Jul 18, 2015

• #4,103

Lafayette

Here are my numbers from my Lr-9090

 

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jk0592

New Member

• Jul 19, 2015

• #4,104

NAD3125
Left channel -33.5mV
Right channel -32.8mV

A bit high, will be keeping an eye on this one.

 

J

jimmymcfarre

New Member

• Jul 24, 2015

• #4,105

Sony str-v5 receiver 4mv & 7mv
Rotel (modern) amplifier 67mv & 56mv
The numbers don't lie & the 35 y/o Sony certainly sounds better than the modern Rotel.

 

15RTPlus

Active Member

• Jul 25, 2015

• #4,106

Realistic STA-820

RT = 8.8mv

LT = 4.4mv

I'm good with that! :thmbsp:


Jeff

 

jimbo2k

AdcomGFT500,2GFA535,BandO,RX2.,MMC3,C101.L810's

• Jul 26, 2015

• #4,107

So i did my mono blocks

SWTPC tiger 01s I built in late 70s One amp is a nice 12mv, but the second is up to 34 mv. Sure would like to get it down to the vicinity of the other. Any suggestions. Here i the topoghraphy of the amp. The .01 was rated at 65 watts @ .01 IM distortion. It was known to blow away amps with more powerful ratings. It was a full complementary symmetry DC coupled class AB design. http://www.tigersthatroar.com/?page_id=12. Thanks in advance. Jim

 

ConradH

AK Subscriber

Subscriber

• Jul 26, 2015

• #4,108

For the Tiger, I'd look at the resistors first. If they used carbon composition like other some other Tigers, they might have drifted off-value. The 100 ohms should be closely matched. Check the front end, but might as well check all of 'em while you're in there. Semiconductors could be changing a bit, but you should be on a pretty good test bench before messing with that.

 

Gazdatronik

Super Member

• Jul 26, 2015

• #4,109

5.4mv and 9.1 mv on an all original(except relay) 1980 Apt Holman. The service manual says the amp auto-biases itself to a point-and after 35 years, I believe it.

 

M

mspw

New Member

• Aug 4, 2015

• #4,110

Aiwa ax-7600

5mv avg both left and right.

 

OldRedneck

Ate up in the head

• Aug 6, 2015

• #4,111

Pioneer SA-7500II reads 3 and 6 mV.

I think it's never been serviced, other than me cleaning up under the hood.

 

jmrosen

New Member

• Aug 10, 2015

• #4,112

Can't seem to locate DC offset on the Sony STR-GX700ES

Just picked up a nice one owner pristine STR-GX700ES for the bedroom. Below is the service manual and I cannot find Bias or DC offset? Anyone know of it's fixed and can't be adjusted or am I missing something?

Thank you in advance.

http://sportsbil.com/sony/STR/STR-G/STR-GX700ES.pdf

 

Last edited: Aug 10, 2015

EchoWars

Hiding in Honduras

Sponsor

• Aug 10, 2015

• #4,113

A brief flip through the manual, and I saw NO adjustments whatsoever.

 

OMGCat!

Super Member

• Aug 10, 2015

• #4,114

This was a bit high.


Full disclosure it that this was a Pioneer SX-8 that had been sitting on a shelf in a garage waiting to be thrown out for around 10 years.
I've since gone through it and it works great.

 

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tylerdurden

Active Member

• Aug 11, 2015

• #4,115

Carver Receiver 900
Right: 6.4
Left: 6.1

Is it common for the reading to bounce around a little?? I let the amp warm up and "settle" and it leveled off but still vacillated from 6.3 to 6.8 6.9 on the right. The same for the left..... 5.9 - 6.3 or so. Both would also rapidly spike occasionaly up to 7.xx etc, and quickly come back down and settle.

My Yamaha R-9 receiver has a Class A option. Should I check the offsets with the option button turned on or off??

I will be doing all my amps/receivers and posting the results as well.

 

Last edited: Aug 11, 2015

EchoWars

Hiding in Honduras

Sponsor

• Aug 11, 2015

• #4,116

If your readings are in millivolts, then a change from 6.3mV to 6.9mV represents a delta of 600µV (0.0006V). So I'll ask you, do you think a change of 600 microvolts is significant?

As far as the R-9, check it in the mode you use most often.

 

tylerdurden

Active Member

• Aug 12, 2015

• #4,117

No I am not concerned about such a small flux. And yes I did check it in the cd mode as well as the tuner mode. same reading in both. I love this tuner.

 

tylerdurden

Active Member

• Aug 12, 2015

• #4,118

yamaha r-9
right: 17.7mv
left: 16.8mv

 

P

pishta

Active Member

• Aug 16, 2015

• #4,119

I hooked up a Teac SA-200 and got 11.5mv and 26mv on the other at the speakers. There are 2 VR's in there but I turned them both and there was no change. Its mostly an IC amp, not much solid state stuff going on in there. I tested my Hitachi SR-904 (after I adjusted its pots to spec) and got 13.2mv on both sides but thats not at the speaker leads, thats off the R725L and R725R resistors per the service manual.

 

EchoWars

Hiding in Honduras

Sponsor

• Aug 17, 2015

• #4,120

Cranking trimpots when you don't know what they do is a terrible idea. Generally, when there's only two, chances are good that they are for adjusting idle current (bias). A mis-adjustment here can easily lead to the death of the amp.

There's a manual on eBay (auction 291291461562) for the Teac if you really want to know what is going on.