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Amplifier Distortion, DC-Offset, and You!

ojTHEd said:
Seems pretty good, but is there any easy way to improve these numbers?
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Nope...the 450 is non-adjustable, and those figures are decent for a unit which does not provide one.

Edit: Strictly speaking, you can improve those numbers by switching to closely matched diff pair transistors, adding a DC servo to provide for correction, or fabricating an adjustment circuit. It isn't worth the effort for such a minor improvement, and this is an SX-450, after all. ;)

Also, the number on my multimeter just keeps drifting around - why? Is it cause it's a cheaper Radio Shack Auto-Range Digital Multimeter?
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No, thermal variations do this...transistors change their gain as they heat and cool, so offset drifts by a few millivolts (I've mentioned this before, but I can understand not wanting to shuffle through 450+ posts to read what you need to).

The meter is fine...most will do this until connected to a source, but if you have any reason to suspect your batteries, replace them with good alkaline batts.
 
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Okay, thank you both! I'm making a new thread in the Pioneer forum now about the small issue I'm having. I think all the pots need a thorough DexOxit-ing, but when I turn on the unit it flickers for a time before it comes on solidly. Am I on the right track thinking it needs cleaning?
 
OjTHEd, thI'm guessing the lights / unit flickering for a while is due to arcing on the power switch (if the 450 is like the 650). Mine does that and someone said the only real solution is to either a) bypass the power switch with your own one or replacing it. A pull apart and clean will only buy you some time (what I was told is not a permanent fix) due to the amount of pitting already on the contacts to make it arc in the first place?

Happy to be corrected.
David.
 
Thanks, David. I do hope you're wrong. I guess I'll have to turn it on, sans cover, and watch the power switch closely.
 
Sansui 210 tuner/amp

Since I'm a newbie at anything electronic, I decided to use my entry level Sansui 210 as a guinea pig. Here are the readings:

L - 23.5
R- 23.0

I know its probably not worth tweaking but is there any pot to adjust here?

Thanks EW!
 
I don't think I've ever even seen a 210...??

Eh...a case of, 'If it works, don't fix it'. :thmbsp:
 
Tested three of mine

Technics SU-V4 R 1.3 L 0.5
Onkyo TX2500MKII R 2.0 L 0.5
Yamaha A-560 R 15.8 L 41.9

The sad part here is that the Yamaha (evidently within spec but appears on the high side per Echo's original posts) was serviced about two years ago and is the unit I listen to in the study. Maybe the "Marantz Consultation" guy (discussed in a thread a couple of months back) could have brought these values down during the months he had it.

The Technics was an ebay deal while the Yamaha was in the shop and the Onkyo was $10 at the flea market a couple of weeks ago.

Alan
 
A lot of the lower-end models from most manufacturers don't have an offset adjust. I don't know where the Yamaha fits in the scheme of things, but considering the way most Yamaha's are built, if it is a halfway decent unit at all, then it has an offset adjust.

Lot of tech's don't bother with it. Repair it good enough to get it to make noise, and out the door it goes.
 
Bought the Yamaha A-560 new in '81. Nice little amp w/55WPC - I think about 250 bills at the time. Used it many years with Klipsch Heresy speakers bought at the same time.

Probably pick up a service manual and see if I dare venture into it myself.

Thanks for this thread. Will always check this on a bargain amp/receiver prior to hooking up speakers.

Alan
 
Yamaha CA-1010 for $150 including shipping:
Lch=32.5mV, Rch=28.5mV. Rainy day project as soon as I find which pots to adjust...

EW, thanx for this thread. :thmbsp:

Tom
 
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Conservation and Relative Worth in Respect to DC Offset Facility

... if it is a halfway decent unit at all, then it has an offset adjust.
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EW: Fiirst let me say that I am always ready to yield to your superior knowledge. And, I am not wanting to be one of those wankers with too sharp a chisel. Still, I have called off my first response to this comment a number of times. After all and strictly speaking, I may be off topic. But the quote keeps scrolling past me, and I have to say that I don't agree. And I want to ask if you would concede to the fact that perhaps there are exceptions to what you say? If so, newcomers to the endeavour of optimising veteran gear may save themselves from the blasphemy of binning some excellent classic stuff thinking that Grandma’s old amp is unworthy of saving. If what you say is true, an integrated amp like my Sansui AU-317 would could be a candidate for the junk pile because it's "less than halfway decent". So — why keep it?

The '317' was indeed near the bottom end of a series line, but in terms of sonic integrity, nothing was spared in terms of the essentials. I have amps that in contemporary terms cost five time as much, but I think that this amp yields nothing to the high end except power and refinements, such as pots for DC offset. This in itself may truly define what you say — ‘less than halfway decent’. So be it! But let us hope that newcomers will not consign musical instruments like this example to the dumpster thinking that they are second rate. The sterile sounds emanating from the AV contagion have me convinced that we should conserve as many true musical instruments as possible, even if they may not possess all the circuit refinements that we would hope for in regards to adjusting DC offset.
 
If I had to consider every word I posted and try to be 110% politically correct, then I'd never post anything.

I reread what I posted, and I can't remember posting it, even though it was a few days ago. Still, what I said should be taken in proper context...

Certain manufacturers loved lots of internal adjustments, Yamaha being one. If you reread my post, I was speaking specifically of the Yamaha. In order for this unit to have no adjustment at all, then for Yamaha it must have been considered 'not worthy of the trouble' (which, incidently, has not a damn thing to do with its potential value to an owner or its sonic qualities).

There are examples at the TOTL extreme also...Kenwood was a big believer in closely matched differential pairs with no provisions for any adjustment whatsoever...neither the TOTL Kenwood KR-9600 or the coveted 700M amplifier have them, and you certainly know that I would not dismiss them as serious attempts at Hi-Fi simply because of the lack of an adjustment pot (regardless of how badly it annoys me...)

So, to end this song and dance, each manufacturer had their own philosophy on what was essential and what was not. My comment was made from the understanding of the mindset of Yamaha at the time...other manufacturers had their own ways.
 
I have to say, I took EW's comment on Bias adjustments, or lack therof, as pertaining to Yamaha philosophy, not neccesaraly a general comment. Easy to see where not everyone would though.
 
EchoWars said:
6. Set your meter to read DC, and set to a low scale (300mV scale is common) Connect directly to the Pos and Neg of the speaker terminals
7. Give the amp 10 minutes to settle. Report back...I'd like to see how healthy all these old amps are.
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Just a question to clarify - should I leave the multimeter hooked to the terminals for 10 minutes, and take the reading at the end of the 10 minutes? Or, take another reading 10 minutes later?

Or, just wait 10 minutes before using the amp?

Thanks for tolerating a simple question!

Jim
 
No matter...if you want to sit there, go ahead.

I have found it better to leave the amp on for a good 30 min or better when I set offset, and I get more accurate readings with a load attached, so you may leave your speaker connected as this is more of a real-world scenerio (offset means little if there isn't a load to drive...)

10 minutes is certainly long enough to get an idea of whether the offset is in the ballpark or not though, and you can monitor it for that time is it pleases you.
 
From nbobby4244@aol.com

EW, you are one he$$of a smart MF"er. You are 99.9% perfect all the time. How come? You on Steroids? You got my business and my respect . I have had the pleasure of your friendship and your help in so many ways. You are a very valued friend. :thmbsp: :beerchug:

I have never met a person who was right 100 % of the time but, you come close! I'll give you a 9.9 :yes: And I am a very fussy and critical person. A 9.9 is something that I would only give myself ! lol :yes:
 
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