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Calling All "Vintage" Integrated/Receiver Owners - Page 294

post #4396 of 13878

 

Quote:

Originally Posted by Wharfrat View Post
 

Also,  though I have been over to AK, their search engine is kinda iffy....so a link to the DC offset thread that you found most instructive would be helpful....


Could it be this sticky?

 

http://audiokarma.org/forums/showthread.php?t=5634

post #4397 of 13878
Yes indeed, that is absolutely the right thread. Very helpful. Note that you can REALLY destroy your amp by adjusting the bias, so I don't recommend messing with that. But adjusting DC offset, while still requiring care, doesn't carry with it the same disaster potential unless you drop your screwdriver on an output device or something - the usual risks of working on an amp with the cover off and the power on, which certainly mean you need to be very careful, as indicated in that thread.

Proper DC offset yields less distortion, and a smoother sound, as well as reducing the risk of speaker damage which can happen if you have a high DC offset.
post #4398 of 13878

Oh yea, one has to be really really careful when adjusting trim pots. They are very very sensitive, just a slight twist with a screw driver could be a few mA. And very important, use a very good DMM. I use a Fluke 89 IV True RMS DMM, not cheap but worth it.

post #4399 of 13878

im interested in the offset as well.

problem is i don't want to accidentally alter the bias instead of the other offset.

theres 4 trim pots in a very close proximity.

guess i should measure the offset before i start worrying about changing it.

 

my latest addition to my listening area:

IMAG0340.jpg

post #4400 of 13878

Here's also a way to measure DC offset from your hp amp http://www.rock-grotto.co.uk/dcoffset.htm

post #4401 of 13878
For sure, measure first! If you have a Multimeter, measuring is very easy. Take a measurement are report back smily_headphones1.gif
post #4402 of 13878

Yes, Skylab's advice is absolutely to be followed on this one. Don't even think about touching any internal trimpots without measuring DC offset first, following EchoWars' procedure outlined in that sticky at AudioKarma. Even then, think at least 3 times before attempting to correct a known problem. Get the service manual and study it. You want to be absolutely certain that the trimpot you're about to adjust is the one you think it is.

 

Meanwhile, for those who don't have a meter (but you're all planning to get one, right?), a quickie go/no-go Danger Test for DC offset. Disconnect all speakers from the amp under test. Fire it up and turn the volume all the way down; silence the inputs; let it warm for at least 5 minutes. Then connect one side of an efficient speaker to the amp (red or black, doesn't matter), then lightly flick the other amp terminal with the other speaker wire. If you hear any crackle from the speaker when you flick, that's DC. A very faint crackle is okay. If it sounds like you're brushing the terminals of a 9v battery-- or even a 1.5v D cell-- something's wrong and further investigation is called for.

post #4403 of 13878
Quote:
Originally Posted by Meewoo View Post

Nice!

 

Here is mine with walnuts wood side.

Optonica SM-4545


Nice, no idea what the wood on mine is. Looks like it matches my Polk's, though, so my guess would be rosewood.

And it seems my function knob isn't stock, may try to see if I can find a replacement. By the way, do you happen to know what the turnover switches do?

 

post #4404 of 13878

Just wanted to update and thanks Skylab for the help. I've hooked up dual subwoofers to my vintage receiver and it works fine. My speakers supposedly go down to 45Hz, so I set the subs' crossovers at 45Hz. Going by ear, since I don't have a good SPL meter to help fine tune. The subs turn on/off automatically.

 

Subs are being used as stands:

 

IMG_20120318_210837.jpg

post #4405 of 13878
Actually, if I may make a suggestion, set the x-over at @52Hz, for better blending. Usually speaker manufacturers measure the FR rating +/- 6dB, you could lose some program info by setting exactly according to their spec.
Edited by Magick Man - 3/19/12 at 12:33am
post #4406 of 13878

Anyone tried the hp out of Marantz pm66se ki sig? I wonder if the amps from that era also are good, as the older Marantz..

post #4407 of 13878
Quote:
Originally Posted by Taowolf51 View Post


Nice, no idea what the wood on mine is. Looks like it matches my Polk's, though, so my guess would be rosewood.

And it seems my function knob isn't stock, may try to see if I can find a replacement. By the way, do you happen to know what the turnover switches do?

 


The "turnover" is just "frequency". When you turn the variable (tone) on, and you turn the bass or treble knob, you can change the tone. If you put turnover under bass to 300hz, the bass knob is controlled to boost or reduce bass at 300hz; same as treble. Many people here don't mess with tone control since tone control adds distortion.(correct me if I am wrong)

 

post #4408 of 13878

 

Originally Posted by Magick Man View Post

Actually, if I may make a suggestion, set the x-over at @52Hz, for better blending. Usually speaker manufacturers measure the FR rating +/- 6dB, you could lose some program info by setting exactly according to their spec.


I made it so. Thanks for the tip Magick Man.

 

post #4409 of 13878
Quote:
Originally Posted by Meewoo View Post


The "turnover" is just "frequency". When you turn the variable (tone) on, and you turn the bass or treble knob, you can change the tone. If you put turnover under bass to 300hz, the bass knob is controlled to boost or reduce bass at 300hz; same as treble. Many people here don't mess with tone control since tone control adds distortion.(correct me if I am wrong)

 


That makes sense, thanks. :D

I'm actually shocked at the quality of the bass and treble knobs. If I don't have an EQ handy (like with MOG), I can throw the turnover to 6Khz, dial the treble down a notch, and kill sibilance (in my headphones) without really affecting any other part of the highs.

The bass knob is just as effective, though I usually don't use it. Doesn't interfere with the mids or any other part of the spectrum at all, and the bass itself isn't any worse off, there's just more of it.

I have noticed that the left channel can get quiet after some time (both headphones and speakers, though it only happened once with the latter). I'm going to see if I can figure out what that is.

post #4410 of 13878
Good tone controls are one of the most awesome things about vintage amps. I use the ones on my SX-1980 quite frequently. Not all recordings are perfect wink.gif
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