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Amplifier is dying, how can I find another one that will sound the same ?

post #1 of 11
12/26/10 at 3:32pm
Thread Starter 

I have an old Technics SA-424 Stereo receiver (Quartz digital synthesizer, if that counts for anything), its been in the process of dying for quite some time now. It's crackling and hissing like mad, no matter what. I've been told that its going to cost me more than its worth to repair it ( because the parts are ancient ... etc. ).

 

But from the times i've been able to listen to it without much hissing/interference going on, its a blast. I love the type of sound it produces.

I listen to it with my SR325is , the sound is amazing. The 325is become more powerful and punchy, its like they're on steroids, just seething with sound and power. There is more bass and treble, but its all much more clear and vivid. They become even more musical than they already are.

 

So, I love my SA-424, but its practically useless now with it degrading. I've tried cleaning the pots and nobs with that special cleaning spray stuff ( i forget what its called, its some were in my garage ). It worked a little at first but as the days past, the receiver went back to its regular ways if crackling and popping.

 

My question is,

How can I find something ( another receiver or whatever is out there ) that will produce the same sound as this one ?

Is there a certain way I can figure this out by looking at the internals and schematics of my SA 424 and comparing the inputs, impedence and sensitivity levels, frequency responses... etc with another one ?

 

Also, does anyone know were I can go to have my receiver repaired in Canada ( Ontario specifically), for a reasonable price ??

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post #2 of 11
12/27/10 at 10:28am
Thread Starter 

Anyone ?

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post #3 of 11
12/27/10 at 2:18pm

Do you have the schematics or can you get the schematics for the amp?  First thing to find out would be if the headphone out is powered by a resistor network from the speaker amp or if the headphone out has its own little separate headphone amp.

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post #4 of 11
12/27/10 at 2:39pm

May I ask why you are so adamant about replacing it with something that sounds the same?

 

Very likely you would be able to replace it with something that sounds even better.

 

Something like this maybe:

http://www.littledot.net/forum/viewtopic.php?f=9&t=819

 

Otherwise I think craigslist would be your best bet.  You might be able to find another Technics receiver, or you might be able to find a nice older Pioneer, Marantz, or Yamaha receiver.

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post #5 of 11
12/27/10 at 2:54pm
Thread Starter 

Thanks for the reply Ham Sandwich,

 

I have the whole manual which includes the schematic diagrams ( among other things ) on my computer, though I don't know were to look ( or what exactly im looking at/ for )... I was hoping I wouldn't have to analyze a schematic and just rather compare specs. But maybe you can guide me on this process by any chance ?

 

GotNoRice,

 

Its because i love the way it sounds ( sounded ), its really awesome, and because I've bought some other headphone amps that really suck, so im kind of reluctant in buying something again that I've never auditioned. It's tough for me to go out and audition things around here and my schedule is quite hectic. So its a combination of things really. ( I would like to buy another receiver but without being able to audition it , how would I know that it sounds better than my Technics )


Edited by AllsWell - 12/27/10 at 2:58pm
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post #6 of 11
12/27/10 at 3:02pm

I you like it that much get it restored or find a mint one. Too bad finding good information on that old audio gear is sometimes so hard. Have you ever wondered why I have two CD690s? Next thing is another Sansui amplifier... 

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post #7 of 11
12/27/10 at 3:35pm
Quote:
Originally Posted by AllsWell View Post

 

 

I have the whole manual which includes the schematic diagrams ( among other things ) on my computer, though I don't know were to look ( or what exactly im looking at/ for )... I was hoping I wouldn't have to analyze a schematic and just rather compare specs. But maybe you can guide me on this process by any chance ?

 


 

If you can figure out what area of the schematic shows the headphone circuit you can post a cropped image or screen capture of that area and someone here will be able to tell you what type of headphone amp circuit it is using.  If I was to bet I'd say it's likely using a resistor network from the speaker amp.

 

Then look through the specs to find the output impedance of the headphone jack.  If it's a resistor network it could have an output impedance in the neighborhood of 120 ohms.  Normally a high output impedance like that wouldn't be recommended for the 32 ohm Grados.  But if the "synergy" with the behavior of the power amp and the Grados manages to fit the result could be what is giving you the magic that you hear with that amp.

 

Another aspect with resistor networks is that the sound character of the speaker amp is going to carry over to the headphone.  After all it's the same amp driving both.  So if the speaker amp is known for a particular flavor of treble or bass or general sound, that behavior will generally carry over to the headphone.

 

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post #8 of 11
12/27/10 at 4:19pm
Thread Starter 

Alright, I think I found the area with the Headphone circuit in the schematic. ( if it needs to be zoomed up I can re-post the image )SA 424 Schem.jpg

 

 

In the specs it says that the "Headphone Output level and Impedance" is 450mV/330Ω .

 

Does this help ?

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post #9 of 11
12/28/10 at 6:17am

It's a resistor network off the power amp.

The 450mV/330 ohm spec probably means that it outputs 450 mV at 330 ohms.  I don't think it means the output impedance is 330 ohms.  330 ohm output impedance would be rather high.  Is there another spec entry that mentions the output impedance for the headphone jack?  I'm not much of an electronics guy.  Perhaps someone else would know hot to make sense of that "450mV/330ohm" spec.

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post #10 of 11
12/28/10 at 11:29am
Thread Starter 

That's the only time in the manual/specs were "Headphones" are mentioned, Thanks for your help so far Ham Sandwich.

 

Anyone else have any input to contribute to this ?

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post #11 of 11
12/28/10 at 1:54pm
The power supply's caps are usually what give out first in these old sets. If possible, have new caps installed in there. You should have no trouble finding ones of the same value.

Look around for people who work on guital amps. They should be able to recap the power supply. Also check to see if there is an amateur radio club nearby. They will have members handy with an iron or will point you in the right direction.
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