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Old 31st January 2010, 11:21 PM   #1
Ecaroh is offline Ecaroh  United States
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Default Improve my old Pioneer Phono Stage?

Anybody have suggestions for getting more detail and dynamics out of this little circuit? I already replaced all the caps.

It's in my wonderful old, vintage Pioneer SX-727 receiver. I recently ran the turntable I use with it into a good free-standing phono stage and on to a Pioneer line-level input. The difference was night and day.

I'm going to update the power supply caps shortly.

Thanks for any ideas.
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Old 1st February 2010, 01:17 AM   #2
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I am in the process of installing an LM4562 based RIAA section in my Pioneer SX-838 -- aren't these great receivers?

I would suggest that you look at the Murata thread I started -- these DC-DC converters are easy to tame with a little choke on the input: When you need +/- 15VDC and have only one pole

Here's how I used the National Semi LM4702 to drive some lateral MOSFET's within the carcase of the SC-838L

LM4702 meets the Pioneer SX-838
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Old 1st February 2010, 07:23 AM   #3
Ecaroh is offline Ecaroh  United States
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Quote:
Originally Posted by jackinnj View Post
Here's how I used the National Semi LM4702 to drive some lateral MOSFET's within the carcase of the SC-838L

LM4702 meets the Pioneer SX-838

Interesting stuff!

What new diodes did you put into the power supply?

Thanks.
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Old 1st February 2010, 12:46 PM   #4
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Most likely they were replaced with On-Semi MUR860's. I did replace the filter caps with 39,000uF Panasonics. the original used wire-wrap to the chassis for all the grounds. this had to go. all of the grounds are now brought to one central locus on the power supply.

There is a 32V takeoff on the preamplifier board. One of the Murata dc-dc converters will accomodate this with +/- 15V -- this way you can use a real ground and eliminate coupling capacitors.

With the LM4702 the dc offset is only a couple of millivolts.
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Old 1st February 2010, 06:14 PM   #5
Ecaroh is offline Ecaroh  United States
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Originally Posted by jackinnj View Post
Most likely they were replaced with On-Semi MUR860's. I did replace the filter caps with 39,000uF Panasonics.

Thanks! (Other stuff also noted.) So you replaced axial diodes with TO-220s?

Ecaroh.
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Old 1st February 2010, 06:32 PM   #6
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Yupp -- the business side of the power supply is downward facing -- there was enough room to install MUR860's and snubbers.

To mount that filter caps I had to use mounting hardware such that the cap protrudes about 0.75 inch into the bottom. No big deal.
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