Saturday, November 1, 2014

Revisiting the Marantz PM-45

Recently stumbled upon the service manual for the unit. Hence time for a revisit.

In the past I had recapped the unit by only swapping the capacitors with better quality equivalents spares (I had on hand) on the main amplifier board.

After reviewing the schematics, it was quite apparent the key area for improvement was the amplifier board - rest of the circuitry adhered to the K.I.S.S philosophy.

The following pix is for the amplifier section of the Marantz PM-45 from the previous post.

Amplifier section from previous post
There were differences in the amplifier section vs the schematics for my unit??? Maybe late production changes?

Top view after 2nd recap
Close-up of the recap area

Important signal path changes
In the last pix above, the red and yellow outlines indicate changes which are necessary for converting the PM45 into quite a decent unit!!

The yellow outlined items are the new changes introduced after the previous post. The yellow box on the RHS shows that the previous EPCOS replaced with WIMA equivalents. Previously the EPCOS replaced the original green poly(s). These poly caps were not present in the schematics of the service manual.

The yellow box on the LHS required better quality 10uF 50V EC - used Panasonic FC.

The red outlined items on the LHS originally had 470uF 6.3V but were 220uF 6.3V in the service manual. Cause for the extra warm sound. Hence I replaced them so with United Chemicon 220uF 6.3V.

The red outlined items on the RHS were as per previous post (Nichicon 100uF 16V). I added 153J poly bypass to them, to permit HF to pass thru.

The results were startling with the above changes.

Note: Other EC caps on the amplifier board need not be audiophile caps - any decent quality EC will do as they are not in the signal path.

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