Yamaha A-720, some modest updates

A few notes on re-capping and modifying an A-720....

First of all, attached is a spreadsheet with a list of the electrolyic caps for an A-720, along with a few notes. They are bunched by function, and should be complete, but if I missed anything please feel free to update it.

I've made a few modest mods to the amp which I would like to share with anyone who's interested.

First off, I replaced the op-amps in the phono section. The original op-amps are 8-pin SIP's. To adapt the new DIPs I bought some Brown Dog adapters. Due to my ignorance of what good subs would be, I relied as usual upon the kindness of strangers and came up with these:
M5218 (or NJM4558): replaced by an NJM4580DD. See this thread for a discussion -- http://www.audiokarma.org/forums/showthread.php?p=6563913
M5219L: replaced with an LME49860 - Decision was based on this thread: http://www.audiokarma.org/forums/archive/index.php/t-330811.html

I wish I had some way to measure the before and after, but I don't, so the post-mod evaluation is totally subjective. I like to use a pair of decent Grado headphones for first-pass listening, this I think keeps comparisons on somewhat of a level playing field. So, after the op-amp update, my report is: yes, records did (subjectively) sound better ;-) I tested with both MM and MC cartridges.



The second mod was shortening the audio path by excising out the run to the adapter jacks -- about 24" of wire is removed. I have a couple photos showing the before and after, highlighting the areas to look for. It's a simple matter to desolder the connector pins and tie wrap the wires out of the way, and just as simple to put them back into place if desired.
I wasn't expecting much, if any difference, but to my surprise taking the accessory jack wire run out of the audio path made a (subjective) difference in improvement, too. Not night and day, but it was there. Or at least I thought so.



Any improvement quickly establishes itself as the new threshold, so the perceived difference is washed out fairly quickly, but I am overall very pleased with the A-720. The cost of both op-amps is just a shade over $4, so the investment is modest, and as hobbyist, it's a fun little thing to do. If anyone else tries these out, or has other recommended tweaks or advice, I'd be interested in hearing about it.

Very nice, clean work!

In future, might want to install sockets on those adapters so you can "experiment". There seems to be ample clearance.
I've had good luck replacing the 4558 with OPA2604 or OPA2132. Just check your specific app for voltage and max amperage available. Other good subs as well, but these are the less expensive. ($5-6)

Nice to see it, 39cross!

Danvee said:

Very nice, clean work!

In future, might want to install sockets on those adapters so you can "experiment". There seems to be ample clearance.
I've had good luck replacing the 4558 with OPA2604 or OPA2132. Just check your specific app for voltage and max amperage available. Other good subs as well, but these are the less expensive. ($5-6)

Click to expand...

I've done the same with 3 or 4 units with stock 5448's. I really like the OPA2604. :yes:

Thanks for the feedback and ideas. It's actually tighter inside than it looks. My first try was with sockets on the adapters, but the only sockets I had sat high off the adapter, so that I had to desolder the green cap in the bottom of the picture and move it slightly. After doing my audio testing, I decided to put things back the way they were and solder directly.

I did forget one thing I meant to mention and see if this is worth doing. The phono connection is also a 12" run of cable from the jacks in back to the front of the amp. Maybe it's overkill, but would replacing the original cable with some shielded cable make a difference?