I am going to take the above advice and get everything else working before I move forward with thinking about the chips. I assume that the way in which these chips are used would make a difference as the designing engineer recommended the swap when I told him that I wanted to warm up the amplifiers.
In the right application the OPA2604 is one of my personal favourite devices.
Some of the other devices you keep mentioning are not duals (OP627)
I also had a 10 year old Sherbourn amplifier 5/1500A that started to sound bad with signal cutouts that would recover with a power cycle. I thought it was faulty low signal cutoff circuitry. A Sherbourn Tech told me to clean the speaker relay contacts. The relay covers pop off after removing the modules. I used emery cloth followed by deoxit liquid. The amp sounded better than ever! No more cutoffs. I know this is late, but I hope it helps someone.
could be diff amp or VAS transistors too.... the innards of that amp looks a lot like the innards of a JBL amp i saw a few years ago.... and i just saw page 2.... i've always used a piece of brown paper bag for cleaning relay contacts.... spray the paper with some deoxit, put the paper between the contacts, hold the relay flapper down in the energized position and rub the paper through the contacts.. you want to burnish the contacts, not strip them.
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This is too late to help the original poster, who I assume has been able to fix his Sherbourn modules. Anyways, the things to look at are the large electrolytic caps (10,000uF/80V, can be replaced by 10,000uF/100V if it fits). Rail voltages are +/- 72V, IIRC. The relay contacts have been implicated in some forums, but I found them to be fine even after 15 years, but YMMV.
One opamp is used to convert differential input to single-ended, and the other is used at the front-end of the power-amp signal path. I'd advise leaving the latter opamp alone.
I also upgraded a few bypass caps on the auxiliary supplies, including +12V.
When the module is being fixed, you may want to use the opportunity to reflow any suspect solder joints - some annular solder cracks and intermittents tend to develop over 15 years.
Apart from that, this is a solid and over-engineered amp with mostly commodity parts, and it sounds way better than it should with commodity parts. Do not attempt to upgrade any capacitors in the signal path - it's fine with C0G ceramics as Miller caps, etc.
One opamp is used to convert differential input to single-ended, and the other is used at the front-end of the power-amp signal path. I'd advise leaving the latter opamp alone.
I also upgraded a few bypass caps on the auxiliary supplies, including +12V.
When the module is being fixed, you may want to use the opportunity to reflow any suspect solder joints - some annular solder cracks and intermittents tend to develop over 15 years.
Apart from that, this is a solid and over-engineered amp with mostly commodity parts, and it sounds way better than it should with commodity parts. Do not attempt to upgrade any capacitors in the signal path - it's fine with C0G ceramics as Miller caps, etc.
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