Just a few:
1. The Syn-1 and Syn-2 can handle dual channel Synergy or Egnater modules. The RM4 was single channel unless you installed a modification. Some M4s were single channel but I think most were dual channel. Syn-1/Syn-2 can use all of the old modules and they sound like they are supposed to sound.
2. Synergy dual-channel modules have the ability to switch the stage 1 cathode components back in the dock between 3 settings:
- A Marshall-style setting that rolls off low end for a tight attack (.68uf)
- A Fender-style setting that allows pretty much all frequencies through. This was only setting the Randall and Egnater modules used. For modules that needed to roll off low end, they just did that on the module (22uf)
- A "boutique" setting that lets a little more low end than the Marshall-style setting. This would be used on an SLO for example. (1uf)
Synergy modules also usually have a switch where the user can tell the dock which setting to use, if they don't like the default. This doesn't work in a Randall/Egnater dock that is always on the fender-style (22uf) setting since that is all it has.
Older modules generally work fine in Synergy docks.
Synergy modules "work" in older docks, but since they can only use the fender-style setting mentioned above, they may not behave as intended. You can look at the manual for the module and it will usually say what its preferred setting is. An external EQ pedal can help. There are also aftermarket mods to allow you to use the newer synergy settings in an old Randall/Egnater dock.
(This seems like unnecessary complexity to me since there are plenty of Randall/Egnater modules that were as tight or fluffy as you want. It probably does help the amp handle pedals in a more authentic way. A Camerock module in an RM4 may sound like a Cameron but the front end would behave like a Fender in terms of pedals.)
3. The Syn-1 and Syn-2 both have 4CM switching built-in. This is a very smart addition because it allows you to "add a channel" to an existing amp without giving up the built-in channel. The amp just has to have a 100% series effects loop. The (R)M4s don't have the 4CM switching built-in, although you can do a trick with the parallel loop and an external switchbox- extra noise in some situations.
4. The Synergy docks weigh about a LOT less than the RM4. My RM4 seems about as heavy as an amp head.
5. The Syn-1 and Syn-2 have a DI output that is said to be quite respectable.
6. The Syn-1 and Syn-2 are readily available, coronavirus pandemic shutdown notwithstanding.
Did I miss anything?
