Instruments becoming more standardized

The modern mariachis are very large, standard instrumentation, standard dress and there really is something very different about the two, that is, between the old and the modern mariachis. The modern ones tend to be over 10 members with five to seven violins, two or three trumpets and then the three or so other instruments. And as we saw earlier, the older mariachis were smaller and much less standardized in dress, instrumentation, etc.
Here's the standard set of instruments. This is the guitarrón. Literally the word translates to "large guitar." It's got a rounded back, six strings - five strings in the old days. They used to come in four strings as well. The guitar, the vihuela - a very small guitar with five strings, also with a rounded back. And the violin and trumpet. The trumpet ia a fairly recent innovation or addition to the mariachi. It occurred at the start of the 1920s but by the '30s it was pretty much standard.

A vihuela.

There are also some stories about how the trumpet entered, all the way from that "a mariachi was out playing one night - had a gig serenading - and a drunk with a trumpet kept following them." They kept saying, "No you can't do that. Were working." Finally at the end it was like "If you can't beat them away have them join you."
Another version is that the trumpet was introduced through radio. There was a station - XEW in Mexico City - that used to broadcast very widely throughout Mexico and they used to do live performances of mariachis. One of the producers said, "There's not enough sound. The string instruments do not produce enough volume. We need something else." Thus enters the trumpet and so supposedly a producer that added the trumpet.
In any case a trumpet is certainly a standard mariachi instrument today.

Steve Carrillo of Mariachi Cobre plays trumpet as Keith Lockhart directs the Boston Pops during a rehearsal fa show.

These are the rhythm instruments (guitarrón, vihuela, guitara de golpe, and harp). The harp has essentially been replaced by the guitarrón, although the harp is making a comeback with show mariachis. Working mariachis usually don't use the harp because it's bulky and thus hard to carry around. It's a larger and heavier instrument.
The guitarra de golpe was replaced by a larger guitar, although the guitarra de golpe, which is about 3/4 the size of a regular guitar, is making a comeback as well.
The the violin and trumpet round out the mariachi instruments, although these two are not considered part of the rhythm.