One thing that comes up on occasions is the use of instruments in Kirtana and like most things there are two divided camps those who feel that any instrument can be used as it enhances the Kirtana and those who feel that only traditional instrument’s should be used.

But I am also aware of my own personal preferences, I love the use of traditional instruments in the temple but seeing the pleasure given to those who play other instruments can enjoy them being used, after all HH Mahavishnu Swami uses and accordion not a classic instrument. And the use of a flute and trumpet by some devotees certainly can enhance the Kirtana especially if played expertly.

So is there a hard and fast rule?

Is there a right or wrong on how music is played and what instruments are used?

As I looked at the different quotes one stood out:

Aside from chanting japa, you can also sing the Lord’s holy names in kirtana. While you can perform kirtana individually, it is generally performed with others. A melodious kirtana with family or friends is sure to enliven everyone. ISKCON devotees use traditional melodies and instruments, especially in the temple, but you can chant to any melody and use any musical instruments to accompany your chanting. As Lord Caitanya said, “There are no hard and fast rules for chanting Hare Krsna.” One thing you might want to do, however, is order some kirtana and japa audiotapes from Temple Services.

Ref: Chanting the Hare Krsna Mantra

One thing that for me stood out was the notation that ISKCON devotees use traditional melodies and instruments especially in the temple and when in the hands of expert musicians they defiantly enhance and have great balance in sound quality.

The importance is constantly reiterated of Kirtana and we see it’s importance as stated by Srila Jiva Gosvami who wrote:

In this regard, Srila Jiva Gosvami states in his book Bhakti-sandarbha (173): yadyapi anya bhaktih kalau kartavya, tada; kirtanakhya-bhakti-samyogenaiva. Out of the nine processes of devotional service, kirtana is very important. Srila Jiva Gosvami therefore instructs that the other processes, such as arcana, vandana, dasya and sakhya, should be executed, but they must be preceded and followed by kirtana, the chanting of the holy name. We have therefore introduced this system in all of our centers. Arcana, arati, bhoga offering, Deity dressing and decoration are all preceded and followed by the chanting of the holy name of the Lord — Hare Krsna, Hare Krsna, Krsna Krsna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare.

Ref: Madhya 15.107

We see the importance of Kirtana and the importance of hearing the holy names of the Lord in the Maha-Mantra and this is were I personally feel things can become a little lost, for me there is two main causes:
An imbalance of instrument’s used that some can over power the other instruments being played.
That the musicians become so ecstatic in there playing, or a subtle competitiveness that one or more instruments become so loud that the other musicians playing cannot be heard or for me what is much worse the holy names is no longer audible

It is in a supportive role that instruments are played to enhance things for the hearer, after all we can remember themes and words of songs much better than if they were just recited in some poetical manor. This too is highlighted in this text:

The brahmanas recited auspicious Vedic hymns, which purified the environment by their vibration. The experts in reciting old histories like the Puranas, the experts in reciting the histories of royal families, and general reciters all chanted, while singers sang and many kinds of musical instruments, like bheris and dundubhis, played in accompaniment.

Ref: SB 10.5.5

I have been in Kirtana’s were full drum kits, guitars, bass guitars, electrical violins, flutes, trumpets, cymbals and traditional Indian instruments are used but they have been harmonized nicely and that the main thing that can be heard always is the Holy Names, for me personally once you can not hear the holy names are the variety of instruments cannot be heard then the Kirtana looses all meaning.