You have a noun and a verb, and what you need is an adjective.
Both nouns and verbs can be used to modify nouns, but in different ways.
With verbs we can use a present participle ("practising amp") or past participle ("practised amp", though "practised guitarist" would be a more realistic example) or a to-infinitive ("amp to practise").
With nouns we just use the noun attributively ("practice amp").
It's the last of these that matches what you are looking for here.
Consider that when the verb and noun for an activity are more strongly different, such as food and eat. You would have a "food shop" but not an "eat shop" and so on, though you might well also have an "eating place" etc.