Ashton Kutcher and Josh Gad have defended their biopic of Steve Jobs as an accurate depiction of the origins of Apple.

Kutcher and Gad, who play Jobs and Apple's co-founder Steve Wozniak respectively in the forthcoming release – called, simply, Jobs – rebuffed complaints from Wozniak that the film bungled elements of the company's origins and phenomenal rise in the 1970s and 80s.

On Thursday, the pair told Macworld/iWorld, an annual gathering of Apple enthusiasts in San Francisco, that they went deep into the roles and even filmed at Jobs's family home in Los Altos to boost authenticity.

"We filmed at the actual house. We got to meet his stepmother and sister. It was surreal for them to see this transpire all over again in the same place that it happened," said Gad.

Gad, who made his name in the musical The Book of Mormon, said he was "computer illiterate" but had prepared for the role by taking programming courses and reading Wozniak's autobiography, iWoz. He said hoped Wozniak would be won over after seeing the film in full when it is released in April.

Wozniak complained last week after seeing a clip from the film, which premiered at the Sundance festival. "What I saw was just so far from anything that really happened or was said in those days," he told Good Morning America.

He said he never wore a tie, as depicted in the clip, or resembled a real professional. He also faulted the film for portraying Jobs as a precocious visionary who evangelised about technology's ability to transform the world, a characteristic which came later.

"As far as the personalities that were in that scene, this was just ridiculous," he said. Jobs would have been offended and embarrassed to be portrayed as a would-be "father of society", he said. "I think he would say that was, you know, a little bit too phony."

The film was directed by Joshua Michael Stern and will be released by Open Road Films and Five Star Feature Films on 19 April, the 37th anniversary Apple's founding.

Gad said the film was not a documentary, and that particularities of wardrobe mattered less than its striving for truth. "I greatly, greatly appreciate [Wozniak], and hope when he sees the movie in its entirety he'll understand we went to great lengths to capture the essence of his journey … It was done with the utmost love, admiration and respect."

Gad said playing a living person was daunting, but that acting was, by its nature, pretending. "You don't become that person unless you're psychotic." He praised his co-star's technical savvy – Kutcher threw out a rogue prop from a scene. "He said no, this wouldn't have been built for another year. That was incredible. I was just trying to remember my lines."

The actors, addressing a packed hall of self-professed geeks, comprised the opening event of the four-day conference, which will showcase new iOS services and apps.

Kutcher said he immersed himself in the role and compiled a SoundCloud of everything Jobs ever said publicly. "All you got to do is start repeating Steve, and you sound really smart."

Kutcher elaborated on reports that he fell ill after emulating Jobs's fruitarian diet. "I read this thing called the mucus-free diet, which he'd read when he was younger. It talks about the value of sugar from grapes and the elimination of mucus from system, which is harbour for disease. I thought: this makes a lot of sense … So for about a month I ate only fruit and drank carrot juice."

Two days before filming was due to begin he "doubled over in ridiculous pain" and went to hospital. Tests diagnosed pancreatitis. Jobs died in 2011 of pancreatic cancer.

Gad broke the melancholy moment, interjecting: "That's why you should do what I do, and eat everything but fruit."

Kutcher said it was intimidating playing a person who remained fresh in so many people's memories. "There's no video around of Lincoln," he said, a reference to Daniel Day-Lewis's acclaimed depiction of the US president. "Playing a guy which everyone will have judgment of or criticism about was really, really scary."

He said he tried not to judge Jobs, the shrewd salesman to Wozniak's technical genius, over pocketing the lion's share of profits. ""As an actor you don't judge your character. You justify them … Historically, we're told he took the margin."

Early reviews of the film have been mixed, with many calling it decent but not a patch on The Social Network's depiction of Facebook's Mark Zuckerberg. © Guardian News and Media 2013