The jury in the case heard the 52-year-old had abused the young girl and sent her saucy Valentine's cards.
The attacks, which took place between 2003 and 2005, began after the girl went to Kruschandl's home after school.He had a recording studio set up in the living room of The Old Steam House, a former Victorian electricity station in Lime Park.
The victim, who cannot be named, said Kruschandl asked her to go to his room 'for a cuddle'.
The girl, now 15, said on later visits he took all but their underwear off and laid next to her on his bed.
She said more intimate touching took place on later visits.
In passing sentence at a hearing in Brighton on Friday, Judge Cedric Joseph told Kruschandl his crimes were 'a gross abuse of trust'.
He said, "There was no doubt from the evidence presented to the jury you abused this child on a regular basis over a lengthy period of time.
"You were in the position of being like a father to the girl. You were trusted by her and you abused her trust."
Judge Joseph said he wouldn't increase the sentence despite Kruschandl's not guilty plea, but told the former planning consultant he had put the girl and her mother through a 'dreadful' period.
He said, "The girl and her mother were subjected to lengthy cross-examination.
"It was a dreadful experience she is never likely to forget."
At the trial, the jury heard Kruschandl had sent the girl a Valentine's Day card two years running. One of them said, "Valentine, you take my breath away, feel free to do the same with my clothes."
The sex attacks came to light after the victim told friends who informed teachers at their school in June 2006.
Kruschandl said he loved the girl like a daughter and claimed she had made up the assaults but did not know why.
He also said he had only ever given the girl a hug after picking her up from school but the jury took just under four hours to find him guilty of all four charges.
At the sentencing hearing, letters sent to the judge from Kruschandl's family and ex-partner supporting his character were read out.
His neice insisted the 52-year-old had 'always behaved impeccably' when she was alone with him.
Defending, Michael Harrison asked the judge to take into account 'the high regard in which he is held'.
He said, "He is one of the true English eccentrics in the lifestyle he leads and the cases he fights for.
"You have to accept it is a fall from grace. He accepts he will be sentence to custody.
"But he has never been involved with sexual allegations in the past with any of the young people has come into contact with before."
Judge Joseph accepted Kruschandl had no history of sexual offences but said Kruschandl had 'not been a man of previously good character'.
He was sentenced to seven years in prison, given a sexual offences prevention order to run for 10 years and will be placed on the sex offenders register.
Kruschandl appeared again in court on Monday to challenge part of the order which would have prevented him publishing details of his court experience in a book or on the internet.
Mr Harrison said the order breached Kruschandl's freedom of expression.
Judge Joseph varied the order to allow publication on condition it did not lead directly or indirectly to the identification of Kruschandl's victim or her family.