A music teacher at one of the UK's most prestigious music schools has been jailed for six years after being found guilty of sexually abusing a pupil.

Michael Brewer, 68, who was director of music at Chetham's school of music in Manchester until 1994, was told by the judge at Manchester crown court that he was a "predatory sex offender" who used his "powerful position to select and groom" his victims.

His ex-wife, Hilary Kay Brewer, also 68, was sentenced to 21 months after being found guilty last month of sexually abusing the same girl as her former husband.

Their victim, Frances Andrade, did not live to see her abusers sent to jail. She killed herself halfway through the trial after being branded a "fantasist" in court. She was 48. Three of her four children, along with her widower, Levine Andrade, were in court on Tuesday to see justice done.

Her death prompted a nationwide police investigation after dozens of former pupils from Chetham's and other music schools and conservatoires came forward to accuse other music teachers of sexually abusing them or their peers as children or young adults.

Many told the Guardian they had suffered the effects of the abuse for decades and finally plucked up the courage to go to the police after hearing of Andrade's suicide. "I do not want Frances to have died in vain," one alleged victim told the Guardian.

On Tuesday, the judge, Martin Rudland, explained that Andrade's suicide could not influence his sentencing but said: "Perhaps one of the few positive features to have emerged from this case is the resulting close scrutiny of this type of behaviour amongst those who should know better."

He expressed surprise that many of the great and good who gave character references for Michael Brewer did so despite knowing he had enjoyed a sexual relationship with another sixth-former – not Andrade – at Chetham's in 1994. When the then head found out, Brewer was allowed to leave with his head held high. Pupils were told his departure was due to "health" reasons and he went on to be awarded an OBE by the Queen and worked with hundreds of young people as director of the National Youth Choir.

After the Brewers' convictions last month, one of Andrade's sons, Oliver, said of his mother: "One of her hopes was that the bravery she exhibited, and the other stories she knew would come out during the trial, would mean that other students who had also suffered abuse at Chetham's would be able to receive justice."

Allegations have since been made against at least 10 current or former teachers from Chetham's, as well as tutors from the Royal Northern College of Music (RNCM), Guildhall and the Royal Academy of Music in London, Wells Cathedral school in Somerset and the Purcell school in Hertfordshire.

Andrade, a professional violinist when she died, was abused by Michael Brewer when she was a vulnerable teenager at Chetham's in 1979 and 1980 when she was 14 and 15 years of age.

Sentencing Michael Brewer on Tuesday, the judge admonished him for exploiting Andrade, who after a tough upbringing – which included being sexually abused from the age of eight by an uncle – just wanted "to be cared for and cherished by a loving family to which she craved to belong".

Andrade appreciated the attention, said Rudland. He said: "The care and attention which you gave her, in so manipulative and depraved a way, were regarded as blessings. She was prepared to submit to almost anything, which clearly she did, as you pushed the boundaries further and further – treating her as your sexual plaything in the context of a false loving relationship which she readily accepted."

Brewer had used his "powerful position" to groom Andrade, said the judge. "You have had an impressive career but that is now at an end," he said. "Sadly there is another side to you and it is this. You were, and you may still be, a predatory sex offender. Of that let no one be in any doubt."

In the witness box Andrade explained how "Mike", as the teacher liked to be known by students, systematically groomed her, telling her she was "bewitching" and "beautiful". Brewer listened to her, she said, and she would often go to see him for chats in his office, which was on the ground floor of the music block and contained a grand piano and a settee.

She was just 14 when he initiated sexual activity. It started with hugs, said Andrade. But soon Brewer went further, she said. "Very quickly Mike would tell me that I bewitched him. That he found me irresistible, that he found me wise and wonderful, hugely talented and that these feelings could not be wrong because they felt so right," she said. She liked it, she admitted. She said: "I felt cared for and nurtured."

She was 14 when he started touching her in his office. She would usually be in her school uniform, she said, and he would get her to strip naked while she gave him oral sex. He always kept his clothes on, she told the jury, just unzipping his flies. She was happy with it at the time, she said. "I did not feel at the time I was a victim," she said. "It was a relationship that developed in a completely normal way. We would kiss, he would touch me."

Andrade also told of how Brewer would get her to have oral sex with him in his camper van as he drove around Manchester city centre.

Hilary Kay Brewer, known as Kay, was found guilty of indecently assaulting Andrade at the Brewers' family home in Chorlton, south Manchester. Andrade was 18 at the time.

Rudland told Kay Brewer that though she had been "in the shadow" of her ex-husband during the trial, she emerged "as someone who colluded in his offending and who had a sexual agenda of your own".

He told her: "You have for many years clothed yourself in a cloak of Christian respectability doing good work for the community and gaining the admiration of others, some of whom gave evidence on your behalf during the trial … However, beneath your latter-day outward good character and desire to care for others, you conceal a secret: namely that you preyed upon and exploited a young girl who was vulnerable, pliable and whom you knew was also being exploited sexually by your husband."

The court heard both Michael and Kay Brewer had been model prisoners since being remanded to prison in February. He had been teaching Spanish and music to fellow inmates and playing the organ in the jail chapel, his barrister, Kate Blackwell QC, said. Kay, meanwhile, has been teaching illiterate prisoners how to read and write.

So far one other teacher as been arrested as part of the police inquiry into abuse at UK music schools. In February Wen Zhou Li, 57, a world-renowned violin tutor who has worked at Chetham's and the RNCM since at least 1996, was arrested on suspicion of rape. He denies the charges and is currently on police bail.

Also under investigation is Malcolm Layfield, who until recently was head of strings at the RNCM. He was forced to step down last month after admitting his position had become "untenable". During the Brewer trial Andrade had talked of Layfield's penchant for sleeping with his young charges while teaching at Chetham's in the 1980s.

Three women subsequently told the Guardian as well as the police that Layfield had initiated sexual activity with them when they were as young as 16, which damaged their mental and physical wellbeing. In 2003 it became a criminal offence for teachers to have sex with pupils aged 16 or 17. This was not the case when Layfield taught at Chetham's. He insists now that he regrets his behaviour but that he only slept with pupils who were over the age of consent, and that all relations were consensual at the time.