Robin Maughan, a Frankie Valli impersonator, is serving a 12-year sentence for offences including grooming and abusing two teenagers.
The 36-year-old, of Market Harborough, Leicestershire, has since pleaded guilty to further charges, including taking indecent photos of children.
The judge at Leicester Crown Court said he would be sentenced on 23 June.
The new charges faced by Maughan, formerly of Western Avenue, involved a number of boys and girls aged 13 to 16 between 2000 and 2015.
They include sexual touching, indecent assault and taking more than 200 indecent images of children.
Det Con Rob Waddington, who led the investigation, said: "As a result of the publicity surrounding his previous conviction, more victims came forward, and we worked to gather evidence to be able to put these charges to him.
"We know there are more victims out there who were abused by Maughan and who haven't been able to come forward for whatever reason, and I would urge them to make contact with us."
An entertainer who was jailed last year for sexually abusing children has admitted 18 further charges.