He denied there was any pressure on him to quit.
"I resigned on moral grounds and to co-operate with the prime minister," he told a crowded press conference in Chennai, adding there was no pressure from any quarters including from the prime minister or Deputy Prime Minister L K Advani.
He said his resignation after the arrest of his personal assistant Perumalswamy by CBI on graft charges was only to uphold probity in public life.
"My conscience is clear and I have not committed any wrong," he said.
Ramachandran denied reports that his office staff had interfered in the functioning of the Income Tax department, when its officials conducted raids at the residences of businessmen and film stars at Chennai.
He said he did not know the chartered accountant A Krishnamurthy, the 'conduit.'
"I saw his face only on television after his arrest," he said.