After a good few years of inactivity I have recently purchased a pro-next debut carbon tt. I already had a maranta cd6003 and kef iQ5 floorstanders plus a marantz pm40se amp. In the last few days the amp appears to have lost its left channel, making it an obvious candidate for an upgrade. But I have no idea where to start and not sure whether my budget of £500 will provide any significant improvement. Advice gratefully received