Strange noises in a 306.

Ovitch wrote on www.ls3-5a-forum.com:

Bonjour à tous,
je viens d'acheter un Quad 306,je ne connais pas le 303 ni le 405 mais la qualité de cet ampli me laisse vraiment rêveur aux vues du prix et des données techniques du 306.
Le seul petit défaut que je constate sur mes enceintes au rendement assez élevé(97db) c'est du souffle et un petit ronronnement lorsqu'il n'y a pas de musique.
Est-il possible d'y remédier?"

"Hallo, all,
I just bought a Quad 306, I don't know the 303 or the 405 but the quality of this amplifier really makes me a dreamer about the price and the quality of the 306.
The only small problem I hear in my speakers with a high efficiency (97 dB) is a noise and a slight rumble when there is no music.
Is it possible to solve this?"

In an amplifier older than 10 years new ones should replace all capacitors above 1 MF. They tend to dry out and change their value over time.

You could also consider replacing the input-Opamp for a more "modern" one like the Burr Brown OPA604 (take care of the power-rail voltages which should be 15V) and reducing the sensitivity (now 375 mV) by increasing the local feedback of the Opamp.

It is somewhat more complicated. The Opamp is used in the feedback-circuit, TR1 is the input-stage.

Stefaan