QUAD 303 NOISE

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09-Aug-2019 12:37 AM

LOWTHERMAN62

LOWTHERMAN62

Posts: 52

Hello All,

Having just completed a 303 revision I notice noise, At normal listening levels thnere is a hiss, white noise and a very low level hum. Increases with volume on both channels. Using a revised 33. When i substitute a 306 or 405-2 all is quiet. I have carried out only the dada revision. but all resistors meter ok. I have not touched any of the aging transistors . Can you point me where to look? I have installed multiturn trimmers and ril voltages are rock stadu 67/33.5 current is set at 10mV.

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09-Aug-2019 09:44 AM

EJP

EJP

Posts: 1638

If it increases with volume it must be coming from before the volume control in the 33. Luckily this doesn't leave much. Try replacing the two transistors on the Tape Adapter board with BC549 or BC550.
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09-Aug-2019 02:33 PM

LOWTHERMAN62

LOWTHERMAN62

Posts: 52

Hi EJP, 

The 33 has just had a full revision including all transistors changed to BC550. This noise doe not manifest itself when used with my 306 or 405-2. Could it be old 303 transistors on the way out? If so which ones should I replace first? Could it be resistors as all the 303 are old carbon types with the exception of the revision resistors. Regards Stewart

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10-Aug-2019 05:51 AM

EJP

EJP

Posts: 1638

Well it can't increase with volume in that case, but start with Tr100 and work your way forwards.
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