NAD 3020 phono hiss and booiizz - UK Vintage Radio Repair and Restoration Discussion Forum

crackleypot · 3rd May 2009, 9:21 am

I have a NAD3020 hifi amp from about 1985 which I bought new. The phono preamp has always been very hissy, maybe I'm being fussy. OK maybe I'm asking for trouble but with cart connected turn up the vol and big hiss, I did mention this to the shop but they weren't interested. So I toured the shops in the area and tried the same test on their NAD3020, rats it was mine.

Question is, what is going to be the most likely source of this noise, my guess is the transistors, maybe one batch was noisey, both channels exhibit the same amount of noise. There are 6 transistors in the phono preamp all from the usual BC559/556/546/549 mob, I plan to replace them.

Another Q, the amp has always issued that big speaker thump on power on (a deep booiizz type sound), which I now find tiresome and want to get rid of. My thought is to make a simple relay circuit that switches from the loudspeakers to a dummy load for 3sec on switch on. Any thoughts?

regards

julie_m · 3rd May 2009, 9:34 am

BC549s and 559s are lower noise devices than the 546 and 556, but otherwise they are of similar specs. I'd be tempted just to replace all the 546s with 549s and the 556s with 559s.

Graham-R · 4th May 2009, 8:59 am

Quote:

Originally Posted by crackleypot

Another Q, the amp has always issued that big speaker thump on power on (a deep booiizz type sound), which I now find tiresome and want to get rid of. My thought is to make a simple relay circuit that switches from the loudspeakers to a dummy load for 3sec on switch on. Any thoughts?

regards

Hi

You could try the design in one of the Doug Self books (forget which one and am away from home at the mo), or the Velleman k4700 kit protection module which is available for about £15 from www.esr.co.uk.

Both of these have additional dc protection as well.

Graham

3rd May 2009, 9:21 am	#1
crackleypot Tetrode Join Date: May 2007 Location: Gloucester, Gloucestershire, UK. Posts: 50	NAD 3020 phono hiss and booiizz I have a NAD3020 hifi amp from about 1985 which I bought new. The phono preamp has always been very hissy, maybe I'm being fussy. OK maybe I'm asking for trouble but with cart connected turn up the vol and big hiss, I did mention this to the shop but they weren't interested. So I toured the shops in the area and tried the same test on their NAD3020, rats it was mine. Question is, what is going to be the most likely source of this noise, my guess is the transistors, maybe one batch was noisey, both channels exhibit the same amount of noise. There are 6 transistors in the phono preamp all from the usual BC559/556/546/549 mob, I plan to replace them. Another Q, the amp has always issued that big speaker thump on power on (a deep booiizz type sound), which I now find tiresome and want to get rid of. My thought is to make a simple relay circuit that switches from the loudspeakers to a dummy load for 3sec on switch on. Any thoughts? regards

3rd May 2009, 9:34 am	#2
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: NAD 3020 phono hiss and booiizz BC549s and 559s are lower noise devices than the 546 and 556, but otherwise they are of similar specs. I'd be tempted just to replace all the 546s with 549s and the 556s with 559s. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.