High THD, Poor RCA Connections

goeat · 13th March 2006, 09:13 AM

I can imagine that this is a popular problem, but I couldn't for the life of my find a related thread using the search, so...

This is for equipment that I've bought, mainly a NAD 1130 Preamp and an Adcom GFA-555 MKI. I'm having a lot of problems getting a good connection between the preamp and the amp with any RCA cable (high or low quality), being especially twitchy at the preamp side of things, often resulting in loud pops and emormous amounts of distortion (~90%) should the cable be jostled. The connection at the amplifier is solid.

Some things that have been recommended to me as problems:
-Ground loop problem between the amp and the preamp's wall connection.
-Ground loop problem within the preamp.
-Poor RCA connections on the preamp.
-Faulty RCA wiring on the preamp.
Are these in the right direction?

I plan on taking apart the preamp tomorrow, mostly to see what's up in there. If anyone can provide any insight as to the RCA issue, thank you in advance. I can provide more information on how these are wired together/to wall power if anyone cares to know.

Greg

richie00boy · 13th March 2006, 09:16 AM

It's nothing to do with ground loops. Simply the RCA connection - probably the springy part that forms the centre contact, or the ground contact - is a bit loose somewhere.

Eva · 13th March 2006, 03:50 PM

It looks like an oxidized contact or a bad solder joint in the female RCA connector.

anatech · 14th March 2006, 01:43 AM

I think Eva's on track. Many newer products have RCA connectors that get cracked solder joints on the PCB. Once you get in there, resolder the lot.

Also, Adcom amps have a resistor between ground and signal ground on the order of 100 ohms. You should measure 200 ohms between the RCA grounds (with the amp turned off!!).

-Chris

myhrrhleine · 14th March 2006, 02:57 AM

> Post #3
It looks like an oxidized contact or a bad solder joint in the female RCA connector.

Or similar problem with the RCA jack.

13th March 2006, 09:13 AM	#1
goeat diyAudio Member Join Date: Mar 2006 Location: Berkeley	High THD, Poor RCA Connections I can imagine that this is a popular problem, but I couldn't for the life of my find a related thread using the search, so... This is for equipment that I've bought, mainly a NAD 1130 Preamp and an Adcom GFA-555 MKI. I'm having a lot of problems getting a good connection between the preamp and the amp with any RCA cable (high or low quality), being especially twitchy at the preamp side of things, often resulting in loud pops and emormous amounts of distortion (~90%) should the cable be jostled. The connection at the amplifier is solid. Some things that have been recommended to me as problems: -Ground loop problem between the amp and the preamp's wall connection. -Ground loop problem within the preamp. -Poor RCA connections on the preamp. -Faulty RCA wiring on the preamp. Are these in the right direction? I plan on taking apart the preamp tomorrow, mostly to see what's up in there. If anyone can provide any insight as to the RCA issue, thank you in advance. I can provide more information on how these are wired together/to wall power if anyone cares to know. Greg

13th March 2006, 09:16 AM	#2
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	It's nothing to do with ground loops. Simply the RCA connection - probably the springy part that forms the centre contact, or the ground contact - is a bit loose somewhere. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

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13th March 2006, 03:50 PM	#3
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	It looks like an oxidized contact or a bad solder joint in the female RCA connector.

14th March 2006, 01:43 AM	#4
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	I think Eva's on track. Many newer products have RCA connectors that get cracked solder joints on the PCB. Once you get in there, resolder the lot. Also, Adcom amps have a resistor between ground and signal ground on the order of 100 ohms. You should measure 200 ohms between the RCA grounds (with the amp turned off!!). -Chris

14th March 2006, 02:57 AM	#5
myhrrhleine diyAudio Member Join Date: Jan 2006 Location: Avalon Island	> Post #3 It looks like an oxidized contact or a bad solder joint in the female RCA connector. Or similar problem with the RCA jack.

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