Extremely noisy DC (Phono Stage PSU) - Page 5

kevinkr · 14th September 2012, 01:49 AM

Good news I'd say. These sorts of things get even the most experienced of us..

danielwritesbac · 02:08 AM

Paraphrased from AndrewT: Try 63/37 solder which is less likely to come loose than 60/40.

And from me: Try Gel Flux (petroleum jelly + rosin), especially for soldering plated contacts.
I'll bet your RCA jacks have that almost nonstick gold-ish plating, right? Well, flux 'em.

lordvader · 14th September 2012, 02:23 AM

The sockets were fine, actually. It was the cable RCAs that were problematic. Fortunately, the rca on my tonearm could be "squished" to make better contact

danielwritesbac · 14th September 2012, 02:55 AM

Sorry that I guessed wrong about the connection fail. There's another reason I was mentioning the 63/37 solder and gel flux: I am in the middle of making a compact portable solar power pa to fit a bicycle rack, and that must resist a lot of vib vib vibration. Meanwhile, back to the tablesaw to finish up the lightweight birch enclosure. . .

Edit:
Good luck with the buzz. Maybe try adjusting the ground loop breaker's resistor value to see if there's a difference possible?

lordvader · 17th February 2013, 07:26 AM

OK.
Time for another update.

Since my last post, it became apparent that it wasn't just the dodgy RCA that was causing noise.
There were HUGE voltage swings on the raw DC supply, so I ended up putting in a SSHV2 regulator before the CCS's. Still, even though that cleared up the swings on the DC voltage, there was still horrible noise.
I ended up chalking it down as extremely microphonic tubes, so I decided to replace the C3G's on the input with D3A tubes, and to keep the gain down, the output C3G was changed from being CCS loaded, to R loaded (10k).

I also replace the C3G sockets. They were originally teflon sockets found on ebay (which I'm not convinved made good contact with the pins, and were extremely fragile). I'm now using good old fashioned ceramics.

The result is now an phono preamp that still has noise if I turn up the volume all the way, but it's not really an issue, as even when I've got my volume about halfway, it's already extremely loud (gain is somewhere between 44 and 46db).
I've also wired up the lundahl step up transformer, and it's working beautifully. No hum whatsoever.

Personally, I would have liked to have a D3A on the output too, but an R loaded D3A would have put the gain at 52db, and a ccs loaded one, 54db.

14th September 2012, 01:49 AM	#41
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Good news I'd say. These sorts of things get even the most experienced of us.. __________________ "Extraordinary claims require extraordinary evidence." - Carl Sagan

14th September 2012, 02:06 AM	#42
danielwritesbac diyAudio Member Join Date: Nov 2007	Paraphrased from AndrewT: Try 63/37 solder which is less likely to come loose than 60/40. And from me: Try Gel Flux (petroleum jelly + rosin), especially for soldering plated contacts. I'll bet your RCA jacks have that almost nonstick gold-ish plating, right? Well, flux 'em. __________________ ♦ Tools & Guides ♦ ClipNipper headroom boost ♦ Parallel LM1875 pt2pt ♦ Easy parallel TDA7293 board ♦ TDA7294 pt2pt ♦ My post has opinion. Last edited by danielwritesbac; 14th September 2012 at 02:08 AM.

14th September 2012, 02:55 AM	#44
danielwritesbac diyAudio Member Join Date: Nov 2007	Sorry that I guessed wrong about the connection fail. There's another reason I was mentioning the 63/37 solder and gel flux: I am in the middle of making a compact portable solar power pa to fit a bicycle rack, and that must resist a lot of vib vib vibration. Meanwhile, back to the tablesaw to finish up the lightweight birch enclosure. . . Edit: Good luck with the buzz. Maybe try adjusting the ground loop breaker's resistor value to see if there's a difference possible? __________________ ♦ Tools & Guides ♦ ClipNipper headroom boost ♦ Parallel LM1875 pt2pt ♦ Easy parallel TDA7293 board ♦ TDA7294 pt2pt ♦ My post has opinion.

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14th September 2012, 02:23 AM	#43
lordvader diyAudio Member Join Date: Mar 2002 Location: n/a	The sockets were fine, actually. It was the cable RCAs that were problematic. Fortunately, the rca on my tonearm could be "squished" to make better contact

17th February 2013, 07:26 AM	#45
lordvader diyAudio Member Join Date: Mar 2002 Location: n/a	OK. Time for another update. Since my last post, it became apparent that it wasn't just the dodgy RCA that was causing noise. There were HUGE voltage swings on the raw DC supply, so I ended up putting in a SSHV2 regulator before the CCS's. Still, even though that cleared up the swings on the DC voltage, there was still horrible noise. I ended up chalking it down as extremely microphonic tubes, so I decided to replace the C3G's on the input with D3A tubes, and to keep the gain down, the output C3G was changed from being CCS loaded, to R loaded (10k). I also replace the C3G sockets. They were originally teflon sockets found on ebay (which I'm not convinved made good contact with the pins, and were extremely fragile). I'm now using good old fashioned ceramics. The result is now an phono preamp that still has noise if I turn up the volume all the way, but it's not really an issue, as even when I've got my volume about halfway, it's already extremely loud (gain is somewhere between 44 and 46db). I've also wired up the lundahl step up transformer, and it's working beautifully. No hum whatsoever. Personally, I would have liked to have a D3A on the output too, but an R loaded D3A would have put the gain at 52db, and a ccs loaded one, 54db.

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