Marantz SA8001 Modification to Eliminate Distortion - Page 3 - diyAudio
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Old 8th October 2010, 07:25 PM   #21
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Unless a VERY strangely designed tube amp, it's input stage should have zero or damn near zero dc volts on it's input at any time, whether or not it has blocking caps. But if you are feeling an electrical 'buzz' with your fingers from the chassis of the amp, it has some kind of AC mains grounding issue. If it has a three pin mains plug, check that the ground pin is actually connected to amp's chassis ground, and, if it is, check that the wall outlet it's using has a proper earth ground. If the amp has a two pin ac plug, try flipping it(with nothing else connected to amp) and see if the electrical feeling from the chassis goes away. On anything in my system with a non-polarised ac plug, I always try the plug in both directions on each piece of gear before connecting up everything, to make sure I have no such ground/polarity issues with the ac mains. If I glide the back of my hand lightly accross the metal of a unit, and get that buzzy feeling, I flip the ac plug around & it disappears, meaning my ac polarity is then proper. If that buzz does not go away, then there is either an insulation fault causing dangerous mains leakage to the chassis, or it's a pre-1970 unit with a ceramic cap from both sides of ac to chassis(in which case I clip one cap out).
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Old 12th October 2010, 12:37 AM   #22
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Swapped in the Marantz PMD-320 Prof. CD player since the SA8001 was belly up. Guess what, same pop between tracks and distortion on loud CDs. Looked at the inside and sure enough, same problematic 2SC2878 transistors at the analog outputs. So, the JFETs are going in. I might as well order a dozen since I have a bunch of Marantz players around here.
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Old 12th October 2010, 02:08 AM   #23
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You know, it's starting to seem to me that your preamp(or amp if fed direct from cd unit) might be throwing back a bit of dc voltage to it's input somehow. I would advise you to do a dc check there. The C2878's are unreliable, and very popular for muting, but you seem to be defying the odds on failure rates with them, plus you had that strange fault happen with SA8001 and the amp connections.
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Old 12th October 2010, 08:01 PM   #24
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Quote:
Originally Posted by stephensank View Post
Very happy to help. Now all you need to do is get rid of all those horrid Elna caps before they start leaking & corroding the hell out of your board. You probably still have a few years before the leakage starts, but you never know. If you do replace them, use Nichicons if you want the unit to last, and sound good.
Oh, and if any of those Elnas are Duorex model series, I would replace them immediately!
My 20+ year old Sony CDP227ESD has several 'Duorex' capacitors on board.

They look fine to me.

Why do you advocate changing them may I ask?
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Last edited by audio_tony; 12th October 2010 at 08:02 PM. Reason: Spelling error
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Old 12th October 2010, 09:05 PM   #25
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I should do a little confessing here, it was late and kids were running around, so being distracted I connected the SA8001 to the low level inputs on the tube amp, either the phono or take head, can't remember. Sound was distorted, so immediately found my error, but the damage was done. I rotate equipment almost on a daily basis, so I should not totally blame the CD players. But the 8001 has been particularly brittle. I did the palm test for vibrating stray charge on the tube amp chassis and it was nill, so the tube amp is well isolated. The Toshiba JFETs are BO until late December, so I may have to settle for some NTE 2SC2878 replacements.
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Old 13th October 2010, 02:10 AM   #26
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Quote:
Originally Posted by audio_tony View Post
My 20+ year old Sony CDP227ESD has several 'Duorex' capacitors on board.

They look fine to me.

Why do you advocate changing them may I ask?
I have found Elna caps in general to be horribly unreliable, but the Duorex series are the worst offenders in my experience(which is prodigious). The caps themselves may look ok, but if you look on the bottom side of the circuit board, you may see some black circuit traces, which is the leakage from those caps corroding the copper. Usually show black residues on top side of board as well, but not always. I can promise you that if they haven't leaked yet, they positively will in the next few years, and they can do some severe damage to the board. So, yes, I absolutely urge you to replace them with Nichicon or Nippon Chemicon caps, assuming you want the player to last.
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Old 13th October 2010, 02:14 AM   #27
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Quote:
Originally Posted by whaleman View Post
I should do a little confessing here, it was late and kids were running around, so being distracted I connected the SA8001 to the low level inputs on the tube amp, either the phono or take head, can't remember. Sound was distorted, so immediately found my error, but the damage was done. I rotate equipment almost on a daily basis, so I should not totally blame the CD players. But the 8001 has been particularly brittle. I did the palm test for vibrating stray charge on the tube amp chassis and it was nill, so the tube amp is well isolated. The Toshiba JFETs are BO until late December, so I may have to settle for some NTE 2SC2878 replacements.
Ahh, the plot thickens. Or thins? Still, I do find it quite suspicious that a)you have another player with muting xstor pops, and b)the popping on the SA8001 has not completely disappeared(or I recall you saying that). So, I would still advise you to check for dc coming back from the amp to the player, which you could check at the player's output jacks, with amp/preamp running, quite safely, even with the volume up(assuming nothing weird with your voltmeter).

As for the jfets, you can also use 2SK117 or 2SK246(GR, BL, Y, doesn't matter), which have the same pinout & will work perfectly as well.
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Old 17th November 2010, 05:47 PM   #28
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Almost forgot to update you all on this. The SA8001 received the NTE85 semiconductors, a straightforward replacement to the 2SC2878. It goes in with the same pin configuration. It cleaned up things really nice, no pops of any kind, great sound. So this may be a great option. The Marantz PMD320 uses the same muting transistors, so it got the same NTE85 treatment. It however continues to pop just slightly between tracks, but the distortion that was in the sound is totally gone. It is actually no problem.
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