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Sony CDP790 and KSS240 Restoration Project
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Old 16th November 2019, 05:53 PM   #161
12Bass is offline 12Bass
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Have a pair of LME49990s on an adapter which I installed in the output stage of my CDP-X111ES along with the ADA4627-1s, giving a bit of improvement in clarity over the OPA211s (LME49990s used for final buffer, ADA4627-1s in differential amplification stage).

My old CDP-65 had a power switch which cut power right at the mains; off was totally disconnected from the wall. However, the power switch on the X111ES is on the low voltage side, meaning that the unit is always drawing power, even when off; I measured 4W with my EM100 Energy Meter, which is a significant amount of vampire power. Given that the unit has no power on by remote function and no apparent stand-by mode, does anyone know why Sony employed such an energy inefficient wiring scheme for the power switch, other than to save a little money on manufacturing costs?
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Old 16th November 2019, 07:08 PM   #162
Mooly is offline Mooly  United Kingdom
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In the UK 4 watts over a year would typically cost around 6.00

As with everything, manufacturers employed standby switching rather than true on/off function on the grounds of cost. The safety requirements will be far more relaxed for low voltage circuitry and case work that can not contact live mains.

You might find a simple power monitor is less than accurate at very low current draws and also may not account very accurately for the poor power factor of an inductive load such as a very lightly loaded transformer.
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Old 17th November 2019, 01:28 PM   #163
audio_tony is offline audio_tony  United Kingdom
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I have found that AC power monitors are typically quite inaccurate at very low power draw.

Looking at the PSU I would be surprised if that draws more than 0.5W in standby.

Also - unless you've already modded the muting circuit, I would remove the various transistors (as highlighted in the attached schematic) and replace them with a relay. Additionally, the combination of resistors (required for the transistor muting circuit) push the output impedance up to around 1k ohm which is rather high.

So in addition to a muting relay, I would bypass the 220 ohm resistors, and then change the 560 ohm to 56 ohm.

Finally, the original NE5532 output OPAMPs are more than adequate for this application, and I suggest you try blind tests to verify you really are hearing differences when substituting those expensive OPAMPS...
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Last edited by audio_tony; 17th November 2019 at 01:31 PM.
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Old 19th November 2019, 10:29 PM   #164
12Bass is offline 12Bass
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Quote:
Originally Posted by audio_tony View Post
Also - unless you've already modded the muting circuit, I would remove the various transistors (as highlighted in the attached schematic) and replace them with a relay. Additionally, the combination of resistors (required for the transistor muting circuit) push the output impedance up to around 1k ohm which is rather high.

So in addition to a muting relay, I would bypass the 220 ohm resistors, and then change the 560 ohm to 56 ohm.

Finally, the original NE5532 output OPAMPs are more than adequate for this application, and I suggest you try blind tests to verify you really are hearing differences when substituting those expensive OPAMPS...
Hi, audio_tony,

What sort of difference should be expected from removing the muting transistors? I've seen this mentioned before, but haven't attempted it yet. What would you suggest for a muting relay, and how would it be wired in?

As for the op amps, over the years, I've spent many hours auditioning various op amps, swapping back and forth to ensure I'm reliably hearing what I think I'm hearing. Usually, the differences are fairly subtle, but they're there.... I've been a musician for decades and have mixed a few projects, so I have pretty good ears and am able to pick out subtle difference that most people would miss. I'm also well aware of various forms of cognitive and perceptual biases, so I make a concerted effort to double/triple/quadruple check what I'm hearing. Sometimes an expected improvement isn't there, so I know it isn't just a matter of confirmation bias.

The ADA4627-1 and LME49990 are the best sounding op amps I've found thus far and I don't have another use for them at the moment. FWIW, I'd say that the ADA4627-1 is a bit more euphonic sounding, with a nice warmth, yet still quite open, whilst the LME49990 might be characterized as more transparent, without much obvious color. I quite like the tonality of the ADA4627-1. Both are better than an NE5532, and much better than the TL082 that was in the differential stage.
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Old 20th November 2019, 07:42 AM   #165
Mooly is offline Mooly  United Kingdom
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These kind of mute transistors are rather unique in that they will operate (at low voltages anyway) without regard to C-E polarity. They have 'gain' with either polarity configuration... so never swap them for ordinary small signal types as they won't work as well.

What to do as an alternative? Well years ago I came across this thread (look at post #9 and onward) and can confirm that using suitable JFET's as a direct replacement works well in most cases.

Marantz SA8001 Modification to Eliminate Distortion
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Old 20th November 2019, 09:19 AM   #166
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When one reads Self's research on muting transistors (even FETs) one wonders why anyone would bother with them.

I would only ever use a relay.

@Mooly - the transistors used for the actual muting are standard 2SCxxxx types. They in turn are switched by those special transistors with built in resistors.

That they have used three transistors per channel with appropriate limiting resistors suggests they had issues getting the mute silent enough. A relay would likely have been cheaper!

@12Bass If you're not sure how to bypass the muting circuit and fit a relay then perhaps this is not the task for you.

But in basic terms, the muting is controlled by Q341, Q342, Q343.

You only need to make use of one of those - and use it to drive a another transistor (pref. darlington) to switch the relay, which you would place in series with the output. You could also place it in parallel, but then you would need to retain the series resistors which would defeat the object to some degree.

You need a low output impedance here.

The current high(ish) output impedance might be why you are hearing differences between opamps (depending on the capacitance of your interconnect as well).
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Old 20th November 2019, 10:35 AM   #167
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FWIW, if I were to make such a modification, I'd likely go with a relay rather than FETs, as that seems to be the least likely to introduce any distortion into the signal. That said, CD players like the X111ES already have vanishingly low distortion, so I'm not sure how much there is to be gained by such a modification, though I have found that changes to the analog output stage seem to make the largest difference in my experience. Still, I'm curious to read what Self found in his research, so a link would be appreciated. A simple way to find out would be to temporarily bypass the muting transistors and see if the difference is audible. I understand the basics of wiring up a relay but am unsure of the potential benefit and tend toward the maxim of "if it ain't broke, don't fix it"... as I've damaged various devices in the past with questionable modifications, and the player is sounding subjectively pretty good at the moment.

The op amp discussion is somewhat of a side topic... however, I've reliably heard differences between op amps in all kinds of circuits, and have tried, many, many different parts... which is what has led me to the ADA4627-1 and LME49990, which are the best of the bunch that I've tried. Others that I've auditioned include: LM4562, AD825, OPA275, OPA2604, OPA2132, OPA2134, OPA211/2211, OPA1612, OPA1642, OPA2107, OPA249, NE5532, LM6171, TL072, AD797, OPA827, and several more....

Last edited by 12Bass; 20th November 2019 at 10:38 AM.
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Old 20th November 2019, 10:50 AM   #168
audio_tony is offline audio_tony  United Kingdom
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Quote:
Originally Posted by 12Bass View Post
<snip>
Still, I'm curious to read what Self found in his research, so a link would be appreciated.
<snip>
You would have to buy his book for that, none of this is available online.

https://www.amazon.co.uk/Small-Signa.../dp/0240521773
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Old 20th November 2019, 11:58 AM   #169
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by audio_tony View Post
@Mooly - the transistors used for the actual muting are standard 2SCxxxx types. They in turn are switched by those special transistors with built in resistors.
The transistors used in the CDP790 are these which were rather special (although common enough in this type of application):

Muting Transistors



They have a high hFE of around 150 when reverse biased at -2 volts.

It looks like the ones in audio_tony's player are more general purpose devices.
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