My_Ref Fremen Edition - Beta build/Fine tuning

[ClaveFremen]

Originally Posted by KSTR

So, before that, the "GND" potential was floating, with respect to Protective Earth?

Exactly

Originally Posted by KSTR

If so, any noise current between your multiple, seperate (?) transformers was forced to mainly flow through through the 1R's, then through the signal cable shields to the point when these combine at your source device (CD?) for then to possibly interact with the source's own GND system.

You can see in the attached picture how things are connected.

Neither the DCB1 or the SACD player are grounded to safety earth.

Originally Posted by KSTR

EDIT: I see something even more suspicios, you used full bridge on each rail. So any leakage current gets chopped, it only flows when the diodes are conducting.

It sounds like a bad thing... Am I right?

But it's like all Gainclone's PS around here...

[KSTR]

Double bridges are not problematic per se, but it can become a problem when the chopping action finds a way into the signal path. The point is that chopped hum current (assuming 50/100Hz hum as the dominant noise) is worse than unchopped when it makes itself apparent in the signal, via a voltage drop accros the 1R resistors. For every mV drop you'll get 30mV at the output.

[soongsc]

I was also wondering about the grounding. Simple circuit simulation shows not connecting to protective earth ground is a problem. But if you put the power supply into consideration, the speaker current flows through the power ground. Although I do not have problems because of the power I use, but I have not looked at the linear power used here. If there is a problem with not connecting ground to earth, then it would be a problem for areas that do not have earth ground. We did not require earth ground here until the last 10 years or so.

[ClaveFremen]

Originally Posted by KSTR

The point is that chopped hum current (assuming 50/100Hz hum as the dominant noise) is worse than unchopped when it makes itself apparent in the signal, via a voltage drop accros the 1R resistors.

I doubt that the eventual ground noise is 50/100Hz related beacuse it is not constant, it's not a noise, it seems more a signal correlated artifact, if it exists at all.

Yes, if it exists...

Since this is my first project I'm, maybe, a bit paranoid and I tend to relate any problem to the project.

In fact I've listened to my player via headphones and at least part of the problem seems also present.

In the next days I'll do more listening sessions and experiments to confirm it or not.

It seems that connecting PGND to the star ground only masked the problem since in this way it sounds fuller and restricted thus partially masking the artifacts but this evening I've heard them again.

BTW it seems to sounds better (airy and natural) if left floating (PGND not connected)

Originally Posted by soongsc

I was also wondering about the grounding. Simple circuit simulation shows not connecting to protective earth ground is a problem.
...
If there is a problem with not connecting ground to earth, then it would be a problem for areas that do not have earth ground.

Let's see what are further tests results... maybe it's only me...

BTW what problems you found through sims?

[soongsc]

Hi frequency resonances. The higher, the larger. This may not be what happens in reality, but does indicate something needs to be dealt with.

Since our APT does not have a ground wire on normal mains, I was amazed that I did not run into much problems, but one channel seems to have some high frequency resonance after playing some time, and I have to shut it down and power back up after it cools off. The resonance seems to happen only in the channel with the original LM318 compensation.

[ClaveFremen]

Originally Posted by soongsc

Hi frequency resonances.

Interesting

Originally Posted by soongsc

The higher, the larger.

I suppose you mean higher the frequency, larger the resonance, right?

Originally Posted by soongsc

This may not be what happens in reality, but does indicate something needs to be dealt with.
...
one channel seems to have some high frequency resonance after playing some time, and I have to shut it down and power back up after it cools off. The resonance seems to happen only in the channel with the original LM318 compensation.

So it seems to happen also with the single diode bridge... if we're talking about the same problem.

With or without C12?

[soongsc]

Yes, higher the frequency, larger the resonance. I did not notice artifacts, but it was noticed when I was switching channels comparing modification differences between channels. The funny thing is it can only be heard when I swap the channels. I operate without C12 all the time now, and also took away the high frequency filter. Since I just modified the input section, I will see if the problem persists or not.

[GloBug]

Originally Posted by ClaveFremen

Just one (incredible) note:

In pictures you can see the 390R Takman REX orientation.

In this config it sound strangely thin, I've reversed that single resistor (matching the orientation I've on TP boards, red band on ground) and the full sound I'm accustomed to got back...

OK, not to flame on your parade, but are you implying that the orientation of a resistor makes your amp go from "strangely thin" to "full sound"?

If so I have some cables and crystals that will really wow ya.

[ClaveFremen]

Originally Posted by GloBug

OK, not to flame on your parade, but are you implying that the orientation of a resistor makes your amp go from "strangely thin" to "full sound"?

Should be read as thinner than usual / full as usual, not a big difference but one I can hear.

Please don't start the n-th war on resistor orientation/cables/capacitors/etc., simply ignore my comments on it if you can't hear/don't trust such things.

[linuxguru]

Originally Posted by GloBug

OK, not to flame on your parade, but are you implying that the orientation of a resistor makes your amp go from "strangely thin" to "full sound"?

That's a typical symptom of either a dry (non-ohmic) joint on one of the resistor leads, or a flaky resistor with a cracked/loose/non-ohmic end-contact. Reversing it probably fixed the dry joint or made the end-contact sit snugly, thus solving the problem - probably not related to the resistor orientation itself, though that's also possible (most resistors are slightly non-ohmic - when measured with a high-precision DMM, they'll differ slightly in value when measured in each direction. I typically see a few ohms difference on "good" 22k metal films, but that could be 10s of ohms on carbon films, and even more when they're flaky).

Note that this is a relatively low-value (390R) resistor, where rectification artefacts due to non-ohmic/dry joints could well be audible. It could also account for some of the hum/crackling artefacts reported - in my experience, the MyRef is sensitive to dry joints at several locations: the Howland resistor networks, the GNFB resistor network and the lift resistor R11 come to mind. Actually, every solder joint in and around the small-signal section/LM318 should be re-checked and re-flowed if it looks suspect.