I put in R12 3k3 "Royal ohm" 100mW 0,1% 25ppm/°C. It is good for me. Detailed and no coloration in midrange.
Iva England used both methods, pull down resistor and CRD. CRD should be better. But I thought resistor sounded better. Maybe more pleasing colonizations.
I have used both methods, pull down resistor and CRD. CRD should be better. But I thought resistor sounded better. Maybe more pleasing coloration.
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Or, perhaps, less undesired interactions which results in less unpleasing coloration... 😉
Let' think about it. The OpAmp output presents a reactive impedance (which is also non-linear; at least, not perfectly linear). Same goes for the supply rail, as well for the CRD itself (or any other active CCS circuit). Connected together they will form a (multi)resonant circuit. With little damping. Thus, that will likely produce a lot of "artifacts".
OTOH, a resistor is a dissipative (and almost perfectly linear) element which will effectively damp the undesired resonances formed by the OpAmp out - PSU interactions, thus will likely introduce less artifacts.
Obviously the NFB loop will try to get rid of any such "artifact" (linear & non-linear distortion, any alteration of the signal WRT the input). But! no amount of NFB can completely eliminate it. Some residual low-level artifact (which perhaps may be described as "noise-floor modulation") will always show up at the output.
And that's likely what we perceive as sound "character" (or "coloration", or however you'd like to call it).
Something which may be worth trying is to use a CRD in series with a relatively large resistor (may be from the higher voltage, unregulated supply rail to get more headroom).
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I'd been having mixed thoughts towards the class A mod, as although it warms up the sound, somehow it looses some of the vivid clarity and sense of presence that it had before. So I've removed the CRD for now, maybe to re-visit at a later date when other mods are done.
that's not a bad idea: you'll have a chance to hear the effect of the various mods separately.
If you're gonna try the "class-A" trick again, I'd try both with the CRD and a with a simple resistor, as well with both a resistor and a CRD in series... it would be interesting to compare the effect of the different configurations.
It is also worth compaing these three options against the three others connecting the ClassA drain to the positive rail. Remember to orient the active with the current flow.
A few hours listening yesterday has convinced me that there is something going on with the class A mod other than the elimination of switching artifacts. Whatever the mechanism at play, I'd be much more comfortable seeing something objective here rather than guessing.
So for now at least I'm going to press on with other mods - plenty left to experiment with!
So for now at least I'm going to press on with other mods - plenty left to experiment with!
Dan, looking forward 🙂
Oloppolo: royal ohm, interesting, I'm also looking around in that zone (R12).
Your part, in what it is different from the susumu RG 0805 parts?
Ciao, George
Oloppolo: royal ohm, interesting, I'm also looking around in that zone (R12).
Your part, in what it is different from the susumu RG 0805 parts?
Ciao, George
That was my conclusion when modifying the output stage of disc players. The bias changed the sound. Never for the better. I tried several opamps to see if the higher current was degrading performance.
It is easy to implement and remove with through hole components. Soldering a SM from lead to lead is doable.
OK so I've linked out C9 (a Black Gate Standard in my case) with unambiguous positive results. Small details become apparent and sounds gain texture and general cleanliness. Recommended!
This unit has a very well working DC protection scheme, you should always check in which thread you are responding..
I recall the output relay works quite nicely. But I have not checked whether DC can pass through or not.
It can't. The relay is in series with the output. If there's too much output DC offset for too much time, the relay opens and disconnects the loudspeakers.