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Old 15th July 2011, 09:00 AM   #191
SimontY is offline SimontY  United Kingdom
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Quote:
Originally Posted by martin clark View Post
If that is 10cm away from the load device, across thin tracks sharing noisy currents with other circuits, then its benefit is often degraded badly. It's always worth a good think about how 'good' drop-in 3pin reg replacements can perform from this POV.
Hello Martin,

Have you seen inside an Arcam Alpha? Specifically, the DAC / output board that Arcam use to differentiate it from the stock Philips design? The -15V reg (LM337 as stock) feeds the -5V reg. Same with the +15 and +5 regs. These then feed the op-amps (removed on my model) and DAC's +5, -5 and -15V. What do you think of this cascaded sort of regulation? I left it as standard for now but thought it might be better done "directly".

What do you think of the layout? Are these regs too far away for high performance? I thought not but you seem to be getting at something, unless that wasn't directed at me (it felt like it was as I am using the good regs round here!)

Thanks
Simon
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Old 15th July 2011, 09:09 AM   #192
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Quote:
Originally Posted by batteryman View Post
The Dac kit from rainbow_hui on ebay appears to feature discrete regulators (haven't received it yet) so here's hoping they sound better than IC regulators. I'll be upgrading some of the caps as well,not to mention converting it to dual differential and listening out for the benefits of dem reclocking and i2s attenuation.
BM
I can't see discrete being as good as typical "super" type regs using an op-amp but maybe it brings something interesting to the party. It'll be interesting to see what you think of those other tweaks.
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Old 15th July 2011, 09:16 AM   #193
SimontY is offline SimontY  United Kingdom
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Quote:
Originally Posted by wlowes View Post
The vocal hiss had a harsh edge on some recordings. Words like this or kiss had a sizzle at the end. Following the reclocking, this has disappeared.
Re-clocking is great at removing that fuzz and sizzle from the edges of treble notes. It's the same in a CD63. You should, however, still expect to hear some unpleasant exaggeration of sibilant sounds (those sssshhh noises, mainly on female voices) because some of it is from using cheap microphones, which most recordings use. If it's there it should be reproduced. The goal is to hear recordings warts and all but not to exaggerate those warts. I find the 1541's basic character to be one of omitting certain details but not making a mess of anything that it does reproduce. The lack of detail is not just layout and other clever things only smart blokes know about, it's got to be intrinsic to the design to a point.
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Old 15th July 2011, 10:17 AM   #194
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Quote:
it's got to be intrinsic to the design to a point.
That's the bit I was really addressing. I certainly do not think it is a limit of the 1541, it's capable of retreiving everything on a CD (ie distortion closely approaching the full 16bits equivalent - the 63's NPC dac doesn't get anywhere near!) and intrinsic S:N of about -110dB - still very, very good for dac of any architecture.

Not sure what you are using for the I/v stage Simon but it is critical to getting the best out of this DAC. IIRC some arcams had OP27s in there - a more ill-suited part I can hardly imagine, though it sounds very 'polite'.

The point about cascaded regs - I'll have to have a look at the Arcam's manual this weekend. I can think of one way it may not help - the internal current source reference in the 1541 is between the -15 and -5 supplies; keeping a constant 10v between these two supplies is more important than it appears and the reg cascade is going to do some (ahem) interesting things to that.

With a conventional hookup of -5 and -15 regs you can experiment with a small but good cap between the -5 and -15v pins of the dac* This one extra cap - say a 10uF oscon - closes the loop and helps maintain this 10v difference nice and quiet at HF, where it matters

(With the regs in cascade this extra cap would be an AC connection across the -5v reg input to output and probably result in a power oscillator or, at the very least, negate the point of having a regulator there - beware!)

* if you have a scope you may find adding a bit of RC damping at the output of one or both regs to 0v is required for best stability / effect.

Last edited by martin clark; 15th July 2011 at 10:27 AM.
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Old 15th July 2011, 10:48 AM   #195
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Very cool post, thanks! I'm using the Pass D1 output stage with quality parts and S Power regs (and the usual huge, dedicated 100VA supply with good smoothers). I love this output stage though as a Naim guy I think you might not agree!!!! It is exceedingly polite / smooth / warm / full.
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Old 15th July 2011, 10:58 AM   #196
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The D1 is definitely good stuff - I'm all for simplicity, when it is sufficient

And I'm not a Naim man at all. OK my cd player is Naim-based, but it glows in the dark inside - without valves
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Old 15th July 2011, 11:17 AM   #197
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Without valves eh??? LEDs then I suppose!

I've got some ideas to mull over now. I've contemplated substituting the feedback resistors on the -5 and -15V S Powers for a resistor + trimpot to achieve a perfect 10V between them but, being honest, thought I'd break them as it's all surface-mount there. Is it worth the risk? Will I hear a gain?! I'm curious.
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Old 15th July 2011, 11:31 AM   #198
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I just shoved a 10uf Oscon in between pins 26 and 15 and am still listening.
No smoke !
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Old 15th July 2011, 11:32 AM   #199
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It would be more effective to feed the -5reg from the same rail that feeds the -15v reg, then try the extra cap. The -5rail only draws about 30mA, so the reg will be ok heatwise dissipating c.0.5w if run off (say) -22v; no extra heatsinking required.

If the rail to the -15v doesn't have a little bit of RC decoupling ahead of the -15v reg, add some. 10ohms and a 10-100uF is enough. It will clear-up noise that otherwise passes right through regs - the 1541 seems sensitive to this to my ears (the -15v goes to the substrate that everything is built off in the dac - you can see in the datsheet this pin has the worst PSRR)
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Old 15th July 2011, 02:55 PM   #200
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Arcam used RC decoupling on the psu for the +-20V (feeds the DAC and op-amps). When I upgraded the smoothing caps I also deleted the RC filtering and the sound quality gain was about the biggest ever from this player. I'm now seriously sceptical about using RC decoupling on the DAC supplies... though I used RC and LC filtering on my SAA7220 and SAA7310 supplies and got a slight gain in SQ. These were massive banks of caps before and after the L/R. I also used LC filtering on my clock supply, which also seemed to improve the SQ a tiny bit.

I seem to have some conflicting circumstantial and incomplete evidence regarding RC filtering in the cd player. I'm not sure what noise I'm removing from the DAC PSU as it's not shared with anything. The transformer, PSU and regs purely feed the DAC's 3 power pins. I'm sure there's ripple and noise from the AC, but I don't know how much.
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