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Old 24th March 2003, 01:10 PM   #11
ALW is offline ALW  United Kingdom
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Default Double regulation

If you try this, do it as a tracking pre-regulator, it measures and most importantly sounds, better in almost every regard.

The LM317 data sheet will have details, but it can be done with any fixed reg.

Andy.
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Old 24th March 2003, 01:18 PM   #12
ALW is offline ALW  United Kingdom
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Default Save you searching

Here's the circuit.

Bypass BOTH adjust terminals - this is really important for best sound - do this by adding a 10-100u cap across R2 and R4.

Also add an output cap.

Andy.
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Old 25th March 2003, 04:26 PM   #13
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Default +/- 15V

I hvae the schematic for a +/-15 volts tracking preregulator board with reservoir caps and bridge exactly as ALW has described above which is very compact. Email me at prod at buildergroup dot co dot uk if you're interested.
cheers
Cedric
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Old 26th March 2003, 11:41 AM   #14
jcarr is offline jcarr  United States
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I think that Andy's suggestion for a pre-regulator is a good one. Another worthwhile direction to pursue is constant-current operation, which can be implemented in a variety of ways. This would include folded cascode main circuits (with constant-current sources), shunt / super-shunt regulators, and some types of push-pull regulators.

In my experience, a major benefit of constant-current operation is that it tends to reduce the sonic differences caused by componentry choices in the power supplies.

hth, jonathan carr
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Old 26th March 2003, 12:34 PM   #15
ALW is offline ALW  United Kingdom
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Default Constant Current Operation

I'm really tempted by this Jonathan,

In your experience does it reduce the impact of transformer size upon the resultant sound?

The super-reg's were such frustration in this regard, since bigger transformers etc. still sounded better, and it seemed to be primarily impedance-related

Even the damn mains quality still makes a difference...

May have to raid the bits box - particularly after your comments on Super-shunts.

Andy.
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Old 26th March 2003, 01:53 PM   #16
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Jonathan's ideas are good ones to try.

If you can limit the peak diode current, a small transformer can be made to sound as good as a big one.

One problem with those 3-legged things that no one thinks about is output Z vs frequency. Those devices were designed to give a specific DC output, without regard to most anything else. If you look closely at most dat sheets, when they measure transient response, they specify what capacitors are used on the output.

A preamp will most likely not pose a transient load problem, but how a regulator handles the residual audio on the rails is something that must be factored in.

Jocko
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Old 26th March 2003, 05:58 PM   #17
ALW is offline ALW  United Kingdom
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Default You've convinced me

That's my spare time disappeared in a box of bits and wire for a while

I'm wondering now, if a good CCS feeding the main reservoir caps is an option. Resistive limiting of peak current was always sonically detrimental whenever I tried it....

Andy.
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Old 26th March 2003, 06:03 PM   #18
jcarr is offline jcarr  United States
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Hi Andy:

>I'm really tempted by this Jonathan.<

That was the idea.

>In your experience does it reduce the impact of transformer size upon the resultant sound?<

My experience and subjective impression is that it does do this, but not to the same extent as it diminishes the differences between filter capacitors. Mind you, in either case I think you can expect a worthwhile reduction, but not a total obliteration (I sincerely wish that this were otherwise).

>May have to raid the bits box - particularly after your comments on Super-shunts.<

For similar reasons, folded-cascodes fed from constant-current sources are also worth trying. And cannibalizing from one of my previous posts, it should be possible to adapt the following circuit for opamp duties:

http://www.diyaudio.com/forums/showt...989#post142989

Whatever you try, I will be very interested in hearing of your results.

best, jonathan carr
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Old 26th March 2003, 06:36 PM   #19
jcarr is offline jcarr  United States
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Andy:

>Even the damn mains quality still makes a difference...<

Unfortunately true. A few years ago a friend and I worked on a flying-capacitor power supply with the goal of cutting the audio unit completely loose from the effects of the mains, but for whatever reason, I didn't like the sound of the results, and we didn't pursue this farther. OTOH, just because I didn't find the results subjectively compelling doesn't necessarily mean that this line of reasoning is faulty. Perhaps _our_specific_design_ was not thoroughly thought out, maybe there were implementation errors, or maybe it was just too much of a kludge.

If you would like, I can try to locate the circuit that I used at that time and email it to you, or if more people are interested, I can post it here as an attachment.

>I'm wondering if a good CCS feeding the main reservoir caps is an option.<

I honestly don't know, as I have always fed the CCS's from the main filter caps, rather than the reverse. On the surface of things, apart from the topological differences, I wouldn't think there would be much difference in the final measurements and sonic results. But again, I have neither tried this myself nor thought about it much, so it is entirely possible that you may discover something interesting.

best, jonathan carr
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Old 26th March 2003, 07:33 PM   #20
ALW is offline ALW  United Kingdom
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Default Flying capacitor / charge pump

I looked at the link (that I think you) posted recently (www.never-connected.com), which on the surface seems to be a form of that.

Reading the online literature though reveals the following in the Q&A, which rather put me off pursuing it further, although I have heard good reports from those trialling the technology: -

"Like all power supplies the Never-Connected is dependant on the dynamic source impedance and voltage of the incoming power supply, if undersize or long cable runs are used between your in-coming supply and equipment, this will reduce the dynamic source impedance of the mains supply. The dynamic output impedance of the power supply will be affected resulting in a subjective loss of dynamic attack, and generally poorer definition in the Bass. This effect will be especially noticeable on Power Amplifiers. For best performance the use of a dedicated heavy current power feed (installed by a qualified electrician) will always ensure best results and can make a big improvement to sound quality"

I recently did some in-depth analysis for a friend whose very expensive system was having more bad days than good, with very large sonic variations (from unmusical to captivating in the extreme...). A long-term noise analysis of the mains showed no correlation with sound variation, local RF was eliminated by borrowing the HP kit form work (!), but some voltage variation was spotted, outside of UK specs.

The electricity co. did a log of their own and classed the supply as 'crap' and he's hoping for a new feed soon-ish. I suspect that mains impedance has a far greater effect than almost any other parameter - I've always found mains filtering to degrade sound for the same reason, even on v.low current PSU's.

Even more frustrating filters that appear electrically across the mains affect the other items plugged into the same socket / spur too

The annoying thing is I'd really like to find an elegant solution to some of this - super-reg's etc. do help, but not eliminate it.

I'll keep trying though, for a bit

A.

P.S. If you can find the circuit, I'm sure others will be interested too - thanks!
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