[jameshuls]

Hi Jim, I took my usual summer hiatus of thinking and tinkering all things hi-fi (usually the former about the latter) and upon my return to your circle I find quite a rebirth! Very exciting!

I was checking out your blog on facebook and noticed your piccolo rebuild/upgrade. I have been toying with the idea of adding an external power supply to my piccolo for some time (in addition to upgrading the passive parts - so far i have only upgraded the enclosure and rca plugs) and I am intrigued by what you have done with the inductors and voltage changes with the original power supply. I would prefer to do something like this than add yet another box and project in the form of an external power supply.

Are you willing to share these modifications?

No worries either way in case you prefer to keep it a trade secret but I would appreciate some guidance.

Good luck with the new lineup! BTW, I couldn't help but notice the similarity between the Korean temple and your new enclosure look. I too was inspired by Asian architecture (and electronics) for my casework, although I put the design emphasis on damping with natural materials (wood, brass, copper and slate) and ease of circuit access for perpetual tweaking. I think your design looks great but one question... Do you really have to remove all those screws to get the bottom plate off? If so, that would definitely discourage tweaking!

Cheers,

James

[hagtech]

Yep, 124 screws. 

The main changes to the PICCOLO power supply section were to replace R12, R14, and R15 with 1mH inductors.  I used M10005-ND from digikey.  Not sure if it is audible, but should effectively drop the noise floor a bit.

jh

[BobM]

Thanks for the tip Jim. I was looking for a way to reduce the noise floor on the Piccolo. I have some albums that require me to turn it way up, and the background noise from the Piccolo (yes, I isolated it as the cause) made them less than perfectly enjoyable. I will definitely give this tweak a try.

[jameshuls]

Thanks Jim, I'll give that a try!

[BobM]

Picked up and installed the inductors Jim recommended below. A couple of things ...

Those resistors are a little hard to get to, so be prepared when uninstalling them. A pair of forcepts worked quite well to get in there and grip them.

The inductors will not fit on the top of the board. They need to be installed underneath, which means setting off the battery case a bit more than normal, and extending the power leads from it to fit into the holes.

The inductors also have leads that are quite a bit narrower than the holes for the resistors. Bending them at right angles "just about" gets them to fit.

As for the sound - I can't A-B directly so I am speaking from memory - I noticed no benefit or detriment to the overall sound. However I do believe the noise floor did drop a wee bit when I turn my volume control waaaay up. There is still some noise, but it seems to be less than before - where it was previously very distracting on low level records and quiet passages it is now bearable.

Thanks again for the suggestion Jim.

[poty]

Some time ago someone rebuilded the power supply part of Piccolo to dedicated pair of power supplies. While for me it is over the top in the amount of iron involved, IMHO, that was the best way of improving the Piccolo powering, clearly audible. Having only around 2-5mA on each rail (not including LED powering), the single power supply (of 9V+5V=14V) to double-rail (+9V and -5V) conversion could be easily achievable by a pair of rail-to-rail opamps referenced by low-noise zeners or integrated voltage references. In such way we have super-clear power lines right from the opamps output without DC-DC conversions with their hi-frequency pollution and needs for long strings of RC filtering (LC in "upgraded" way).  I think the real voltages needed are +8V and -4V, so it's possible to use even widely available 12V sources. It's definitely will ask for PCB changes, but I hope the PCB will be changed anyway.
The second source of noise is the input stage with questionable switch and plain resistors.

[hagtech]

Right - the inductor trick is reserved for the new PICCOLO, which eliminates the internal battery pack.  Everything is a compromise...

The ARCHIVER had the original version of this circuit and used +/-10V rails.  As poty mentioned, the ideal case would seem to be a clean linear regulated supply such as that found in the HAGCLOCK.  But "ideal" always has it's own unintended consequences; such as yet another transformer, magnetic coupling, more sources for noise, etc.  That's what happened with the VIOLIN design - I didn't want to add yet another AC transformer.  With the PICCOLO the choice was to have the ability of a simple (single supply) wall wart while also not using bucketloads of batteries.  The FLUGELHORN did use it's own AC transformer.  Everything is a compromise...

jh

[poty]

... yet another transformer, magnetic coupling, more sources for noise, etc.  That's what happened with the VIOLIN design - I didn't want to add yet another AC transformer.  With the PICCOLO the choice was to have the ability of a simple (single supply) wall wart while also not using bucketloads of batteries...

I didn't mention transformers in my post. Wall wart usually has had already that parts of the power supply (power transformer, rectifiers, sometimes even regulators). I wrote about the possibility to use linear technologies to "convert" single supply with enough voltage to double-rail. Looking at the HAGCLOCK power supply schematic and thinking about a single supply connection to VCC-VEE of J1, tweaking R3, R6 (to achieve +8V) and R7, R11 (for -4V) and eliminating Q1 and Q2 (probably, as far as the ouput current of opamps is sufficient for powering the circuit) we'll have the ideal power supply without the addition of any transformer. To be super-more-precise - you can "form" the ground rail with the third opamp. OPA2134s are not rail-to-rail, but it only adds "margin" to the input voltage to be in safe output voltage area of the opamps. There are many other opamps (rail-to-rail output capable) which are great for this circuit without any margins.

[BobM]

I used to use my Piccolo with the battery pack, but found that there was a certain lack of dynamics that way. Putting a cap actoss the + and - helped with that a bit. The batteries seemed to last quite a while too, as long as it is turned off when not in use. But now I use a wall wart and don't notice any degredation in sound and perhaps a bit more dynamics. So this inductor tweak is just fine for my purposes.

One thing though - now the LED from the power switch doesn't turn off when the switch is in the "off" position. It stays lit, but there is no sound coming out. I have to unplug the unit to get it to go out. What could I possibly have done wrong when replacing the 3 resistors with the inductors?

[poty]

I used to use my Piccolo with the battery pack... Putting a cap across the + and - helped with that a bit. ... now I use a wall wart and don't notice any degradation in sound ... this inductor tweak is just fine for my purposes.

In every abovementioned usage between your power source and the amplifier itself there is the DC-DC converter, delivering +9V and -5V from the single source of 5V. The converter adds to the noise level, not so dramatically, but.. in some installations the noise level is hearable.

One thing though - now the LED from the power switch doesn't turn off when the switch is in the "off" position. It stays lit, but there is no sound coming out. I have to unplug the unit to get it to go out. What could I possibly have done wrong when replacing the 3 resistors with the inductors?

Solder bridge? Maybe the bended leads are touching something?

[BobM]

Solder bridge? Maybe the bended leads are touching something?

Yeah, that's what I was thinking too. I think I will just remove the plastic battery holder completely.