The simplistic Salas low voltage shunt regulator

[nicoch58]

Originally Posted by disco

It wil stay charged for a while when you pull the power cord

nice

[disco]

Originally Posted by AndrewT

what is the resistance of the primary winding?

The bigger trannies (300VA) have lower Rdc as their primaries are wound with thicker wire. The least I've measured was 4 ohm. The danger lays in the smallish trannies which can have as much as 100 ohms. Left school too long ago to give you the exact time it takes to discharge 10uF over 100 ohm

[wheezer]

Originally Posted by AndrewT

could you explain why you think it is dangerous?

That size cap, or any in x.00uf on AC mains is dangerous.
I've used them to break in caps and hold one helluva charge and take same when energized. If you energize it at the peak of the cycle it can explode. Lots of info on this. DC does not have a wave form...it's a flat line on a scope.
You also, playing with phasing.
I know what JC is doing and it was a product that Bob Crump sold. I suggest NOT doing so. I sent you links for doing AC filtering the proper and safe way. They work great.

[claudio]

Originally Posted by HiFiNutNut

Claudio,

First I would like to thank you wholeheartedly for your enormous efforts for publishing your extensive Speaker Workshop guide .......

Thank you Bill for the kind words on my SW tutorial: it's always nice to know that my work helped someone.

[HiFiNutNut]

Originally Posted by disco

The PSSR depends on the circuit topology, not that much on using tubes (especially penthodes) or semi conductors. Pi-filters are efficient ripple killers, more so if you combine several sections. Besides they filter noise introduced by (too) big caps after the bridge, creating ringing. Pi-filters are usable up to a certain current as coils are getting lumpy and stray fields are getting cumbersome. Also, the voltage drop and raise in impedance must not be counter productive.
The few cases I've studied benefitted from a distributed ripple rejection. The loads were steady, which is paramount to raising impedance in the PSU. For a dynamic load I wouldn't recommend it. Lowering a PSU output voltage can be done by inserting a small resistor between tranny and bridge, also between bridge and reservoir cap. That way you alter the conduction angle, changing the load currents from the reservoir cap.

I was playing with the raw supply before a shunt regulator. The shunt regulator should theoretically have very high ripple rejection but it depends on an electrolytic capacitor for filtering. We all know that electrolytic capacitor does not work well at high frequencies due to its inductance. So in practice I found that inserting a 390uH in the raw supply did clean up a bit at high frequencies, resulting in cleaner sound. Not a night and day difference, but still audible.

This led me to investigate different configurations in my power amps - C, CRC, CLRC, LRC. Originally I had C = 3 x 10,000uF per rail per channel. These capacitors have inductance of 16nH and ESR of 0.015R at 20kHz. I tried CLRC 10,000uF - 220uH (0.05R) + 0.1R - 2 x 10,000uF. From LTSpice modelling, I must insert a resistor 0.1R so that it won't have a peak at around 80Hz. While I found the higher frequencies were definitely cleaner, the sound became a bit unnatural to me, perhaps due to increased impedance. I then tried more Spice modelling, and found that LRC 220uH (0.05R) + 0.1R - 3 x 10,000uF would give another a few dB ripple rejection. I tried it. The sound was subjectively the best comparing to C or CLRC. Then I wired up the 4 rails differently and measured them with my scope. The scope confirmed my subjective impression, that LRC is better than CLRC. Note that the total 0.15R resistance in series with the rail is higher than the impedance provided by the capacitors, in the case of CLRC, it was 0.015/2=0.075R, and in the case of LRC, it was 0.015/3=0.05R.

So I am going to redo my preamp level raw supply before the CCS-shunt regulator to change it from CLRC to LRC and see if I can find any subjective improvements.

The above may only work with soft recovery rectifying diodes with which no snubbing high Q film capacitors are used, or possible severe ringing can occur due to the interaction of the C and the L, unless you pack sufficient resistance for damping, but in which case, the increased impedance may do more harm than good.

My hypothesis is this: Filtering can only be done with either capacitor or inductor, (along with resistors), or both. Electrolytic capacitors are OK at lower frequencies but not higher frequencies. Bypassing electrolytic capacitors with ceramic or film caps (all of them are of high Q) can easily cause ringing. Inductors are naturally good at higher frequencies (but watch out for parasitic capacitance, as Salas reminded me, so the proper inductors need to be selected). The idea is to use electrolytic capacitors for lower frequency filtering, and inductors for higher frequency filtering. In this case, only a small RF choke is needed, with the significant advantage of much lower impedance (comparing to a large L or R), minimal voltage drop, minimal heat dissipation, minimized RF rediation, minimal space required, and lower costs. My hypothesis is in sharp contrast to conventional LRC or CLRC in which the large L is to filter ripples down to the audioband or even the mains frequencies.

The only thing I am not sure is this: there may be a significant amount of DC which may saturate the inductor core making the inductor ineffective. I don't know if this can be a case so am seeking experts' advice on this.

[Ekkeri]

I'm building QuangHaos Salas for DAC End:


Any recommendation what leds & diodes to use? Thanks!

[Salas]

Use garden variety red or green 1.8-2.1Vf LEDS, best quality capacitors across Vrefs and lose the 0.1uF bypasses, its a hit or miss. Stealth II diodes for the rect bridges or MUR 120, more compact for size and easier on budget.

[Salas]

Originally Posted by HiFiNutNut

The only thing I am not sure is this: there may be a significant amount of DC which may saturate the inductor core making the inductor ineffective. I don't know if this can be a case so am seeking experts' advice on this.

It can be. If there is DC current you need a properly rated core in any inductor. In case of using small values to dump RF, small air core coils are feasible though.

[HiFiNutNut]

Originally Posted by Ekkeri

Any recommendation what leds & diodes to use? Thanks!

I have not tried a lot of diodes but only a few.

The cheapy shottky diodes 1n5822 (and its series) actually sound pretty good, and sustantially better than the normal 600V 35A bridge, although I have heard comments that the 1n58XX series do not sound as good as other shottky diodes, such as D10XXXXX, etc. I measured with my scope and found the 600V 35A bridge (in both my preamp and power amps) produced horrific switching noises, if I show you the magnified spectrum, you would believe these diodes are dedicated noise generators.

Salas then recommend trying the Fairchild Steath. I tried them. They sounded a bit cleaner than the 1n5822. I measured the rectified wave forms, the result was much much better than the 600V 35A bridges.

Actually, I am spending this week replacing the 600V 35A bridges with the Steath on my 3 pairs of monoblocks (and other upgrades on them as well). I will possibly finish them tomorrow and will measure them again. It will be interesting to see if they make any improvements on sound, as these power amps are very well designed and should have a theoretical 115dB PSSR across the entire audio bandwidth. In theory, these diodes should make no difference to the sound of my amps.

[HiFiNutNut]

Originally Posted by Salas

It can be. If there is DC current you need a properly rated core in any inductor. In case of using small values to dump RF, small air core coils are feasible though.

Salas,

I thought of air core inductors for loudspeakers. But since they have quite a bit of windings I suspect that the parasitic inductance is on the high side, making the inductor less inductive at higher frequencies.

I am trying these:

http://www.bourns.com/data/global/pd...120_series.pdf

The datasheet says that until the current reaches 5.21A the inductance of the 220uH will lose half. To me that is pretty good, as my class AB amps would never draw that amount of current.

The question is, with the inductor immediately after the bridge rectifier, what is regarded as DC? Would the rectified wave form be considered consisting of any DC component?