If your intention is to bypass high frequency noise with the 0.47uF polystyrene caps, I would use 0.1uF multilayer ceramic capacitors instead. They have lower inductance at RF frequencies and are thus more effective.
To me, I even wonder why we should bother with the JC-80 on-board regulator... Why don't we feed it 24V directly?
Does anyone know?
Do
Thanks, John.
@pinnocchio We started down that path in post #4
This is a cap multiplier circuit. The 'apparent' capacitance is multiplied by a characteristic of the transistor(s) so smaller and cheaper caps can be used. Hence the Y suffix in the BOM.
@pinnocchio We started down that path in post #4
This is a cap multiplier circuit. The 'apparent' capacitance is multiplied by a characteristic of the transistor(s) so smaller and cheaper caps can be used. Hence the Y suffix in the BOM.
Each "voltage reducing" stage is a filter, hence beneficial.
The choke plus electrolytic capacitors cannot filter well enough noise on RF frequencies, which is detrimental to high quality audio amps. Therefore the capacitance multiplier reducing 30VDC to 24VDC is really necessary for high quality audio.
As for going down to 15V, I assume it's only for the servo OpAmp, which is designed for up to 15V.
If it was me and it was SOTA amp, I'd add another filtering stage between the electrolytic capacitors and the on-board capacitance multiplier.
We "pay" power real-estate for the sake of sound quality, by having an as-good filtering as we may attain.
Actually, some RF filtering before the primary of the power transformer may add a benefit.
Wrong about what now? I said that multilayer ceramic capacitors have lower inductance and therefore bypass better at RF frequencies. Do you have some kind of proof that polystyrene works better in this capacity? Those capacitors are not in the signal path.
@Joshua_G The quote you requoted was purely rhetorical and intended to point Do to post #4 where a much fuller explanation of the points you have made (and others) can be found. If there were things overlooked there, please mention them. The schematic in a recent post shows the full power train with a Kubota regulator. Other contributors using Borbely regulators and many others have been suggested.
I am having difficulty locating the cm choke as indicated in the schematic and wonder if locating it just before the Kubota would be nearly as effective.
I am having difficulty locating the cm choke as indicated in the schematic and wonder if locating it just before the Kubota would be nearly as effective.
Ceramic capacitors are highly microphonic, therefore they have no place in any audio design, not even in the power supply, since the power supply serves as a return to the signal path.
Wolfsin, the schematic you posted looks all right to me.
As I wrote above, an RF filter before the primary may add a benefit.
Also, 2 small capacitors, 0.1-0.47uF right before the CM choke to the ground may be a good idea (to filter RF coming from the mains and the rectifying diodes noise).
I don't know if snubber capacitors are necessary for soft recovery diodes.
What is the value of the CM choke?
As I wrote above, an RF filter before the primary may add a benefit.
Also, 2 small capacitors, 0.1-0.47uF right before the CM choke to the ground may be a good idea (to filter RF coming from the mains and the rectifying diodes noise).
I don't know if snubber capacitors are necessary for soft recovery diodes.
What is the value of the CM choke?
The following cm choke, while small, will not fit without adding leads where shown in the schematic.
Laird Industries CM2545X171B-10 Common Mode Filters Impedance: 170 Ohms
Maximum DC Current: 10A Maximum DC Resistance: 0.01 Ohms
For that reason I would like to move it after the electrolytics, but still on the rectifier board. In that location small caps could easily be located just before it. Not sure if it will be as effective in that location but no leads would be required.
Preprimary RF filter planned, thanks.
Laird Industries CM2545X171B-10 Common Mode Filters Impedance: 170 Ohms
Maximum DC Current: 10A Maximum DC Resistance: 0.01 Ohms
For that reason I would like to move it after the electrolytics, but still on the rectifier board. In that location small caps could easily be located just before it. Not sure if it will be as effective in that location but no leads would be required.
Preprimary RF filter planned, thanks.
For your rectifier diodes, are you using something like MUR1020, MUR2020?
Wouldn't a CLCRC configuration yield better filtering or just a simple CLC be better. CLCRC to me would filter even better but a voltage drop after the resistors could be an issue depending on your transfo and wanted to reach the 30V goal in the final chain...
Do
Hi Do,
FFP20UP20DN is a soft recovery rectifier, in keeping with John's recommendation but those you mentioned are not. I am not entirely happy with that part because it is EOL.
I am sceptical of the available placement position for the choke so will likely test the effect once I have established the ability of the chain to hold 30 volts before the cap multiplier.
FFP20UP20DN is a soft recovery rectifier, in keeping with John's recommendation but those you mentioned are not. I am not entirely happy with that part because it is EOL.
I am sceptical of the available placement position for the choke so will likely test the effect once I have established the ability of the chain to hold 30 volts before the cap multiplier.
Test Plan
The following is a description of the test plan for the entire power chain, including the capacitor multiplier on the JC-80 board itself. On the JC-80 pcb only the cap multiplier will be populated, along with a series pair of 4w 12v bulbs on each rail. Is it reasonable to assume incandescent bulbs will add negligible noise? The voltage could then be measured and adjusted at all points along the chain. In addition noise can be measured just after the regulator and also after the cap multiplier filter.
Before measuring lets discuss what we expect to find. Given the r-core, soft recovery rectifiers, and capacitors we would expect that most mains noise would be gone and the Kubota ought to get rid of remaining ripple and leave not much more than around 100nv of noise. The cap multiplier should reduce that noise even further. Note that under a constant resistive load none of the dynamic current demands caused by the JC-80 preamp circuitry will be causing this noise. Is it pure power chain residual? By having both Kubotas and the cap multiplier portions of both JC-80s populated it will be possible to swap modules in and out. If it turns out that, say, noise measurements are higher in one particular configuration, the source can be traced readily to the module level.
Keeping these measurements and repeating them later with the JC-80s fully populated will then measure noise generated by the amplifiers dynamic demands during music playback and or silence.
The following is a description of the test plan for the entire power chain, including the capacitor multiplier on the JC-80 board itself. On the JC-80 pcb only the cap multiplier will be populated, along with a series pair of 4w 12v bulbs on each rail. Is it reasonable to assume incandescent bulbs will add negligible noise? The voltage could then be measured and adjusted at all points along the chain. In addition noise can be measured just after the regulator and also after the cap multiplier filter.
Before measuring lets discuss what we expect to find. Given the r-core, soft recovery rectifiers, and capacitors we would expect that most mains noise would be gone and the Kubota ought to get rid of remaining ripple and leave not much more than around 100nv of noise. The cap multiplier should reduce that noise even further. Note that under a constant resistive load none of the dynamic current demands caused by the JC-80 preamp circuitry will be causing this noise. Is it pure power chain residual? By having both Kubotas and the cap multiplier portions of both JC-80s populated it will be possible to swap modules in and out. If it turns out that, say, noise measurements are higher in one particular configuration, the source can be traced readily to the module level.
Keeping these measurements and repeating them later with the JC-80s fully populated will then measure noise generated by the amplifiers dynamic demands during music playback and or silence.
End of life is no big deal at this point. I don't think we're planning mass production of the JC-80... Unless you have plans I'm not aware of! 😀
Why don't we buy 40 of those and split? It would bring down the cost and we would have a few spares?
Ciao!
Do
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SCHOTTKY DIODE?
Tea-Bag, the designer of the nice DCB1 has actually tried several rectifiers and according to him, those ones sound pretty good
SCHOTTKY DIODE 1200V, 2A
C4D02120A Cree, Inc. Schottky (Diodes & Rectifiers)
They're on the expensive side but it is surely worth a test!
Do
Tea-Bag, the designer of the nice DCB1 has actually tried several rectifiers and according to him, those ones sound pretty good
SCHOTTKY DIODE 1200V, 2A
C4D02120A Cree, Inc. Schottky (Diodes & Rectifiers)
They're on the expensive side but it is surely worth a test!
Do
I would certainly drop the thermistor after the rectifier bridge has there's not merrily enough capacitance to create an "in-rush" effect. What type were you planning to use?
Ciao!
Do
Ciao!
Do
yeah i find the Cree are nice, i use them in my little stick regs and DCB1, but the SMD version of that same part (on the stick regs i use the to220 in the dcb1). there is some consensus that using zero rec diodes in audio is not a great thing to do, because if being too fast and creating unwanted resonance. this is probably why John recommends against them. the soft recovery IXYS parts are pretty nice, if only i could get them more easily i would, but they are export restricted from DK
dont use that part exactly though, you'll save a little coin if you go for the 600v version of the same C3D03060A or the isolated version of same. even cheaper if you can deal with 1A and lets face it this is a headamp
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