Using the HYPNOTIZE as a general shunt reg PCB - Page 61 - diyAudio
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Old 21st April 2013, 02:31 PM   #601
c_door is online now c_door  Italy
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Hello,
I've just ordered three Mezmerize boards from the store, one for a DCB1 linestage, the other two in order to feed a Pearl Two phono.
Need now to size the psu parts. I'd like to use R-core trafos from Selectronic. I've read that their actual Vout is something higher than the specs, about 10%.
Since the Pearl2 needs 24V, and following the formula on the first post here, what's the better trafo choice: 2x21V or 2x24V ?
On the Pearl2 thread, Tea-Bag gave me the advice of splitting the psu by placing trafo+rectifiers+caps on a separate enclosure, and the regulator boards near the riaa boards. In this case, should I leave the Mezmerize onboard 4700uF in place?
I mean, filtering caps on both ends of the umbilical, or only near the trafo/bridge ?
Last question Do the current Mezmerize boards require the "jfet leg trick" or not ?
Thanks a lot in advance. Carlo.
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Old 22nd April 2013, 03:27 AM   #602
Salas is offline Salas  Greece
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-Use 2x24VAC.
-Leave it in place but don't use the diodes. Incoming DC goes directly to that local capacitor.
-Do the leg trick in your case.

Good luck
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Old 23rd May 2013, 08:13 PM   #603
c_door is online now c_door  Italy
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Quote:
Originally Posted by Salas View Post
-Use 2x24VAC.
With the above trafo I built an external PSU, using MUR820 diodes and CRCRC filter.
Its output is about 36V per rail (with no load).
My 2sk170BLs' Idss is about 10,8mA.
I've bought a bag of 593-VAOL-3HCE4 yellow leds (from Mez BOM). Using a 9V battery and a jfet for measuring, I'm getting 1.96V to 1.97V.
Am I good to go with these components ?
My board is a Mezmerize, and the goal is +/-24V 200mA, to feed a Pearl Two channel.
Thanks!
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Old 23rd May 2013, 08:23 PM   #604
Salas is offline Salas  Greece
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Your parts and DC input are good enough. Now go through the post#1 steps for +/- 24V. Allow for enough extra mA above the Pearl two channel consumption regarding your sinking. If there is no published figure, use 1 Ohm in series with +/- to Pearl with any 24V DC PSU, measure the voltage drop over 1 Ohm and calculate. Or put an Ameter inline to Pearl.
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Old 23rd May 2013, 08:30 PM   #605
Salas is offline Salas  Greece
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P.S. The CRCRC thing will need adjustment for not having under 34VDCin under final load. You got to know where your CCS will be first is even more imperative than just allowing a "quality" spare current.
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Old 23rd May 2013, 09:14 PM   #606
c_door is online now c_door  Italy
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Quote:
Originally Posted by Salas View Post
P.S. The CRCRC thing will need adjustment for not having under 34VDCin under final load. You got to know where your CCS will be first is even more imperative than just allowing a "quality" spare current.
Thank you Salas for ultrafast answer
So, once the shunt circuit is completed, I'll attach to it the external PSU and, if the input voltage doesn't drop under 34VDC, I'll tweak the filter accordingly. Right ?
About the CCS amperage, should we aim for a total current let's say double the load requirements, or something to keep the mosfets warm ?
I mean, sound improvement is to be expected when we have a certain amount of dissipation or when the mosfets themselves reach a target temp ?
This to avoid excess of sinking.
This is something I'd like to know for class A power amps too: better sound is a matter of high bias only, or actual temperature of the output devices ?
bye. Carlo.
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Old 23rd May 2013, 10:22 PM   #607
Salas is offline Salas  Greece
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1. Yes. You will use either a dummy or the real load to the reg and you will apply the DCin PSU to the reg. If the CCS demand drops the DCin PSU under 34 min 32V, readjust the RC elements for smaller drops.
2,3,4. +150mA from load demand is a good conservative figure. If your MOSFET sinking allows you may add double that to get an audible plus.
5. In our case more current means more transconductance from the big MOSFETS as in CLASS A amps, but not to extract more AC domain linearity. It is to flatten out and minimize the regulator's output impedance across the audio band and beyond. More current damping. That thing is a benefit since the audio circuit is always closing the power loop through its PSU. Sideways benefit in other words.
Temperature is a byproduct, a linear electronics efficiency % problem. There is a zero temperature coefficient zone we would like to stay but our VMOSFETS have it way too high for current. 1.5-3A.
They are still OK enough in our region the way we put them to work nonetheless.
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Old 26th May 2013, 05:32 PM   #608
c_door is online now c_door  Italy
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Finished my first regulator. With a 220R test resistor I'm getting Vout=6.96V, and 1.94V across the test R itself. Dummy load is 800R on each rail.
Replaced test R with 2k2 on both rails. I'm now getting Vout=+/-22.4V.
Vin dropped to about 32.4V per rail.
With 2x22.1R and small sinks (75*30*4mm) the temperature on IRF cases reached about 65C (149F).
The yellow leds are happy and shiny
Going to raise the current to at least 300mA, with finned sinks, and trim the V resistor once the actual Pearl Two channel is completed.
What a nice toy Salas! thanks a lot for sharing this idea.
Attached Images
File Type: jpg Shunt-1.jpg (374.5 KB, 133 views)
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Old 31st May 2013, 07:08 PM   #609
c_door is online now c_door  Italy
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Hooked one Pearl2 channel to the regulator, with 3x22.1R and bigger sinks.
Looks like the phono card is asking for about 40mA on each rail.
Across 3x22.1R I'm reading 1.96V on the plus side, and 1.76 on minus.
So, the current dissipated by the mosfets is >200mA per side.
The current mosfet on the minus rail is sensibly hotter than its + brother.
Everything looks stable, no unexpected heat, smoke or fireworks
Now, time to complete the second channel and fight against hum&buzz.
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Old 31st May 2013, 07:17 PM   #610
Siberia is online now Siberia  Lithuania
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Hail, hail your effort and happy ending! What's on Tx side of things?
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