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Old 26th February 2009, 03:46 PM   #11
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Stopped sctratching my head. The opamps are not really running open loop. Getting ready to build one.
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Old 26th February 2009, 04:10 PM   #12
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One thing to watch in the linked shuntreg schematic - that opamp is stable only for a gain of 5x or more. You need the OPA627 to stay with the same device family and operate at lower gain of the voltage reference - or another unity -gain-stable opamp

(That reg is also clearly set up for valve B+ voltages - you may need other componenet adjustments for low-volt useage)
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Old 26th February 2009, 04:20 PM   #13
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Thanks Martin. You can just as well tell me to watch i don't burn my fingers with the soldering iron
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Old 27th February 2009, 05:07 PM   #14
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This is a cool thread. For me, the Superreg was the best reg for phonopres for me as well so far, including a less optimum discrete shunt reg, which gives a more laid back (but no fluffy bass!), and, regrettably, less transparent sound, which nevertheless gives a nice impression at a first (and second) glance.

I simmed syn's proposal with an AD797 and got no less than spectacular results, maybe to good to be true. I will try it the next time I re-build my phonostage.

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Old 27th February 2009, 06:46 PM   #15
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Quote:
Originally posted by Onvinyl
a less optimum discrete shunt reg, which gives a more laid back (but no fluffy bass!), and, regrettably, less transparent sound, which nevertheless gives a nice impression at a first (and second) glance.



I finished something very similar to syn08's circuit last night, gave it a quick listen and let it burn in during the night. Used IRF610/9610 and OPA627s fed from a preregulated (317/337) 22v for a 15.5v output. Tried a very small output cap and eventually settled for 220uF Nichicon Fine Gold. The LED noise-cleaning electrolytic was moved across the LED as the circuit wasn't stable as shown (probably my grounding).

My subjective impression is very similar to yours: softer, less etched sound than the ALW, probably more suited for acoustic/classical music. Bass has slightly less weight but acoustic bass shows pleasing detail. Overall very high quality sound with possibly better highs than ALW but worse imaging and less PRAT. It then occured to me that these qualities may be attributed to the carbon oxide 50ohm ballast resistor. I am about to make simple CCSs using 317s and replace the resistor.

Needless to say, dropping the raw 30v dc down to 15.5v generates an amazing amount of heat compared to a series regulator.
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Old 27th February 2009, 07:07 PM   #16
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After some experiments by member Ikoflexer on my reg for the Simplistic NJFET RIAA that I did in the analogue section, he arrived in a boosted hfe Darlington driver plus op amp buff version that simulated well and performed stably with very good results. Op amp can be your choice as long as the whole thing stays stable. Mosfets can be faster TO220s as well. You may try it if you fancy.
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Old 27th February 2009, 07:18 PM   #17
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Default Shunt reg

Try place shunt reg close powered circuit as close as possible....optimal few mm form it (preferably mosfet source directly to GND point). Also CCS but something better then 317 improves bass. With shunts layout and CCS play major role that's why to the best results shunts regs PCBs can't be universal boards unlike serial regs.
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Old 27th February 2009, 07:26 PM   #18
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Great comments and suggestions but at the moment i am too excited about the difference the simple CCSs made. An almost complete transformation in bass and dynamics. Trouble is the sound now is too similar to the Jung/ALW Will have to do some more listening before other improvements.
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Old 27th February 2009, 07:30 PM   #19
Salas is offline Salas  Greece
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Its a bit different sounding with my Mosfet shunts with discrete Mosfet CCS. Still robust but calm. Try the one I posted at a point, it may suit you.
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Old 27th February 2009, 08:25 PM   #20
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Quote:
Originally posted by analog_sa

The LED noise-cleaning electrolytic was moved across the LED as the circuit wasn't stable as shown (probably my grounding).
This is not good, it changes the HF behaviour a lot. Better fix your grounding, 627 should be unconditionally stable.

Also, use separate grounds and sense the output at the load terminals.

These are things that are 1000 times more important than the output cap model.
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