Have you looked at a CL60 style soft start?
What voltage will come out of the transformer while the soft start is in circuit?
How will it vary as the CL60 heats and then cools?
What will that voltage do to all the other circuits connected as the sch?
Will the relay across the CL60 pull in to short the CL60 out of circuit?
A soft start should use a reliable voltage and timer to ensure reliable bypassing of the resistance. Otherwise the resistor or Thermistor may get hot and if you have a drop out, the soft start may not work as expected.
What voltage will come out of the transformer while the soft start is in circuit?
How will it vary as the CL60 heats and then cools?
What will that voltage do to all the other circuits connected as the sch?
Will the relay across the CL60 pull in to short the CL60 out of circuit?
A soft start should use a reliable voltage and timer to ensure reliable bypassing of the resistance. Otherwise the resistor or Thermistor may get hot and if you have a drop out, the soft start may not work as expected.
>>>Have you looked at a CL60 style soft start?
CL60 thermistor is an NTC device which in this particular case can be used to limit the inrush of current.
>>>What voltage will come out of the transformer while the soft start is in circuit?
I believe we are only limiting the inrush current. At the start the PSU caps will be a short and will slowly build up voltage.
>>>How will it vary as the CL60 heats and then cools?
Voltage should stabilize within a few micro-seconds once the xfr core is loaded the purpose of CL60 is served. It then should be available to trigger the relay. CL60 should be shorted to cool down and be ready for another start as and when needed.
>>>What will that voltage do to all the other circuits connected as the sch?
Pretty much nothing I guess.
Will the relay across the CL60 pull in to short the CL60 out of circuit?
Yes.
CL60 thermistor is an NTC device which in this particular case can be used to limit the inrush of current.
>>>What voltage will come out of the transformer while the soft start is in circuit?
I believe we are only limiting the inrush current. At the start the PSU caps will be a short and will slowly build up voltage.
>>>How will it vary as the CL60 heats and then cools?
Voltage should stabilize within a few micro-seconds once the xfr core is loaded the purpose of CL60 is served. It then should be available to trigger the relay. CL60 should be shorted to cool down and be ready for another start as and when needed.
>>>What will that voltage do to all the other circuits connected as the sch?
Pretty much nothing I guess.
Will the relay across the CL60 pull in to short the CL60 out of circuit?
Yes.
The aux power is to hold the relay into position. For the MyRef, you do not need a thermistor to suppress the inrush current, because the voltage capacitance does not cause much of a problem. You generally use this when the inrush current is so high it starts to blow fuses or dim house lights, etc.
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The 12v aux power has a current rating of just about 20 mA at chipamp rail voltages of +/- 32 V DC and R1, R4 = 1 k. In short, just about enough to power the opamp.
The 1 ohm resistor R11 can smoke for a variety of reasons, including unequal ground potential between signal ground and power ground (sometimes caused by human error when connecting the trafo wires to AC1, PGND and AC2), problems with the ground potential in the signal source, ill-advised attempts to bridge or parallel two MyRef boards for higher power (no, it can't be done with the stock Rev C), etc. Think of it as a fuse - replacing R11 gives you a 50% chance that a blown MyRef board will come alive and work perfectly.
The 1 ohm resistor R11 can smoke for a variety of reasons, including unequal ground potential between signal ground and power ground (sometimes caused by human error when connecting the trafo wires to AC1, PGND and AC2), problems with the ground potential in the signal source, ill-advised attempts to bridge or parallel two MyRef boards for higher power (no, it can't be done with the stock Rev C), etc. Think of it as a fuse - replacing R11 gives you a 50% chance that a blown MyRef board will come alive and work perfectly.
Short answer: NO.
Those resistors constitutes the "bridge" which define the NFB/PFB loop of the HCP. Which is at the core of Mauro's design. Their values are extremely critical. Changing them will deeply alter the behavior and performance of the whole amplifier. Thus altering them is definitely NOT recommended. A "wrong" choice of their values may even result in instability, up to destructive self-oscillations.
Not only those resistors must be of the required value, but they must be of the highest possible precision, too: 0.1% or better (0.01% recommended).
It's very unlikely that you can source adequate parts from a local supplier. You should get 'em from some major distributor (like Farnell, Mouser, RS, etc) or a good "specialized" audio components supplier.
Beware: not only the values are critical. The "My_Ref" is extremely sensitive to components "quality" too. That is brand and model. You may get anything from excellent to horrible sound quality depending on which parts you use to build it!
As for R7/R10 (which define the overall NFB network) and other "critical" places, the best choice would be the use of Charcroft Z-foil (very expensive, though). Other cheaper (but definitely worse) choices could be Takman metal film, PRP, Dale, etc (if not using Z-foil, avoid the smaller ones. Use only resistors with allowed dissipation rated from 0.5W to 2W even where much less would be required).
Finding the right "blend" of parts to get the "right" sound is not easy. I suggest you to read all the related topics to learn about other builder experiences and suggestions. Particularly the "My Ref Rev.E/FE" related threads, where people have done a lot of research to find the best "BOM".
http://www.diyaudio.com/forums/group-buys/160768-myref_c-ultimate-bom.html
http://www.diyaudio.com/forums/chip-amps/234032-my_ref-fremen-edition-build-thread-tutorial.html
http://www.diyaudio.com/forums/chip-amps/207390-my_ref-fremen-edition-beta-build-fine-tuning.html
http://www.diyaudio.com/forums/chip-amps/197120-my_ref-fremen-edition-need-help-pcb-evaluation.html
http://www.diyaudio.com/forums/group-buys/229358-my_ref-fremen-edition-interest-group-buy.html
etc.
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I think he wanted to know if *matched* 50k and 20k resistors can be substituted for *matched* 47k and 22k resistors at R6, R9, R5, R8 - and the short answer to that is *Yes*. I do it all the time, and it works well - because the only change is the transconductance of the inner loop, and the change in ratio is negligible: 50/20 vs. 47/22.
The sonics are largely governed by the quality of resistors in the *outer* loop, including R7 and R10. I use the best resistors for the money (PRP, Holco, etc.) at those locations.
The sonics are largely governed by the quality of resistors in the *outer* loop, including R7 and R10. I use the best resistors for the money (PRP, Holco, etc.) at those locations.
It is YES alsofor me: i'm using in a myref C in fact 51k and 24K. It only needs to be carefully selected for symmetry in the feedback, the two values had been hand selected for less than 0.1% tolerance between them.
Also, my humblest apologies, I have done measurements on a MyEvo amp and I'm late with the link:
http://www.diyaudio.com/forums/chip...on-build-thread-tutorial-216.html#post4407354
Also, my humblest apologies, I have done measurements on a MyEvo amp and I'm late with the link:
http://www.diyaudio.com/forums/chip...on-build-thread-tutorial-216.html#post4407354
Short answer: NO.
Beware: not only the values are critical. The "My_Ref" is extremely sensitive to components "quality" too. That is brand and model. You may get anything from excellent to horrible sound quality depending on which parts you use to build it!
A few months ago I built a My_Ref Rev C using no esoteric components except for a couple of silver mica capacitors that were not really necessary, and the amp sounds very good. I really don't think its possible for a well constructed My-Ref that uses appropriate components to sound "horrible". In this case selecting the "right" components simply makes a very good amp excellent.
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