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-   -   My_Ref RevO (http://www.diyaudio.com/forums/chip-amps/196237-my_ref-revo.html)

ClaveFremen 8th September 2011 11:54 PM

My_Ref RevO
 
2 Attachment(s)
From Mauro Penasa home page:

http://www.webalice.it/mauro.penasa/...tti_audio.html

Apart Evolution presentation (Google translated) It's possible to read some interesting documents about the My_Evo.

In addition the Italian magazine 'Costruire HI-FI', issue #116 published a simplyfied schematic (no compensation network, no limiter schematic, no values).

Obviously I can't post it but the My_Evo main topology is identical (apart the DC-Servo and the second pump) to the My_Ref Rev C one.

So, probably, the My_Evo is basically a RevC with a different compensation network, better LM318 PS (14V), a 28V voltage limiter, a second current pump, a DC-Servo and a new and improved PCB.

So, is it possible to made a My_Ref RevC that takes advantage of some of the feaures presented by the My_Evo without infringing Mauro's IP?

IMHO it could be possible for quite all features:
  • a more stable amp using SMD
  • raise LM318's PS voltage with voltage limiter
  • LM318 compensation
  • Better PS for LM318
  • DC-Servo
  • Parallel current pump (already done and tested by a forumer)
The most difficult to design is the DC-Servo so, for now it would be left out (as the second pump) but obviously we should start from something so I've designed (starting from Russ White's Eagle schematic) a brand new (and untested) PCB with these features:

  • bigger caps (16mm diameter) for C1, C2, C9
  • large use of SMD components
  • all small caps and some critical resistors are still through-hole
  • the feedback resistor (R7) can be through hole or MELF
  • very small paths thanks to SMD
  • new and untested TL431 14V shunt PS for LM318
  • zener limiter based on schematic 5b from this link (which seems pretty similar to My_Evo one)
  • a double diode bridge like in most gainclones (tested by Suburra with great results)
  • If we find a better compensation scheme the PCB will still be valid (only values, not positions can change)
If you look at the attached schematic a resistor in the feedback net has been removed (R42), like Mauro himself suggested.

Both PCB and schematic are untested and prone to errors so any comment, fix, suggestion on both is welcome and appreciated.

PreSapian 9th September 2011 02:43 AM

the original myref thread is such a dinosaur than i would rather look the part of a bum asking it here but... would it lower stability or raise the temp of any component when r42 is replaced with a jumper?

btw, i'm very interested in this pcb, clave. will definitely be making it my next amp when it becomes available. keep up the good work! :)

quadtech 9th September 2011 05:20 AM

Double diode bridge similar to this? It is useful with 2 separate
secondary windings, and see how the ground is taken from the bridges.

http://www.tnt-audio.com/jpg/psu3.jpg

bcmbob 9th September 2011 07:11 AM

Dario,
I understand the goals of this project in terms of amp stability and physical component changes. Can you give some information about the anticipated sonic differences , if any, between this design and the current version of the MyRef?

Also, I noticed you are proposing the same 10,000 uF caps, Would increasing that value provide more head room?

ClaveFremen 9th September 2011 12:33 PM

Quote:

Originally Posted by PreSapian (Post 2703055)
would it lower stability or raise the temp of any component when r42 is replaced with a jumper?
...
keep up the good work! :)

You're welcome PreSapian :)

In fact, according to Mauro, removing R42 should improve stability.

Quote:

Originally Posted by quadtech (Post 2703135)
Double diode bridge similar to this? It is useful with 2 separate secondary windings, and see how the ground is taken from the bridges.

Exactly, and like you pointed out my schematic is wrong!

Thanks, that's the kind of feedback I'm looking for...:cool:

I'm updating the schematic and I'm redesignig the associated part of the PCB...

Quote:

Originally Posted by bcmbob (Post 2703197)
Can you give some information about the anticipated sonic differences , if any, between this design and the current version of the MyRef?

If the PCB will be correctly designed we should exepct a lower THD and noise floor.

According to Suburra the double bridge gives more contrast, bass is more articulated, a general refinement.

I really don't know what to expect from the new LM318's PS, I hope to test it on the RevC next week.

If and when the new compensation scheme will be fully investigated and tested we should expect much more refined highs and a much tighter bass, like in the My_Evo.

Quote:

Originally Posted by bcmbob (Post 2703197)
Also, I noticed you are proposing the same 10,000 uF caps, Would increasing that value provide more head room?

It's possible but also the My_Evo has 10000uF smothing caps for each pump.

The PCB is already tight and full with 30mm caps, in this moment I can't imagine how to stretch in 35mm ones (and bigger value caps are mostly 35mm...)

ClaveFremen 9th September 2011 01:04 PM

Hopefully fixed double bridge...please check
 
1 Attachment(s)
Now it should be correct.

bcmbob 9th September 2011 01:17 PM

Dario,
Sounds very promising and I wish I knew enough to contribute at this level. None the less, you've got my full encouragement and support.

Thanks for your efforts.

ClaveFremen 10th September 2011 01:51 AM

Updated PCB and schematic (fixed dual bridge)
 
2 Attachment(s)
The dual bridge was more difficult to route than what I've expected and I've had to sacrifice the wire holes, only fast-on...

AndrewT 10th September 2011 10:33 AM

Why have you adopted a dual bridge rectifier for use with a centre tapped transformer? They don't work together !
What is VR2? It can't be a +ve regulator turned upside down !

If adeqaute smoothing cap values result in too large a footprint, then move the main capacitance off board and put in adequate decoupling.

What about replacing the mechanical relay with the mosFET relay described recently? The space left over after changing to smaller footprint caps can be used to fit the mosFET triggering circuits.

ClaveFremen 10th September 2011 11:46 AM

1 Attachment(s)
Hi Andrew,

Quote:

Originally Posted by AndrewT (Post 2704488)
Why have you adopted a dual bridge rectifier for use with a centre tapped transformer? They don't work together !

It's not so, if you look at the schematic there are two complete AC input (AC1/PGND1 and AC2/PGND2) for a dual secondary transformer.

GND is for safety ground/CL-60 to safetyground/resistor to safety ground.

Maybe the names are not the best ones, any suggestion is welcome.

But maybe I've implemented it wrong, if you can check it would be nice. ;)

Quote:

Originally Posted by AndrewT (Post 2704488)
What is VR2? It can't be a +ve regulator turned upside down !

It's a TL431 voltage reference, I've taken the schematic here for both the positive and negative regulators.

And actually I've made an error also here, now checking and fixing, thanks for pointing me on it. :)

Quote:

Originally Posted by AndrewT (Post 2704488)
If adeqaute smoothing cap values result in too large a footprint, then move the main capacitance off board and put in adequate decoupling.

It can be an alternative but I'm trying to keep all on single PCB.

Quote:

Originally Posted by AndrewT (Post 2704488)
What about replacing the mechanical relay with the mosFET relay described recently? The space left over after changing to smaller footprint caps can be used to fit the mosFET triggering circuits.

Can you point me to it, please? :)

Thanks in advance for any help/suggestion.

In the meanwhile I've revised polygons and power traces...


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