Student's guide to myref

[varun21]

So I come here after some good reading:

1. 4278 posts in the original myref thread.
2. The "Current Pump": App Note Abstract: AN-1515 A Comprehensive Study of the Howland Current Pump (Rev. A)
3. Musical Fidelity AN 370:
4. Mauro's myref rev A schematic: View attachment my_ampli.pdf
5. Mauro's technical description and design criteria for the myref: View attachment project_my_ref.pdf
6. A second and third read of the first 100 posts in the original myref thread.
7. The myref rev C schematic: View attachment my_ref_rev3.pdf

Mauro said:

Naturally all am clear of interprets to like them my circuit, but in my layout it is "hidden" different years of technical "analysis"...

I have certain questions that will help me understand the topology of the circuit and the pros and cons of it, in the interest of science, for my own knowledge and for fixing the issues with my own copy of the myref rev C.

Q1: What makes myref a better audio amp than others? (What are the pros and cons?)
Q2: What makes myref unstable? (A member even termed it "dangerous" which Maouro found an exaggeration). Mine has a hiss/HF oscillation (rev C) using a standard board and components. Replacing the LM318n with a TL071a fixes it.
Q3: What functions do the additional passive components serve in myref Rev C (as against the rev A)? I'm specifically interested in C10 (22pF), R3 (.47 Ohms) other than the compensation network of rev C.
Q4: What makes the LM318n "more musical" or "valve like sounding" (than any other op amp)? Is is the slewrate or some other parameter? Or is it just the ears?
Q5: Can just the LM318n block be used as a headphone amplifier to appreciate the sonic musicality of the system?
Q6: Can C10 (22pF) be responsible for parasitic HF oscillations?
Q7: Is there a way to find out if I have a fake LM318n? I guess the recommended NS LM318 is now TI LM318n. Does it work?

Sorry for the long list of questions. I happen to be a nerd-level DIYer as a teen but lost touch with electronics in 2002 due to my career.

I really respect Mauro's effort to explain things in English. I'm a little slow and there are certain posts I just couldn't understand.

In brief, say that this type of amplifiers "feelses" the load that in minimum departs comes to be part of the feedback network, on account of the presence of the bridge in exit (or an other high impedance current driver).

Besides there is the fact that the loss of profit of IC1 high frequency does works hard of more U1.

And it is not that simple to substitute that opamp, I agree. This design of his is really a very well thought over, blanced one. I tried to list some opamps, which are known for good sound, and are having similar characteristics to the LM318.
What were You having in mind with the assymetrical slew rates? It is time to learn for me!

Just warming back up to electronics after 14 years to appreciate the myref topology. Thanks and I really appreciate your inputs.

 

[twest820]

Rod Elliot's "project" 56 is one of the better introductions to amplifier output impedance. Between than and some Spice parameter sweeps you should be able to answer most of your questions (it wouldn't surprise me if the MyRef isn't designed to ensure stability at all tolerance corners---look for degraded phase margin from 318 peaking as it overdrives the 3886's GBP in particular). Nelson Pass has a fair bit on the topic over at www.firstwatt.com as well.

The LM318 remains an active part. Both parts are inexpensive so if you're concerned about faking just buy from a proper distributor. Volumes have been written here and elsewhere about subjective changes in op amp rolling. Most reflect uncontrolled, sighted trials with small sample sizes so take that as you will.

 

[Mark Whitney]

After studying the My_Ref don't you think that some of the beauty of the original design has been lost? A clone of a clone of a clone syndrome. If this contributes to the instability I don't know, it must take away from the sound quality.