My_Ref Fremen Edition - need help on PCB evaluation

[ClaveFremen]

Originally Posted by AndrewT

And I would be asking "why".
Why has the sound changed?
What is causing that effect?
Has something electrically changed that is affecting the sound (waveform)?

Hi Andrew,

reading the datasheets my hypothesis on minimum current seems reasonable.

The LM3x7L (TO92 100mA) seems to need at least 5mA of output current while LM3x7T (TO220 1,5A) seems to need at least 10mA.

With the 68R value a current of circa 18mA is generated so the margin on minimum current is pretty different.

With 50R we can have 25mA, I suppose that it will fill the gap.

Maybe also the different origin (Onsemi vs NatSemi) could have a role since the specs are very similar but not identical.

A more fair comparison will be the one between OnSemi and NatSemi TO220 1.5A LM3x7s.

[soongsc]

Originally Posted by ClaveFremen

I suppose this is the case, with the OnSemi, after warm-up, sound became more 3D, richer in harmonics and decay.

If the harmonics and decay are higher in both dead studio recordings and live hall recordings, then it may mean less fidelity. However, it may be more to one's liking. This is where it gradually becomes difficult to make decisions.

[ClaveFremen]

Originally Posted by soongsc

If the harmonics and decay are higher in both dead studio recordings and live hall recordings, then it may mean less fidelity. However, it may be more to one's liking. This is where it gradually becomes difficult to make decisions.

When we will build the beta boards we will compare our results.

It shouldn't be difficult to source some NatSemi to compare...right?

[soongsc]

What I am going to do with the beta boards first is to give it the same +/- 27VDC that I use now, try to keep as close to your LM318 DC power as possible but put the LM3886 C4 mod in, use the original MyRef values in other components and see how they compare. I just increased the cap size parallel to C4 to 3300uF, further increase triggers the power supply protection circuit on the MyRef but not my other amp (yet). Increased differentiation between hall reflections and instruments make instruments stand out more.

[AndrewT]

Now you are thinking this through.
You have asked yourself "does the change in regulator type, lead to a change in the quality of the regulation?"

That question needs an answer and not by ear ! The ear is the evidence that something has changed.

The next question should be "what type of regulation parameters suit the amplifier?" and the supplementary question could be "what regulation parameters make the amplifier misbehave?"

BTW,
the 317 (5mA) and the 337 (10mA) often have different minimum current for specified performance.

[soongsc]

I think what also needs to be considered is the balance of idle current on the + & - rails for the LM318 chip.

[ClaveFremen]

Originally Posted by AndrewT

The next question should be "what type of regulation parameters suit the amplifier?" and the supplementary question could be "what regulation parameters make the amplifier misbehave?"

Spot-on questions that, sadly, I'm only in part able to answer (remember that my electronics knowledge is very limited, I've asked help also for this reason).

My goals (in part inspired by Mauro's recommendations on a private e-mail) were:

• isolate LM318 from LM3886's PS pollution (mostly current, I suppose)
• isolate LM3886 PS lines from LM318's PS pollution (mostlly voltage, I suppose)
• simple with low count parts
• Shunt type

Some of them could be arbitrary or even wrong.


Since I've got no help for the shunt regulator here I've found it on an italian forum and the FE's LM318 PS is the result.


Any help, suggestion or instructive post about it is welcome.

Originally Posted by AndrewT

the 317 (5mA) and the 337 (10mA) often have different minimum current for specified performance.

Yes, I've seen.

Do you think I should expect problems from this difference, it should be compensated and how?

Originally Posted by soongsc

I think what also needs to be considered is the balance of idle current on the + & - rails for the LM318 chip.

If I've understood correctly the shunt topology should take care of it by design:

The LM318 use the needed current, any excess is shunted by both the transistor and the zener.

This is not perfect, though, since the possible different amount of current shunted would change a bit the output impedance of the regulator.

Any suggestion?

[soongsc]

Getting to the next step is going to take lots of time in a lab with adequate equipment.

[ClaveFremen]

Originally Posted by soongsc

Getting to the next step is going to take lots of time in a lab with adequate equipment.

Yes, it's probably so but, nevertheless, I must learn a lot of things about it and any instructional post would be appreciated...

For the Fremen Edition II (one to two years in the future... ) also a completely regulated PS could be interesting.

In the meanwhile it would be interesting to find out if a bigger current for the negative rail would improve performance in an audible way.

[soongsc]

I have an amplifier with power regulator. Have not compared it lately because it's a really old amp.