F2 Initial Listening Impressions

[apassgear]

Originally posted by Nelson Pass

I think www.6moons.com put up a nice interior shot.

Thank you very much Nelson for sharing a bit more and pointing to those 6moons.com excellent pic's.

Now is clear that the power supply is a CRCRC and no voltage reg for that matter.

What called my attention were those 4 seemingly AB 2W resistors midway on the main PCB, any clue?

[Blues]

Nelson, what's the resistor (1/4W) in one of the legs of the CCS power resistor seemingly jumpered over to another 1/4W resistor? This is from the close-up pic of the F2 ckt board showing the CCS part.

[Vix]

Hi!

Nice review of the F2. I agree that its interior revealed a couple of things. There is no doubt about the power supply. CLC, and the board looks very similar to the one used in F1. (Or, is it the same?) As for the 2 w resistors, they look like source resistors (?). I can’t see if all six of them are in parallel or not. If not, then it looks like 3 of them might have some other purpose?

However,what confuses me is a big electrolytic capacitor near the CCS. I understand that the one near in/out connectors is the output coupling cap, 15.000 uF if I remember correctly.

But the other one (near the front plate) is puzzling me.


Nelson, is it too early for a hint?

By the way, have you noticed how pics are shot? It is possible to see that caps are rated at 85 deg.C, but the most interesting info, their value, is “On the dark side of the moon”

Best regards,

Vix

[Vix]

Uups, I just saw that I have made a mistake in my previous post. "CLC". I meant CRC. I think it is obvious. Sorry.

Vix

[apassgear]

Vix,

I still belive the Power supply is a CRCRC. Part of the blue string of resistors is the second R (near where the PSU cables enter the board) and the lytic you mention near the CCS correspond to the last C which is bypassed by an orange film cap. I would also guess that all lytics (6 of them on each channel) are 15,000uf at 35V.

There are lots of blue power resistor which are rated at 3W. I have seen in the past that Nelson likes to parallel these in order to adjust values and give them a safe rating of 6W (2 parallels) good enough in the case of this circuit, but in this board there seem to be groups of three in some cases such as the source resistors. We still have some resistors to be identified such as the 4 seemingly Allen Bradly's 2W that sit half way on the board.

[steenoe]

We still have some resistors to be identified such as the 4 seemingly Allen Bradly's 2W that sit half way on the board.

Yes, its not the norm that NP uses part's like those. I wonder what the purpose of those are. I am sure NP had his reasons for using those, as always. A little hint here would be greatly appriciated Also the "Daddy long legs" resistor puzzles me a bit. Can't imagine NP made a mistake on the board and had to P2P that resistor later on

Steen

BTW, Tony, your P-fets are on their way to Mexico

BTW, BTW Vix if you are talking about the carbon resistors, there is only 4

I can’t see if all six

[Vix]

Originally posted by apassgear
Vix,

I still belive the Power supply is a CRCRC. Part of the blue string of resistors is the second R (near where the PSU cables enter the board) and the lytic you mention near the CCS correspond to the last C which is bypassed by an orange film cap.

Hi

Yes, I thought about this capacitor. So, you say it is just a power supply filter cap?

As for the resistors, I was thinking about those blue ones(nesr the gain mosfet), 6 of them, but three of them seem to be wired separately.

I also have no clue what those four (on the middle of the board) serve for. Only the Master could provide an answer

I suspect that there might be "something else" , which we haven't seen yet...

Regards,

Vix

[steenoe]

I suspect that there might be "something else" , which we haven't seen yet...

I have a sneaking feeling about that too Just thought we had this figured out, but no

Steen

[apassgear]

Originally posted by Vix


Hi

Yes, I thought about this capacitor. So, you say it is just a power supply filter cap?

As for the resistors, I was thinking about those blue ones(nesr the gain mosfet), 6 of them, but three of them seem to be wired separately.

I also have no clue what those four (on the middle of the board) serve for. Only the Master could provide an answer

I suspect that there might be "something else" , which we haven't seen yet...

Regards,

Vix

Yes, thats a power supply filter, the last of the string of a CRCRC. Nelson aparently had the intention to put 2 of those lytics if you see the footprint on the board but finnaly decided to replace one of those with a film bypass, guess he found it was better soundwise.

All the components shown on the board are quite clear to me with a couple of exceptions.

Those 6 blue power resistors are 3 for the PSU last R and another 3 for the source resitor of Q1. The other 3 resistor near the back plate are the shunt resistor of the output. Maybe the Master found that using a higher wattage raiting (an array in this case) will lower noise.

"Daddy long legs" still puzzels me too. The only component I don't see clearly on that area is the 0.001u cap (C3 on the posted schem) but sincerely it does not look like a cap and the connection would not suggest this. There is a possibility though even if it is unlikely that could be a parallel resitor to R6, same schematic.

I Suspect that there are some components under the board since the input cap is not seen and you can see the signal cables reaching the underside of the PCB. Something not very common on Nelson’s layout but remember that this amp is of limited production.

The blue cap near the output lytic seems to be the bypass. He has mention that it has a 1uf bypass, though it seems small for that value.

And of course we still have those 4 AB resistors with no clue to them. Maybe there are some other components beneath? Who knows but Nelson and those happy owners of F2's.

[apassgear]

Originally posted by steenoe

BTW, Tony, your P-fets are on their way to Mexico

Great Steen, guess they will take some 2 weeks to arrive.

I'm working on the PCB, still with the rail regulator. Should we continue with the reg? or are you having second thoughts on a CRCRC supply?