MyRefC build guide

[AndrewT]

Wester,
your 1.2C/W for each 3886 chip is on the nail for 70Vcc, 8ohm speaker and Ta25degC.
National say 2.4C/W, you have chosen exactly double.

I will be using 78Vcc, 8ohm speaker and Ta=35degC (sink inside the chassis)
I will need 1C/W for 1off 3886 or 0.5C/W for two 3886.

[regiregi22]

Originally Posted by udailey

Thanks Regi,
Grey band and transparent: Both for same - you pick. I had the transparent mica ones for this buy and then Steve at APEXJR threw in the grey band which will do the trick as wel.
LM318H you might try the datasheet. I dont know but I imagine you worry about it touching the Caddock heatsink. I might put some grey band on the top of it to be sure.
The 100k remember is excess that I had on hand and is linear. This was thrown in for free as I had hundreds and no use for it. It will get you running but wont give very smooth volume control. It will change volume rather abruptly. You will want to change to a dual log when you get a chance. 5k is for balance. Goes to 'Series Balance' on the little board. Regi, the schematic you drew represents my board perfectly so you already know how to use it.
Dont be afraid as long as you put the components in the right spot as per your schematic.
A few things to consider when using the LDR board.
1: dial that 200R pot to midpoint and THEN fire up the board. This way you have the protection of half of the pot plus a 68R resistor for each shunt LDR. You can not damage the series LDRs.
2: the paper with the numbers: its basically a measurement sheet of your LDRs. If you have a low 'max db difference' on the lowest measurement then use those for shunt LDRs. If you have a high 'max db difference' on the lowest measurement then use those for series. What is High or Low? Its only relative to the 'max db difference' at the other end of the measurements sheet. Pick the best numbers for shunt. All the numbers are "GOOD" numbers. I wont send out anything that isnt a very good match.

What I can see is how to hook up the 5k pot to it. It has already two trimmers there, of 200ohm. The 5k isn't shown in my schematic, I can't see it, sorry I would thank any help about that matter.

Sabre, those heatsinks are definitly too small. Also your speaker output wires seem too thin, hook up there something of higher gauge. I would also place the obligattos between the connectors and the heatsinks.

I have made a plan for testing the tantalum resistors and the LM318 in both packages. First, I will populate both boards with the PRP resistors, but one with the metal can encapsulation and one with a DIP-8 ic. I will let it burn-in for some days, like 100 or 150 hours, to not address false results due to not burned-in components. After a detailed extensive listening session (to be able to memorize it's sounding characteristics), I will try to find any difference between both boards. Listening one board at a time, of course. Though, I am not expecting any discernable audibly difference between both IC's.
Then, I will put the same IC in both boards, and listen to it again. After having memorized it sound, I will quickly change the PRP resistors for the tantalum ones, and I will listen for further changes. I will expose all the differences my humble ears are able to discern.

My heatsinks are really killer ones at 30x12x5cm (12x5x2 inches) size, one of them for each board.

[ClaveFremen]

Originally Posted by regiregi22

Then, I will put the same IC in both boards, and listen to it again. After having memorized it sound, I will quickly change the PRP resistors for the tantalum ones, and I will listen for further changes. I will expose all the differences my humble ears are able to discern.

Use sockets in both cases...

[AndrewT]

Originally Posted by regiregi22

My heatsinks are really killer ones at 30x12x5cm (12x5x2 inches) size, one of them for each board.

I don't have data for your build nor your ambient conditions, but if I were allowed to guess then 300 by 59 by 50mm (sawn to half height) would probably do for a pair of 3886, not just one.

[regiregi22]

I bet one heatsink should be able to handle even 4 LM3886. I wasn't intended to buy this one so big, but the enclosure I liked had that big heatsinks. Is this one:
modushop.biz

And I am going to put inside a Myref_C and an standar gainclone I have without enclosure, from chipamp.com.

[troystg]

Originally Posted by sabre66

Thanks for your reply will get done right away, but I dont understand the heat spreader thing. Some photos I've seen are what look like aluminum U bar if thats all It is thats simple enough. Or I'll mount the chips to copper like in Peter Daniels Patek

Yes I am able to hear music when the "good" 318 is installed in each of the boards.

A heat spreader can be as simple as a piece of 1.5 -2 inch wide piece of aluminum from a hardware store. When I make "cheap" chipamps for people I cut a 6 to 8 inch long piece of Aluminum strap from Home Depot. Different store but:
Shop Steelworks Aluminum Flat 1/16" x 1-1/2" x 6' at Lowes.com'

Just cut a length of that and mount it between the chips and the chassis with thermal paste. This bar will spread the heat to a larger area of the thin chassis and the chassis will dissipate the heat. The chassis wall is too thin to spread the heat quickly enough but a 1.5 wide x 8 long x 1/8 inch thick piece of metal will spread the heat to a larger area on the chassis. Remember the thermal paste and insulation!!

As for the 318, if the amps work with a good 318, then it has to be a pin compatibility issue or a voltage supply issue. Easiest first step is to measure the voltages to the 318.

[PJN]

Hi guys,

I have a few more dumb questions as I continue to stuff my boards.

- Does the 220 uF Blackgate go to C9, it's unclear from the boom ?

- I recieved 4 tiny little ceramic caps with my kits and I'm having trouble figuring out where two of them go. One came attached to a peice of cardboard and is labeled uc221, the other is loose with shorter legs and is labeled 100 on one side and K2J on the other.

- As added info could anyone tell me where the other two go, I installed them in C12 and C21, but would like to make sure before I'm done and fire them up.

- I'm assuming that you just leave the spots for the caps that aren't being used blank without jumpers (C17-20), am i correct ?

Many thanks,

PJN

[ClaveFremen]

The Black Gate goes in C9.

The ceramics are C10 (22pF), C12 (220pF) and C34 (10pF), if you have only two values something could be wrong... and for sure none of them goes to C21...

Regarding C17, C18, C19, C20 positions simply leave them empty, no jumpers!!!

[AndrewT]

Originally Posted by PJN

.......labeled 100 on one side and K2J on the other.

the 100 is likely to be DC voltage rating.
The Jis +-5% tolerance.
I think the K2 is the same as 0k2 which would read as 200. This is likely to be a 200pF +-5% 100Vdc capacitor.
Does anyone disagree? Speak up.

[PJN]

Thanks Dario, I'll double check everything when I get home tonight.

PJN