MyRefC build guide

[AndrewT]

Originally Posted by troystg

It has been established that having the LM318 nested in the feedback loop causes the LM3886 to run warmer.

I don't recall that. Would it be easy to find the discussion?

[troystg]

Easy? Most likely not.
Possible? Certainly.
Will I try to reinvent the wheel? No.

You are welcome to read every post in the multiple threads. I have read somewhere about the 95 percentile of them over several years time.

Has heatsinking and larger than normal heat sinks been brought up in those past posts? Yes.
Where? Good luck finding. This is an OLD subject / topic with LOTS of information to sort through.

[PJN]

Hi Guys,

First let me say thanks to Uriah for taking the time to make this group buy a reality.

I've begun stuffing my boards and have a few questions.

- Are the 1K Dale resistors supplied for R1 and R4 really rated for 1W, they seem small ?

- The BOM call out for Q2/Q3 to be BC546A, but BC546B supplied. Probabily ok but wanted to make sure.

- R11 spec'd as 1R, reading ~ 1.3 - 1.4 R with my meter. I'm assuming it is simply meter error with my cheapy meter.

- The BOM calls for two 75 K resistors For R15 & R16, but I got three in my kit. Is the third 75K just a unintended bonus part ?

Thanks,

PJN

[udailey]

A sink that size is pretty small. It also depends on what you mean by 'pretty hot'. If you put it in a closed box with no way to vent I wouldnt expect it to last long. I usually use a P4 sink around 3x3x2. About double what you are using. More than enough for the load they have to drive in my house. 96db speakers make it easy on any amp. If you are running 87db and play it loud you will need larger and larger sinks. With my speakers the P4 sinks rarely got warm. I mean you could hardly tell the difference between them and air temperature.
URiah

[udailey]

Originally Posted by PJN

Hi Guys,

First let me say thanks to Uriah for taking the time to make this group buy a reality.

I've begun stuffing my boards and have a few questions.

- Are the 1K Dale resistors supplied for R1 and R4 really rated for 1W, they seem small ?

- The BOM call out for Q2/Q3 to be BC546A, but BC546B supplied. Probabily ok but wanted to make sure.

- R11 spec'd as 1R, reading ~ 1.3 - 1.4 R with my meter. I'm assuming it is simply meter error with my cheapy meter.

- The BOM calls for two 75 K resistors For R15 & R16, but I got three in my kit. Is the third 75K just a unintended bonus part ?

Thanks,

PJN

I think those 1k's were actually 2W so you are safe. They LOOOK small but have you seen Panasonic 1/4W
Yep, BC546B is fine.
Its your meter.
Its a bonus part.
Let us know how it sounds Cant wait to start hearing some impressions.
Uriah

[PJN]

I have an original RevC from Twisted Pear that I built several years ago to compare it to, so it should be interesting.

[troystg]

Originally Posted by PJN

I have an original RevC from Twisted Pear that I built several years ago to compare it to, so it should be interesting.

I would definitely like to hear (pun intended) your opinions.

I think this circuit is fully capable of resolving the differences in components.

I have purchased six channels (2 from twisted pair, 4 from Uriah's 1st GB), built four, , so I couldn't justify another two....

[regiregi22]

Got my package! Thank you one more time, Uriah. Having a fast look at the contents arise me some questions, which I will ask later, when I get time to look at it closely.
BTW, you made a great effort in packaging it, tons of nearly individual bags and very compact all of it. Pictures promised.

Regards,
Regi

[udailey]

Youre welcome Regi. Note that you have the tantalum and metal hat in there for experimenting.
Uriah

[Bill_P]

Originally Posted by udailey

I think those 1k's were actually 2W so you are safe. They LOOOK small but have you seen Panasonic 1/4W

Just a few words about the power ratings resistor manufacturers publish:

There is no free lunch - the temperature rise at a given power will be greater the smaller the resistor. The small resistors are constructed of materials that can withstand very high temperatures, up to 230C in the case of the CPF2 resistor. For printed circuit board mounting you can't run anywhere near the rated power and maintain sane temperatures.

The highest DC voltage for the amplifier should be under +/-35 volts so the resistor will dissipate at most 1/2 Watt. That should produce a temperature rise of 40C according to the datasheet. At a normal room temperature and with allowance for a slightly higher internal enclosure ambient temperature, this produces a reasonable operating temperature. But there is no way you could realistically run 2 Watts dissipation with these resistors. In fact they aren't good for much more than 1/2 Watt the way we are using them.