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Old 16th May 2013, 04:35 PM   #981
toobhed is offline toobhed  United States
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Eric (or anyone else who collected ACA parts themselves):

Did you tap threads into the heatsink or simply drill holes and use small bolts/nuts for fastening PC board and MOSFETs to heat sink?

Any tips for someone who's never done metal work and needs to drill holes in heat sink (beyond some of the threads in Construction Tips - heatsink holes)?

Thanks!
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Old 16th May 2013, 04:56 PM   #982
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Before you drill the hole, use a hammer and nail sinker to score where you will drill.
This prevents the drill bit from walking from the spot where you want to place the hole.

If tapping after drilling, use wd-40 to lub and turn the tap in 1/4 turns, back out and continue with another 1/4 turn, back out a 1/4 turn, and so on.

You might want up try self tapping screws, if no tapping tools available, but the screws are not pretty, not like button head or hex key screws.
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Old 16th May 2013, 08:24 PM   #983
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Quote:
Originally Posted by toobhed View Post
Eric (or anyone else who collected ACA parts themselves):

Did you tap threads into the heatsink or simply drill holes and use small bolts/nuts for fastening PC board and MOSFETs to heat sink?

Any tips for someone who's never done metal work and needs to drill holes in heat sink (beyond some of the threads in Construction Tips - heatsink holes)?

Thanks!
I tap threads into the heatsink, I bought some 6/32 screws and drilled all holes with a 7/64 bit and then used the 6/32 threading tap. Doing this is aluminum is very easy. Put some light oil or WD-40 while threading and you are all set. Before doing it on your heatsink, why not practice on another piece of aluminum, you'll see it's fun and easy.

p.s. My previous pics showing the 3 bolts (3rd pic of post no.950) were just to show the required height of a stand-off I don't have.

Rgds,
Eric

Last edited by e_fortier; 16th May 2013 at 08:27 PM.
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Old 19th May 2013, 03:36 PM   #984
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Hi,
Newbie questions:
- What is the "more correct" position of the outer leg of P1: in the junction between (R1-R2-R3-R4-C1) or (R3-R4-Q1)? I saw this difference between schematic and PCB in Mr. Pass's article and tried both in my prototype but saw no difference in operation.
- What is the main purpose of the 4 resistors R1-R4, beside of biasing?
If I use R1=R2=0.68R, R3=R4=0.47R; or R1=R2=R3=R4=0.56R (bias will be the same), what will be the difference?
Or if I replace those by only one resistor 0.56R (same bias, but C1 & P1 will be connected to Drain of Q1), what will be the difference?

Rgds,
Duong
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Old 20th May 2013, 03:14 AM   #985
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Quote:
- What is the "more correct" position of the outer leg of P1: in the junction between (R1-R2-R3-R4-C1) or (R3-R4-Q1)? I saw this difference between schematic and PCB in Mr. Pass's article and tried both in my prototype but saw no difference in operation.
Changing the connection to P1 doesn't make much difference, but slight changes in the bias voltage will change the measured distortion (and the gain). Search for some of my earlier posts in this thread for graphs.
Quote:
- What is the main purpose of the 4 resistors R1-R4, beside of biasing?
If I use R1=R2=0.68R, R3=R4=0.47R; or R1=R2=R3=R4=0.56R (bias will be the same), what will be the difference?
R1, R2, R3, and R4 set the bias current, but they also control the ratio of signal sent to Q2. This in turn changes the linearity and distortion profile of the amp. Making them equal will increase the distortion and will reduce the gain, but you may like the sound. I think Nelson found a good compromise between measured performance and listenability. In the PLH article Nelson discusses this. Link: https://www.passdiy.com/pdf/PLH_amplifier.pdf

Notice how C2 is connected to the bottom side of R3, R4. When Q1's current is reduced in response to a negative going input, Q2 is encouraged to turn on more. So Q2 does not act like a constant current source, but more like a negative resistance (current goes up as the voltage goes down). As Nelson discusses in the ACA article, you can play around with the ratio of R1, R2 to R3, R4.
Quote:
Or if I replace those by only one resistor 0.56R (same bias, but C1 & P1 will be connected to Drain of Q1), what will be the difference?
Q2 would become a constant current source. The distortion will be higher, gain lower,
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Old 20th May 2013, 10:57 AM   #986
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Quote:
Originally Posted by Loudthud View Post
Changing the connection to P1 doesn't make much difference, but slight changes in the bias voltage will change the measured distortion (and the gain). Search for some of my earlier posts in this thread for graphs.

R1, R2, R3, and R4 set the bias current, but they also control the ratio of signal sent to Q2. This in turn changes the linearity and distortion profile of the amp. Making them equal will increase the distortion and will reduce the gain, but you may like the sound. I think Nelson found a good compromise between measured performance and listenability. In the PLH article Nelson discusses this. Link: https://www.passdiy.com/pdf/PLH_amplifier.pdf

Notice how C2 is connected to the bottom side of R3, R4. When Q1's current is reduced in response to a negative going input, Q2 is encouraged to turn on more. So Q2 does not act like a constant current source, but more like a negative resistance (current goes up as the voltage goes down). As Nelson discusses in the ACA article, you can play around with the ratio of R1, R2 to R3, R4.

Q2 would become a constant current source. The distortion will be higher, gain lower,
Looks like I've missed some parts in Mr. Pass's article.
Anyway now I'm digging the 99 pages of this thread, and will take another look at the article, hope this will help.

Thanks very much,
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Old 24th May 2013, 12:14 PM   #987
dodog is offline dodog  United States
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Does anyone know a source for the "quasi heatsink" that's listed in the DIY store? It's not for sale there, however. Is there a real name for this type of piece and/or a source? Anyone know the dimensions of this material?
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Old 24th May 2013, 12:20 PM   #988
bcmbob is offline bcmbob  United States
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Check out Heatsinks USA. They have several products with a 1/4" back web the allow blind threaded holes. They will cut to customer specs, or you can use a carbide blade on a table saw. Depending on what you are building, PC CPU heatsinks come in a bunch of shapes and sizes and are low cost on eBay. See ex. HERE
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Last edited by bcmbob; 24th May 2013 at 12:26 PM.
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Old 24th May 2013, 03:20 PM   #989
dodog is offline dodog  United States
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Quote:
Originally Posted by bcmbob View Post
Check out Heatsinks USA. They have several products with a 1/4" back web the allow blind threaded holes. They will cut to customer specs, or you can use a carbide blade on a table saw. Depending on what you are building, PC CPU heatsinks come in a bunch of shapes and sizes and are low cost on eBay. See ex. HERE
Sorry, I should have been more clear. I'm referring to this material:

Quasi Heatsinks

I don't need it for a heatsink but as a side to build a temp case. I'm looking for something that I could attach the heatsink to, perhaps with a bolt, nut and t-slot.

Any ideas for a cheap aluminum enclosure that would accommodate attachment of the heatsinks they sold in the DIY store would be great.
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Old 24th May 2013, 03:34 PM   #990
billyk is offline billyk  United States
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Quote:
Originally Posted by dodog View Post
Sorry, I should have been more clear. I'm referring to this material:

Quasi Heatsinks

I don't need it for a heatsink but as a side to build a temp case. I'm looking for something that I could attach the heatsink to, perhaps with a bolt, nut and t-slot.

Any ideas for a cheap aluminum enclosure that would accommodate attachment of the heatsinks they sold in the DIY store would be great.

I use wood for the front and rear and the heatsinks from the store as the sides.

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