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Old 12th April 2012, 06:10 AM   #51
slomatt is offline slomatt  United States
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Since I'm blocked from tweaking until I can improve my testing equipment how about some more build pictures?

Here are the KP1830 0.01uF 63v bypass caps installed.
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The top and bottom are 1/2" oak with grating from the IKEA garbage can installed to keep fingers out.
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The MOSFETS are mounted using aluminum oxide pads and large washers. They are torqued to 7in-lb.
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Currently the heatsinks are attached to the front and back panels using "hidden" screws on the inside. These are a major pain to install and I'm going to switch to external fasteners next time I have the amp apart. The two amp boards just barely fit inside.
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The bottom and top are bolted on using recessed pan head bolts.
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Here's the back panel with the recently added grounding lug.
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- Matt
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Old 12th April 2012, 06:16 AM   #52
Atilla is offline Atilla  Norway
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Very very pretty. I am quite jealous.

Also a bit worried about how am I ever going to test mine. Once I eventually finish it, of course
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Old 12th April 2012, 06:26 AM   #53
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Looks great! Where did the channel aluminum come from?
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Old 12th April 2012, 06:45 AM   #54
slomatt is offline slomatt  United States
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Quote:
Originally Posted by Atilla View Post
Very very pretty. I am quite jealous.

Also a bit worried about how am I ever going to test mine. Once I eventually finish it, of course
Thanks for the kind words.

Quote:
Originally Posted by oneplustwo View Post
Looks great! Where did the channel aluminum come from?
Thank you. Variac kindly provided the aluminum channel. You can likely find it locally, or online at McMaster.

McMaster-Carr

- Matt
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Old 12th April 2012, 09:01 AM   #55
zyker is offline zyker  Malaysia
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A handsome build Matt! Great job
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Old 12th April 2012, 10:07 AM   #56
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Very very cool!From where the grid come from?
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Old 12th April 2012, 12:53 PM   #57
Eric is offline Eric  United States
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Very nice build, Matt! I've been following your thread since the beginning and I really like the dual-chassis layout. I've seen a few others take this approach and it seems to have a number of interesting advantages.

Thanks for sharing!

Eric
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Old 13th April 2012, 07:03 AM   #58
slomatt is offline slomatt  United States
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Quote:
Originally Posted by Minisemi View Post
Very very cool!From where the grid come from?
Are you referring to the metal mesh on the power supply casing and the top and bottom of the amps? If so, that is a $2 garbage can from IKEA.

Quote:
Originally Posted by Eric View Post
Very nice build, Matt! I've been following your thread since the beginning and I really like the dual-chassis layout. I've seen a few others take this approach and it seems to have a number of interesting advantages.

Thanks for sharing!

Eric
Thanks. Pass recommends placing the power supply 2+ feet from the amp, so I figured I'd put them in separate cases.

- Matt
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Old 21st August 2012, 08:52 PM   #59
slomatt is offline slomatt  United States
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I finally got my oscilloscope repaired and purchased a function generator that can output a clean 10kHz square wave.

The attached photos show the output of my MiniA (biased at 1.2A) with a 10kHz square wave input signal of varying amplitude. The amplifier was driving a 50w 8ohm resistor. The oscilloscope is set at 2v/div and was recently calibrated so it should be fairly accurate.

Some calculations for future reference:
Vrms = Vp-p / 2.82
P = V^2 / R
R = 8ohm

Photo 1: The testing setup in case anyone is interested.

Photo 2: Output at 4Vpp = 1.42Vrms = 0.25w
To my eye this looks pretty clean with no oscillation and just a bit of angle in the ramp up which I believe means a small amount of loss at high frequencies.

Photo 3: Output at 8Vpp = 2.84Vrms = 1w
Looks pretty much the same as 4Vpp.

Photo 4: Output at 12Vpp = 4.26Vrms = 2.3w
Here the flat top of the square wave is getting a bit more angled.

Photo 5: Output at ~15Vpp = 5.32Vrms = 3.5w
Above this level the leading edge of the square wave gets progressively more "bent" and the small overshoot bump appears at the top.


I'm just learning how to evaluate amps based on their output waveforms and would greatly appreciate any help interpreting these results. How much deformation of the square wave is reasonably expected? Does the photo of 15Vpp indicate a major compromise in sound quality, or just some high end roll off? When I have time I plan to go through a similar process with a sine wave to see when clipping starts to occur.

- Matt
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File Type: jpg IMG_6049.JPG (116.2 KB, 120 views)
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Old 21st August 2012, 11:08 PM   #60
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Matt: That leading edge looks quite good to me....although I forget what the tilt means...LF rolloff??.... as far as the leading edge, that's about what I'm hoping for with a 15pf feedback comp cap (which I'll get with my next Digi-key order). With a 20pf cap, my leading edge is a bit rounder IIRC.

Did you also calibrate your probe with your scope?

Last edited by boywonder; 21st August 2012 at 11:11 PM.
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