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Old 9th March 2013, 09:44 PM   #601
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Quote:
Originally Posted by CaféNoir View Post
Files have been sent to production; I ordered 10 PCBs with 2oz copper.
Below is a virtual render of a populated board using Eagle3D.
Hi CafeNoir,
Would be interested in a couple of these boards pls. Also any advice on bits to use and match up if needed,
Was there someone on here selling kits of matched semi conductors?
Pingushome
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Old 11th March 2013, 09:01 PM   #602
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Pingushome,
jackinnj has been very kind to provide some kits (pcbs and parts) to the DIYers. They are available here, and I highly recommend it if you want best bang for the buck:
Tech DIY Company Store

My boards were made to accommodate mounted heatsinks, as well as other options (bias, filtering, etc.). They are a bit more expensive ($9 per board, so $18 for a stereo set), but if you still want it, I can put you down for two PCBs.
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Old 11th March 2013, 09:08 PM   #603
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One small note about Tech-DIY boards: the copper plane on one of the channels of the PCB is not connected to anything, even with the jumpers mentioned earlier. If one wants the pour to be connected to ground, one must scratch some silkscreen off and make a connection there. The issue is in the right part of the pcb, when seen from the top.
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Old 12th March 2013, 07:47 AM   #604
RNMarsh is offline RNMarsh  United States
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One of the reasons for making a gnfb amp with moderate nfb is to get a flat thd curve vs. freq. Usually you get a rising thd as frequency increases. With the same amount of nfb at all frequencies the thd should be constant over the audio range.

In fact this is the case. I see only 2 harmonics with either 1KHz or 10KHz and they are the same level. Plus, No higher orders -- no 5, 7, 9th etc.

1-10KHz THD.jpg

-110 -120dB

Thx-RNMarsh

Last edited by RNMarsh; 12th March 2013 at 07:50 AM. Reason: flat thd curve
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Old 12th March 2013, 11:15 AM   #605
Telstar is offline Telstar  Italy
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Doesn't this depends on the BW of the loop?
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"The total harmonic distortion is not a measure of the degree of distastefulness to the listener and it is recommended that its use should be discontinued." D. Masa, 1938
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Old 12th March 2013, 11:31 AM   #606
jcx is offline jcx  United States
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there are plenty of distortion mechanisms that rise with frequency despite flat global loop gain - anywhere you have a nonlinear C

and if we are most concerned with IMD products in the most sensitive hearing bands then we don't want to "throw away" loop gain that gives distortion reduction there - global feedback does reduce even IMD difference products

so if you can have 26 dB more loop gain at 1 KHz than 20 kHz with common single pole compensation, the CCIF 19+20 kHz test 1 kHz IMD product is ~26 dB lower with the integrating loop gain curve than with the same amp with flat audio frequency loop gain below 20 kHz for typical output stage dominated distortion
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Old 12th March 2013, 05:58 PM   #607
RNMarsh is offline RNMarsh  United States
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The point here is a narrow one. yes, i admit that. never-the-less, when one looks at all forms and causes there are a multitude of mechanisms to be sure. And, yes more fb will reduce distortions more Etc etc etc.

BUT --- if you look at the harmonic distribution - the harmonic structure, the harmonics them selves and which ones and their relative amplitudes to one another.......

With the Same amount of gnfb appplied at all freqs tends to give the same characteristics for the harmonic structure anywhere. You dont get one set at low freq and another at high freq. levels are the same and structures are the same. This has an affect on the percieved sound, I believe. A continuity in the sound that cant be duplicated any other way.

Thx-RNMarsh
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Old 13th March 2013, 02:31 AM   #608
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Quote:
Originally Posted by CaféNoir View Post
Pingushome,
jackinnj has been very kind to provide some kits (pcbs and parts) to the DIYers. They are available here, and I highly recommend it if you want best bang for the buck:
Tech DIY Company Store

My boards were made to accommodate mounted heatsinks, as well as other options (bias, filtering, etc.). They are a bit more expensive ($9 per board, so $18 for a stereo set), but if you still want it, I can put you down for two PCBs.
Thanks CafeNoir I'll check it out
Martin
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Old 20th March 2013, 06:21 PM   #609
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Good news; boards just arrived

Time for a quick inspection. They look good to me so far
All people interested, expect a PM soon
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File Type: jpg Marsh_PCB.jpg (378.7 KB, 487 views)
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Old 22nd March 2013, 06:57 AM   #610
RNMarsh is offline RNMarsh  United States
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Looks very nice. I'm in for a pair.

Thx-Richard Marsh
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