Patchwork Reloaded: Circuit Optimization and Board Layout.

[MJL21193]

Originally posted by jacco vermeulen


Oh Johnny Boy,

can't be, your ears haven't ripened enough to distinguish between head and tail of a wire.

Ah, but I do know the female from the male end

I like to keep an open mind to these things but sometimes it gets a trifle silly.

[MJL21193]

Update!!

Board layout:

[KLe]

Happy New Year everybody

[MJL21193]

Hi Kl,
You're a ways ahead of me (still 23 hours till 2009 here) but Happy New Year anyway!

[MJL21193]

I have been playing with RMAA and decided to do some tests on the Patchwork amps that are being used in my 6 channel amp.

Tests were at about 20 watts output into 8 ohms. Signal was attenuated by a resistor divider. Ignore the stereo crosstalk figures, as the attenuator used a common ground.

The scores:



THD:



Noise:



Frequency response:



IMD:



I just posted results for the same tests on the K10A amp for comparison.

[MJL21193]

I have completed this project and I will be running some final sims and posting the details. There has been some interest in the design and there are a few builders out there, so I have some final construction details to post.

First, a complete and final schematic:

[MJL21193]

Final board layout:



Board is single sided 3" x 5" and all outputs, drivers and Vbe are mounted underneath.


Bill of material:

[MJL21193]

Board copper bottom in high quality .pdf for those (like me) who can make there own boards:

[MJL21193]

Silkscreen top:

[MJL21193]

My simulation of the amp puts the THD at ~0.001% at about 50 watts output. I ran some more tests with RMAA, this time getting all of the settings right (checked the "do not monitor" box in the recording properties - I didn't do this with the results above and it makes a big difference) and the results are below. Actual output from the amp is about 20Vrms, so ~50 watts into 8 ohms.

First the numbers. First 2 tests are for the soundcard itself. The second 2 are with the amp in the loop. I ran these tests several times to verify consistency.



Soundcard THD = 0.0019, therefore the amps THD = 0.0002% (0.0021 - 0.0019 = 0.0002). Very good!

Frequency response comparison between the soundcard only and the amp looped in:



Noise spectra, soundcard only compared to amp looped in:



IM distortion, again a comparison between the soundcards native IMD and with the amp looped in:



Finally, the THD spectra. Soundcard alone is the white trace, amp in the loop is the green trace. We see 3k and 6K (these are present in the same magnitude for the soundcard test) but they are below -100db: