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Old 30th May 2014, 04:03 PM   #1771
Zen Mod is offline Zen Mod  Serbia
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compare

Pa is making his amps using his own ears

yours don't must be the same

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Old 30th May 2014, 04:40 PM   #1772
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Quote:
Originally Posted by kacernator View Post
Why is there no source degeneration of Q1? According to simulations 0.22R resistor at Q1s source lowers distortion to almost half at 1 kHz.
It will cost a bit output power on an already low-power amp. It's worth a try, however, if your speakers are of suitable efficiency.
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Old 3rd June 2014, 06:17 PM   #1773
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Hey all!

I've finally mounted everything on 2 veroboards (both channels) and .... sounds awesome Complete winner, 2k2 mod of course running @20 volts SMPS. Tough I have a ~24volts (rectified and ripple-regulated) linear supply that I'm gonna use soon.
@6L6: indeed, I might also give a go to this mod.
I find this amp in general powerful enough for my room, consider that I'm not using high-end spearkers of any sort (8 ohms).
Sound is very clean and I very much like basses.
Overall completely satisfied: my motto is something around the words "If it's yours, then it must sound good either way"
...but this really sounds sweet hihi
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Old 11th June 2014, 07:39 PM   #1774
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In the ACA schematic, why is the input cap C3 reversed? Is it because of the feedback from R12?
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Old 11th June 2014, 07:47 PM   #1775
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input (- side of cap ) is on gnd potential , while Jfet gate (+side of cap) is on approx. 4V potential
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Old 25th June 2014, 04:19 PM   #1776
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Is there an updated Distortion vs Output graph for the 2k2 mod? I read in the thread that distortion was reduced but I didn't see any specific measurements? Sorry in advance if I just missed it but I always love the graphs and stuff!
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Old 28th June 2014, 03:55 PM   #1777
6L6 is offline 6L6  United States
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The 2K2 'mod' just gets the operating point of the amp to it's designed values. It's really more of a patch than a modification or upgrade.
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Old 28th June 2014, 08:31 PM   #1778
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Quote:
Originally Posted by Dilliw View Post
Is there an updated Distortion vs Output graph for the 2k2 mod? I read in the thread that distortion was reduced but I didn't see any specific measurements? Sorry in advance if I just missed it but I always love the graphs and stuff!
My AP System 1 is has a slight problem so the graphs it produces now don't correlate with earlier measurements. In general the 1KHz THD vs Power graph is pushed down to about half the THD with the 2.2K mod. If you look at THD vs Frequency however, the improvement is only below about 2KHz. At 10KHz there is a small increase in THD. See the graph in post 713.

Setting the quiescent output voltage is a little different with the 2K2 mod. I found that setting Q1's Drain to 9.2V gave the cleanest looking graph with a 19.0V rail. The 19V power supply bricks I've looked at are around 19.5V. Premature clipping on one rail causes a lump in the THD vs PWR graph above 3 Watts or so.
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Old 29th June 2014, 10:54 PM   #1779
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Has anyone tried different enhancement mode parts and the ACA?

I was thinking to change out both Q1 and Q2.

Quote:
" These elements are chosen to control Q2 in such a way that it acts as a DC constant current source which also varies AC-wise so as to favorably help the amplification provided by Q1."

My interpretation is that Q2 does double duty as current source, and helps the circuit "AC-wise" and that it has an overall effect on the sound.

Is SJEP120R100 for both Q1 and Q2 feasable? with a slight change in current source bias? Or just changing Q2 to a enhancement JFET?

I have a diy F2J for comparison.

Thanks.
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Old 30th June 2014, 04:17 PM   #1780
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Quote:
Originally Posted by Loudthud View Post
My AP System 1 is has a slight problem so the graphs it produces now don't correlate with earlier measurements. In general the 1KHz THD vs Power graph is pushed down to about half the THD with the 2.2K mod. If you look at THD vs Frequency however, the improvement is only below about 2KHz. At 10KHz there is a small increase in THD. See the graph in post 713.

Setting the quiescent output voltage is a little different with the 2K2 mod. I found that setting Q1's Drain to 9.2V gave the cleanest looking graph with a 19.0V rail. The 19V power supply bricks I've looked at are around 19.5V. Premature clipping on one rail causes a lump in the THD vs PWR graph above 3 Watts or so.
Thanks Loudthud, that's a great comparison and it came before the mod was discussed so that's why I didn't see it. My Q1 is still set at 10v using the bricks that came with the kit. I'm very happy with these amps paired with my Hornshoppe horns.
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