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Old 10th April 2013, 08:29 PM   #9631
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by massimo View Post
Thank you Ricardo. Thus K117's Idss the lower the better, right?

I missed the point: why did you lower R11 from 47k to 30k? If I'm not wrong you double up the value of C1 too.

P.S. trimmer on the source, not gate I guess
Yes, I use low Idss k117 for this purpose.

I reduced R11 to get higher lower wondering in output voltage and it seems the higher current on the ccs fet reduced it's operating noise.... it works , but I am on the limit now... can not go lower than 30k, bypassed by a quality foil 10u cap... lowering the vref increases Zo

Yes... trimmer on the source...
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Old 10th April 2013, 08:36 PM   #9632
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Originally Posted by Salas View Post
The folded runs at around 80% in first stage.
I should report last mod.... 4 x k170 with 12r for Rs proved floppy in the bass and noisier tan the 2 x k170 build so I reduced it to 3 x k170 with 4ohm for Rs... R14 went to 1k and now I have 63dB instead of 65dB total gain....

Now playing with the BiB.... very happy with the results... full on sound, snappy, detailed, low noise....

PS: this build is very sensitive to magnetic fields from the TX.... had to place the tx at 90 and 1 meter away.... very rewarding results in terms of bass definition... induced hum can kill bass deinition
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Old 10th April 2013, 09:24 PM   #9633
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High gain is very sensitive. 63dB=x1400 65dB=x1800.
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Old 15th April 2013, 01:04 PM   #9634
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Back to the BiB

Once more Vref cap proves it's significance.... After listening for some time with a 330uF cap over the vref trimmer and finding that something could be done to improve highs, I replaced that HQ EL cap by a smaller value MKP... incredible difference in terms of detail... highs are more fluid and fast and that translates to better discernibility in the bass also.

Strangely, I do not notice any increase in noise by reducing this cap value from 330u to 4u.....
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Old 15th April 2013, 02:30 PM   #9635
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In fact there is less hiss with only one 4,7u film cap than with the 330u EL.... but there seems to be a stability issue because the shunt sags when I touch the heatsink and also when I rotate the preamp volume to the max.

Now with two 4,7u in parallel, the sagging disapeared and sound is even better.... more detail and better spatiality... the problem is the hiss came back.... it seems the big cap in this place is prone to collect noise (like an antena)
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Old 15th April 2013, 02:41 PM   #9636
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The folded is less prone to pick up the PSU hiss so it gives more leeway for smaller value Vref filtering.
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Old 15th April 2013, 02:42 PM   #9637
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Its a p2p or a pcb bib we are talking about?
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Old 15th April 2013, 02:43 PM   #9638
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pcb bib
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Old 15th April 2013, 02:48 PM   #9639
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I could enhance results from medium size good electrolytic with a C0G right on its pins without using big size film.
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Old 15th April 2013, 03:22 PM   #9640
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Yes... maybe that is the way to go... anyway I learned that too small capacitance over resistive vref can compromise output current capabilities... because it sags when I touch the heatsink (the heat sink is totally isolated so it must be a magnetic happening).

It puzzles me that it also sags if I turn the volume up.

This volume thing is quite strange... untill 90% all is ok and the noise is really low, that it sags at 95% and than it wakes up again at 100% but with a lot of noise.

Maybe increasing the ccs current might cure it.... but it allready runs at 300mA.

With two 4,7u there is no problem but noise is much lowder than with the 4,7u alone.
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