Switchable Hi-Z input impedance, how ? - Page 34 - diyAudio
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Old 1st October 2012, 02:15 PM   #331
shanx is offline shanx  Canada
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Hi Tinitus, glad you tried out the bypass caps. It may help also with hum and radio interference too.
The different cap types can affect the subtle differences in sound. Also tolerance on caps is wide so was could to try different types to get it sounding right. Was the 2.5 uF a film cap?
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Old 1st October 2012, 03:08 PM   #332
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by shanx View Post
Was the 2.5 uF a film cap?
yes, the 2.5uf was poly type
a bipolar smooth foil might be worth a try

still happy with the 2.2uf
30year old and weird Wima MKC4 type

my regulator is finished
only needs power, and a check
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Old 1st October 2012, 08:29 PM   #333
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by tinitus View Post
my regulator is finished
only needs power, and a check
and its working, 16.6V
sounds more precise, and plays faster
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Old 1st October 2012, 08:38 PM   #334
shanx is offline shanx  Canada
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Nice work! I put two 10uF in parallel (electro type)on my first stage fet bypass. One with a switch to play with frequency response/gain, so will see what happens.
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Old 2nd October 2012, 01:22 PM   #335
tinitus is offline tinitus  Europe
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I have removed bypass cap again
with the regulated supply something changed
sounded out of phase, like loosing hearing on one ear
I did try to increase cap from 2.2uf to 3.3uf
and it did help, but still better without
seem I got my sound back, in the most simple way
small simple regulated supply, and nothing else

wonder if it works a bit like a ccs
then there should be no bypass cap, right ?
maybe thats what it needs, a ccs
will look at inserting a LED in the source res
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Old 2nd October 2012, 02:26 PM   #336
shanx is offline shanx  Canada
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The bypass cap is increasing normally the gain on the stage, and you could be hitting saturation. Ids, gate bias and bypass cap will all play a part in whether you are at a signal operating point that is pleasing on the ears. For guitar there is more reasons to play with saturation and cutoff, but you may want a clean signal for bass at least at the first stage, with plenty of headroom.
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Old 2nd October 2012, 06:37 PM   #337
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by shanx View Post
Ids, gate bias and bypass cap will all play a part in whether you are at a signal operating point that is pleasing on the ears.
I think you have a good point with that
regulator drops about 2V
heck, right now Im thinking maybe 2V is too small
anyway, I still measure about the same 80mv over the source resistor

well, that said, I found the sound nice softy round
but I prefer a more dry sound in the long run
fells kind of less 'picky'

so I threw in a couple of 3300uf, seperated by a 1ohm resistor, and the bleeder/LED
and that actually gave a much more dry sound

I will try to go down to 15V
experiments not over yet
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Old 2nd October 2012, 10:01 PM   #338
tinitus is offline tinitus  Europe
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measured voltage before and after regulator drops only 1V from 17.8V to 16.7V

and thought I would see what kind of DC I have before output cap
close to 8V(or -8V), and about equal to drain voltage
sounds like a lot
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Old 2nd October 2012, 10:33 PM   #339
tinitus is offline tinitus  Europe
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trying to figure out that LED thing
a found interesting stuff
well, I have heard it before, and not had a clew what
lets see how it works

plate voltage divided by plate resistor gives bias current
ups, sorry, drain and not plate
I have about 8V and 1K5
and that gives 5ma
wow, I think 5ma have been mentioned by Nelson
and to check source resistor, I have 80mv and 15R
funny, but thats also 5ma...wow, it works

so, to calculate the LED current flow I would need to know its inner resistance, I guess
and ups again, forgetting about jfet type and idss
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Old 2nd October 2012, 11:24 PM   #340
tinitus is offline tinitus  Europe
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ahh, appears that 5ma is close to where a led turns off
does not sound very nice
but whatever
if I have undestood any of it, the LED bias is meant to lower source(cathode) resistance to achieve better or more stable gain
but a 15R resistor is already low, so whats the point anyway
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