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Old 6th May 2012, 01:57 PM   #71
dgta is offline dgta  United States
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Quote:
Originally Posted by M Gregg View Post
If this is so then the above seems to suggest that high current = low treble/ low
M. Gregg
No it doesn't. It suggests that we have no data to base any opinion on.

My guess is that in at least one of the configurations the circuit is improperly biased and you are hearing gross distortion.

Post the circuit with values, etc. and the frequency response and distortion data and then we can talk.
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Old 6th May 2012, 02:34 PM   #72
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leds are interesting fun in the cathode. I use them in fuzz/od effects section of guitar ampness.

but I am set in my ways with audiophile circuits and a really nice resistor is all you need. (no solid state junk in my tube audiophile)

and caps stink in the cathode.
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Old 6th May 2012, 04:21 PM   #73
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"really nice resistor is all you need"

It isn't the resistor that we are trying to eliminate; it is the bypass cap. I know many go cap-less, but I have found that the bass suffers when I do.
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Old 6th May 2012, 04:27 PM   #74
DF96 is offline DF96  England
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Omitting the bypass cap raises anode impedance, which generally degrades PSRR. Like everything, it is a matter of careful design.
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Old 7th May 2012, 01:40 PM   #75
tim614 is offline tim614  United States
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ok, so ive been following this thread and i experimenting on LED on my own amps.
so the amps are using 6n6p as driver, before the led i had 150v on the plate and 150ohms on the catode with bypass cap, 3.5v cathode to ground so thats around 23ma.
after reading the thread i put 2 RED led in series and measured 4v cathode to ground.

now what im wanting to know is did i raise the current with the LED?

what i notice is the sound are more detail not mush together and i think allitle less gain but im not sure, also they sounded clean when i turn the amps all the way up, with the resister in cathode i can hear the amp distord when volume is max.

so what does this mean?
am i on the right track?

BTW, amps are PP kt120 with IT phase splitter.

thanks
Tim
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Old 7th May 2012, 01:50 PM   #76
DF96 is offline DF96  England
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4V at the cathode vs. 3.5V means you have slightly less quiescent current and so less small-signal gain. On the other hand for stronger signals the bias point will shift less with the LED so this might give less distortion.
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Old 7th May 2012, 02:16 PM   #77
tim614 is offline tim614  United States
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so if i want more current i need to eliminate one of the led?
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Old 7th May 2012, 03:13 PM   #78
DF96 is offline DF96  England
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Yes, but you could get too much current and increased distortion. What does the load line show?
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Old 7th May 2012, 03:57 PM   #79
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If you omit one LED you will need to draw new load lines and re-engineer the front end.
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Old 7th May 2012, 06:53 PM   #80
tomchr is offline tomchr  United States
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Quote:
Originally Posted by tim614 View Post
so if i want more current i need to eliminate one of the led?
Or try an LED of a different color. Many blue LEDs run 3.5~4 V. The HLMP-D101 red LEDs that I use tend to be 1.75 V - so two of those in series would give you 3.5 V. Yellow LEDs tend to be around 1.75 V, green around 2 V.

I suggest looking at Digikey's LED selection. Download datasheets for different LED types (IR, different colors, etc) and look at their forward drop for the current you want. It's tedious work, but I'm sure you can find an LED that'll give you 3.5 V either as a single LED or with two in series.

~Tom
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