Cub wrote: ↑21 Jan 2023, 21:54
Wow jeepe, you really put your back into it ! It's so awesome that after all these years, this fine sounding box of dirt is finally giving up its secrets.
I was only reading the color codes, this is just a check, just a subtle layer over the HUGE work that Kasper carried out...
mirosol wrote: ↑02 Jan 2023, 18:13
Nice work on the schem!
However. Are you sure about the way the boost switch is wired? In that position, when activated it takes the 2k2 in parallel with gain pot + the 150R. And that would mean the ohm value on feedBack loop would be set at something like 2K1 even with 47K pot maxed.
Otherwise this looks good. Well drawn, easy to read etc.
+m
This question with the gain pot and the extra gain resistor
was really annoying me, too...
although I'm really new in electronics, it seemed illogical...
until I visited
Electrosmash's rat analysis page...
where they say:
Gvmax = 1 + 100K / 47||560 = 2305 (67dB)
I didn't understand it
then I looked up
the meaning of double slash : equivalent resistor value of two parallel resistors
(I'm saying it for everybody's sake, not yours, Mirosol
)
this, BTW assumes a parenthesis...
so, it actually reads like: Gvmax = 1 + (100K / (47||560)) = 2305 (67dB)
43//560 = 43,36
now we can see how that "2305" came out
// it is actually 2306... and we should also add +1...
What we know is that without the boost ON, the (voltage) gain is at 15dB
and we also know that the
RAT can yield
67dB (voltage) gain...
so, 100K resistance gives us 67dB gain
then, how much gain do we get using 47K ??
I thought (stupidly, but it's normal) it would be 33dB ....
but no! logarithmic calculations don't work like linear ones (as it seems), and
gain in dB is logarithmic
47K will yield around 60dB ... (
check the calculator, voltage gain)
now, let's see, how much is 15dB gain!
I'm sure that many of you know it, even for me this wasn't the first time converting gain number to dB...
but I was
surprised to see that 15dB only means gain around 6..., like 6x -- "6 times"
so, we could think that the small feedback resistance (ca. 2.1k) would produce this...
and the case would be solved
however,
the electrosmash calculation of gain goes like this:
when we
instead of 47000 / (47//560)...
i.e.:
instead of 47000 / 43.36 (which would be ca. 1080x gain -> ca. 60db)
take
2100 / 43.36, it will produce
NOT "6x", but 48x gain...
which is 33.dB gain NOT 15 dB...
But the Mudhoney produces 15dB gain when the boost is limited by that switch...
So... something is still not clear yet
doing the math "we can solve this equation"
BUT I might be wrong, especially because I'm only playing with numbers and formulas I know nothing of...
anyway,
the gain we look for is 6x (6 times), and that comes out as
1+ (Feedback resistance / 43.36) = 6
that is:
5= Feedback resistance / 43.36
so, Feedback resistance = 216 ohms
OR, let's not forget that the maximum 15dB boost is achieved by the whole box! which can have attenuation,
I mean, the opamp might do 48x amplification while the box will only produce 6x altogether
(this is just a tipp)
and
please don't trust me!!! I've been only playing with numbers and formulas I know nothing of...