Green-pre LED-bar mods (smaller stepsizes)

Hi,

FWIW, I've been toying around a bit with the levels of
the Green LED-bar.

Personal preference (that's just me) is to have a smaller steps,
of say 10 dB i.s.o. the original 20 dB (obviously a smaller range results).
I've done a quick & dirty redimensioning - I thought I'd share in case
this happens to suit someone else as well.


Here's what I came up with. Taps are a bit less accurate than the original
(Peter C has found a real nice set of values with standard E12-range resistors !),
but the following is still within 0.1 dB (0.3 dB for the lowest tap) so
that's still accurate enough.


Orig set: 47 / 100 / 10 / 1 / 0.12 [kOhm]

Modified set: 39 / 56 / 18 / 5.6 / 2.7 [kOhm]


Non E12-values could of course be used for further increased accuracy but hey,
the summer is beginning - don't stay too long inside recalculating for even
higher accuracies - it really doesn't matter anymore beyond this (to say the least).


Original taps (@ trimmed for orange LED @ 0 dBu): +20 / 0 / -20 / -40 [dBu]

Modified taps (@ trimmed for orange LED @ 0 dBu): +20 / +10 / 0 / -10 [dBu]


This all might seem an odd modification, but I'll be mainly using this preamp directly
to a HDD-recorder with inputs of 0dBu_typ/12dBu_max so a downward shifted and/or
reduced meter range suits me better.

A 10 dB shift downwards w.r.t. the modified set of taps is done by the 100k trimmer.

We finally get this then: +10 / 0 / -10 / -20 [dBu].



Regards,

Peter

I am interested by your modification of the LED meter, but I am not shure to have well understand it (I'm a newbie in DIY).

Did you change all resistors correponding to the value you mentionned (47k,100k, 10k, 1k, 120R) in LED-meter part of the PCB, or did you just changed particular ones ?

So, if it's the last issue, which resistors did you change ?

thanks,
Yoann

[quote author="Yoannv"]I am interested by your modification of the LED meter, but I am not shure to have well understand it (I'm a newbie in DIY).

Did you change all resistors correponding to the value you mentionned (47k,100k, 10k, 1k, 120R) in LED-meter part of the PCB, or did you just changed particular ones ?

So, if it's the last issue, which resistors did you change ?

thanks,
Yoann[/quote]

Hi,

It's 'the last issue':
I replaced all five of them by the 'modified set' values, so using 39k i.s.o. 47k etc etc.
This gives you the same 'top-level', but smaller stepsizes. To correct for that (so that the 'top-level' becomes +10 dBu i.s.o. +20 dBu) is simply done by (re-)adjusting the already present 100k trimpot (whose value stays unchanged, but now gets another setting).

Bye,

Peter

WOW, thanks for that's fast answer !! :grin:
Ok, so I just have to change the 5 resistors around the LM339, I think I gonna try this mod...
Thanks again,

Yoann

[quote author="Yoannv"]WOW, thanks for that's fast answer !! :grin:
Ok, so I just have to change the 5 resistors around the LM339, I think I gonna try this mod...
Thanks again,

Yoann[/quote]

My pleasure. There's little that can go wrong; and if you solder carefully it's easy to reverse it all.

Bye,

Peter

My original intention was to have the -40 indicator as a "signal present" indicator, & it took a shite load of effort to make it work. This very low level is the reason for the extra voltage (from the 20k trimmer) being summed in with the detector voltage.

It would have been a lot simpler to have the lowest LED triggering at -30.

Your mods should work fine :thumb:

Peter

[quote author="peterc"]My original intention was to have the -40 indicator as a "signal present" indicator, & it took a shite load of effort to make it work. This very low level is the reason for the extra voltage (from the 20k trimmer) being summed in with the detector voltage.

It would have been a lot simpler to have the lowest LED triggering at -30.

Your mods should work fine :thumb:

Peter[/quote]

Hi Peter,

Sorry to have kind of ruined your hard work ! If you had told us this before, I might have... :wink:

Bye