Hi-Fi mod for Boss GE-7

[HeaD]

Hi, excuse me... I've tried to do a search but I've not found anything of precise. So, I have understood that to remove noise just change the 3 TL022s and the 4558 with 4 low noise TL072s, add a 270 pF in parallel to R26 (10k resistor) and change the R1 (470 ohm) to a 140 ohm resistor. Ok?

Here is the schematics http://img267.imageshack.us/my.php?image=ge7pg28oc.jpg ...

I have heard that to increase the sound quality some caps must be changed with others of better quality, but what? Thanks to all!

[HeaD]

no one knows?

[cd]

Use the search.  All of your answers are in the archives:

http://www.diystompboxes.com/smfforum/index.php?topic=33765.0
http://www.diystompboxes.com/smfforum/index.php?topic=24865.0

Make educated and logical decisions with respect to part replacements - in other words, you can't polish a turd (graphic EQs are inherently flawed) and don't try to accomplish anything based on someone else's marketing hype.

[Eb7+9]

no matter what op-amps you use these inductor sim eq's are pretty noisy by nature, esp at extreme cut or boost ... if you really want to bring the noise down you'll have to replace the inductor simulators by real coils ... Shin-Ei made such a circuit in the late 60's

~jc

[mr_doyle]

no matter what op-amps you use these inductor sim eq's are pretty noisy by nature, esp at extreme cut or boost ... if you really want to bring the noise down you'll have to replace the inductor simulators by real coils ... Shin-Ei made such a circuit in the late 60's

could you please give me any more inputs on this? i guess the simulators are some sort of Gyrator design... that would mean that a few op-amps/resitors/caps could be replaced by inductors right?
looking at the schematics i see that - say - the 100Hz band is controlled by VR1, C10, C13, R16, R17 and a part of IC3. using an inductor instead would give better results?

tia,
D.

[Eb7+9]

... there a few different Gyrator based simulators - the single op-amp variety seems to produce more noise than the dual ones ... regardless, if you search out active Eq circuit examples you'll recognize how this works in the GE-7 ... the grampa Shin-Ei FY-2 schematic shows what you're aiming for ...



In the 100Hz slot of the GE-7 circuit C10 is the frequency setting cap and C13, R16, R17 and the op-amp follower circuit form the inductor simulator - note these later values also affect the Q of the combined L-C circuit ... C1, R3 form a shelving stage, so leave those alone ... what you want to do is keep C10, C9, C7, C5, C4, C2 and replace gyrator blocks by respective physical inductors of appropriate value connected to ground ... notice how the GE-7 cap values are similar to the FY-2 values ...

To figure out the appropriate inductance you need to know that the peak frequency occurs where capacitive and inductive reactances equate ...

namely,

XC = 1/(2pi*F*C) = XL = 2pi*F*L

yielding

L = 1/[(2pi*F)^2*C]

because the rest of the circuit is also op-amp based and still somewhat noisier than a low-gain single ended gain block if you're gonna go to through all this kinda trouble I'd suggest you start over and follow the FY-2 gain block for best noise performance with this type of architecture ...

... while we're at it, the biasing in the FY-2 circuit can be altered for increased headroom and linearity ... if you tie the front-end FET reference to a 1.2v volt source instead (change the two 10k resistors in the divider network and sourced from the rails) and tie the Drain to +9 instead of collector of Darlington bipolar device you'll get a +/-2volt input headroom instead of +/-0.5 volt ... my simulator tells me this would work equally well with BF245A or 2n5484 ... this means you could use such a circuit for other things than eq/ing instruments ...

the person I got the schematic from says he tried an original FY-2 unit out and it sounded very nice, he also said they were assembled by Gar Gillies in Winnipeg in the 60's under license ... maybe someone in the Peg can ask Gar and verify if this is true or not ...

~jc

[mr_doyle]

Thanks a lot, this is huge information: i'll do the math and try to figure it out!

D.