Massive Active

[Harpo]

.., but the method of the 7k5s on top and bottom of the gainpot works very well, possibly better than changing the feedbackresistor.

Difference between a 7K5 and 4K7 standoff resistor is 0.77dB.
Main difference is the missing pots center tap connection from Fabios schematic and pcb.

 

[simonsez]

The schematic : Cool, I'll send you a pm in a minute with my emailaddress. The low shelf isn't working properly, schematics would make a lot clear, I think.

Regarding the 7k5's : No, I'm not entirely sure, but copied from the BOM :
"8 7k5 R-EU_0204/7
'USE 4K7 FOR MORE BOOST/CUT; INSTALL ON BOTTOM SIDE OF FILTERS PCB ".

These are also the only 7k5 resistors in the BOM, so.....

I don't know why Igor mention that, like Harpo said that it's only make small differences. Did you try it?

http://groupdiy.com/index.php?topic=27972.msg623070#msg623070

 

[simonsez]

.., but the method of the 7k5s on top and bottom of the gainpot works very well, possibly better than changing the feedbackresistor.

Difference between a 7K5 and 4K7 standoff resistor is 0.77dB.
Main difference is the missing pots center tap connection from Fabios schematic and pcb.

Harpo, what if I'm using stepped/rotary switch? what actually the center tap doing?
And why the original schematic don't have those 7k5 resistor?

 

[Harpo]

Harpo, what if I'm using stepped/rotary switch?

you could calculate the amount of boost or cut for each step. Roughly +/-dB=LOG(attenuated level * gain of filter stage * value of summing amp feedback resistor / value of summing amp input resistor that connects to filter output)*20.

what actually the center tap doing?

connecting the pots (hopefully electrical=mechanical) center position to 0V reference voltage. Imagine a center tapped pot as two series connected pots with a single wiper that travels from one pot end thru the center tap connection to the other pots end. Both series connected pots (the center tapped pot) are simple voltage dividers with their highest attenuation position at the center tap connection. Turning the wiper more CW or CCW feeds the filter input with an increasing in-phase or out-of-phase signal that returns to the summing node of the output amp, so depending on phase the signal gets boosted or cut.

And why the original schematic don't have those 7k5 resistor?

not needed/contraproductive with value this high, only increasing resistive noise. You'd need some more of these paralleled center tapped level pots before the driving stage runs out of beef. Instead of the Igors 7K5 or 4K7, value of the MEP250a was 100R or nada R in the 430.
The center tapped 50K value might have been the only available part at that time.

 

[dagoose]

Just wondering, I just noticed the trimpots in every filterband. What does it do?

 

[simonsez]

Just wondering, I just noticed the trimpots in every filterband. What does it do?

It's wrote on the original schematic, for noise canceling...adjust for 0mV DC across C27 with freq control CCW.

 

[dagoose]

Just wondering, I just noticed the trimpots in every filterband. What does it do?

It's wrote on the original schematic, for noise canceling...adjust for 0mV DC across C27 with freq control CCW.

ah! i see!  8)

 

[simonsez]

It's done! some screenshot....

Thank you guys!!



The M/S matrix is a must!

Merry X'mas

 

[creal]

Congratulation,
Very nice build, it looks very great.
Can you share the schematics and/or the doc for ordering the PCBs ?
Maybe you plan to organize a group buy for PCB of this project
i 'll like to build the same EQ very soon for my setup.
Merry Chrismas

 

[leadbreath]

yes someone please organise a PCB groupbuy for this lovely EQ?
even some schematics will be nice.

cheers
mick

 

[simonsez]

yes someone please organise a PCB groupbuy for this lovely EQ?
even some schematics will be nice.

cheers
mick

Congratulation,
Very nice build, it looks very great.
Can you share the schematics and/or the doc for ordering the PCBs ?
Maybe you plan to organize a group buy for PCB of this project
i 'll like to build the same EQ very soon for my setup.
Merry Chrismas

Thanks, you can find the schematic here http://gyraf.dk/schematics/Sontec_MEP250a.GIF


Merry X'mas......peace and joy be with you

 

[frazzman]

any chance of releasing the PCB overlays for us self etchers ? This looks like an incredible project, and if you make public the layout you will have benefit of getting input from these knowledgable diy diehards on suggestions to improve the design!

 

[simonsez]

any chance of releasing the PCB overlays for us self etchers ? This looks like an incredible project, and if you make public the layout you will have benefit of getting input from these knowledgable diy diehards on suggestions to improve the design!

The pcb design contain some error,  It's dual layer through hole PCB, I don't think it's easy for self etcher.


Regards,

Simon

 

[creal]

Hi Simon,

Pm you for the single side PCB Overlay and more

cheers
Cyril

 

[leadbreath]

hi simonsez

pm sent for sontec info, thanks so much for your help.

mick

 

[frazzman]

Hi Simonsez,
Send you a pm also, this is an amazing and exciting project, look forward to seeing the detsils

 

[radiance]

Very nice work!

 

[stevesteve50]

Beautiful! Please let us know if pcb's become available

 

[janps]

wonderfull project, congratulations