Fodera, Sadowsky, aguilar, and other bass preamps

Stompboxes circuits published in magazines, books or on DIY electronics websites.
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LuisMerino
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Post by LuisMerino »

davidmochen wrote: 30 Jul 2021, 20:47 Hi guys,

Been checking the posts in this thread in search of a reply for a question I have. Please see schem below:

Image

It strikes me that this configuration has been used in many types of EQ (particularly mid bands), from 3-band HAZ to Gallien Krueger RBs. Please see the similar-looking mids section schematic of the 3-band HAZ below:

Image

However, I can see that for R9 and R10 in the top circuit (270K), for instance, the HAZ has 1M. Same for R3 and R4 (2.0K) vs. 20 K for the HAZ.

Finally, the relationship between caps (2n2 for both caps in HAZ, 33n and 3n3 for the other circuit) is completely different.

My question is, is there any calculator readily available for checking the differences in this topology? Does a specific value of matched resistor influences in, say, the total Q? Does the relationship between caps influence on Q as well? Do R3 and R4 in the top circuit limit the boost/cut for the EQ?

I take it all these parameters interact, so that is why I am curious about a calculator or, at least, some explanation behind the different approaches taken in the examples above.

Thanks very much in advance!

David
i´m new to this forum, if it is useful, i share a schematic from the ken smith middle module

i copied from a 90´s haz/smith board, it works!!
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davidmochen
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Post by davidmochen »

lietuvis wrote: 31 Jul 2021, 21:10 Hi David, download yourself a LTSpice run midrange circuit from link at the below and have a play with values of resistors, capacitors, potentiometers and have your own calculator-simulator.
https://mega.nz/folder/0NgAFDoL#uYQUSBQ9f2HWW4R94PuO_A
Hi Lietuvis, many thanks, I have just downloaded LTspice so I guess I will have to learn it!

Best,

D

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subbass
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Post by subbass »

davidmochen wrote: 18 Aug 2021, 12:11
Hi Lietuvis, many thanks, I have just downloaded LTspice so I guess I will have to learn it!

Best,

D
Hi, not such an industry standard I guess but I find Micro-Cap more intuitive and easier to learn and work around.
AC analysis is real time. It's for free as well.

Also there's the almost-perfect Live SPICE. I dig that! You can try running such circuits as VST in an audio workstation app like Reaper before making a single solder. How cool is that?!
It can be such a perfect tool if it kept developed further.

A hint for LiveSpice: Don't build and run vref parts of circuits. Just give 4.5V or whatever, straight. The more you simplify the circuit, the better it'll run.

https://www.spectrum-soft.com/download/download.shtm
https://www.livespice.org/
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LuisMerino, thanks for the mid board. It's weird that it's wired different to what I could find or see. Glad it's working at last.

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karul
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Post by karul »

1991 Fender Prodigy (PJ) Bass onboard preamp
viewtopic.php?t=31937

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difesa98
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Post by difesa98 »

Does anyone have the Uni Pre from John East schematics? It seem to be unobtainable :(

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difesa98
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Post by difesa98 »

lietuvis wrote: 16 Jan 2011, 11:39 Hi all, I've been working on onboard preamp. Tried to achieve few things : low noise, non interactive controls, switchable mid frequency @ 250Hz, 500Hz and 1kHz, small footprint. The circuit itself is nothing new, as a base I used GK RB400 preamp EQ section, then just shrunk to what I needed. Mid frequency is selectable by installing different values on capacitors, where 250Hz=103, 500Hz=472, 1000Hz=222. The treble can also be chosen to different frequency lets say for 7kHz capacitor is 222, for 4kHz-103. Bass is controlled @ 60Hz.
To keep the pcb as small as I can I run wires to pots directly from corresponding pads. all resistors mounted standup, caps standard box type 5mm spacing. I've used mc33178 chips, they quite low noise an low current, tried TL062 but boosting highs had too much hiss.
All work done on DipTrace software.
To me this preamp sounds cleaner, more transparent an not harsh when all controls are up, than stock fender 3band EQ.
So here are the files I worked from, any questions wellcome.
This is an awesome preamp! I'm not really into electronics and i was wondering if there is a way to know the capacitor value for changing the frequency for treble and mids? Why it can't be done with bass as well? LTspice is the only way to obtain those value? How many db boost/cut?

Maybe the same reasoning can be extended to this 2-Band Baxandall preamp that use the same IC and have a +- 13 db boost/cut : you will find a .pdf in the video description with different capacitor value for different frequency center, in this case both for bass and treble using 2 caps fo each band:


In this thread the author of the 2- Band preamp tells a way to add a trimpot for an overall gain, can it be done in the same way with the 3-band one?
https://www.talkbass.com/threads/diy-on ... p.1424282/

Thanks for any information! :worship:

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