Fodera, Sadowsky, aguilar, and other bass preamps

Stompboxes circuits published in magazines, books or on DIY electronics websites.
quaternotetriplet
Resistor Ronker
Posts: 377
Joined: 19 Nov 2008, 14:37
Has thanked: 10 times
Been thanked: 4 times

Post by quaternotetriplet »

jay42 wrote:I don't have permission to share the Sadowsky preamp schematic, however, I can describe it to the point that you can develop your own. First off, it's a Blackface preamp done with JFets. The tone stack is scaled appropriately...which is to say, the 100K slope resistor becomes a 10K slope resistor and the capacitors go up by a factor of 10. For a built-in, you've got a 500K audio pot for volume up front instead of after the tonestack. 2x 2N5457 You could add a mid-range pot in lieu of the fixed resistor, which is 750 ohms instead the 960 you would expect. I've been told that the Aguilar two-knob built-in is the same circuit, but I can't confirm it.

I sort of think it's ironic that some bassists will say, "I'm all modern here with active electonics and all. I need a flat pre-amp." They're really just playing through a Fender.
will you send it to me please.

User avatar
Silent Fly
Resistor Ronker
Posts: 425
Joined: 27 Feb 2008, 23:40
Has thanked: 24 times
Been thanked: 32 times

Post by Silent Fly »

Based on the indications supplied. It should be correct:
Sadowsky Preamp (v.1.1)
Sadowsky Preamp (v.1.1)
"Remember - all I am offering is the truth, nothing more". Morpheus

User avatar
lietuvis
Breadboard Brother
Posts: 101
Joined: 27 Sep 2008, 10:01
Location: Coalville,UK
Has thanked: 80 times
Been thanked: 57 times

Post by lietuvis »

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.
Attachments
ONBOARD PREAMP SCH PCB.zip
(8.57 KiB) Downloaded 238 times
ONBOARD PREAMP PCB.jpg
ONBOARD PREAMP SCH.jpg

User avatar
lietuvis
Breadboard Brother
Posts: 101
Joined: 27 Sep 2008, 10:01
Location: Coalville,UK
Has thanked: 80 times
Been thanked: 57 times

Post by lietuvis »

this is how it looks ...
Attachments
P1020918.jpeg
P1020916.jpeg

roseblood11
Tube Twister
Posts: 1862
Joined: 23 Aug 2008, 15:21
Has thanked: 344 times
Been thanked: 298 times

Post by roseblood11 »

This is a great preamp:
http://www.albertkreuzer.com/preamp.htm

For onboard use it should be modified a bit.
-Most (all...) of the switchable options and the clip indicator can be left out
It´s still a bit overkill...
-Instead of symmetrical power supply, a voltage divider could be used. (18V from two batteries will give more than enough headroom)
-the original has a +/-15V power supply. But the JFET´s only see Vref (0V)..+15V (maybe to protect them - 30V would be their maximum rating). With a 18V supply, this could be changed, to increase the headroom.

andregarcia57
Cap Cooler
Posts: 458
Joined: 16 Nov 2008, 16:42
Been thanked: 75 times

Post by andregarcia57 »

hello how are you?
I'm in need of schematic "Sadowsky Outboard Bass Preamp"
you can send me?
Grateful
andré

User avatar
Silent Fly
Resistor Ronker
Posts: 425
Joined: 27 Feb 2008, 23:40
Has thanked: 24 times
Been thanked: 32 times

Post by Silent Fly »

andregarcia57 wrote:hello how are you?
I'm in need of schematic "Sadowsky Outboard Bass Preamp"
you can send me?
Grateful
andré
I don't know what you need it for but if you want build one, in theory if you use this schematic and you add a balanced line driver it should be equivalent to the outboard version...
"Remember - all I am offering is the truth, nothing more". Morpheus

marsbel
Posts: 13
Joined: 20 May 2009, 10:29
Has thanked: 4 times

Post by marsbel »

Silent Fly wrote:Based on the indications supplied. It should be correct:
Sadowsky-pre (1.1).gif
Thanks Silent Fly!
Somehow this reminds me vaguely of the Acoustic 360 tone stack. I don't know why...

Jay42: can you confirm SF's schematic?

Rgdz,
Mark

t-mibik
Posts: 5
Joined: 29 Aug 2008, 09:25
Been thanked: 2 times

Post by t-mibik »

Marsbel, just put the two 1meg resistors to ground unless Vref an it'll be ok :wink:

EDIT // you can also remove the 2nd source capacitor for lower distortion, and the 100n cap after the tone stack.

marsbel
Posts: 13
Joined: 20 May 2009, 10:29
Has thanked: 4 times

Post by marsbel »

t-mibik wrote:Marsbel, just put the two 1meg resistors to ground unless Vref an it'll be ok :wink:

EDIT // you can also remove the 2nd source capacitor for lower distortion, and the 100n cap after the tone stack.
Thanks.
Do I have to change something when I run 18V? I think the Sadowsky outboard preamps run 18V.

Regards,
Mark

t-mibik
Posts: 5
Joined: 29 Aug 2008, 09:25
Been thanked: 2 times

Post by t-mibik »

no you don't have to change anything.

i think you can use log pots.
you will have a flat sound when bass and treble are CCW because this tone stack is "boost only", so there's no need of center detent pot.

jay42
Posts: 33
Joined: 06 Aug 2010, 01:36
Been thanked: 2 times

Post by jay42 »

marsbel wrote:Jay42: can you confirm SF's schematic?
it's accurate.

marsbel
Posts: 13
Joined: 20 May 2009, 10:29
Has thanked: 4 times

Post by marsbel »

jay42 wrote:
marsbel wrote:Jay42: can you confirm SF's schematic?
it's accurate.
Thanks!
I never expected such a simple circuit. I knew it was Fender tone stack derived, and it's not linear at all, but it makes a bass sound so good.
Parts are ordered.

Brink
Degoop Doctor
Posts: 307
Joined: 11 Jul 2009, 21:22
Location: NY
Has thanked: 2 times
Been thanked: 18 times

Post by Brink »

Silent Fly wrote:Based on the indications supplied. It should be correct:
Sadowsky-pre (1.1).gif
Is that really the way the volume pot is wired? The way I'm used to seeing them would be with lug 3 to input, lug 2 to C4, and 3 to Gnd.

quaternotetriplet
Resistor Ronker
Posts: 377
Joined: 19 Nov 2008, 14:37
Has thanked: 10 times
Been thanked: 4 times

Post by quaternotetriplet »

im looking for american deluxe preamp. anyone?

quaternotetriplet
Resistor Ronker
Posts: 377
Joined: 19 Nov 2008, 14:37
Has thanked: 10 times
Been thanked: 4 times

Post by quaternotetriplet »

where can i get center detent pots?

thanks josh

ezugaru
Breadboard Brother
Posts: 109
Joined: 15 Feb 2010, 03:58
Has thanked: 36 times
Been thanked: 3 times

Post by ezugaru »

quaternotetriplet wrote:
jay42 wrote:I don't have permission to share the Sadowsky preamp schematic, however, I can describe it to the point that you can develop your own. First off, it's a Blackface preamp done with JFets. The tone stack is scaled appropriately...which is to say, the 100K slope resistor becomes a 10K slope resistor and the capacitors go up by a factor of 10. For a built-in, you've got a 500K audio pot for volume up front instead of after the tonestack. 2x 2N5457 You could add a mid-range pot in lieu of the fixed resistor, which is 750 ohms instead the 960 you would expect. I've been told that the Aguilar two-knob built-in is the same circuit, but I can't confirm it.

I sort of think it's ironic that some bassists will say, "I'm all modern here with active electonics and all. I need a flat pre-amp." They're really just playing through a Fender.
will you send it to me please.
So for the MID control I just add another 25K Audio pot in place of the 750 ohm resistor?
You are not dumb if you are a good person, is just that dumb people don't recognize the good things.

ezugaru
Breadboard Brother
Posts: 109
Joined: 15 Feb 2010, 03:58
Has thanked: 36 times
Been thanked: 3 times

Post by ezugaru »

ezugaru wrote:
quaternotetriplet wrote:
jay42 wrote:I don't have permission to share the Sadowsky preamp schematic, however, I can describe it to the point that you can develop your own. First off, it's a Blackface preamp done with JFets. The tone stack is scaled appropriately...which is to say, the 100K slope resistor becomes a 10K slope resistor and the capacitors go up by a factor of 10. For a built-in, you've got a 500K audio pot for volume up front instead of after the tonestack. 2x 2N5457 You could add a mid-range pot in lieu of the fixed resistor, which is 750 ohms instead the 960 you would expect. I've been told that the Aguilar two-knob built-in is the same circuit, but I can't confirm it.

I sort of think it's ironic that some bassists will say, "I'm all modern here with active electonics and all. I need a flat pre-amp." They're really just playing through a Fender.
will you send it to me please.
So for the MID control I just add another 25K Audio pot in place of the 750 ohm resistor?
P.S. for the sadowsky preamp, are the values of C6 (5uF) and C7,C9 (50uF) correct??? they seem hard to find :s
You are not dumb if you are a good person, is just that dumb people don't recognize the good things.

Victor Nery
Posts: 47
Joined: 18 Nov 2011, 04:29
Has thanked: 28 times
Been thanked: 4 times

Post by Victor Nery »

Greetings,

I think you could try 47u and 4u7 without much problems.

enakar
Posts: 14
Joined: 23 Nov 2010, 17:30
Completed builds

Orange Squeezer, Wolly Mammoth (modded with blend knob), Demeter Compulator, Sadowsky-like bass preamp with integrated AMZ Super Buffer

Location: Finland
Been thanked: 1 time
Contact:

Post by enakar »

Hi,

Thanks for all info, I just built the "Sadowsky"-preamp (based on Silent Fly's layout, with some modifications). It works great!

Some notes/modifications:

- 2.5n (in tonestack) => 2.2n
- 5u output cap => 4.7u (still electrolytic)
- 750R (tonestack to gnd) => 2k lin pot (mid control)
- Moved the 500k log Level control to between the tonestack and the second amp stage
- Skipped the 300p (second jfet gate to gnd) because I first had a 330n due to a mislabled bag, which resulted in a very noticeable hi cut. Took me a while to debug, as I first suspected the tonestack, but when I found the problem, I just removed it, works fine without.
- I run the preamp on 18V
- Another resource for a very similar preamp can be found here: https://www.diystompboxes.com/smfforum/i ... ic=73173.0
- Built it all on vero

So far so good, it sounded great with my Vox headphone amp. But when I took it to rehersal, and plugged it into my PA Power Amp i use for head (Peavey IPR 1600, drove it with a Sansamp VT Bass before), there was lots of noise and very low output. Some investigation proved the output impedance of this preamp is much too high for my power amp (which takes max 7.5kohm).

So i found a rather simple solution. I built an AMZ super buffer (this one, used OPA2134 for opamps) into the same casing, right before the output jack (so that the buffer is on even if the preamp is bypassed). This was a very good solution. The preamp is now completely noise free, and the output inpedance is so low that you can use this preamp as a headphone amp! The only thing that's missing is balanced DI-out, but I could never fit a DI tranny (or anything else for that matter) into this box.

My Sansamp VT Bass goes into the bottom drawer now :)

The preamp is the top left one. I didn't put in a footswitch, since it's always on, but there's a bypass switch on the back side, should I want to use it as buffer only:

Image

/Fredde

Post Reply