Sansamp Bass Driver distortion only

[ghiekorg]

Hi guys! It's been a while since I did my last pedal and today I thought about something:
I built a DOD FX91 and a b3k but the first has a weird distortion on high notes and the second doesn't go distorted enough for my taste. I was then thinking about taking a Sansamp Bass Driver and remove everything leaving just 3 knob: blend, volume and drive (and getting rid of the DI too), as I use a GEB7 for the EQ, so I can fit it in a 1590B.
Can someone help me with it? I have no idea on how to modify a circuit 
I found this http://techniguitare.com/forum/realisation-montage/bass-t15242.html
and this https://www.....org/viewtopic.php?f=1&t=422&start=60
Any suggestion is, of course, well accepted (also the ones saying "buy a behringer BDI21!") 
Thank you

[strungout]

Hey,

A SABDDI clone schematic:

First you'd have to decide how much 'presence' you want, so you can hardwire it without a pot.
Then, I would cut the tone section (bass and treble stage) and connect the level knob's wiper (center lug) to the 2.2uF cap that goes into the output op amp's non-inverting (+) input (U3:D), keeping the 10k from Vref.
You can ommit everything from the 22K connected to U3:D'S inverting output. The DI part. Remove that.

I think that would do it. But, you can try it on a breadboard...

[ghiekorg]

Thank you strungout
is it like that what you mean? I am kinda ignorant about mods.



I just have some questions, if you wanna help me:
1. Is it correct how I removed the balanced output?
2. I have set the presence halfway to 50k as the pot is 100k. does it make sense without trying it out?
3. I can't remember something: the VCC/2 they all have to be connected to each other, right?
4. What about the VCC, they also have to be connected? I just don't understand what's the scheme on the upper right corner with the C33 and those 4s and 8s and 11s 😔
5. I forgot to say: I wanna remove the switch too. In the schematic I just removed it, but I guess I would have to change something else too or at least connect R47 and C21.

Thank you for your help!

[anotherjim]

I believe the opamp used for the distortion stages is a TLC2274. A CMOS opamp & very different from TL074.

[Rob Strand]

There was a stripped down version put up but it seems to have disappeared from the web.
I managed to get this slightly shrunken schematic,

I agree with Jim about the opamps.

[strungout]

Thank you strungout
is it like that what you mean? I am kinda ignorant about mods.



I just have some questions, if you wanna help me:
1. Is it correct how I removed the balanced output?
2. I have set the presence halfway to 50k as the pot is 100k. does it make sense without trying it out?
3. I can't remember something: the VCC/2 they all have to be connected to each other, right?
4. What about the VCC, they also have to be connected? I just don't understand what's the scheme on the upper right corner with the C33 and those 4s and 8s and 11s 😔
5. I forgot to say: I wanna remove the switch too. In the schematic I just removed it, but I guess I would have to change something else too or at least connect R47 and C21.

Thank you for your help!

Yeah, that'S what I meant, but you can remove everything from R30 down. If you remove the switch, you don't need R47 and C17. It should work as drawn. The 50k pot for presence will work.

Yes, Vcc/2 all connect together. And then all the Vcc together.

[ghiekorg]

I believe the opamp used for the distortion stages is a TLC2274. A CMOS opamp & very different from TL074.

Thank you, I read somewhere that the behringer uses 074, while the real tech21 uses TLC2274. Probably that's why, I guess.

There was a stripped down version put up but it seems to have disappeared from the web.
I managed to get this slightly shrunken schematic,

I agree with Jim about the opamps.

Thank you very much! That seems cool. I am just not sure how to get rid of bass and treble control... 😕

Yeah, that'S what I meant, but you can remove everything from R30 down. If you remove the switch, you don't need R47 and C17. It should work as drawn. The 50k pot for presence will work.

Yes, Vcc/2 all connect together. And then all the Vcc together.

I did a new schematic to clean it up. Should be correct, right?



Also do you think I can use just 2 TL074 (leaving one opamp unused)?

Thanks

[Rob Strand]

Thank you very much! That seems cool. I am just not sure how to get rid of bass and treble control... 😕

The simplest way to do that would be to connect C20 back to the output of U1:B.   In this case stages U1:C and U1:D could be completely removed.

If you wanted to strip it back further it's possible to remove the U1:B stage but you will lose the buffered output.   There's not a lot gained in removing U1:B anyway since that leaves an odd number of opamps, you might as well leave it in.

[anotherjim]

I come back to the opamp choice. The only distortion is in overdriving the opamp in the Presence and Drive section. It's here where most opamp types differ in guitar audio. If you want the Sansamp sound you need the same opamp. Behringer use a TL064 in their clone and it sounds like sh!t if allowed to clip. I don't like the sound of TL072/074 clipping either, although some apparently do. The tone controls use the same opamp, since it can boost, it can also distort. Hence they used a quad chip, the 4th being used for the 1/4" jack output driver.

CMOS opamps tend to be slower & noisier compared to bipolar and JFET input ones so not ideal the for rest of the circuit. At the time they designed the BDI, they used the RC45xx series for input and XLR output line drivers as they were a good choice then (still are really).
The other part of the BDI sound is in the signal path arrangement that includes the Ampeg SVT mids tone and speaker eq simulation in RC filter networks. This will affect the tone of any distortion. However, I think it's still worthwhile to use distortion from CMOS opamps, and a dual TLC2272 would be the choice but if you socket the chip, you can try many types.

[ghiekorg]

So.. I just finished breaboading the Lite version without the treble and bass controls. I don't know why I can't upload pics atm...
Anyway, here is some notes:
- I used the opamps I had: 2x 072 and a 5532. I don't mind the sound, but I will try to find one or two 2274 (can a 2264 be ok? I checked the sheets but it's greek fro me 😕. Does it make sense to use 2 of them and use just half of one as I have 6 opamp instead of 8?)
- The switch kinda "deactivate" the knobs, even the level one. When disengaged I kinda hear the clean sound. So I removed it to have one problem less to solve  I just remove C17, R27b and the switch and connected R27 to R28
- The drive knob is kinda uneven: it's a mild overdrive till 75% then a good overdrive till 95% and a distortion only the last 5%. Shall I use a different pot or it could depend on the opamp?

Today I will start to prepare the PCB

[strungout]

I used a bunch of duals for my build, 4558. The drive sucked at higher levels. Then, after what Jim suggested, I remembered I still had TLC2262 (also CMOS) from building the guitar version of the sansamp. Popped one in the drive stage and the distortion is way better, smoother, less aggressing (as opposed to aggressive). Put one in the tone section while I was at it. Can't say I notice anything very different. Not to say there isn't any change. I'll play it more later today and see.

@ghiekorg: If you can, I think it's worth getting the TLC2274.
When you have an unused amp in your quad op amp, tie its output and inverting (-) input together, and ground (or tie it to Vcc/2) its non-inverting input (+). I think that's the proper way to 'terminate' it.
Your schem looks good.

For the Drive pot, you could use a reverse-log (C-taper), the clean part will pass quicker as you turn the pot and then slower past 50% into distortion, allowing you to set it more precisely.

[ghiekorg]

Ok, then I guess I will have to find some 2272... I don't know how easy it is. I will have a look around, thanks.

About the unused side, you mean like this?


I made a first draft of the PCB, I need to double check it and be sure it fits a 1590B or max a 125

I will post it here when done, for sure there will be a jumping cable in the middle of the board and some jumpers. As an idiot I started from the beginning instead of the ICs

[strungout]

About the unused side, you mean like this?

Yup, you got it.

[ghiekorg]

Hi everyone 😊
so... I prepared a PCB, double checked it and it matched the schematic. Do you see any major errors?
Of course the IC are only 2 but I didn't have a 14 pin IC so I used 2x 8 pin overlapping as reference. and I have a horrible jumping cable and 3 jumpers unfortunately



I used the lite version and I removed the red part and connected the green ones. Should it work, right? I just hope won't be too noisy :/

[ghiekorg]

Hi everyone
I am having, as ALWAYS, problems with the delivery. After a week they told me they don't have the 2.2uF (C20) i need and they will send me polarized ones. I am not sure in which direction i should put it. I see R27 goes to ground, shall i put the - of the cap facing R27 while + faces the out put of the opamp?
Thank you

[anotherjim]

Yep, C20 negative points to 0v via R27. A polarized cap will be fine like that.

Hate to say it, but TL07x opamps should not have inputs tied to the same voltage as the negative supply pin, which is 0v in this case. You should use VB.

[strungout]

Hate to say it, but TL07x opamps should not have inputs tied to the same voltage as the negative supply pin, which is 0v in this case. You should use VB.

My bad.

Found this on how to properly configure unused opamps: https://www.ti.com/lit/an/sboa204a/sboa204a.pdf?ts=1624474825341&ref_url=https%253A%252F%252Fwww.google.com%252F


@ghiekorg: are you using DIYLC? If so you can double-click on the opamp and there's a dropdown list for the number of pins you need, instead of using two 8-pin opamps.

[ghiekorg]

oh, I see... can someone help me understand how to then "close" the opamp? a resistor between - and output and another resistor to ground?

yes I it and I didn't think about doing it, thank you haha

[anotherjim]

There are extremely cautious schemes for unused opamps, including a feedback resistor for out to -input and a resistor from +input to the reference voltage. In practice, it would be a very nervous opamp that won't be fine with the output wired to the -input and the +input wired to the reference voltage or any voltage source that is within the allowed input voltage limit of the opamp.
If the unused +input is too far away from the existing VB, there's no reason you couldn't make another VB voltage divider closer to the chip provided you can fit the necessary pair of voltage divider resistors to a convenient 0v and +supply. All you need are the resistors, there's no point adding a capacitor and 100k would be a good value to minimize wasting supply current.

Actually, there is a cheat, and that is to instead of using Vb to tie any unused +input pins to the output of a nearby opamps output pin. A used opamp in the same chip will be running about the Vb voltage or within the allowable range. You still add the connection between the unused output and the unused -input pins. This means the unused opamp will be copying the output it's tied to for no purpose, but who cares?

[ghiekorg]

Thanks anotherjim. Do you mean like that? Did I get it right?