Tech 21 - Bass Driver DI

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.

Re: Tech 21 - Bass Driver DI

Postby bramofon » 15 Mar 2012, 16:06

I recently built the pedal from the schematic in the first post. I like it a lot. For now I only have a jack in, and a jack out. I'd like to add an XLR and possibly have it run on phantom power. People seem to be saying that this unit doesn't run on phantom power "as is". I wonder what would happen if someone accidentally attached it to phantom power? This happens pretty regularly at the venue I play at now. Some of our equipment will stop functioning while receiving phantom power, other units totally ignore the phantom power "so to speak". I've heard of some units being fried by phantom and I'm nervous to find out what would happen to my latest project if this happened.

Assuming I built the project according to the schematic what would happen? I guess that's my real concern with the device. It would be cool to have the option to run it on phantom, but I'm more concerned about eliminating any hazards at this point.

Thanks.
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Re: Tech 21 - Bass Driver DI

Postby mirebusspesial » 04 May 2012, 03:51

i've build this awesome pedal..and yes, it has sansamp bddi tone color.
but there's still some problem for me...
# treble pot on full (10) there's a 'hiss' noise..any idea how to eliminate this noise?
# drive pot on full (10) blend (0) i hear there's still a little drive.. any idea how to fix this?
# theres no drive from 0-7, the drive starts jump from 7++... any idea how to fix this?

im sorry for my english...i hope you all understand what im talking about :D
help are very appreciated


thanks
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Re: Tech 21 - Bass Driver DI

Postby p.h.etti » 27 May 2012, 11:55

bigbadbob76 wrote:
(...)

I'll also add a ground lift switch by putting a 51ohm resistor and a 10nF capacitor in series between pin 1 of the xlr and ground and connecting the switch between these same points.

(...) noit


Hi,

I want to build a Bass Driver myself and I really want to add a ground lift switch. I'm not sure, if I've understand how to add these parts, so I've drawn a little scheme. I'd appreciate it very much, if somebody could tell me that this is right. :)
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Re: Tech 21 - Bass Driver DI

Postby p.h.etti » 27 May 2012, 12:00

Sorry, i've posted the wrong picture :oops:

This is the right one:
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Re: Tech 21 - Bass Driver DI

Postby freakazoidas » 12 Jul 2012, 09:51

Bump

Does anyvone know where to find a layout with the Mids mod?
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Re: Tech 21 - Bass Driver DI

Postby skylark44 » 04 Oct 2013, 20:45

Sorry to wake a dead thread, but is it possible to add a "distortion" control to a BDI21...by adding a pair of clipping diodes (like LEDs, or IN4001s, etc.) ? If so...what value pot should be used ? Thanx :mrgreen:
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Re: Tech 21 - Bass Driver DI

Postby skylark44 » 09 Oct 2013, 06:18

BUMP...any info? :mrgreen:
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Re: Tech 21 - Bass Driver DI

Postby Gila_Crisis » 02 Sep 2014, 18:36

Do anyone still have the schematic? I have a friend's original unit and I have to repair its switch.
Zwischen Ordnung und Chaos fangt die Musik an
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Re: Tech 21 - Bass Driver DI

Postby MrRundas » 15 Nov 2015, 16:20

Hi guys, I'm new in this forum. I'm an italian guy and I'm finishing my first cycle of electronics studies here in Italy. I would like to built my own bass driver too 'cause I really need it but I can't buy it (neh..). Are we sure the schematic of the first post is the one of the tech 21 sansamp and not the Behringer bass 21? (sorry for my bad english)
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Re: Tech 21 - Bass Driver DI

Postby Leito79 » 19 Oct 2016, 05:54

p.h.etti wrote:Sorry, i've posted the wrong picture :oops:

This is the right one:


First of all sorry about the necrothread... Is this ground lift verified? What are the benefits of it against just putting a plain SPDT switch to connect/disconnect ground? Also does anyone figured out how the line/inst switches work? I´ve built it and it works great, but i´ll like to have the 3 switcvhes options. Had the chance to compare it to my bass player´s Original Tech 21 Bass Driver, going direct to a mixing console and using the XLR output (each pedal used a different desk channel, exact same settings, being switched with an A/B box to try to make the comparaison as neutral as possible), and with all pots at maximum, the original is way hissier/noisier than my build (kinda makes me proud you know)!!! I´ve used 1% MF resistors and Bipolar electrolytics for the 2.2uf coupling caps, maybe that´s the reason why is quieter. My build´s output level is definitely instrument level, compared to the original. I´ll like to add the switch to get LINE level, the volume difference is huge and very useful whrn going direct to a PA or mixing board, I believe the difference is 0dB vs -10dB, any thoughts on how to achieve this? Thanks!
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Re: Tech 21 - Bass Driver DI

Postby mojo4blues » 11 Apr 2017, 22:33

some more necromancy, sorry! I hope my post contributes.

The Tech 21 BDDI can be powered by phantom power,however, phantom power is limited to 10 mA current. The Tech21 BDDI (and VT Bass DI) draw about 6 mA current (according to manual), the Behringer BDI21 draws 25 mA (according to manual and measured)! If the circuit and part-list in this thread is for the Behringer (as the "Triandular Ear" suggests), then phantom power is not possible, if it is the Tech21, then it would work.

Could one of you, who build the circuit from this thread measure the current that is drawn?
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Re: Tech 21 - Bass Driver DI

Postby ericlaw02 » 12 Apr 2017, 06:52

mojo4blues wrote:some more necromancy, sorry! I hope my post contributes.

The Tech 21 BDDI can be powered by phantom power,however, phantom power is limited to 10 mA current. The Tech21 BDDI (and VT Bass DI) draw about 6 mA current (according to manual), the Behringer BDI21 draws 25 mA (according to manual and measured)! If the circuit and part-list in this thread is for the Behringer (as the "Triandular Ear" suggests), then phantom power is not possible, if it is the Tech21, then it would work.

Could one of you, who build the circuit from this thread measure the current that is drawn?

I can't say for the circuit built from the schematic, but on a actual Behringer BDI21, phantom power does not work, as I've (unsuccessfully) tried to implement it before.
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Re: Tech 21 - Bass Driver DI

Postby abakuzam » 30 Apr 2017, 17:13

i have built this pedal based on layout on the first post. And i have a very very low output volume on the normal 1/4" jack output, but currently im testing it with guitar and guitar amp, can it be the problem? on the bypass guitar signal is stays same.
İ checked all the resistor and cap values and cap's orientations , as well as solder job and bridges, jacks etc. these are me voltages;(all pots are in the 12 o'clock, battery voltage is : 9v, switch was on active)

TL074 under the level pot;

1)4.4
2)4.4
3)2.16
4)8.79
5)3.6
6)4.88
7)4.4
8)4.33
9)4.57
10)4.34
11)0
12)4.11
13)4.32
14)4.32

Other TL074:

1)2.38
2)2.38
3)0.76
4)8.67
5)4.3
6)4.3
7)4.3
8)4.3
9)4.3
10)4.15
11)0
12)2.3
13)2.3
14)2.3

Upper TL072

1)4.3
2)4.3
3)4.3
4)0
5)4.3
6)4.3
7)4.3
8)8.61

Other TL072

1)4.3
2)4.3
3)4.3
4)0
5)4.3
6)4.3
7)4.3
8)8.61

i appreciate all the help, thank you.
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Re: Tech 21 - Bass Driver DI

Postby febarbosa » 28 Jul 2017, 12:25

I'm confused if we have a final layout or not...
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Re: Tech 21 - Bass Driver DI

Postby 12afael » 28 Jul 2017, 22:56

Ha! good to find a layout that I did so long ago still in use.

I have seen 14mA as a phantom current in many designs. using TL0XX series the typical current should be arround 16.8mA. If you use TLC226x series it should be arround 6mA.

if I remember correctly it had some strange behaviour (oscilation maybe?) in a extreme pot position. worked ok on normal settings. at the time I thought it was because the original circuit had jfets for switching and those have some resistance.
I never solved that problem.
y
abakuzam: I think you have a problem with IC2 there is some bias problems in one of those stages or the chip is bad. There is a lot of DC coupled stages maybe would be good idea to put a cap and a resistor to Vb in R9 or other point. offset could be a problem. Diz did the reverse engineering I don´t know if it was corroborated with an original tech 21.
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Re: Tech 21 - Bass Driver DI

Postby Sebdeploudal » 20 Mar 2018, 17:34

Hi, I have a my own version of this pedal on vero board (but in french version) here
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Re: Tech 21 - Bass Driver DI

Postby Visualdistortion » 25 Mar 2019, 00:18

Someone know how the parrallel output is wired on the pedal? I would like add it on the programmable bass drive that doesn't have this output.
From what I see, it looks like that the jack seems simply connected to the input... But there is maybe more.
Image

Thanks for your help.
I wanna make it
I wanna make it wit chu
(again and again and again)

French... sorry ;)
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Re: Tech 21 - Bass Driver DI

Postby mojo4blues » 06 Apr 2019, 22:51

Visualdistortion wrote:Someone know how the parrallel output is wired on the pedal? I would like add it on the programmable bass drive that doesn't have this output.
From what I see, it looks like that the jack seems simply connected to the input...

This is exactly how I would expect a "parallel output" to be wired.
Hope it helps.
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Re: Tech 21 - Bass Driver DI

Postby plush » 07 Apr 2019, 10:51

mojo4blues wrote:
Visualdistortion wrote:Someone know how the parrallel output is wired on the pedal? I would like add it on the programmable bass drive that doesn't have this output.
From what I see, it looks like that the jack seems simply connected to the input...

This is exactly how I would expect a "parallel output" to be wired.
Hope it helps.



I'd expect at least a buffer.
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Re: Tech 21 - Bass Driver DI

Postby Disco_Gee » 13 Jun 2019, 08:36

12afael wrote:if I remember correctly it had some strange behaviour (oscilation maybe?) in a extreme pot position. worked ok on normal settings. at the time I thought it was because the original circuit had jfets for switching and those have some resistance.
I never solved that problem.


I'm having the exact same problem. I built one, omitting everything after C20 (which leads to the bypass switch) because I didn't need the balanced output. When the drive and presence pots are turned up to about 3/4 or more, I get really high pitched oscillation type sound. Not sure what's causing it.
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