Baja B K Butler Tube Driver

DrNomis · Post by **DrNomis** » 23 Mar 2011, 07:48

It is very hard to see where that resistor originally was on the PC Board, I can just make out where C2 is....

Kitrae · Post by **Kitrae** » 23 Mar 2011, 12:16

Sorry, R2 on the upper left, not C2. Not much time to edit a post here when you can't type

.

DrNomis · Post by **DrNomis** » 23 Mar 2011, 12:27

Kitrae wrote:Sorry, R2 on the upper left, not C2. Not much time to edit a post here when you can't type .

Lol, I know what you mean mate, they really need to make the edit button a bit more prominent, so that folks like me won't keep forgetting to use it.....

bajaman · Post by **bajaman** » 23 Mar 2011, 19:23

your pictures are not very helpful - I cannot see where r2 is and as for your board pictures - they are too small.

SERIOUSLY - ask Pete

bajaman

DrNomis · Post by **DrNomis** » 23 Mar 2011, 19:53

Kitrae, as bajaman says, you'd probably be better off asking Pete Cornish himself, after all, he did do the mod, so he would be in a better position to explain why he did it, and we can only guess.....

lolbou · Post by **lolbou** » 23 Mar 2011, 20:11

R2 is the 1M input resistor that sets input impedance, then maybe Pete removed it because he uses a buffer before the TD...

R18 is the 470 ohm resistor in the power decoupling network. He might have changed the value for better decoupling or higher/lower V++?

Kitrae · Post by **Kitrae** » 18 Apr 2011, 03:42

lolbou wrote:R2 is the 1M input resistor that sets input impedance, then maybe Pete removed it because he uses a buffer before the TD...

He put a buffer before and after it. Clip R2 off the board. It behaves with buffered pedals much better without it now. Night and day.

fjv2102 · Post by **fjv2102** » 16 Dec 2011, 19:56

Hi everyone,

Could anyone go through explaining the filtering at the last stage?

I am attempting to build this tube driver, but i am confused as to what the filtering is actually doing.

Thanks!
Francisco

DrNomis · Post by **DrNomis** » 16 Dec 2011, 22:47

fjv2102 wrote:Hi everyone,

Could anyone go through explaining the filtering at the last stage?

I am attempting to build this tube driver, but i am confused as to what the filtering is actually doing.

Thanks!
Francisco

Do you mean the filtering in the tone controls or the power supply?....

fjv2102 · Post by **fjv2102** » 17 Dec 2011, 22:57

Tone controls- I see that the 330p and 500klog||220k form a high-pass filter and so does the 100n and 100klog, but with a lower cut-off frequency, is this correct?

So what does the 2 37 n capacitors and the 22k resistor do?

Thanks!

DrNomis · Post by **DrNomis** » 18 Dec 2011, 02:14

fjv2102 wrote:Tone controls- I see that the 330p and 500klog||220k form a high-pass filter and so does the 100n and 100klog, but with a lower cut-off frequency, is this correct?

So what does the 2 37 n capacitors and the 22k resistor do?

Thanks!

The 100nF and 100k Log pot forms a low-pass filter for controlling the amount of bass in the tone, the 22k resistor and the two 47nF caps form a bandpass filter which controls the amount of midrange in the tone....

fjv2102 · Post by **fjv2102** » 18 Dec 2011, 03:40

DrNomis wrote:
fjv2102 wrote:Tone controls- I see that the 330p and 500klog||220k form a high-pass filter and so does the 100n and 100klog, but with a lower cut-off frequency, is this correct?

So what does the 2 37 n capacitors and the 22k resistor do?

Thanks!
The 100nF and 100k Log pot forms a low-pass filter for controlling the amount of bass in the tone, the 22k resistor and the two 47nF caps form a bandpass filter which controls the amount of midrange in the tone....

Dr. Nomis,

The low and high frequency of the bandpass filter are determine by the low-pass part (22 k 47 n) and the high-pass part ( 22k 47 n) which comes out to 154 Hz. Am I looking at this wrong?

Thanks a bunch

DrNomis · Post by **DrNomis** » 18 Dec 2011, 12:42

fjv2102 wrote:
DrNomis wrote:
fjv2102 wrote:Tone controls- I see that the 330p and 500klog||220k form a high-pass filter and so does the 100n and 100klog, but with a lower cut-off frequency, is this correct?

So what does the 2 37 n capacitors and the 22k resistor do?

Thanks!
The 100nF and 100k Log pot forms a low-pass filter for controlling the amount of bass in the tone, the 22k resistor and the two 47nF caps form a bandpass filter which controls the amount of midrange in the tone....

Dr. Nomis,

The low and high frequency of the bandpass filter are determine by the low-pass part (22 k 47 n) and the high-pass part ( 22k 47 n) which comes out to 154 Hz. Am I looking at this wrong?

Thanks a bunch

Something like that, you could think of the tone controls in the BK Butler Tube Driver as a modified Fender/Marshall/Vox tonestack circuit, here's a good website that has some good info, the document to download is the PDF document describing how the P1 circuit works, have a read of the section dealing with how the tonestack works:

http://www.AX84.com

Alternatively you can download this attachment:

Dave78 · Post by **Dave78** » 07 Jan 2012, 00:34

I've got a another dumbe question - What is the 2v5 zener in the bias mod that BK Butler applies - is it a 1N4007 or something?? Thanks.

PokeyPete · Post by **PokeyPete** » 07 Jan 2012, 00:53

Dave78 wrote:I've got a another dumbe question - What is the 2v5 zener in the bias mod that BK Butler applies - is it a 1N4007 or something?? Thanks.

Generally speaking, a diode is a pn junction semiconductor that only allows current to flow in one direction.
However there are several types of diodes, each having a different function and purpose.
The 1N914 and 1N4148 are both examples of high speed, switching diodes.
The 1N4007 is an example of a rectifying diode, typically used to convert AC into DC.
All the above diodes only pass current in one direction, but have different functions.
Now the zener diode has a totally different function. It still only allows current to flow in one direction,
but it, along with a series current limiting resistor, acts as a voltage regulator. You can purchase a zener
to regulate a large number of voltages.
An LED is another diode. This one emits light! It, too, only allows current to flow in one direction.

Dave78 · Post by **Dave78** » 07 Jan 2012, 06:10

Thanks for the reply PokeyPete. I take it then that I will need to source a 2volt 5amp zener diode to make the bias circuit work?

DrNomis · Post by **DrNomis** » 07 Jan 2012, 11:23

Dave78 wrote:Thanks for the reply PokeyPete. I take it then that I will need to source a 2volt 5amp zener diode to make the bias circuit work?

You only need a 400 or 500 miliwatt Zener Diode since the Led doesn't draw much current, a 5 Amp Zener Diode is overkill.....

PokeyPete · Post by **PokeyPete** » 07 Jan 2012, 23:44

DrNomis wrote:
Dave78 wrote:Thanks for the reply PokeyPete. I take it then that I will need to source a 2volt 5amp zener diode to make the bias circuit work?

You only need a 400 or 500 miliwatt Zener Diode since the Led doesn't draw much current, a 5 Amp Zener Diode is overkill.....

It's been a long time since I read through this tread and I only responded to the diode question in a general way.
Since you asked I went back and looked at Baja's Rev 2 schematic. I'm not seeing a zener diode. Where is it?

Dave78 · Post by **Dave78** » 08 Jan 2012, 06:54

It is the BK Butler Tube Driver PCB, and is listed under bajaman's first entry on page 1 of this topic:Tube Driver Bottom Layer parts placement and bias control
https://i197.photobucket.com/albums/aa2 ... cement.png It connects one of the 1K5 resistors to a 470uF capacitor.
It is shown as "add 2V5 zener". I have just noticed that on one of the Butler PCB's the 22uf capacitor and 47K resistor are there for the bias control but not he 2V5 zener.

PokeyPete · Post by **PokeyPete** » 08 Jan 2012, 09:35

Dave78 wrote:It is the BK Butler Tube Driver PCB, and is listed under bajaman's first entry on page 1 of this topic:Tube Driver Bottom Layer parts placement and bias control
https://i197.photobucket.com/albums/aa2 ... cement.png It connects one of the 1K5 resistors to a 470uF capacitor.
It is shown as "add 2V5 zener". I have just noticed that on one of the Butler PCB's the 22uf capacitor and 47K resistor are there for the bias control but not he 2V5 zener.

Dave, thanks for pointing that out. I've studied the board pics and that drawing and I think I have a handle on it.
First off, that zener has nothing to do with the bias circuit. It is not shown on the Rev 2 schematic, but if you print a copy of the
schematic out, I'll try to point out where it goes and what it's doing. I did see an error in that drawing that you showed me.
The side of the zener with the + is wrong. If you look at the picture of the board that shows the diode, you'll see that the black
stripe on the diode is on the side marked + in the drawing....the black strip denotes the cathode (-) on the diode. Remember
that I told you that diodes only allows current to flow in one direction. However, every diode has a point at which if too high a
voltage is applied, it will start to conduct in the wrong direction. For example, a 1N4001 diode is rated at 1 amp, 50 volts. That
50 volts is its PIV or peak inverse voltage ( I believe it is now called PRV or peak reverse voltage ). It denotes the maximum
voltage that can be applied in the reverse direction before breakdown occurs. A 1N4007 is rated at 1 amp, 1000 volts. Now, the
zener is a special case. It is designed to breakdown at a known voltage, and hold that voltage even as applied voltage increases.
The series resistor is chosen to keep the current within the diodes operating range while, at the same time, dropping the excess
voltage from the power source. Because of this unique property, zener diodes are placed in the circuit in the wrong direction.
Instead of the anode (+) on the V+ side as a normal diode, the zener has its cathode (-) on the V+ side. OK, looking at the
schematic:

Can you spot the red LED at the top just left of center? That's where this zener is placed. The cathode of the zener is connected
at that point where the 1k5 (actually read as 1.5k...just like that zener is labeled 2v5 is actually read as 2.5v) connects to the
LED. The anode is connected to ground just like the center pole of that switch going to the red LED. That 1.5k resistor is acting
as current limiting resistor for both the LED and the zener. Typically LEDs have a 2V voltage drop. When the switch is in normal
working mode, the LED is on, and the guitar signal passes through the device. When the switch is off, the LED is turned off,
the middle of the circuit connects to ground, the guitar signal passes straight to the output, and the power is still very much 'on'.
The LED and zener are in reverse directions and parallel. The 1.5k resistor and zener are always 'hot', while the LED is off and
on. I believe that the purpose of the zener is just to help prevent 'pops' when the switch is operated and the LED is switched
in and out of the circuit.

Dave, I think I made that more complicated than I meant to. Sorry 'bout that. If the above doesn't make sense, I'll try to
simplify it. I'm sure most everyone here could find a way to say it in a couple sentences and do a better job of explaining.

Baja B K Butler Tube Driver [documentation]