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Question on DOD FX75 Flanger Schematic

Started by StereoKills, January 10, 2011, 10:27:15 AM

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StereoKills

January 10, 2011, 10:27:15 AM
I'm getting ready to breadboard and design a PCB for the FX75 circuit. Looking through the schematic, I'm having trouble figuring out the purpose of the power section including Q1 and Q2 through the 56uF cap. Can anyone shed some light on this?

Schematic (PDF):
http://www.freeinfosociety.com/media/pdf/1930.pdf
"Sometimes it takes a thousand notes to make one sound"

Govmnt_Lacky

#1
January 10, 2011, 10:51:23 AM
This is just a hip shot so here goes....

Could that portion of the power section possibly be there to INCREASE the input voltage to the BBDs?

It looks as if the Op Amps are fed their VDD BEFORE the input 9V goes through the power section you are referring to. Possibly, this "power section" ups the voltage to 10-11V to increase the working headroom for the BBDs  ???

Just my take.  ;D
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Mark Hammer

#2
January 10, 2011, 12:59:26 PM
Quote from: StereoKills on January 10, 2011, 10:27:15 AM
I'm getting ready to breadboard and design a PCB for the FX75 circuit. Looking through the schematic, I'm having trouble figuring out the purpose of the power section including Q1 and Q2 through the 56uF cap. Can anyone shed some light on this?

Schematic (PDF):
http://www.freeinfosociety.com/media/pdf/1930.pdf

If you're connected with Cornell, go ask Bernie Hutchins.  The man is a god amongst synth designers.

OC16

#3
January 10, 2011, 01:02:08 PM
Reverse polarity protection...

StereoKills

#4
January 10, 2011, 03:04:43 PM
Quote from: Govmnt_Lacky on January 10, 2011, 10:51:23 AM
Could that portion of the power section possibly be there to INCREASE the input voltage to the BBDs?
Interesting thought, do you know how the J111 would accomplish that?

Quote from: Mark Hammer on January 10, 2011, 12:59:26 PM
If you're connected with Cornell, go ask Bernie Hutchins.  The man is a god amongst synth designers.
Alas, I am not. Now that you mention his name though, I did have the pleasure of meeting him before I got into electronics. I was working at the 1-Hour Photo and he brought in some pictures of some synths. Crazy awesome looking stuff!

Quote from: OC16 on January 10, 2011, 01:02:08 PM
Reverse polarity protection...
I think that is what the 1N4001 is for.....

"Sometimes it takes a thousand notes to make one sound"

Govmnt_Lacky

#5
January 10, 2011, 04:23:58 PM
Quote from: StereoKills on January 10, 2011, 03:04:43 PM
Quote from: Govmnt_Lacky on January 10, 2011, 10:51:23 AM
Could that portion of the power section possibly be there to INCREASE the input voltage to the BBDs?
Interesting thought, do you know how the J111 would accomplish that?

I am not an expert on this so I have no idea  ::) I only thought of this because the Boss CE-3 does kinda the same thing except in reverse. It takes a 9V input and sends it through an NPN tranny in some fashion to put +8V on the BBDs.

Like I've said before, I may not be right but I thought I would throw it out there.

Maybe take a look at the CE-2 (another MN3007/MN3101) and see if something similar is done.
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

oldschoolanalog

#6
January 10, 2011, 08:00:24 PM
Somebody has to ask...
Of all the flangers out there, why this one? :icon_confused:
Mystery lounge. No tables, chairs or waiters here. In fact, we're all quite alone.

StereoKills

#7
January 11, 2011, 08:11:53 AM
Quote from: Govmnt_Lacky on January 10, 2011, 04:23:58 PM
I am not an expert on this so I have no idea  ::) I only thought of this because the Boss CE-3 does kinda the same thing except in reverse. It takes a 9V input and sends it through an NPN tranny in some fashion to put +8V on the BBDs.

Like I've said before, I may not be right but I thought I would throw it out there.

Maybe take a look at the CE-2 (another MN3007/MN3101) and see if something similar is done.

I'll take a look here, I've glanced before, but nothing in depth.

Quote from: oldschoolanalog on January 10, 2011, 08:00:24 PM
Somebody has to ask...
Of all the flangers out there, why this one? :icon_confused:

Two reasons:
1) Runs on 9V unlike the Electric Mistress or the Ibanez 301.
2) Call it nostalgia. It was my first effect pedal when I started playing guitar and it was stolen years ago.

Plus no one else has a layout for this circuit yet, I thought it would be nice to get one out there.
"Sometimes it takes a thousand notes to make one sound"

Govmnt_Lacky

#8
January 11, 2011, 08:23:22 AM
Quote from: StereoKills on January 11, 2011, 08:11:53 AM
Plus no one else has a layout for this circuit yet, I thought it would be nice to get one out there.

+1  ;)

Always helpful!
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

StereoKills

#9
January 11, 2011, 08:52:45 AM
The pinouts on the MN3007 datasheet have confused me a bit when comparing to schematics including the part. The pin marked GND (1) on the datasheet, always seems to have the positive power supply to the chip in practice.
"Sometimes it takes a thousand notes to make one sound"

Govmnt_Lacky

#10
January 11, 2011, 09:52:38 AM
Quote from: StereoKills on January 11, 2011, 08:52:45 AM
The pinouts on the MN3007 datasheet have confused me a bit when comparing to schematics including the part. The pin marked GND (1) on the datasheet, always seems to have the positive power supply to the chip in practice.

If you look at the datasheet for the MN3007, the chip utilizes NEGATIVE voltage to operate. The threshold on Vdd is -18 to +0.3V
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

StereoKills

#11
January 11, 2011, 10:28:33 AM
Ah, that makes perfect sense. Thanks!
"Sometimes it takes a thousand notes to make one sound"
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