MI Audio - Blues Pro

ponq · Post by **ponq** » 02 Feb 2008, 11:19

Does anyone have the schematic for this one? I've been asked to implement the 'fuzz' mod by removing a 1N4001 diode. I'd like to understand the function of that diode.

If there's a schematic available, much appreciated! Else I'll probably have a chance to trace it myself (and post here ofcourse)

Post by **modman** » 02 Feb 2008, 13:37

I readthis thread (in Dutch) and wondered, did this mod come from looking at the difference between the two boxes on gut shots?

If you look closely, you see you could do with a SPST switch, as the second lug isn't used in the SPDT. But don't understand the function of the alleged 1A in the front of this IC ovedrive circuit.

Couldn't you provide some close ups from your unit?

thanks

ponq · Post by **ponq** » 16 Feb 2008, 12:47

I've had a chance to look at the guts of the Blues Pro while preparing to mod it with the 'fuzz-mod'.

The picture above shows Rev 1.1. My version is Rev 1.0. From what I can tell the difference seems to be the Big Green Cap just below the read arrow above. It's a polarized cap in Rev 1.0 (the orange one).

Very well, some pics:

Outside:

Inside:

Top of PCB

Bottom of PCB:

And the schematic. It's my first trace... so bear with me, it's prone to errors:

tuemmueh · Post by **tuemmueh** » 16 Feb 2008, 12:56

Great, thank you very much!

ponq · Post by **ponq** » 16 Feb 2008, 14:54

You're welcome. Hopefully the schematic is correct.

Here's a pic of how I modded it:

Push-pull 250k A replaces the gain pot. Push: normal, pull takes the 1N4004 diode out of the circuit.

Nothing really special, Just louder and harsher.

doh · Post by **doh** » 17 Feb 2008, 16:01

Hey Ponq and Modman,

I described the mod on gitaarnet forum,

I have the version with fuzzmod and a friend of me has the version without the fuzzmod.

By putting the fuzzmod in his blues pro, I just looked at the differences between those two boxes, and didn't look at the schematic.

pakalolo · Post by **pakalolo** » 22 Feb 2008, 09:53

Hello,

Comparing the schematic to other ODs, something puzzles me.

Is C4 really connected to ground and not to VR ?

JHS · Post by **JHS** » 22 Feb 2008, 12:10

C4 can be connected to ground or VREF. If it's connected to ground the sound is more loose with slightly softer, more fuzzy distortion.

IMHO 22uF is a bit oversized.
I recommend to replace C4 with a 220nF-1uF MF or tantal electrolytic cap for a clearer tone.

JHS

pakalolo · Post by **pakalolo** » 22 Feb 2008, 12:34

Thanks !

I learn something new everyday on this forum.

madbean · Post by **madbean** » 22 Feb 2008, 14:14

There was an interesting topic on diystompboxes recently about the differences in connecting frequency caps to ground or vref. I think RG and our old pal Jay Doyle had some good explanations.

Seljetnoma · Post by **Seljetnoma** » 28 Apr 2008, 10:35

Hi,

If I want to reduce some mids in the blues pro, which cap/resistor should I change?
And what change for some more bass? ( not on the 1st stage or input )
For the sake if not too much bass I like the changes around the 2th opampstage.
Anyone can help me out? I'm still learning here haha.....!!
Anyway, thanks a lot.
Regards,

Frank

lynessmy · Post by **lynessmy** » 29 Apr 2008, 03:03

Looking at the schematic....does Blues Pro has 3x 1n4148 diode in forward clipping and 1x 1n4001 in the reversed?
i asked this because there is a -3 after the 4148. Is that literally mean 3x4148?

Seljetnoma · Post by **Seljetnoma** » 29 Apr 2008, 05:42

No there's only one 1n4148 and one 1n4004 which is switchable to make the fuzz mod.

ponq · Post by **ponq** » 29 Apr 2008, 07:34

Nope, just 1 1N4148. The -3 says something about the package I used, related to the spacing of the leads of the diode.

Has anyone built the Blues Pro with this schematic?

sevinisthenumber · Post by **sevinisthenumber** » 07 Jan 2009, 05:00

anyone have a layout?

flood · Post by **flood** » 07 Jan 2009, 05:07

if ponq uploads the eagle schem file (.sch), i can do a PCB...

of course, i could do it copying from the image, but it would save me a wee bit of effort, i'm lazy, like everyone else

EDIT: sorry, just saw the date of the last post before yours... been nine months, high time that we deliver this baby!

I'll get cracking soon... will post once i have something ready.

PmCimini · Post by **PmCimini** » 07 Jan 2009, 07:05

I like those knobs, know where I can get some?

flood · Post by **flood** » 07 Jan 2009, 07:43

and here we go....

PCB is ready to transfer, it's quite cramped but then i tried to emulate the space saving PCB of the original.

if there are any errors in my schematic, do let me know. please throw your brickbats gently, i'm new at this.

i've learned a lot from this forum, hope i can do my bit more often...

rexnomad · Post by **rexnomad** » 11 Jan 2009, 19:42

I'm real interested in the tone control in this circuit. Can anyone tell me what's going on there. Is that some kind of notch filter in the feedback loop? How can I calculate what frequencies are being affected? Any info is helpful...thanks.

mattpas · Post by **mattpas** » 12 Jan 2009, 14:42

modman wrote:I readthis thread (in Dutch) and wondered, did this mod come from looking at the difference between the two boxes on gut shots?

If you look closely, you see you could do with a SPST switch, as the second lug isn't used in the SPDT. But don't understand the function of the alleged 1A in the front of this IC ovedrive circuit.

Couldn't you provide some close ups from your unit?

thanks

Here's the dutch text translated:

The mod: Dear lords & ladies, Fuzz-switch the mod are very simple carry out mod. Everything what you have necessary are: 1 x MI audio Blues pro 1 x SPST on-on switch 1 x soldering bolt 1 x drilling machine with correct diameter (?) 1 x soldering tin 2 x wire Fuzzmod: The possibility for and eliminating 1N4001 a diode (in my Blues pro ?drunk? 1N4001, last for a friend and those done had a diode with what other signs, but the impact sound identically with the fuzzmod change you in principle nothing to your sound when the switch on off stand! This is the large black diode with a grey (?) for polarity.

There sit two of these diodes on the (?). The one which we will use for the fuzzswitch are the diode which sits beside IC. (pay attention to there sit two diodes, you must therefore that have like on the above blade. The diode sits with the grey (?) up and runs it post down. Now it is the intention the point where the diode runs down snip off him. The post that down runs (therefore that piece without diode) can snip off you, but let sit also quietly. Now it is best that you the switch in your (?) places and as from the diode (therefore that black thing with that grey randje) a wire solders to the switch.

Do this to one of the outer posts of the switch. Now you solder a wire as from middle the post of the switch to middle the pot of the Gain pot meter. You can solder these ordinary on the pcb to middle the pot of Gain-pot fixed. Of the outer post of SPST-switch remain open therefore. Then it is now test time or your Blues pro with fuzzmod works!

(the photograph which I use above is of analogguru, on or other manner got I no sharp photograph of my own Blues pro) The implementation of the mod is on own risk, I do not feel myself responsible for broken pedals!