MonGoose...Gottfried Divos ? Marty Mart ?

[petemoore]

I'm working off of a schematic of the RM MOngoose Fuzz, but now I can't find the little thing.
 I'ts provided by Anubics copyright 2005 by Gottfried Davis.
 ...Now I read the fine print...says: "Schematic traced from pictures posted by Marty Mart.
 Anyway I've got a Mongoose board 'started' but...
 Pin 1 and 8 are compensation pins, 4 is Gnd , 7 is V+
 Pin 6 output .72V
 Pin3 +input  .68V
 Pin2 -input  1.28V
 I looked it over a few times, and then read down where it says it's a copy of a tracing of pictures...oops...my oops, I don't know that it's right or if it is right.
 I'm getting gated Fuzz, the Fuzz knob has a little bit of gain effect, those voltages are what's causing the gateing.
 Any help trying to help me figure out this day's board would be greatly appreciated, I would guess I'm alone trying a board off this schematic, I sure wish I could just post a link...
 The schematic shows no voltage divider for opamp biasing.

[analogguru]

I'ts provided by Anubics copyright 2005 by Gottfried Davis.
...Now I read the fine print...says: "Schematic traced from pictures posted by Marty Mart.

where is the problem ? it is easy:

For the reason that i know the guy who draw the schematic very well i can explain it to you:

Marty Mart posted inside pictures of the mongoose fuzz in a different thread.
This guy who is mentioned is the copyright-holder (only) for the specific schematic drawing because (he traced and) drew it.
And for the reason that I know him better than my own brother or sister, he allowed me, to post this schematic under the nick analogguru.


Maybe for this reason I also can help you out:

Pin 1 and 8 are compensation pins, 4 is Gnd , 7 is V+
Pin 6 output .72V
Pin3 +input .68V
Pin2 -input 1.28V

The Schematic is a 100% tracing of the pictures of Marty Mart of a "real" unit.

Pin numbering is ok.

but looking at your voltages, your IC must have been brocken, or you messed up -input with +input.  It is never possible, that the DC-voltage pf the -input is higher than the voltage at the output, because it is fed from the output via resistor r8.  So there must be something wrong.

As mentioned in the thread where the schematic has been posted first, the DC-bias of the Opamp is directly influenced by the collector-voltage of Q1.

It can be, that the DC-voltage is not half the supply voltage, and this will influence the symmetry of the signal at clipping levels.  But 1,28 V really is to low for the collector voltage, maybe something wrong with the transistor stage.

analogguru

[petemoore]

Ahhh, I'll check a few more things out !!!
 Thank's Analoguru !!

[MartyMart]

Pete, I built one from looking at my original/analogguru's schemo on vero, which I'll post up "drawn" tomorrow.
It works great, and my "subs" are listed on another thread, also an mp3
of this working version.
The most important being a TL070 rather than LM308.
You must have a wiring error, as analogguru has said, 9v goes direct to
pin 7 and VCC is from the network of 47k's/ 22uf to ground and the 3904.

Hope you get it going tomorrow ?  

Marty.

[petemoore]

Yupp...I found the problem...
 I used two 330k's seriesed where it says 680k, but when measured [from input cap socket to Gnd] I got a reading of ... 19.XX MEG !!!
 So, I untied the two resistors, stuck a resistor lead into the spare input socket lug, twisted the other end around the 330k to ground ... that brought the bias voltages up real nice.
 Kinda wierd, I'm using a round NTE941 Opamp, and had it right wired the first time...lol.
 So ... All is good ...thanks for the help !
 I'll correct the base to ground resistance..

[MartyMart]

THERE ARE SOME DIFFERENCES ON THE ORIGINAL MONGOOSE !!!

The 680k is a 640k
The 47k's are both 42k's.....
I'm not sure if this is "within tolerance" but thats what the coloured bands
are saying ... ??

Marty.

[analogguru]

@Marty

There is no reason to get nervous.... it´s only the mongoose fuzz.  :roll:

Maybe you should a vist a doctor to control your eyesight, or the easier way ist to look at:

http://www.xnview.com/

and download a freeware graphic programm.

With this program you can very easy improve even bad and dark pictures from digitalcameras.
There is a menue and unter picture adjust even a child can control with three sliders the brightness, contrast and gamma.

When you do this, then your picture can look within seconds like this:



So...how you can see now, the 680k IS a 680k resistor : blue, grey, yellow.

Now lets have a look at the 47k resistors:

when you compare the color of the second ring to the color of the 22K in top and the 2M2 on the right, you will see, that there is more blue content than in the color of the mentioned resistors.  This let us assume that this color is not red, it could be red-blue or violett.  Violett stands for 7, so this resistor would be 47k.

So, as can see in the picture, these resistors have a gold ring, for this they are 5% resistors, metal-film, produced by Philips until the mid 90s.  When these resistors are 5% then the value of the resistor can only be 39k, 47k, 56k, 68k and so on....

Philips also produced with the same base color 2% resistor marked with a red ring for the tolerance.
Even then the resistor could only be: 33k, 36k, 39k, 43k, 47k, 51k, 56k and so on, but NEVER 42k.

so, you can cool down now, and use with good conscience 680k and 47k resistors.

Have fun,

analogguru

[MartyMart]

Analog, thanks for the "eyesight tutorial" !!
I put the pictures into Photoshop, so that's covered, here's what happened....
Using the "on-line" 4/5/6 band resistor calculator and entering my "version" of the colours, it gave me values of ..... 640k and 42k !!!
But you're correct, it can't possibly be those values at those tolerances :roll:
I guess I should stop using that calculator then .......  :oops:

No worries,
Marty.

[petemoore]

These 1/2w '330k's'...measure 'funny...
 I have one in there measures about 660k...the other one...anywya, my voltages look good, and the Mongoose is Goosing bigtime on the 'ol amp input.
 I'm getting a real cool 'compression type thing, I'm calling it a "Bias Bounce'...it sounds like the bias is swinging back and forth, and sounds as though it is hitting something like rail or 'near rail'...snazzy effect.

[analogguru]

I have found a mistake in the V1.0 schematic.

Sorry about that mistake in the mongoose schematic, R6 should be 22k instead of 1k.  The mistake comes from the automatic-value function in my program.

The correct schematic you can find at the original link:

http://forum.musikding.de/attachements/RogerMayer_Mongoose.gif

Please delete earlier versions than this (1.1) to avoid confusions.

analogguru