RM "Mongoose" Fuzz photo's

[brian wenz]

Hello Hello--
     Good deal Marty!!   Thanks for the research......I guess one of these days I'm going to have to get some op-amps!
Brian.

[brian wenz]

Ooopss-
  Thanks to Torchy and everyone else, too!
Brian.

[MartyMart]

Hello Hello--
     Good deal Marty!!   Thanks for the research......I guess one of these days I'm going to have to get some op-amps!
Brian.

Hello Hello-- Brian,
Do yourself a favour and get a few, you wont regret it !!
~BTW~ TLO70 sounds "the buisness" in this circuit, better than the 308
IMO.

Marty.

[Alpha579]

great marty, yeh, the sound clips at custom-sounds sound fantastic!

[WGTP]

IIRC the Rat doesn't have an input stage before the op amp, but a buffer stage afterword to isolate the tone control from the output impedance that varies with the output control.  Some folks claim to have seen a version with an input buffer though.

I'm curious as to why you would use a discrete input stage, rather than using a dual op amp.  
:shock:

You could put the Rat tone control and output buffer stage at the end if you wanted a tone control.  

[mlabbee]

I tried Torchy's vero layout and had some problems - has anyone else made it work?

One problem is that C4 - the cap from the collector to groundafter the input buffer was missing.

I squeezed that in and used a TL070 - got a lot of over the top crunch, but the fuzz pot really didn't seem to do anything to the circuit - no effect at all - just full blown fuzz (sounded nice, buy the way, but a little too much)

I had socketed the chip and tried putting in an LM308 - smoke ensued . . . .

The changes I made:  R7 is a 51R instead of 39R (all I had - since there's a 10k pot following I figgure it was just there to make sure there was never a short to ground)

C7 is supposed to be 22 pF - all I had was 51 pF, so I put two in series, to get to 25 pF

I used 2u2 caps for C5 and C8, but I see MartyMart used 4u7's - would this make enough of a difference to fry the 308?

[Pedal love]

Now that I think about it, the mongoose fuzz I had, used a 22k log pot  for the volume control, one of the clipper diodes was a 1n4148 the other looked different maybe a 1N4007 or 1N914. The problem is its been about seven years since I had it and twenty since it was built, back when they used carbon film resistors everywhere and ceramic disc capacitors.pl

[brian wenz]

Hello Hello---
      Marty--  Yeah, I wanted to get some TL070 's  for the past year -or-so and kept getting swept up with more germ and silicon tranny circuits.
Thanks for the reminder!
By the way, i've had an old Rat pedal for years and never used it......good circuit, though!
Brian.

[MartyMart]

I tried Torchy's vero layout and had some problems - has anyone else made it work?

One problem is that C4 - the cap from the collector to groundafter the input buffer was missing.

I squeezed that in and used a TL070 - got a lot of over the top crunch, but the fuzz pot really didn't seem to do anything to the circuit - no effect at all - just full blown fuzz (sounded nice, buy the way, but a little too much)

I had socketed the chip and tried putting in an LM308 - smoke ensued . . . .

The changes I made:  R7 is a 51R instead of 39R (all I had - since there's a 10k pot following I figgure it was just there to make sure there was never a short to ground)

C7 is supposed to be 22 pF - all I had was 51 pF, so I put two in series, to get to 25 pF

I used 2u2 caps for C5 and C8, but I see MartyMart used 4u7's - would this make enough of a difference to fry the 308?

I Had done a layout just as Torchy finished his !!
So mine is different and not "drawn" yet, just built and working.
I fried my 308's by having .22uf tantalums rather than 2u2's, I went with 4u7's just because that's all I had !!.... so not sure why you fried your's?

The "Fuzz" pot does work and like my original, its quite "fuzzy" at zero
but gets very much louder and more distorted at max
So..... there must be another issue/error in your wire/track cuts or the layout.
Marty.  

[Rob Strand]

I think there is an error on the posted schematic.  Someone might want to check it.  R5 should connect to VCC not to the filter cap.

[MartyMart]

I think there is an error on the posted schematic.  Someone might want to check it.  R5 should connect to VCC not to the filter cap.

Isn't R5 (47k) half of VCC ? with the other 47k from 9v, it connects through filter cap, 2M2 and on to the 3904......?
My version is built as the schem and works fine  

Marty.

[Torchy]

C4 added to layout.
Node checked only - thats why I asked other people to check it. Any other probs let me know.

[Dragonfly]

I think there is an error on the posted schematic.  Someone might want to check it.  R5 should connect to VCC not to the filter cap.

the way its drawn looks confusing, but r4 isnt connected to c6 ....it connects to pin 7 of the op amp..... the drawing appears to be correct, but it is drawn a little odd

andy

[mlabbee]

After hearing the mp3, I'm guessing the schematic and vero (with c4 added) are correct - I guess I was expecting to be able to pull the sound back a bit - it really is over the top (in a good way).

I'm still not sure why my LM308 fried (a TL070 in the exact same circuit worked  fine).

[MartyMart]

After hearing the mp3, I'm guessing the schematic and vero (with c4 added) are correct - I guess I was expecting to be able to pull the sound back a bit - it really is over the top (in a good way).

I'm still not sure why my LM308 fried (a TL070 in the exact same circuit worked  fine).

Even on the original, at "zero`' fuzz there is still quite a bit of drive going
on ! rolling back the gtr vol in this state does "clean" things up some !
But on my build there's quite a difference between "zero" and "10" on the
fuzz pot.....
Remember that I did not use the Torchy layout, so I can;t comment on that, I'll post mine tomorrow when its drawn up.
I fried both my 308's but I can only put that down to my "badly" marked
tantalum caps which were 10X too small  !!
The TL070 is way better anyway ! so I'd use them in this/Rats from now on.
My "new clone" sounds better than the RM original, fuller, fatter and the break up is very "tube" sounding.........Ebay for me then ....

Marty.

[Dragonfly]

.........Ebay for me then ....

Marty.

WANNA TRADE IT FOR SOME 3PDT FOOTSWITCHES, A COUPLE NICE SIZE VEROBOARDS, AND A BOTTLE OF HOT SAUCE ?!?!?!?  :d    :wink:


Andy

[MartyMart]

.........Ebay for me then ....

Marty.

WANNA TRADE IT FOR SOME 3PDT FOOTSWITCHES, A COUPLE NICE SIZE VEROBOARDS, AND A BOTTLE OF HOT SAUCE ?!?!?!?  :d    :wink:


Andy

Well, if I hadn't just bought 10 3DPDT and 10 DPDT switches, plus I have about a metre square of vero.........
HOT SAUCE ! Now you're talkin Andy  :twisted:  !!!

Plus the RM mongoose was a steal, so I'll make enough to pay for my clone/others with it .....  

Marty.

[Rob Strand]

the way its drawn looks confusing, but r4 isnt connected to c6 ....it connects to pin 7 of the op amp..... the drawing appears to be correct, but it is drawn a little odd

On the ckt it looked like something to check.

Just looked at the photos, the schematic looks OK.

+V rail -> first 47k
other side of first 47k -> second 47k (+ filter cap + 2M2 resistor).
second 47k to the collector

good!

(didn't check anything else)

[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.

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

[MartyMart]

Thanks analogguru, the vero board layout is updated, though my version was built and worked with the 1k resistor R5 !!
( on the vero layout its R5 )
Marty.