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DIY Rat Problem... HELP!

Started by w437776, September 20, 2009, 06:25:01 PM

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w437776

I just finished building my 3rd ProCo Rat replica today. There are 2 problems:

1. The output volume is very low, half the volume of the bypass signal with the knob turned all the way up.
2. Sound is very fuzzy and compressed even on the lower gain settings.

Here's the voltage chart:

IC1:

P1: 8.32V
P2: 4.19V
P3: 2.04V
P4: 0
P5: 0
P6: 4.20V
P7: 8.42V
P8: 8.32V

..and schematic:
http://www.generalguitargadgets.com/pdf/ggg_rodent_sc.pdf

Compared with my other Rat clones all voltages are ok except the P3 and P8, they should be somewhere around 4.5 volts.

Any ideas?

J M Fahey

Pins 2 and 3 should match within millivolts, or less.
Simpl circuit=few possibilities: mistake on PCB, bad chip, solder bridge, etc.
Change the chip first and take a good close look with loupe or good glasses.
Scratch between pins that are close but shouldn't be interconnected.
Worst case: build another.
Good luck.

w437776

Quote from: J M Fahey on September 20, 2009, 11:43:59 PM
Pins 2 and 3 should match within millivolts, or less.
Simpl circuit=few possibilities: mistake on PCB, bad chip, solder bridge, etc.
Change the chip first and take a good close look with loupe or good glasses.
Scratch between pins that are close but shouldn't be interconnected.
Worst case: build another.
Good luck.
I took the IC out and measured the voltage on the pin 3 socket, it's the same. Pins 7 and 8 aren't directly connected in any way. Maybe a bad IC?

J M Fahey

1) Please don't say "it's the same" because it means nothing.
Say : "it's xxx volts" or "it's the same as that in pin yyy".
2) on pin 3, without the IC, you *must* have the same as in the union of R15/R16, around half the battery voltage.
If you don't, and the IC is not present, *very* probably is a bad homemade PCB, make another.
Good luck.

Brymus

Also I would suggest telling us what IC you are using- the original Rat uses LM308N an IC that has a different pinout than most dual op-amps.
With that chip your v-ref is on pin 3 via the 1M resistor btween the input cap and the 1k resistor that connects to pin 3.Your V+ is on pin 7.And pin 4 is ground.
This all changes if you used a different chip.

dsmnoisemaker

lm308 has the same pinout of most common single opamps..i have directly replaced lm308 for TL081 & 071´s and worked fine..even better IMHO.
check your board, resistor values, and check the fet.

Brymus

Thats IF used a TL071 if he used a more common DUAL opamp the pin out is different.

J M Fahey

I think w437776 has already built other two Rats, successfully.
I guess he home made the boards, that's why I find them the most obvious suspect.
Considering the low cost , I'd rather build another and not waste time.
Personally, when I build a (physically) small project such as this, I just print 4/5 or more boards on the same sheet, then iron and engrave all together, it takes exactly the same time.
I choose the best, and, if successful, can easily build a couple more for my friends or to give out as bonuses or to build different, modded versions, to test.
You can fit easily 8 Rat boards on a single sheet of paper.
Besides, transfer methods are not flawless at all, it's easy to get tiny cracks in the tracks or unwanted copper bridges , so producing more and choosing the best is very cost effective.
The expensive part is the power supply and the case+hardware, the board and components themselves are the cheapest part.

w437776

Just replaced the output transistor and and it works fine now  :) The problem with the voltages was in the multimeter with very low internal resistance...  ;D

J M Fahey

 I don`t think you had a "bad" transistor, that`s very difficult nowadays, but rather some soldering problem.
Anyway, now it works, that`s the important thing.
Congratulations.

w437776

Thank you for all the advices and help!  :)

And a sound sample:
http://www.box.net/shared/q1baxvm44t

J M Fahey

Hi w437776. *Excellent* graphics and finish. :tu:
Congratulations on your *very clean* sound. :trouble
Would you now treat us to some of your .... oooommmhhh !! ..... how do I say it ? .... some of your *distorted* sound? (Considering you have not one but *two* Rats under the hood)
Pliiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiizzzzzzzzzzzzzzzzz !!!!! :'( :'( :'(

joecool85

Quote from: J M Fahey on October 13, 2009, 11:29:03 PM
Hi w437776. *Excellent* graphics and finish. :tu:
Congratulations on your *very clean* sound. :trouble
Would you now treat us to some of your .... oooommmhhh !! ..... how do I say it ? .... some of your *distorted* sound? (Considering you have not one but *two* Rats under the hood)
Pliiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiizzzzzzzzzzzzzzzzz !!!!! :'( :'( :'(

Agreed, let's hear some distorted goodness :-)
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

w437776

I must have posted the wrong link... :o Here's the right one and a few more ;D :

1. Very old Fender Mexico Strat ---> Dual Mice ---> Marshall Plexi
(first with cut switch on - Ruetz mod, and then with cut switch off)

http://www.box.net/shared/ruo4ttdxgh

2. Hamer Californian ---> Dual Mice ---> Guitar Rig 3 Twin Reverb Simulation  xD

http://www.box.net/shared/8rrmbql0xi

3. Hamer Californian ---> Vintage Rodent (another Rat clone I built) ---> BrandX X-15R  ;D

http://www.box.net/shared/15nqbkffs8
http://www.box.net/shared/gvbsu4fbrd
http://www.box.net/shared/ta5bt7xuv3
http://www.box.net/shared/65ppumpf0y

More samples soon...  ;)

J M Fahey

Now that´s much better !! ;)
Only problem is that I sent yesterday a killer ninja team to your house, and their cell phone seems to have no signal. :-\
Hope it´s not too late to stop them.
Congratulations on your mice  :tu:
Feed them a lot of good cheese.