AMZ FX ANALOG ALCHEMY GEOFX MEF ROG DIY WIKI

UPDATE--Rodent problem--Finally got it!

Started by jimbob, October 03, 2004, 02:31:09 AM

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jimbob

October 03, 2004, 02:31:09 AM
OK, Ive gone over this thing a million times and it seems to be right except the drive is screwed up. I have req. 100ka and kb-tried both (also a 250kb) and this thing only has a small portion of the pot where it can dial in sound--less than 1 mm before it squeels to high hell. I can carefully dial in some mild distortion. So theres something wrong here and i cant figure it out. I noticed i can take the 2.2 elecrto out and itll still work? hmmm

any ideas?
"I think somebody should come up with a way to breed a very large shrimp. That way, you could ride him, then after you camped at night, you could eat him. How about it, science?"

strungout

#1
October 03, 2004, 12:16:09 PM
What opamp? Try another :P I used a NE5532 in my modded rat.

Taking out the 2.2uf cap will still have it work because of the action of the other arm (560ohm with 4.7uf).

I used a 1M pot for more gain and didn't get any squeeling at all (maybe a little hiss). I did get some with a bad ceramic cap (the 100pf in the fb loop), so I'd check that. Otherwise...

Ciao.
"Displaying my ignorance for the whole world to teach".

"Taste can be acquired, like knowledge. What you find bitter, or can't understand, now, you might appreciate later. If you keep trying".

petemoore

#2
October 03, 2004, 12:19:19 PM
Did you take OA pin voltage readings and audio probe it?
Convention creates following, following creates convention.

MartyB

#3
October 03, 2004, 12:19:48 PM
I have an aunt in Kansas City who fixed her rodent problem with dobermans - sorry - do you have pics available?

jimbob

#4
October 03, 2004, 01:55:50 PM
I  tried the lm308n and the tlo71 and it does the same thing-- today ill chk the ceramic cap--which was a cheapo one i had lying around, and chk voltages and use the audio probe..Ill also try the 1m and see what happends.

Btw- a good portion of this used to be a Pro Co Brat (the worst pedal ever made next to the Snarling Black Dog) Btw--both de-gutted to be used as parts for other projects.

This cant be too hard...There are only so many parts..This is all on perf.
"I think somebody should come up with a way to breed a very large shrimp. That way, you could ride him, then after you camped at night, you could eat him. How about it, science?"

jimbob

#5
October 04, 2004, 02:21:46 AM
Ok- im getting this d-d-d-d-d-d-d-d-d kinda thing like a tremolo pedal would have--very odd. and sounds like that too w my audio probe it starts at the 1m meets 10k passin by the 47ohm and 560 ohm.
"I think somebody should come up with a way to breed a very large shrimp. That way, you could ride him, then after you camped at night, you could eat him. How about it, science?"

Mark Hammer

#6
October 04, 2004, 09:58:42 AM
It sort of sounds like you have a gain pot that is going open circuit.  I've had such pots baffle me on several occasions.  They may look brand new and pristine, but one of the anchor points where the solder lug connects to the resistive element may have a less than perfect connection.  What I do in such cases is to simply pinch the rivet with suitable pliers and secure the connection.  It usually helps.

Honestly, sometimes I think we place too much faith pots.  They are inherently mechanical devices, and prone to all the issues that mechanical devices are.

In my previous career as researcher, I logged several thousand hours with rats.  Hopefully that highlyh specialized experience counts for something here. :lol:

Peter Snow

#7
October 04, 2004, 12:09:54 PM
Mark wrote:
QuoteIn my previous career as researcher, I logged several thousand hours with rats. Hopefully that highly specialized experience counts for something here

... and you are STILL working with them (PWGSC)!! :D  :twisted:  :wink:

Peter
Remember - A closed mouth gathers no foot.

jimbob

#8
October 04, 2004, 07:28:23 PM
OK..i think i got a big part of the problem fixed. One if the 2 47 electro's wasnt grounded causing it to make a helicopter type sound. I got that ..now i have a high pitch feedback like problem and its coming from  where the 2.2uf electro goes. No matter what value i put in the socket for 2.2uf it still causes that sound once i take stop playing(hitting the strings) and hold it. Its makes for a great overdrive pedal though without the 2.2uf.. But ive come too far to settle now..Btw- im using a tl071 not the lm308. Ill put that in last--not that it matters..i dont think anyway.

any ideas?

Hopefully soneone can use this as a reference down the road with problems with their Rodent as ive had so many..
"I think somebody should come up with a way to breed a very large shrimp. That way, you could ride him, then after you camped at night, you could eat him. How about it, science?"

David

#9
October 04, 2004, 10:04:21 PM
Jimbob:

Now I remember what was bothering me!  IIRC, the LM308 is an uncompensated op-amp.  I believe also that the TL061,71,81 op-amps are compensated.  If I am correct, this could be part of your trouble.

If I have erred, I hope the esteemed ladies and gentlemen of this forum will apply judicious and merciful correction...  No Harmony Central, please!

jimbob

#10
October 04, 2004, 10:25:43 PM
Ill try the lm308. GGG said that those others sound decent but not as good as the lm308. It just didnt say anything about feedback ect..as a result of using a diff op amp..

btw- a pro co Brat had to die as a result of making this. It was a slow and miserable death and well deserved. Brat 's the worst distorion ever! A total waste of a lm308. I saved it though.
"I think somebody should come up with a way to breed a very large shrimp. That way, you could ride him, then after you camped at night, you could eat him. How about it, science?"

RDV

#11
October 04, 2004, 10:53:58 PM

jimbob

#12
October 05, 2004, 12:45:24 AM
Ok !! Damn finally got it. Turns out it was from the tl071. So if anyone researches this down the road--maybe theyll learn from my lengthy lesson. Say no to tl071. Lm308n was the key..Although, except for the noisey feedback, i liked the sound.. It just wasnt really usable..

So this thing sounds pretty cool. This effects seems to have a little more girth than a lot of the others. But also a well rounded sound. I leaned that you can take a little of the highs out  by socketing and pulling out the 2.2. It seems that part just gave it a little clarity. Unless anyone else knows a better reason for it.
"I think somebody should come up with a way to breed a very large shrimp. That way, you could ride him, then after you camped at night, you could eat him. How about it, science?"

David

#13
October 05, 2004, 10:47:09 AM
Quote from: RDVNope. Compensated. http://www.national.com/ds/LM/LM108.pdf

RDV

My mistake...   :oops:
Better do my due diligence before I post.  I could have sworn on a stack of datasheets that Anderton used the 308 in his compressor -- which I thought used an uncompensated op-amp.  Guess I was wrong.

petemoore

...
#14
October 05, 2004, 11:28:33 AM
Yupp I tried that...lol
 Compensated OA is a Compensated OA...or your Rat Type won't work right  :shock:
Convention creates following, following creates convention.

jimbob

#15
October 05, 2004, 03:10:24 PM
Are there many other effects out there like this- where it has to be "A" and not B,C, D, ect?
"I think somebody should come up with a way to breed a very large shrimp. That way, you could ride him, then after you camped at night, you could eat him. How about it, science?"

David

#16
October 05, 2004, 09:47:08 PM
Yeah,  the stuff John Hollis did.  If he calls for a TL064, he bloody well means a TL064 (or at least 2 TL062s)!
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