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Sansamp GT2 op amp choices

Started by Govmnt_Lacky, August 09, 2013, 02:52:38 PM

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Govmnt_Lacky

August 09, 2013, 02:52:38 PM
I have read a lot of information about getting the right sound out of a GT2 build. Unfortunately, I have not gotten a good feel for which dual op amps to use and where. I believe the original used TLC2262s for IC1, IC2, and IC3 and then a TL072 for IC4.

Can anyone offer suggestions?

I have built this in the past but, I was never able to get the same tone change between the different settings that the original has.

Thanks  ;)
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

iq01221

#1
August 09, 2013, 03:03:54 PM
TLC2272 from TI ;)

Govmnt_Lacky

#2
August 09, 2013, 03:09:30 PM
I have heard that the 2272 can be used as well but, most of what I have read refer to the use of 072s and 2262s to get the original tone. I have come to the conclusion that I will need 3 of the 2262s and 1 of the 072s.

My problem now is WHERE do they go?  :-\

Also from what I have read, the 2262s are DEFINITELY used in IC2 and IC3 spot. So I guess my problem is where to put the TL072. Does it go in IC1 or IC4?
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

armdnrdy

#3
August 09, 2013, 03:41:47 PM
I know nothing about this pedal except that I have one.

To help a forum member, you, I cracked it open to find that I would have to unsolder the input and output jacks to get to the component side.

With that being said....what will I find when I get there?

You've probably researched this a bit, looked for gut shots ect. Are the IC markings visible or have they been altered?
I just designed a new fuzz circuit! It almost sounds a little different than the last fifty fuzz circuits I designed! ;)

Govmnt_Lacky

#4
August 09, 2013, 03:49:16 PM
Quote from: armdnrdy on August 09, 2013, 03:41:47 PM
You've probably researched this a bit, looked for gut shots ect. Are the IC markings visible or have they been altered?

Dont bother...

I have seen pics of the component side and it appears that they sand or erase the SMD IC markings on them  :-\

Appreciate the help though...  ;D
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Davelectro

#5
August 09, 2013, 04:00:35 PM
IC1,4= TL072 (or TL062)
IC2,3=TLC2262

armdnrdy

#6
August 09, 2013, 04:03:00 PM Last Edit: August 09, 2013, 04:15:39 PM by armdnrdy
How come on the gut shots I see a quad op amp and two dual op amps? different version?

Like I said....I know nothing about this box!

I just designed a new fuzz circuit! It almost sounds a little different than the last fifty fuzz circuits I designed! ;)

Govmnt_Lacky

#7
August 09, 2013, 04:17:50 PM
Quote from: armdnrdy on August 09, 2013, 04:03:00 PM
How come on the gut shots I see a quad op amp and two dual op amps? different version?

Like I said....I know nothing about this box!

According to what I have read and seen, the quad op amp is just a quad version of the 2262 (TLC2264??) The dual op amps are (1) 2262 and (1) TL072.

@Davelectro

Thanks for that. Are you sure that there are not (3) TLC2262s in there?
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Davelectro

#8
August 09, 2013, 06:17:59 PM
Quote from: Govmnt_Lacky on August 09, 2013, 04:17:50 PM
Are you sure that there are not (3) TLC2262s in there?

Absolutely. Two rail-to-rail and two jfet-input.

Govmnt_Lacky

#9
August 09, 2013, 06:28:37 PM
Quote from: Davelectro on August 09, 2013, 06:17:59 PM
Absolutely. Two rail-to-rail and two jfet-input.

Thanks!! Gonna try this. Worse comes to worse... I have sockets too!  8)
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

SISKO

#10
August 09, 2013, 08:21:46 PM
--Is there any body out there??--

pappasmurfsharem

#11
August 10, 2013, 12:17:02 AM
If you don't have the chips btw you can get them free from TIs sample program
"I want to build a delay, but I don't have the time."

ggedamed

#12
August 10, 2013, 08:02:00 PM Last Edit: August 10, 2013, 08:03:55 PM by ggedamed
One big annoyance I always felt the GT-2 clones had was the sputtery decay caused by the op amp clipping. I heard that the originals had the same problem and it makes sense. So I once tried all the op amps I had at hand. The sounds were not very different, although there were some differences. Most differences come from the first and mainly the second dual op amp (the second one does the bulk of the clipping).
LM833 was really bad. TL072 (JFET input), RC4580D, NE5532 (bipolar), OPA2140 (rail-to-rail, JFET input), TL2262, TL2272, OPA2703 (rail-to-rail, CMOS input) were good. If you have one, try a OPA2132 in the first socket, it solved my decay problem.

And yes, you can get most of them for free from Texas Instruments through their samples program.
Minds are like parachutes. They only function when they are open. (Sir James Dewar, Scientist, 1877-1925)

Govmnt_Lacky

#13
August 31, 2013, 02:43:55 PM
OK... so i debugged my board and I found a ground trace that was "cut" when I was trimming the board in an attempt to fit it into a BB enclosure  :icon_rolleyes:

Fixed that with a jumper and now it is working with TL072s in IC1 and IC4 and 2262s in IC2 and IC3.

My only problem NOW is what I see is a pretty comon one that I have found no solutions for while combing the forum.  :-\

I get high pitched squeeling/oscillations when the HI pot is between 75% to MAX.

Thoughts??
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

ggedamed

#14
August 31, 2013, 07:03:49 PM
Either:
1. you make it buffered bypass (simply take the bypass from the output of the first op amp, that's what many, myself included, do)
2. remake the wiring to be shielded, shorter, further apart or non-existant (ideally)
Minds are like parachutes. They only function when they are open. (Sir James Dewar, Scientist, 1877-1925)

Govmnt_Lacky

#15
August 31, 2013, 07:08:30 PM
Quote from: ggedamed on August 31, 2013, 07:03:49 PM
Either:
1. you make it buffered bypass (simply take the bypass from the output of the first op amp, that's what many, myself included, do)
2. remake the wiring to be shielded, shorter, further apart or non-existant (ideally)

This build has onboard EVERYTHING. Pots, Jacks, DC jack, 3PDT, LED, and rotary switches  :icon_eek:
The squeeling is when the effect is engaged. Not in bypass. I may be misunderstanding #1

I have read quite a few posts here and elsewhere from folks with the same problem. Just no solutions (posted that is)
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Davelectro

#16
September 01, 2013, 07:23:00 AM Last Edit: September 01, 2013, 08:49:05 PM by Davelectro
I think this is a known issue.

Try wiring your 3pdt with input and output grounding (but i'm not sure if this will help since your bypass signal seems to be ok).

Davelectro

#17
September 01, 2013, 08:48:26 PM
Sorry. Double post.

candidate

#18
September 02, 2013, 04:45:03 AM
For sure, wiring is way more important than the op amp selection in this build.

DIMstompboxes

#19
September 02, 2013, 12:34:53 PM
Hi to all,
Does anyone has a pcb layout with onboard Alco switch or alike?
http://epektos.com/product/fdd436d9-e628-4e8b-b8d2-f676644b0ce7.aspx
To minimize that wiring and to prevent some issue....
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