Sansamp GT2 op amp choices

[ggedamed]

The high pitch oscillation is common problem of high gain circuits. The output signal finds a way back to the input of the circuit and a buffer blocks that. Put a buffered pedal like a Boss one - in bypassed mode - in front of the Sansamp. The buffer from the Boss pedal should kill the squeal.
Can you provide a picture of the PCB?

[Govmnt_Lacky]

Does anyone has a pcb layout with onboard Alco switch or alike?

Can you provide a picture of the PCB?

You can contact forum meber "nomorebetts" for these layouts. They are his to share. 

[DIMstompboxes]

Does anyone has a pcb layout with onboard Alco switch or alike?

Can you provide a picture of the PCB?

You can contact forum meber "nomorebetts" for these layouts. They are his to share. 

Thanks buddy

[nomorebetts]

Does anyone has a pcb layout with onboard Alco switch or alike?

Can you provide a picture of the PCB?

You can contact forum meber "nomorebetts" for these layouts. They are his to share. 

Maybe some signal traces are too close together and they are "cross talking"? or some such??    If you can't tell I'm way out of my depth here...  Greg's been the unlucky one to build from this layout first and uncover a number of issues. 

Here are the latest versions (unverified).  I think Greg built from Rev 2: https://dl.dropboxusercontent.com/u/75388200/GeeTee2_rev2_too_big.pdf

https://dl.dropboxusercontent.com/u/75388200/GeeTee2_BOM_Schem.pdf
https://dl.dropboxusercontent.com/u/75388200/SansAmpGT2pcb_AlcoPots_rev3%20-%20Layout.pdf
https://dl.dropboxusercontent.com/u/75388200/SansAmpGT2pcb_AlcoPots_rev3%20-%20Transfer.pdf
https://dl.dropboxusercontent.com/u/75388200/SansAmpGT2pcb_Roatary3pdtPots_rev3%20-%20Transfer.pdf
https://dl.dropboxusercontent.com/u/75388200/SansAmpGT2pcb_Roatary3pdtPots_rev3%20-%20Layout.pdf

     

[Govmnt_Lacky]

I think the oscillations are a known issue.

We're you able to cut the size down to fit into the BB enclosure?

[nomorebetts]

I think the oscillations are a known issue.

We're you able to cut the size down to fit into the BB enclosure?

Yeah these ones should fit comfortably.  BUT I would still check before etching! 
I also moved the switches down toward the 3PDT for aesthetics as requested.

Its a shame about the oscillations. I would have thought no off board wiring would prevent this.  Did you try putting a buffer in front like ggedamed suggested?

[teemuk]

When high gain stages oscillate it's often an issue of one or more of the following:

- poor layout (tracks too long, tracks in wrong places, poor "noding" scheme, etc.)
- insufficient or lacking decoupling capacitance near opamp power supply pins (or gain stages in general)
- insufficient or lacking HF feedback in gain stages

As is, the circuits/layouts seem to fullfill at least the last two of those.

I suppose you can solder some caps to the copper side to compensate. (e.g. 100nF caps from opamp supply pins to ground + 20 - 50 pF caps from opamp output to inverting input in all high gain stages).

[DIMstompboxes]

I think the oscillations are a known issue.

We're you able to cut the size down to fit into the BB enclosure?

Yeah these ones should fit comfortably.  BUT I would still check before etching! 
I also moved the switches down toward the 3PDT for aesthetics as requested.

Its a shame about the oscillations. I would have thought no off board wiring would prevent this.  Did you try putting a buffer in front like ggedamed suggested?

Wow! thank you so much nomorebetts for your great effort mate. I'll try to check this out.
BTW, can it be mod or include additional switch to OFF/ON that cab sim feature to have an option for Direct FRFR with cab sim features and OFF without cab sim in front of guitar amp.
You see our set up usually mic'ed the amp going to mixing desk already so I can switch OFF the cab sim  BUT some of the venue we use DI direct then I can switch ON that cab sim for FRFR set up.
Again thanks guys specially to you nomorebetts 

[nomorebetts]

Wow! thank you so much nomorebetts for your great effort mate. I'll try to check this out.
BTW, can it be mod or include additional switch to OFF/ON that cab sim feature to have an option for Direct FRFR with cab sim features and OFF without cab sim in front of guitar amp.
You see our set up usually mic'ed the amp going to mixing desk already so I can switch OFF the cab sim  BUT some of the venue we use DI direct then I can switch ON that cab sim for FRFR set up.
Again thanks guys specially to you nomorebetts 

I wouldn't be thanking me until you have built it and it works! Otherwise you might be cursing me out instead 

I'm not entirely sure what mod you are talking about or what's involved in implementing it.  But I was planning to just leave the PCB as stock.  But you should still be able to do what you want off board I guess?

[DIMstompboxes]

Wow! thank you so much nomorebetts for your great effort mate. I'll try to check this out.
BTW, can it be mod or include additional switch to OFF/ON that cab sim feature to have an option for Direct FRFR with cab sim features and OFF without cab sim in front of guitar amp.
You see our set up usually mic'ed the amp going to mixing desk already so I can switch OFF the cab sim  BUT some of the venue we use DI direct then I can switch ON that cab sim for FRFR set up.
Again thanks guys specially to you nomorebetts 

I wouldn't be thanking me until you have built it and it works! Otherwise you might be cursing me out instead 

I'm not entirely sure what mod you are talking about or what's involved in implementing it.  But I was planning to just leave the PCB as stock.  But you should still be able to do what you want off board I guess?

Yeah maybe the mod can be done offboard. It's only a switch to bypass or engage the cab sim feature but I haven't study the circuit yet. I will look more into the circuit/layout. Meanwhile continue the discussion.

[qlovely19]

Does anyone has a pcb layout with onboard Alco switch or alike?

Can you provide a picture of the PCB?

You can contact forum meber "nomorebetts" for these layouts. They are his to share.  

Maybe some signal traces are too close together and they are "cross talking"? or some such??    If you can't tell I'm way out of my depth here...  Greg's been the unlucky one to build from this layout first and uncover a number of issues.  

Here are the latest versions (unverified).  I think Greg built from Rev 2: https://dl.dropboxusercontent.com/u/75388200/GeeTee2_rev2_too_big.pdf

https://dl.dropboxusercontent.com/u/75388200/GeeTee2_BOM_Schem.pdf
https://dl.dropboxusercontent.com/u/75388200/SansAmpGT2pcb_AlcoPots_rev3%20-%20Layout.pdf
https://dl.dropboxusercontent.com/u/75388200/SansAmpGT2pcb_AlcoPots_rev3%20-%20Transfer.pdf
https://dl.dropboxusercontent.com/u/75388200/SansAmpGT2pcb_Roatary3pdtPots_rev3%20-%20Transfer.pdf
https://dl.dropboxusercontent.com/u/75388200/SansAmpGT2pcb_Roatary3pdtPots_rev3%20-%20Layout.pdf

please help me the file PDF, I can't dowload, it does not exist
https://dl.dropboxusercontent.com/u/75388200/SansAmpGT2pcb_AlcoPots_rev3%20-%20Transfer.pdf

[nomorebetts]

please help me the file PDF, I can't dowload, it does not exist
https://dl.dropboxusercontent.com/u/75388200/SansAmpGT2pcb_AlcoPots_rev3%20-%20Transfer.pdf

Hi,
yeah I stopped sharing it as the first builder; DIMstompboxes, encountered high pitched oscillations and was debugging it.
He was having good success and I was waiting for the final fix before uploading a corrected version.
However this was late last year and I haven't heard from him in a while.  Maybe contact him as he is best positioned to give you his prototype version.
I would however like to get a corrected version up and running, oscillation free.
Cheers

[qlovely19]

please help me the file PDF, I can't dowload, it does not exist
https://dl.dropboxusercontent.com/u/75388200/SansAmpGT2pcb_AlcoPots_rev3%20-%20Transfer.pdf

Hi,
yeah I stopped sharing it as the first builder; DIMstompboxes, encountered high pitched oscillations and was debugging it.
He was having good success and I was waiting for the final fix before uploading a corrected version.
However this was late last year and I haven't heard from him in a while.  Maybe contact him as he is best positioned to give you his prototype version.
I would however like to get a corrected version up and running, oscillation free.
Cheers

thanks a lot

[armdnrdy]

Maybe some signal traces are too close together and they are "cross talking"? or some such??    Here are the latest versions

I see a major problem with your board layout.

It looks like you did the layout in Eagle. You used the "polygon" tool to make a copper pour because it looks better and saves etchant.

Problem with that....you didn't name the polygon/copper pour "ground". You have "orphans" all over the board. Orphans are isolated pieces of copper that are not attached to a signal, ground, or voltage source.

Orphans will act as antennae and pick up surrounding signals. (especially in a high gain circuit)

You can go back to your original eagle files and delete the polygon, or connect (name) it to ground and delete the orphans.
To delete the orphans: Right click on the polygon and left click on properties. The properties window will be displayed. (as in my image)
Uncheck the box that says "orphans". All of the isolated pieces of copper within the copper pour will be deleted.



How do I know this? I did a build a few years back that had some noise issues. I was audio probing the board when I came across this issue. A quick search on the net confirmed the problem. Since the board was already etched, I had to connect all of the orphans to ground with wire jumpers. It solved the problem.

[Govmnt_Lacky]

Great info Larry.

Another problem I ran into is the sizing. The PCB is sized for a 1590BB but if you look at the pots, they hang over the board. When you try to push them closer to the rotaries, they will run into the rotary switch bodies before they will fit into the enclosure.

So, you would need an enclosure that is slightly taller than the BB or you need to wire the pots off board 

[armdnrdy]

It looks like there would be enough room to incorporate 9mm PCB mount pots.
I don't know how that would work with the rotary switch height though.

Small Bear sells those little 9mm panel mount. 

I don't know! I don't even want to build one of these! I have an original from years ago....and I'm not a real big fan. 

[DIMstompboxes]

Hey guys long time nomorebetts, armdnrdy and lacky

I have been able to get some let say very satisfying result for me   In using nomorebett's  PCB alcoswitch  version design.
Take note, all of these modification is an attempt to make the GT2 in truebypass mode with good deal to dial those Drive/Level/High knobs without (Drive pot with much control oscillation) /(LEVEL pot feedbacking volume controllable in some setting)/(HIGH pot high pitch frequency whining over loading when max.

So, I've set aside the nitty gritty and just wanna make a direct few pointed tweaks. BUT this may varies from PCB to PCB design as armdnrdy stated....

For the Drive pot ( I solved this Feedback  issue)
Let us base and use TONEPAD schematic
As to my (early) previous post modification done with the IC1b by changing 1M into higher value 2.5M or 3.5M vb (recommended)metal resistor help lessen the feedback especially high gain setting
Replacing that 3k3 on the drive with higher value like 10k vb plus lowering the feedback frequency of original  220p cap into 1000p or 102 on IC2a were spot on. The Drive has still lot of more gain travel unto it knob and that crazy feedback is eliminated even when the Drive pot is crank. Or max

For the Level pot
I was musing around just to reduce that 330k feedback resistor on IC4a first with half of the value which is 150k nope then half more 82k is just enough that will tamed the Level pot unto max which also still have a healthy plenty volume without feedback and oscillation  at the same time. BUT the good news .like the GT2 stock I tried on music store can't also even not set max the Level pot or past even 2 oclock 

For the High pot, 1 to 10 is the max  problem start to overload the HIGH frequency pitch especially going setting nearing to max which is 10. I always get clipping signal (overloading) and high pitch whining when the high knob is near three forth up to the max, this issue is both on stock version OR Darkangel mod version.

BTW, I also made the Darkangel  mod version all of its mod (removing the output buffer and  Q1 and making it not a truebypass plus connecting IC1a2 inverting to IC1b5 non-inverting for buffered input.  See Dark angel schematic below for reference

I  say it works, the DRIVE pot issue Oscillation is gone PLUS the LEVEL pot feedback is solve even slightly to max BUTTTT the big but is that it did not resolved still the HIGH pot High Frequency Pitch whining too (I would say HiGH PITCH CLIPPING overload when HIGH pot is max 

So what I did was just the same as 100k wiper value of the LOW pot and change that 3k3 into 10k on the HIGH pot wiper. Now the key point here is making that 104 cap after the IC4a higher value (224, 334 or  474 cap  just experiment some value to get the right one) meaning lowering (giving more of the low frequency in would pass through so it will NOT clip the high knob frequency when max) YET the high knob still have good HIGH response

Last TIP this I never yet done a friend suggest to put 100p-200P cap between IC4b pin 6 and pin7 output. To control the high pitch and use not ceramic cap.

Sorry I don't have dropbox for you to have nomorebett GT2 Alcoswitch design transfer and layout BUT I will email the copy to him so he could further refine the design...





So yes indeed I may further experiment more and give you my own observation. Just trying to make some logical sense out of these mod, like yourself, I constantly inquire of the good folks here in this forum AND in whichever little ways I can give back, I try to do so. If your "ON" to something let it share.
Cheers,

[Govmnt_Lacky]

I personally built the rotary switch version of Dave's and the only problem I had was with the high pitch whining/oscillations when the HIGH pot was near max.

I don't know what op amps you used DIM but, I used the TLC2262 in 2 of them and TL072 in the other two (the inner-most op amps were TL072s) The original units used TLC2262s in 3 of the 4 positions.

Like I mentioned above, when I use 16mm pots, I cannot get it to fit into a 1590BB. Its about4-5mm too tall 

[DIMstompboxes]

I personally built the rotary switch version of Dave's and the only problem I had was with the high pitch whining/oscillations when the HIGH pot was near max.

I don't know what op amps you used DIM but, I used the TLC2262 in 2 of them and TL072 in the other two (the inner-most op amps were TL072s) The original units used TLC2262s in 3 of the 4 positions.

I have all TI TLC2262C, TL072, TL062D, TLC2262CP, TLC2262AIP,TLE2082ACP, even TLV2252AIP and TLC2201CP which are all new from TI sample. I even swapped OPA2137P dual FET all IC1 all have the same issue.  I decided just to use IC1 TL072, IC2 TLC2262C, IC3 TLC2262C and IC4 TL062D which Darkangel suggested but still with the same annoying issue is there......
So my logic was only just to lower those values that directly affect the feedback gain level coz I can or could just add volume on my amplifier in case I needed
I even used shielded wire and ALCO switch and 3pdt direct solder to board thinking it would eliminate or at least lessen the problem avoid  by not using wire wiring....

[nomorebetts]

I'd really like to see this project be successful but I just don't have the time to spend on it these days.

If someone is motivated and up to the challenge I'm happy to share the Dip Trace files and they can pick it up and hopefully salvage it from the wreckage.

Let me know if you're interested!