[audiovisceral]

I have a SansAmp PSA-1, and I want to try it with some new IC's.  However, as you can see many of the chips in the unit are unlabeled:

http://www.freeimagehosting.net/uploads/397234b749.jpg
http://www.freeimagehosting.net/uploads/dcc1da1a5b.jpg

The GT-2 pedal from the same company uses one TL072 and three TLC2262's. I am guessing the component choices are similar. However, before I do anything, I would really prefer to know for sure what is what.

Does anyone have a service manual or schematic for this unit they might be willing to share? If so, PM would be great. Any other helpful info on how I could figure this out would also be nice.

Thanks.

[okgb]

Gtr pedal ? check this site

http://freestompboxes.org/index.php

respect the requests folder though
and search the 1975 + catagory

[audiovisceral]

Gtr pedal ? check this site

http://freestompboxes.org/index.php

respect the requests folder though
and search the 1975 + catagory

Thanks, but no luck. It's a rackmounted unit. And it seems Tech 21 does a very good job keeping the components to themselves... 

[okgb]

it's definitely a gtr crowd over there , though

[DimebuGG]

I have a SansAmp PSA-1, and I want to try it with some new IC's.  However, as you can see many of the chips in the unit are unlabeled:

http://www.freeimagehosting.net/uploads/397234b749.jpg
http://www.freeimagehosting.net/uploads/dcc1da1a5b.jpg

The GT-2 pedal from the same company uses one TL072 and three TLC2262's. I am guessing the component choices are similar. However, before I do anything, I would really prefer to know for sure what is what.

Does anyone have a service manual or schematic for this unit they might be willing to share? If so, PM would be great. Any other helpful info on how I could figure this out would also be nice.

Thanks.

Hi, my first post in here! ..Provide me some HIGH RESOLUTION close up pics of your PSA 1 in all angles (e.g. top and bottom PCB, capacitor ID's, etc) and I'll do the tracing for a schematic of this beast!.

[audiovisceral]

Hi, my first post in here! ..Provide me some HIGH RESOLUTION close up pics of your PSA 1 in all angles (e.g. top and bottom PCB, capacitor ID's, etc) and I'll do the tracing for a schematic of this beast!.

Wow. Great first post! That's very generous of you. I will take you up on that offer. Give me a few days to get the pictures together, and I'll post them here. Thanks.

 

[DimebuGG]

Wow. Great first post! That's very generous of you. I will take you up on that offer. Give me a few days to get the pictures together, and I'll post them here. Thanks.

 

No problem.  .

[audiovisceral]

I got the pics.

They seem to have sanded off the identification on only five of the opamps (which I've numbered 1-5). I'm guessing based on what I've read of Tech 21's other products, these are the ones directly responsible for the distortion/eq the unit produces, and are TLC2262 & TLC2264.

The other 7 TL072's I'm guessing are buffering the inputs, outputs, and 0/-10dB push buttons, but I am uncertain.

Do you have any thoughts on what each of the unlabeled opamps is doing or if that's what they might be? What right about the TL072's? Are there any other obvious parts I might want to consider upgrading? I like the unit and sound, but I'm looking for lower noise and a bit clearer clean signal.

Thanks!

Labeled:




Unlabeled:

   

[Kingston]

The 14-pin unlabeled chips are most likely some standard quad opamps. Certainly the 100nF (or so) rail compensation caps seem to match the standard quad opamp VCC pins.

TL074 is popular among the guitar pedal designers, and I suspect they are used here as well. SansAmp is probably being clever here smudging out the labels so that people don't realise what cheapskate part was used here.

Changing them to anything else won't fix noise issues, and will likely just ruin the sound and subtly change the type of distortion produced. You will just end up making the sound sharp and nasty with fast modern opamps.

any thoughts on what each of the unlabeled opamps is doing or if that's what they might be?

gain, filters and buffers (summing). Not much else they can do. That big black slab of epoxy contains a lot of diodes (overdrive and distortion) and filter caps (probably simple 2nd order topologies) which these quad opamps are buffering and gain staging to create the actual distortion.

[DimebuGG]

Not that doable really but anyway thanks for the pics. Maybe it would be better if you divide them into 3 for better close up pics. Well, just a suggestion.

I see +/- 15V volt regulators, so opamps are not likely TLC2262 and TLC2264.

[audiovisceral]

The 14-pin unlabeled chips are most likely some standard quad opamps. Certainly the 100nF (or so) rail compensation caps seem to match the standard quad opamp VCC pins.

TL074 is popular among the guitar pedal designers, and I suspect they are used here as well. SansAmp is probably being clever here smudging out the labels so that people don't realise what cheapskate part was used here.

Changing them to anything else won't fix noise issues, and will likely just ruin the sound and subtly change the type of distortion produced. You will just end up making the sound sharp and nasty with fast modern opamps.

gain, filters and buffers (summing). Not much else they can do. That big black slab of epoxy contains a lot of diodes (overdrive and distortion) and filter caps (probably simple 2nd order topologies) which these quad opamps are buffering and gain staging to create the actual distortion.

I see +/- 15V volt regulators, so opamps are not likely TLC2262 and TLC2264.

Interesting to hear. I had read from numerous sources who have built Tonepad Tech 21 GT2 pedal clones that TLC2262/TLC2264 are what Tech 21 uses to get their 'trademark' sound.

Here's what one person wrote (which is backed up by the people behind the Tonepad GT2 clone):

TLC2262 is the Cmos (all fet internal) rail to rail "version" of the TL062 dual op amp. - low current drain device.
Like the TL062 the TLC2262 has a much slower (slew rate) high frequency power gain, and can sound quite mushy when driven hard.
This feature is exploited by TECH 21 of NYC in their SANS AMP series, for a supposedly better MARSHALL and MESA sound.
http://www.diystompboxes.com/smfforum/index.php?topic=59068.0;prev_next=prev

So I am surprised you guys think those might not in fact be TLC2262/2264's with the marks scuffed off. The specs say these chips can take up to 16v, so 15v supply wouldn't necessarily rule them out, I don't think.

Regarding the black epoxy block, just curious - how exactly does that work? Is it like a little circuit board with diodes and caps soldered into it, then they just cover it in epoxy to keep that aspect of their layout secret?

There is also a gentle humming coming from the unit (not in the audio path, just acoustically audible hum in the room if it is on), and I can't see or feel anything loose in the chassis that might be causing it. I am thinking it might be a problem with the power transformer they have on there. If so, I will have to replace that, and I will probably just install some opamp sockets at the same time. As long as I know the unlabeled ones are just duals and quads, there should be no harm in experimenting.

Thanks.

[Kingston]

So I am surprised you guys think those might not in fact be TLC2262/2264's with the marks scuffed off. The specs say these chips can take up to 16v, so 15v supply wouldn't necessarily rule them out, I don't think.

We're all just guessing here, nothing is ruled out. I've experimented with some overdrive pedals and opamps in the past. Replaced some TL072's with OPA (can't remember which) and some filtering caps. Not such a good idea since it drinks the battery double time, but the distortion products changed to worse. Think digital. It lost its character.

Just saying that the tech21 folk probably had ears and knew what they were doing.

Regarding the black epoxy block, just curious - how exactly does that work? Is it like a little circuit board with diodes and caps soldered into it, then they just cover it in epoxy to keep that aspect of their layout secret?

Exactly. Sometimes they even try to mislead reverse engineers using them.

There is also a gentle humming coming from the unit (not in the audio path, just acoustically audible hum in the room if it is on), and I can't see or feel anything loose in the chassis that might be causing it. I am thinking it might be a problem with the power transformer they have on there. If so, I will have to replace that

Many PSU transformers "sing". Especially transformers that aren't toroids. Doesn't mean there's anything wrong with them, just that the magnetic fields within are, well, transforming. Replacing the one in the picture would be a fools errand as the PCB layout is designed around it. A new one might still vibrate. What most likely is going on is the trafo is using the chassis/PCB as an acoustic amplifier. Kind of a layout design error, but can be fixed. You can try to physically isolate the transformer from the chassis and PCB. rubber/foam/etc. damping works, as long as you make sure they're fireproof.

[DimebuGG]

TLC226X's datasheet says maximum voltage at 16V(+/- 8V). Anything above it kills the chip instantly.

So I am surprised you guys think those might not in fact be TLC2262/2264's with the marks scuffed off. The specs say these chips can take up to 16v, so 15v supply wouldn't necessarily rule them out, I don't think.

I'm talking about a split supply in here and that PSA uses a + and - 15V, TLC226X chip can handle only +/- 8V. And BTW, I use this chip all the time.

[MartyMart]

DimebuGG is correct, no chance that they are TLC2262's

I would agree that it's all TL072's for duals and TL074's for quads.
There's nothing at all wrong with those opamps and the unit will be setup
and voiced around them.

You will just make it sound crap by randomly swopping parts, you would need a
full schem and have to work out every gain stage / filtering etc etc before changing
them.
I would leave it "as is"
MM

[audiovisceral]

I've experimented with some overdrive pedals and opamps in the past. Replaced some TL072's with OPA (can't remember which) and some filtering caps. Not such a good idea since it drinks the battery double time, but the distortion products changed to worse. Think digital. It lost its character.

Just saying that the tech21 folk probably had ears and knew what they were doing.

Fair enough, and you guys are probably right. But I still want to try. Call it a fool's errand if you will, but I still want to find out for myself. I think some AD chips (AD823, AD713) might do well tonally. We'll see.

Many PSU transformers "sing". Especially transformers that aren't toroids. Doesn't mean there's anything wrong with them, just that the magnetic fields within are, well, transforming. Replacing the one in the picture would be a fools errand as the PCB layout is designed around it. A new one might still vibrate. What most likely is going on is the trafo is using the chassis/PCB as an acoustic amplifier. Kind of a layout design error, but can be fixed. You can try to physically isolate the transformer from the chassis and PCB. rubber/foam/etc. damping works, as long as you make sure they're fireproof.

That's what I was thinking. I wasn't planning on replacing with a different model transformer, just a new one of the same model, under the assumption that the one in there was defective. But since it's a relatively quiet 'hum', perhaps that is just how the part/design works? I don't know. It's a bit annoying, but not terribly.

I think you may be right about the chassis amplifying it, because when I took the top off to listen, it seemed much quieter. Perhaps I will try some 2-3 mm foam glued to the inside of the top/bottom. Or neoprene like this stuff:
http://www.foamorder.com/neoprene.html

TLC226X's datasheet says maximum voltage at 16V(+/- 8V). Anything above it kills the chip instantly.

PSA uses a + and - 15V, TLC226X chip can handle only +/- 8V. And BTW, I use this chip all the time.

Okay, got it. Thanks again.

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