SansAmp GT-2 build report (UPDATE: Sound Clip)

gak · February 20, 2005, 03:37:04 AM

well, after a couple of weeks i finally bought the parts for this build
some weeks ago i've etched the PCB based on tonepad's layout, drawn with permanent marker (tonner cartidge diying :roll: )
soldering parts took only a couple of hours, it wasn't hard at all
as i couldn't find the switches i'm using jumpers instead
after fixing some mistakes, it finally got working! at first i got an extreme background humm, but after soldering again some pads i think that's gone
what can i say? i think this is the best thing i've built... sounds great and there're lots of different sounds
i still have to test it a lot more tomorrow and also i'm recording some sound clips that i'll be posting soon
it's amazing for direct recording!
BTW, i'm using 4 TL072 op-amps... i wonder how would it sound using TLC2262... (i'll have to wait until i get some money... they're a little expensive here in argentina...)

last thing... i consider myself a begginer and i could build this without any major difficuilties... i don't think it's as hard as it's said... go ahead and build one!

Sound: i've uploaded a shot clip recorded with my sansamp clone direct into my soundcard (software reverb added)
look here http://www.geocities.com/guidokritz/

Pics:

Thanks to ImageShack for Free Image Hosting

gak · February 20, 2005, 04:04:57 AM

one question about the ICs... can i use a MC33202P as a replacement for the TLC2262?
here are both datasheets:
http://www.alldatasheet.com/datasheet-pdf/pdf/MOTOROLA/MC33202P.html
http://www.alldatasheet.com/datasheet-pdf/pdf/TI/TLC2262.html

thanks!

gak · February 20, 2005, 03:29:42 PM

updated with sound clip and pic

JimRayden · February 20, 2005, 05:51:07 PM

Now these huge circuits need too much patience for me to build. Though a completed circuit is a joy to look and listen at. Why don't you flip that thing around and let us see the marker-drawn layout... I'm planning on moving to PCB's myself. And I thought to use a marker at first. Does any permanent marker do?

Oh and I'm too lazy to search, point me the way to the SansAmp schematic.

I'd love to see it enclosured! Keep up the good work.

--------------
Jimbo

sir_modulus · February 20, 2005, 06:04:20 PM

I'd go to tonepad for the schematic, and PCB layout.

Now in response to Jim:
I'd go with toner transfer, or something like photo transfer. Markers don't work all that well for big layouts. In case you do want to still use markers, here's a link to a past thread about that issue:
http://www.diystompboxes.com/sboxforum/viewtopic.php?t=29832&highlight=pcb+etch+resist

Cheers,

Nish

sir_modulus · February 20, 2005, 06:07:58 PM

Congrats on a good build btw!

In answer to your question about opamps, the TL072's buzzed madly when I used them in mine (I used the tonepad layout). When it comes to the opamps, I'd use the TLC2262 for the opamps. They don't make much noise etc.

Now, are you gonna get some switches? I've looked around, and from what I can see, you basically have to go with rotary switches, unless you wanna file out square holes for slide switches. A good set of 2P3T will be what you need.

Cheers,

Nish

gak · February 20, 2005, 06:28:16 PM

i couldn't find the switches yet but today a guy from argentina from another forum told me where to find em, so i think i'm getting them this week
after that i'd start building the enclosure

i know TLC2262 are better than TL072, but they're so expensive here, that's why i'm asking if i could replace them with MC33202 which are cheaper and they are also rail-to-rail op amps with the same pinout as the TLC2262
anyway, i have to say i have no hum at all after fixing all my mistakes on the pcb... after reading a lots of reports and some articles, i can't understand that... :?
the guy at the electronics store told me multilayer ceramic caps are better than poliester ones for audio applications so i used multilayer... could this help to improve results? otherwise, i can't understand how it's so quiet even using TL072 op amps...

more pics and clips comming!

gak · February 20, 2005, 08:49:22 PM

Thanks to ImageShack for Free Image Hosting

sir_modulus · February 20, 2005, 09:22:34 PM

I dunno...Mine kept self-oscillating..

I'm sure those'll work in there too. NE5332's worked for me too.

Cheers,

Nish

JimRayden · February 21, 2005, 01:52:16 AM

It looks a bit messy but those drawn lines sure have a mojo to them. Reminds me of the innards of my old russian synchro-wah.

-----------
Jimbo

SirPoonga · February 21, 2005, 11:21:59 AM

I have a question on the build for this

I'm looking at the schematic on tonepad. I am looking at S1A and S1B. What does that switch do? It looks like it switches.
Let's say the switch is is set so pole 1 is on. There is a circuit from the 100k pot, to the S1A, to the 0.022 cap, tot he top 0.0047 cap, to S1B, to S2B.
Let's say the switch is is set so pole 2 is on. There is a circuit from the 100k pot, to the S1A, to the 0.022 cap, to the bottom 0.0047 cap, to S1B, to S2B.
Same thing. Nothing is different. What's the purpose of the switch?
If the top and bottom 0.0047 caps were different values I could see it doing something.

sir_modulus · February 21, 2005, 11:41:36 AM

You know what....I don't know :?

Let's look at SW1:

when it's in pos 3, the 100K pot is shunted to ground via a 22k res.

When it's in pos. 2, it goes through the little circuit through the middle 0.0047uf cap. When it's in 1...it goes through the little circuit through the other 0.0047uf cap.

Pos 2, and 1 are apparently the same...and that's (supposed to be) the difference between centre and off axis miking...hmm...

Cheers,

Nish

JimRayden · February 21, 2005, 11:42:22 AM

As you can see, S1B has a permanent connection to the top "bubble" so if the switch is there, it stayes at 0.0047. If it's in the middle, it's two of 0.0047's in parallel.

And S1A has it wired so the first 2 positions would be the same. (only cap value in S1B changes)

I hope I got it right.

------------
Jimbo

sir_modulus · February 21, 2005, 11:45:44 AM

You know what? I think it's an error in the schemo! Try following the traces: You'll find that when the switch is in B, it just goes through the circuit, but when in C, the 0.0047 uf cap is also connected to a 22k res to vb, and another 22k resis. that is the feedback loop for the little circuit.

Oh! I get it now When in switch pos 2, itgoes through the 0.0047uf cap first. Then it goes through the other one, then is shunted to vb through the 22k resis etc...

When it's in Pos 3, it goes to vb via the 22k resis. first, then it goes through the 0.0047 uf cap, then into the rest of the circuit.

This is all happening on S1B, and you can only really get it if you follow the PCB traces.

Cheers,

Nish

SirPoonga · February 21, 2005, 08:23:13 PM

I followed the traces first, that's how I noticed this. What am I missing? I still don't see it.

SirPoonga · February 21, 2005, 08:29:41 PM

oh, I get it now,

sir_modulus · February 21, 2005, 11:04:35 PM

It's odd eh? I've never found an error in a tonepad schem before... :shock:

Cheers,

Nish

SirPoonga · February 21, 2005, 11:21:29 PM

I get it now. What does putting caps in parallel do? I always get them mixed up with resistors.

SirPoonga · February 22, 2005, 12:32:40 AM

finally downloaded the mp3 (modem sucks). Very cool. I wonder how it would work with bass... I thought I saw threads here before of people using this for bass.

JimRayden · February 22, 2005, 01:11:09 AM

In parallel they add up.

-------------
Jimbo

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SansAmp GT-2 build report (UPDATE: Sound Clip)