Switching between preamp channels (Sansamp GT2 based) ? - diyAudio
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Old 28th June 2008, 06:44 PM   #1
danV is offline danV  Europe
diyAudio Member
Join Date: May 2008
Question Switching between preamp channels (Sansamp GT2 based) ?

Hi all!

I started building a new 3 channel preamplifier, based on 3 Sinamps (the Sansamp GT2 clone from Tonepad)

I need help with electronic switching, which is a new thing for me. This is what I'd like to do:

Sw1a and SW1b : between channel 1 and Switch 2
Sw2a and Sw2b : between channel 2 and 3

Sw1c: activates Led for channel 1
Sw2c: activates Led for channel 2 or 3

This could be done with 2 3PDT footswitches, however I'd prefer a separate 'pedal' for controls. Therefore I need to use eletronic switching.

I have read some documents on thise topic on GEOFEX and The Tone God:

I have checked the datasheets of the 4053 and 4066. They both offer the same resistance to the signal path when engaged, so I think there should be no audible difference when in operation.
My choice will then be based on the better configuration. The three channels are basically 3 Sansamp GT2s. I'd like to know which could be the best place in order to add these switches.
Judging from the schematic at Tonepad, I think there are 3 possibilities (see attachment).
1st one:
- I can 'split' the signal after the 22n cap and 10k resistor (point A), by wiring the 3 GT2s in parallel (blue wires). I don't think this should cause audible treble loss, since the driven impedance is pretty high (~= 100Mohms). So no switch here.
- I can select the channel after IC4b (point B, just before the output buffer), or at the output C (I will add another buffer, in order to have a controllable output line out, or a headphone amp.)

2nd one:
- I select the channel at point A;
- I mix all the channels after IC4b, or the output buffer

3rd one:
- I select each channel both at point A and at the output (like a DPDT switch configuration).

In all these configurations, there is no need for the 1M pulldown resistor at the input.

Which one do you think is the best choice?


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File Type: png gt2_3ch.png (49.8 KB, 257 views)
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Old 6th July 2008, 03:24 PM   #2
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Join Date: Dec 2003
Location: Germany - Bavaria
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I'm into quite the same thing, some http://www.tech21nyc.com/triac.html cloning
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File Type: jpg 3sinamp.jpg (86.0 KB, 223 views)
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Old 6th July 2008, 03:30 PM   #3
diyAudio Member
Join Date: Dec 2003
Location: Germany - Bavaria
Send a message via ICQ to karahara
About the switching: I just would split the Input-Signal before each channel. Then route it to 1, 2 or 3 via Relais/electronic switch/etc, haven't decide yet, just like the Tria AC has a push-switch for each channel. The "off-channels" should be seperatet from the Output signal by switching them off(floating), maybe also set the input to Gnd.

I have also thought about using a C and digital pots to have just one set of knobs/switches...

I'll begin with it in a couple of weeks, further infos then.

Happy building danV!
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File Type: gif switch.gif (8.3 KB, 203 views)
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Old 19th October 2011, 02:11 AM   #4
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Join Date: Sep 2009
May I bump this thread? I'm also interested in using cmos switch to toggle between gain and amp model of the sansamp GT-2. Did you finish this project?

This could be done with 2 3PDT footswitches, however I'd prefer a separate 'pedal' for controls. Therefore I need to use eletronic switching.
May I ask how to implement this?

thanks a lot.

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