Thanks a lot for this Daniel, I'm still trying to figure out how to remove the cab sim from the signal path but I can't find it for the Oxford since there's still little info on it's circuit. The mods related to cab sim removal are all for the other models of the series, and I can't do it to the Oxford. Any help would be highly appreciated!
Tech21 Character Series [schematic]
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- Joined: 24 Feb 2023, 21:06
Information
- Posts: 2
- Joined: 24 Feb 2023, 21:06
I'll use the Oxford with amp only so no need for the cab sim switch. I also prefer top mount jacks so the final (?) version looks like this (will change knobs to Orange type later on):
Last edited by Overdriver1970 on 26 Feb 2023, 14:47, edited 1 time in total.
Hi all. I'm a newbie, but I've been lurking for quite a while - I love this forum. I have a Liverpool (v1).x-tn wrote: ↑01 May 2013, 18:15bajaman wrote:...
Anyway - back to the CH34-4 module
This module uses the LINCMos TLC2262 dual op amp - internally entirely constructed with mosfets - it gain swing the signal full rail before it clips and Tech 21 have used this same device in all of their pedals from the original Sans Amp onward. It has a very soft clipping characteristic and can sound a bit "mushy' in the bass region in my opinion. However it's implementation in the character series pedal is a little different With reference to the schematics earlier in this thread you may notice two back to back 3.3v silicon zener diodes in the feedback loop of the second stage of the CH34-4 module.
It is THESE zener diodes that clip FIRST in this module according to my simulations NOT the op amp as in the original Sans Amp pedals. These zeners also roll off the high frequency response of this stage - the signal is -3dB down at 5khz and drops to over -22db at 100khz. Without the zeners, the response is flat to 100khz and beyond
I must emphasize that the signal is attenuated at high frequencies by these zeners EVEN when the signal is NOT being clipped by them
The TLC2262 NEVER has the chance to influence the clipping behaviour in these pedals - all the clipping and high frequency rolloff is performed by the two back to back zener diodes - food for thought
Cheers
bajamanIf "The TLC2262 NEVER has the chance to influence the clipping behaviour in these pedals" what would be the reason to change the TL062 with a TLC2262?bajaman wrote:I just bought a JOYO California sound pedal
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I changed the dual op amp (TL062) - put a TLC2262 in it's place - i left the other two quad op amps (TL064).
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bajaman
My belated $0.02: The clipping zeners "nominally" clip at about 2x(3.3V + 0.6V) peak-to-peak, or 7.8Vp-p. Even with a TLC2262 the circuit might cease to clip properly running on a battery under 8Vdc, meaning that you'd only be able to use about 1/3 of the battery's useful capacity. Because of its limited output swing, a TL062 would never work properly, even with a regulated 9Vdc supply.
In reality, the high impedances of the circuit (and the very "rounded" shape of a 3.3V Zener's I-V graph) mean that clipping actually occurs at somewhat lower voltages, but it's still WAY safer to use a TLC2262 (and really a requirement if you might use a battery), or else use a 10-11Vdc supply instead of 9Vdc.