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New board--Bias offset with adjustable Level
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cslammy



Joined: Apr 27, 2018
Posts: 66
Location: USA

PostPosted: Tue Nov 06, 2018 11:02 am    Post subject: New board--Bias offset with adjustable Level Reply with quote  Mark this post and the followings unread

Hi there, latest thang.

Custom PCB, 2 quad op amps used for 4 buffers, each with independently adjustable gain and bias offset.

I already built this twice (no errors I could find) and have posted 2 different designs. Audio demo as well in 3rd link.

http://www.charlielamm.com/gear/gain/forums.html#quadwoffset

http://audiodiwhy.blogspot.com/2018/10/bias-offset-with-adjustable-level-aka.html

http://audiodiwhy.blogspot.com/2018/11/small-bowal-creating-dc-bias-offsets.html

Hope someone finds this useful.....


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g.gabba



Joined: Nov 29, 2008
Posts: 451
Location: berlin
Audio files: 23

PostPosted: Wed Nov 07, 2018 10:18 am    Post subject: Reply with quote  Mark this post and the followings unread

nice,
when ur want to use this also for protecting cmos of negative voltages, may diodes on the output would protect even more?

or have two outputs per channel, one with and one without diode protection.

cu
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cslammy



Joined: Apr 27, 2018
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PostPosted: Wed Nov 07, 2018 11:31 am    Post subject: Reply with quote  Mark this post and the followings unread

Good point. To protect vs. negative voltages, just thinking out loud: perhaps you could power the board from GND to V++ instead of V++ and V--? And maybe use Rail to rail quad op amps vs. say TL074?

Suggestions for negative protection are indeed needed--what does the group think is the best way? Link anyone?

This certainly comes up with getting signals into MPU like Arduino. You don't want high current V- for that. Zeners? 4148's? Something else?
I have seen a lot of circuit clamp fragments but don't know what works best.

Thanks.

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g.gabba



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PostPosted: Wed Nov 07, 2018 11:49 am    Post subject: Reply with quote  Mark this post and the followings unread

you Smile wrote here about cmos http://www.charlielamm.com/gear/gain/forums.html#quadwoffset

i thought about something simple like this


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cslammy



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PostPosted: Wed Nov 07, 2018 12:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks! Good suggestion.

Q: Do you take a diode drop doing that? 700mV or so? I thought so....

For many applications that won't matter, but sometimes it will. Assuming we do see that, I'd need the voltages pass through unencumbered. Same for signals coming into the buffer.

I am trying to figure this out, since I will be using 4066 and 4053 on an upcoming project and the voltages are driving some sensitive gear.

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g.gabba



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PostPosted: Thu Nov 08, 2018 11:12 am    Post subject: Reply with quote  Mark this post and the followings unread

dunno but may the precisicion-rectifier could help you?

there u dont have to deal with the voltage drop.
as an example i did a simulation with 1Vpp input.

if so, than moving the offset to the first stage would make sense.


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cslammy



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PostPosted: Thu Nov 08, 2018 1:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Cool--thanks Gabba, I have not seen diodes used in a feedback loop like this. I will do some sims....

How about a Zener? The signal will not exceed the zener rating (right?) it does go a diode drop below ground--OK in my case--gets the basic job done with 2 parts.


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MapacheRaper



Joined: Feb 15, 2018
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PostPosted: Thu Nov 08, 2018 7:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey Charlie, I have no idea on how to protect it, but I have recently discover your audiowhy blog and Im totally addicted to it... I just had to say it loud.

Very Happy
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g.gabba



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PostPosted: Thu Nov 08, 2018 10:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

i know almost nothing about zeners Shocked

the circuit is really called Precision_rectifier:
https://en.wikipedia.org/wiki/Precision_rectifier

it is also used as SAW2TRI converter, eg in the Yusynth VCO and LFO
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cslammy



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PostPosted: Fri Nov 09, 2018 8:56 am    Post subject: Reply with quote  Mark this post and the followings unread

MapacheRaper wrote:
Hey Charlie, I have no idea on how to protect it, but I have recently discover your audiowhy blog and Im totally addicted to it... I just had to say it loud.

Very Happy


Thanks so much Mapache. I really enjoy writing it.

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cslammy



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PostPosted: Fri Nov 09, 2018 9:00 am    Post subject: Reply with quote  Mark this post and the followings unread

g.gabba wrote:
i know almost nothing about zeners Shocked

the circuit is really called Precision_rectifier:
https://en.wikipedia.org/wiki/Precision_rectifier

it is also used as SAW2TRI converter, eg in the Yusynth VCO and LFO



Ha! Thanks gabba, great link! I will try to breadboard it this weekend.

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cslammy



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PostPosted: Fri Nov 09, 2018 3:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

[quote="cslammy"]
g.gabba wrote:
i know almost nothing about zeners Shocked

the circuit is really called Precision_rectifier:
https://en.wikipedia.org/wiki/Precision_rectifier




Hi Gabba, no surprise, my sim works like yours. The precision rectifier preserves "top" of waveforms accurately, but dips below 0V by a diode drop. The zener one I showed clips the top but still has the same diode drop below 0 for anything that goes negative.

Both are subject to temperature variation, since diodes can be temperature sensitive.

Not sure how to get rid of those dips below 0. There has to be an easy way, but so far I can't figure it out. maybe I'll just tell the Arduino to eat what's below 0V. Surprised


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g.gabba



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PostPosted: Fri Nov 09, 2018 11:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

cant confirm ur findings Shocked


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