custom Atenuverter circuit (POLAMIX style)

cybermoogly
New Member

Posts: 3

custom Atenuverter circuit (POLAMIX style) Jan 3, 2021 22:44:57 GMT

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Post by cybermoogly on Jan 3, 2021 22:44:57 GMT

Hi,

I'm trying to adapt a schematic from befaco dual atenuverter eurorack module (https://befaco.org/docs/Dual_Attenuverter/Dual_Attenuverter_V2_Schematic.pdf).

The aim is to make a custom multifunction module in order to save space, including one channel offset+atenuverter like in the POLAMIX module.

I thought with my small knowledge in electronics that it would be "easy" to adapt a -/+12V schematic by creating a "virtual ground" at 2,5V with 2 same value resistors (connected to +5V and ground), but after prototyping on a breadboard, it doesn't seem to work as expected...

Does anyone can help to find what's the problem on my adapted schematic ?
AE_atenuverter_test.pdf (44.09 KB)

Thanks

keurslagerkurt
Admin Member

Posts: 1,010

custom Atenuverter circuit (POLAMIX style) Jan 15, 2021 8:41:13 GMT

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Post by keurslagerkurt on Jan 15, 2021 8:41:13 GMT

Hey, I didn't notice your post earlier on, so maybe i'm to late to try to help you, but as far as my knowledge goes from basic guitar pedal diy, your 'virtual ground' part should work fine.

What is the problem exactly you get with the circuit? Do your measured voltages correspond with the 5V and +2,5V at the right places?

I think the use of TL072 might be the problem. 5V is it lowest possible operating condition, and what I heard from other ppl on the forum, it gives lots of clipping problems (it can run on 5V, but then the voltages it can 'pass through' on its pins are lower than 5V, making the output signal topped off). Most people around here are working with MCP6002 as a substitute (I'm still waiting for mine!).

Hope this helps in some way! I'm not a specialist in any way, so I might overlook a more obvious problem

Live music, from techno to hiphop. www.linktr.ee/keurslagerkurt

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cybermoogly
New Member

Posts: 3

custom Atenuverter circuit (POLAMIX style) Jan 16, 2021 21:29:59 GMT via mobile keurslagerkurt likes this

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Post by cybermoogly on Jan 16, 2021 21:29:59 GMT

Hi Kurt,

Thanks very much for the reply.
No problem for the delay, I was doing a pause with this project, anyway !
I haven’t resolved yet, because I was getting some weird measurements that I couldn’t explain (depending on the resistors I used for the “virtual ground”, 2x 1M or 2x 10K, I didn’t get 2,5V as expected for half voltage...).
I started to think that it was maybe a problem with the breadboard ! (maybe some shorting that I didn’t had time to verify)

Anyway, your tip about the TL072 seems to be a very good one.
I will try some MCP6002 on this circuit.
Then, according to my results, I will update this post, if something’s working