Understanding Noll mixpot schematic

[papasteack]

Hi,

I've token some photos of Noll Mixpot 1, and tryed to redraw the shematic. As all can be seen without opening anything, it's not a problem to show this on the forum, is it ? I'll delete files if it is.

It's a active blend pot with two separate input stage with +18db trim gains and a output buffer.
There's not many active blend without eq. The only other one i know is emg abc, but seems only to be two buffers.
I'm really newby in electronic. There's maybe some mistake. It's seems me a interesting schematic for study.
It's only 0,6mA. No idea of the op amps, but they must be very low current, a bit lower than a tl061.
Blend pot is 50k.

_wouldn't it be better if there were decoupling capacitor for op amp supplies in parrallel of 1M resistors ?

_isn't it a problem all those electrolytic caps on signal path ?

_any mod suggested ?

Thanks !!

[papasteack]

(i didn't find how to edit last post to add this...)
Working on the last schematic, i made something that would suit more my needs. But i need help to verify and improve.
I want a "rechargeable" bass, instead of having to change batteries. So, i will take the full power management of this schematic :


Its a awesome headphone amp (http://nwavguy.blogspot.fr/2011/08/o2-details.html)
So, i would have 2 batteries, and a real ground. I would add too for each battery this battery tester :

from here : http://www.paulinthelab.com/2013/02/sel ... ttery.html

As i have 2 magnetic pickups, and a piezo, i add a input stage. As now i have a true ground, i use it instead of the virtuals grounds.


I've put the volume control between stages as in the headphone amp.
I want to use a quad op amp for space saving. TLE2064 and AD8643 are low power amp. TLE2064 is a "super" TL064, very common. AD8643 seems a bit better on the paper from what i manage to understand, with lower distortion, but, it is only as far as i'm able to understand...it came in soic and not in dip, but i should solder it on a adaptator...

What do you think about this ? I probably done big error, as i'm newbie, but it can easily be seen what i want to try.
Still do not have any idea of non polarized input capacitor value.
I'm not sure about how i connected all to ground.

Power management draw around 1mA. Each channel of op amp draw near 0,25ma=> x4 = 1mA. So total current draw would be around 2mA. Wich probably give around 125 hours with 9v nimh 250mah batteries.

Thanks !

[phatt]

My advice FWIW,, back up a bit.
You need to perfect the circuit long before you ponder how you intend to implement on board charging of battery.

Your mixer circuit is dead shorting the audio path (The pot labeled Volume in front of U1d) so you won't hear a thing, turn it sideways like a normal volume and it will work.

With complex one off circuits like this you have no choice but to breadboard test it and by trial and error you arrive at the end product. (There is no free lunch)

I've been an audio electronics hobby geek for a long time and I can tell you there is no free lunch with odd ball circuits.
A bread board test circuit will actually be the faster route otherwise you can spend months if not years soldering land fill.

The piezo setup might need some tweaking and if dual rail supply then you don't need the input decoupling caps though it might help define some low frequency roll off which is often useful with guitar mag pu input.

Others here will likely know more about the fine detail meantime just find similar circuits to test out ideas.
Phil.

[papasteack]

Thanks,

I'm still working on it, and learning about eletronic. The circuit as yet changed since yesterday.
Still ac power supply for charging (with reg), but no more power management needed as batteries will never get off, and transient response is only a problem for headphone.
No more decoupling input capacitors. More coherent values resistors. One stage more for "serie pickups" balance (MN type pot), instead of parrallel active blend, so one AD8643, and one AD8641.
Probably different values for input impedance (as audere z preamp) will have to be tested instead of 1M.
From what i'm learning about op-amp, trim pots must be around 150k and not 150. Delete ground reference 1M before buffer.
Switching from parallel (active) to serie (passive) blend, with a 4pdt. Switching for each pickup two bobbin between serie/single/parrallel with a 4p3t (MEC).

Thanks for help before breadbording state !