Fishman Rare Earth Blend replica: Passive blender pot wiring

[Mikheil]

Hi All!

Just wanted to share my, entirely handmade, Fishman replica project.

The issue: I wanted to control the two pickup sources on the small external mixer but now, I think that it was a wrong way; so, I am looking for the passive blender pot wiring to mix the two pickups into the one Out and attaching it to the pickup either the instrument.

Here are the photos and some technical data of this mic/magnetic pickup system I have built, it took a month of constructing and testing.

The Fishman replica pickup system:

1. ECM MKE-5B with miniature audio-transformer (40-16000 Hz, 250 Ohm, 4,5 V. Made in USSR)
2. Magnetic pickup of Single and Hum-canceling options (On/Off) - 3,4 kOhm and 1,6 kOhm
3. Weight: 2,5 Oz (70 gr)

The pickup is built using neodymium magnet disks, magnet wire 43" AWG, three batteries LR44; the housing of the pickup is built of different plastic components which are easy to shape and available around.

Testing:
Just a few aspects about the overall sound and quality... switching into the laptop's mic In, the pickup has almost '0' hum even with the single coil; with switched hum-canceling coil and mic, the pickup is absolutely clean, that can be considered as a good result.
The housing of the pickup and all the internal connections have 3 different layers of shielding in total, I think, that is why the pickup has such a clarity.
Note: turning the mic closer to the top, even 1-2 mm out of the sound-hole makes it sound more natural; in the body of the guitar it has more 'boxy' sound...
More photos on my website (in Georgian)
Here are the pictures:

[David Schwab]

I don't think you will be able to passively blend the two because of the impedance differences. The mic transformer will load down the magnetic pickup.

Welcome to the pickup maker's forum! That's a nice looking pickup.

[Mikheil]

I don't think you will be able to passively blend the two because of the impedance differences. The mic transformer will load down the magnetic pickup.

Welcome to the pickup maker's forum! That's a nice looking pickup.

Hi!
Thanks for the reply!
I have the third pickup installed on my guitar - SBT piezo active, similar to K&K Pure Mini and switched to the on-board B-Band preamp, it also works great. I have replaced my UST pickup with my own SBT system, my thought is that any acoustic UST (Under Saddle Transducer) system is a wrong way of reproducing the acoustic instrument's sound because it works opposite of transferring sound from strings to the soundboard....
So, the Fishman replica uses a stereo end-pin jack's both channels, I just want to make it work into one channel and wiring and having the piezo pickup onto the same end-pin jack out....
Any thoughts how to make it work with less efforts ?
In the past, I have got the suggestion to make it with one pot like this


ECM mic---->
PPPPPPPPPPP|
PPPPPPPPPPOT----wiper----> Out
PPPPPPPPPPP|
Magnetic--->

Ground--------------------->

But, this is just an idea and I would prefer to hear on some real experience than starting my own journey :-)

[David Schwab]

No, you can't mix them like that, unless you put an active mixer stage in the instrument. They each have to be buffered before they are mixed together.

Why not just get a stereo end pin jack?

[Mikheil]

Why not just get a stereo end pin jack?

It uses stereo end-pin but I want these pickups mixed to go to one of the end-pin;s outs and the second to use for the piezo..... this way, I will get all three pickups mixed into one stereo cable and controlled and balanced right on the instrument. That is the issue.

[the great waldo]

Hi Mikheil

It might be an idea to have the microphone pointing in to the guitar.

Cheers

Andrew

[David King]

I'd say the pot, if it's big enough in value will work as a resistive network to sum the two sources passively but you probably won't be thrilled with what you hear and the = balance point may be way off center. Worth trying just to see what you get.

Pointing the mic in may result in a lot of feedback and or a honky tone. Use whatever works best.

[Mikheil]

The idea of blending with ONE audio pot was about the 10-20 kOhm nominal, higher nominal pot would probably change the tone of the acoustics...
It is very interesting how Fishman, LR Baggs and others do design such a circuits ?

[David King]

I was thinking 1 MEG as a starting point. Less loading should equal less change in tone but I have no idea how an ECM mic works so I could be way off base there.

[Mikheil]

Just found this small circuit summing two signals.... using stacked audio pot at the Input, it should work as Pan pot of the two signals.... sadly it has no volume pot at the output and no idea on its quality.... any thoughts???



Or this one:

[David Schwab]

It uses stereo end-pin but I want these pickups mixed to go to one of the end-pin;s outs and the second to use for the piezo..... this way, I will get all three pickups mixed into one stereo cable and controlled and balanced right on the instrument. That is the issue.

The best way to do this is make a small 3 channel mixer that fits in the guitar. Or you will need an extra jack.

Or you can mix the mic and magnetic pickup with a small mixer in the guitar and run the piezo out on the other output. But the piezo also needs a preamp, so why not take care of it all at once.

[David King]

MIMF used to have a nicely designed set of schematics and pcb artwork for a mixer that could handle magnetic, mic and piezo inputs.
I can only find a thread relating to it but worth reading through:
MIMF ? View topic - MIMF preamp questions

[Mikheil]

The piezo pickup is an active system, the SBT pickup has B-Band on-board preamp..... mono output jack.
Mic + magnetic ..... stereo end-pin jack.

The piezo preamp has no mixer/blender pots, if I would have that then I would switch all the three into the one preamp......

[Mikheil]

Looks interesting and easy to do.... I guess I will try it when I complete my combo project... Thank you!