simple mixer suggestions sought

[pinkjimiphoton]

so... recently i got a decent, if cheap, ibanez accoustic 12 string. of course, being me, i had to electrify that suckah, which i accomplished the other nite after hours of dremel'ing holes to fit the preamp and battery holder etc... btw, i chose a cherub gt5 i found on ebay for about 50 bux, really nice little piezo dealio with phase inversion, 3 band eq, onboard reverb and chorus and a decent tuner. worth every cent, it sounds freaking great, ridiculously so. i can't hear much diff if any with super high end expensive systems i've tried on guitars that cost more than i make in a decade. so if ya need one... check 'em out.

https://www.ebay.com/itm/Acoustic-Guitar-Preamp-Piezo-Pickup-3-Band-EQ-Equalizer-LCD-Tuner-w-Reverb-W2G4/123242151667?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

anyways, while waiting to get the piezo set uo installed, i bought a fishman "rare earth" soundhole pickup to try. sounds ok, nothing great... BUT in combo with the piezo system, supplies all the ass the piezo's lack.

barry at guitarpcb.com <god, i love that guy, he's really an ace dude and good friend> sent me one of his "sonic tonic" enhancer boards to try. its da BOMB. sounds incredible!
https://guitarpcb.com/wp-content/uploads/2018/06/BI_Sonic-Tonic.pdf

nice simple build. of course i had to molest it some to suit my needs, and came close, but no cigar.

i ended up making a really simple passive mixer stage with two input jacks, each feeding a 1 meg pot,  100n iso cap and 100k resistor that goes to the "input" of the footswitch... figuring, cool, piezo in one in, mag in the other, mix til sounds good and enhance... well, it works, sorta... with a bit of interaction between the controls as expected.
but the piezo side has about 3 or 4x the balls of the mag pickup. so its not an ideal situation, and by the time ya get the mag about unity gain, the piezo is barely on, which of course affects the effect of mixing the two signals.

so i thought to my tardfounded ass, tardfounded ass, use a simple boost stage for the weaker mag... but... not a great solution, as most boosts i've built, tho great for making your gee-tar LOUD AS @#$%, tend to color the sound and add some distortion. i wanna keep this clean, and kinda worry about the interaction of the two preamp signals "fighting" each other instead of lieing down together and making sweet electron love.

so next thought was i need a very simple active mixer stage. as we all know by now, i know nada, zip, zilch, nothing about actual electronics... i may  cobble together a mean fuzz box from time to time <usually about once a day, lol, you guys have no idea how many "designs", tho amusing, i never share with the world for fear they'd unleash demonic banshees from hell or washingtoon or someplace evil like that> but i am strictly a monkey with a breadboard and 10,000 years of accidents leading to meagre food for fuzz forgotten.. so i need help to figure this one out...

what i need to do, is basically take an opamp, and make an active mixer with it.  i was thinking an ne5532 kinda deal would likely work out, as there's two inputs etc, but not sure if i would use the inverting or non inverting inputs to mess with? or should i use a switch so i can switch between the two so i can maintain proper phase between pickup systems if need be, or for feedback control?

what would be a good input impedance to shoot for? output impedance? does that shit matter? or can i just simply connect each input to one stage, and then sum that to the switching? this will be used ONLY for the 12 string, so not really worried about true bypassing it.

am i correct in assuming i can't use a single opamp for this? boy-howdee, be nice to plug one in + and one in - and have it all come out one output, but i know that isn't gonna work

if i use a dual, will i need another mixer stage after that to  feed the input stage of the enhancer? or can i  just "passively" use a couple resistors to mix the two outputs together?

are there any preferred chips or styles of chips to do this? reccomended layouts?

again, all i need is two active stages that i can use as a buffer to a boost.. mixed together to drive one mono input on the enhancer.

its gotta be point to point or vero i imagine, as somehow i gotta squish it all into the 1590b i've already got it assembled inside of.

sorry for all the stupid questions, but hey, i AM the stupid pedal tricks guy....

any suggestions, criticisms, or leads to pertinant info that can help my dumb ass work this out would be sincerely and gratefully appreciated!!

i promise to pay it forward.

thanks fam
peace to you n yours
PjP

[Fancy Lime]

Hi Jimi,

there's a million ways to do this and then some. What I would do in your place, is install a stereo Jack and get the magnetic and piezo signal out separately and the do the mixing in a wee box on the floor. Lets you do crazy things like running the mag through an overdrive or fuzz and the piezo through a chorus. Or whatever. Like, literally: whatever. That is, *IF* you are the kind of guy who likes interesting tonal options, wink wink, nudge nudge.

In the little mixer box, I would use half a NE5532 in summing amplifier mode to mix the signals, as seen here:
https://en.wikipedia.org/wiki/Operational_amplifier_applications#Summing_amplifier
It is probably a good idea to first boost the mag signal with a non-inverting amplifier:
https://en.wikipedia.org/wiki/Operational_amplifier_applications#Non-inverting_amplifier
Be aware, though, that these schematics assume a dual power supply, so "ground" should be replaced with half supply voltage (+4.5V for a +9V design), if you are using a single supply.

Hope that helps,
Andy

[pinkjimiphoton]

awesome help, andy, thanks mate!!
makes sense... its already done in a wee box on the floor, i need to design a daughterboard i can stuff in there. i will scope the links out and try n digest it as much as possible. there IS a buffer built into the enhancer, so hopefully i can scoot without having to add a recovery stage. thinking i have about as much room as a postage stamp square or a 9v battery to fit it in there... its kinda tite, but i think i can do it.

APPRECIATED!!

[ElectricDruid]

+1 wot Andy sed.

You need a simple op-amp mixer like you thought. Something like this:



This is set up for single 9V supply, but they added a second inverting stage to make the whole thing non-inverting overall. You probably don't care for your purposes, but a dual op-amp is about as cheap as a single, so its not like it makes a lot of odds either.

You could tweak the input resistors into the first mixer to adjust the ratios to suit the levels of the signals. If one signal is twice as loud, it needs a input resistor twice as big (so go to 220K, for example).

T.

[Mark Hammer]

1) +1 on suggestions so far.

2) The Sonic Tonic is a clever little circuit.  It's a basic state-variable filter, just like found on the Mu-Tron III or EPFM Super Tone Control, with some of the component values tweaked and worked out to provide a particular tonal balance.  So thanks for the link.

3) Acoustic guitar can have bigger transients than electrics.  Plus I'm naively assuming you're not going to use the guitar like Liona Boyd or Nick Drake.  Given that, I would suggest having a supply voltage greater than +9V, just to provide some headroom.  That can either involve a charge pump, two batteries, or an external wallwart like 15, 18, or 24V.

4) A tunable highpass filter can be useful for taming feedback in an acoustic; particularly when amplified in small-stage venues where feedback risk is high.  C3/R4 on the Sonic Tonic provides a bass rolloff around 16hz.  Changing C3 to 2u2 moves that up to 72hz, and changing it to 1uf moves it up to 160hz.  It's only a 6db/oct slope so you may want to move it up a bit higher than that.

[pinkjimiphoton]

thanks tom!!!
gonna def give it a shot.
right now, only cuz i'm lazy, i'm trying to graft in one of jack orman/amz's mosfet boost boards .......

scratch that idea;)

don't try it at home, kids...i'm a highly underpaid amature. armature?

oyyyyyyyyy

[pinkjimiphoton]

hey, sir mark!

glad you dig the circuit, check barry's demo out. the demo is good, but MAN the compression really detracts from how good it REALLY  is... big ass props to bar and ray and tonman on it. great with electrics, too.. bass...mandolin..

adding the 1m gain pot as i did, with a 100n cap and 100k resistor i think helped a bit... the bigger load seems to let a smidge more guitar thru, i thiMk.
and cutting it a smidge helps "blatty" spikey transients get padded down a bit too if you get over enthusiastic from the tone of it and get a bit bashy   

i built it with robust enough components i can definitely run the whole thing on an 18v tap on my board or a wart. pretty much wanna use it for live use, and the combo of mag and piezo is heady when blended right. i figure i'll take the output to a volume pedal, and send that to a di box to the board.

i'm actually toying with drilling some horrible holes and mounting it
IN the guitar... but a lot of work for a potentially hummy mess.

i've got active 3 band eq on the piezo, the fishman is perfectly balanced warm n phat and offsets the brighter piezos great, but just not loud enough.

i've got just about enough room to stuff a dual oa n passives in on the side of the switch, so will try n work up a tiny vero to do the trick.

larry/rutabaga bob sent me a beautiful perf layout, just a smidge bigger than i can fit tho. i may go ssod and go p2p on the back of the chip socket. see if my chops are up for it.

but first, some questions...

in the examples posted, aren't they close enough for rocknroll to the first stage of the sonic tonic?

i did pretty much the same thing for the input mixers, but i used 1 meg pots for the 100k resistors, then used 2 100k resistors to sum the two pots wipers.

i'm wondering if the return of adding another mixer stage is gonna work significantly different enough to merit changing it? full up, the mag is about unity gain, so maybe i should not worry about it, and just use it as i had first tried? worried it will be noisier, too.

perhaps i could take the output of the simple passive mixer i made thats similar to the examples, and bypass the input load resistor and cap and go right to the + input on the board itself? or would that affect the input gain of the circuit too much?

sorry for all the dumb questions. i am kinda surprised the different "channels" of the mixer don't use individual preamp stages. probably my inherent stupidity there, again... lol

thanks guys! i humbly await your response. peace out!

[GGBB]

Impedances matter. Piezos want to see very high Z inputs. Magnets - high Z. We typically have 1M input Zs for e-guitar stuff. I've seen recommendations for piezo at 10M - my Baggs pre is 10M. So those 100k mixers are probably going to load down your signals - especially the piezo. I would tend to think buffer each separately - and then just passively mix the output. Low gain might be just fine. Use JFET input opamp.

[pinkjimiphoton]

thanks gord,
that makes a lot of sense to me. i gotta see what i can work up guess i'll be breadboarding stuff tonite

[pinkjimiphoton]

ok, thought about it a little, and combined all the ideas presented, kinda. this is what i came up with... literally this is the graphic tom posted almost verbatim, but instead of using one stage as a mixer, and one stage as not an inverting amp, but as a second channel. both sides of the chip exit thru a 100n and 100k resistor, and the two resistors then sum the two signals together before the sonic tonic. gonna leave the pots at 1 meg for now for the actual mixing at the input. dunno if this is gonna fly, but it seems like it should?
thoughts appreciated. going to head for the dungeon and start messing with this.
yeah, its got standy-uppy resistors, but i'm trying to fit it all on a 10x10 piece of vero so i have room to get it in the box




do you guys think i will need to add a volume control at the end of it as well? or just use the input pots? do ya think it will fly?

stay tuned

thanks for the advice... even after all these years, ya'll are the best

[pinkjimiphoton]

OK, LEARNE
ooops ... shouting, sorry
d
some things. first, the mixer i cooked up just tain't worth poo.
removed. tried a few other things, finally went back to the passive mixer.
least noise, good gain.

but

that fishman pickup is a seriously low-gain/output pickup. i think the tonal dif was either too many shrooms or tonal load changing the sound when i added it in.

so low output, i had to turn the toob skreemer in my bench amp on.

waste of time. i mean, if ya gotta use a freegin fuzzbox to get enough output from a dang single coil pickup, i'd say its likely a piece of

anyways... abandoning this one, i think. at least for now. seems like it would be a major redesign to get enough gain to run that crummy thing with

so,.. appreciate the help and advice, but i'm not gonna use the fishman, so i'll just leave the unused channel off.  easier that way

peace and thanks

[highwater]

Weird idea that somebody else might spot a problem with: the Sonic Tonic has an inverting mixer at the end already, IC1B... I wonder if you could add a buffer for the magnetic pickup, then a 50k pot wired as a variable resistance between that and pin 6 on the ST's mixer, and call it a day?

[pinkjimiphoton]

yeah, a buffer won't do it. it needs a high gain stage for that piece of shit. pretty sure the mag pup is toast. pisses me off, as tho i bought it months ago, apparently it arrived DOA.

pretty sure the warantee period is wayyyy over sux.

i may still dick around with it, but i've never used an accoustic pickup that needed that much gain, the tube screamer part of the bench amp <some lame little ibanez thing someone traded me, 5 watt tube amp with a screamer for the front end> was literally cranked.

i'd call that garbage

[Ben N]

Jimi, I'm not clear on where that Cherub preamp thingie fits in all this. You might want to crack it open, as many onboard preamp manufacturers have different versions with various bells and whistles, including mixing mag/condenser inputs with the piezo, so it might be a board with some empty spots for the extra circuitry. I imagine anything like that would be SMD, though.

In any case, as noted in various posts above, you need a mixer (- input opamp), a level matching booster for the mag pup and a high impedance (>=1meg) buffer for the piezo, possibly an inverting stage somewhere to match up the phase of the two sources, and, as Mark suggested, generous rails would make a lot of sense here, too.

Have a gander at this: http://www.mimf.com/old-lib/piezo_preamp.htm and http://www.mimf.com/old-lib/mimf_preamp.pdf for some interesting designs that do what you need, although I don't know if the parts are all still available.

[pinkjimiphoton]

hey ben, long time bro, hope all is good!

the cherub preamp fits in like this, i installed the thing in my guitar. sounds ab-fab.

before i had gotten that a couple months ago, i had ordered the fishman to use. i never did, it sat in the case since it arrived in may. my original intention was to use the cherub piezo system as the main pickup, and blend in a little mag to give it some ass, and fill in the frequencies i find kinda lacking in most piezp systems.

as it turned out, i never got back to it until a couple days ago, when i finally gotta break from building commercial stuff. the cherub system sounds DEVASTATING, better than systems i've tried that were crazy expensive. 

so anyways, i wanted to just mix between the two circuits and then enhance both with barry's circuit in a box on the floor.
so initially i set it up non/true bypass, where it has two input jacks... each feeds 2 1 meg pots, each with a 100n cap and 100k resister, then the resistors come together at the input pin of the 3pdt. so its always got the volume controls in the circuit, which for my purposes is fine, as i'll only use it "on" anyways, and then, infrequently.

i gotta 3 band and phase switch on the cherub, so phase isn't really an issue. but i DID wanna get it all in a 1590b, which is where stuff gotta bit weird. there's very little room to work with inside. i tried adding one of jack ormann's mosfet boosts to the mag, didn't help. tried the mixer circuit tom posted. didn't help. tried my own variant, as posted... just lost gain compared to the original simple passive deal i'd come up with already.

then finally, i began to figure out the fishman was DEAD. luckily, they waranty for a year, so i am returning it for a replacement, but likely won't ever use it now as i had hoped. pretty turned off that the first time i used it, it was dead , ya know?

thanks for the info, i will explore it when i get home from tonite's gig. peace bro!

[GGBB]

yeah, a buffer won't do it. it needs a high gain stage for that piece of shit. pretty sure the mag pup is toast. pisses me off, as tho i bought it months ago, apparently it arrived DOA.

pretty sure the warantee period is wayyyy over sux.

i may still dick around with it, but i've never used an accoustic pickup that needed that much gain, the tube screamer part of the bench amp <some lame little ibanez thing someone traded me, 5 watt tube amp with a screamer for the front end> was literally cranked.

i'd call that garbage

But it does produce sound right? What's the DC resistance of it? I would expect an acoustic soundhole/magnetic pickup to be pretty low so as to sound less "electric" and therefore be lower output than typical electric pickups. So maybe not pooched just low output? You can add gain to the "Mag" buffer in my schematic by upping R2 100k - try 1M for starts.

[Ben N]

Ah so the piezo is already buffered, and maybe even boosted a little.That is, your "piezo" channel is actually a piezo>preamp channel, so no buffer needed there. OK, that simplifies things to a mixer and a boost for the mag, doable with a dual opamp, but phase may still be an issue. Hey, I wouldn't count out the replacement mag just yet; it may have just been a fluke.

[pinkjimiphoton]

hey bros,

i haven't even bothered doing a dc resistance check on the pickup.  even by itself, no output ... i mean, in a cranked 5 watt amp, it should EASILY be able to overpower the accoustic volume of the 12 string.  the actual guitar will drown the amp out. to get it audible, it needs the amount of gain of a literally cranked on 10 toob skreemer. naaaaah, its hosed!

i contacted musician's friend, out of their return window, but within the fishman warranty period. so i gotta box it up and send it back to them so they can either repair or replace it.

yes, the accoustic piezos are  internally preamped, and capable of a decent amount of gain.  i DID try to use one of jack's mosfet boosts just on the magnetic side, made no diff, still didn't pass signal. tried it with the piezos and my ears are still bleeding.

i'll try the replacement pickup with it and see how it does; if it WORKS this time <g> perhaps the load of the 1 meg pot will be enough.