Carl
Please read my Post #19!!

 

Ok, my apologies. I skimmed through it and didn't realize you answered my concerns.

 

Hi,

Unless your guitars have on-board or inline pre's or other form of impedance conversion (before your mixer), you shouldn't worry over sound quality, as there'll be nothing but The Sound of Silence (+noise)

For a clean guitar pickup (i.e. just the wire), you need around 1M Ohm of input impedance (and good cable) for clean highs - 5k Ohm will quench even the lowest notes.

 

Hi,

Unless your guitars have on-board or inline pre's or other form of impedance conversion (before your mixer), you shouldn't worry over sound quality, as there'll be nothing but The Sound of Silence (+noise)

For a clean guitar pickup (i.e. just the wire), you need around 1M Ohm of input impedance (and good cable) for clean highs - 5k Ohm will quench even the lowest notes.

The guitar input i'm connecting is coming from my Zoom G3x Guitar effects processor. I just want it to be linear, nothing fancy..

Here's the link of the processors specs ... http://www.zoom.co.jp/products/g3/spec/

 

The guitar input i'm connecting is coming from my Zoom G3x Guitar effects processor. I just want it to be linear, nothing fancy..

Here's the link of the processors specs ... http://www.zoom.co
.jp/products/g3/spec/

Yeah, it's nice! And it's got ZOOM written all over its displays
But still...

(Output load impedance 10kΩ or higher)

5k won't quite cut it, if you go for the best result.

I don't quite understand your wish to go from a ZOOM to a crude mixer and into whatever though (the word sacrilege enters my brain )

If you want to feed it into some sort of recording device, I'd recommend the ZOOM H4. I think they upped it into a H5 now, but my experience is with the H4, which I highly recommend (although their menu system is a little hard to operate quickly) - you can record in very high quality(.wav up to 96kHz/24 bit and MP3 up to 320kbps ), it has got several input options (balanced as well, with switchable phantom supply) and you can use it as a killer USB sound card, a 4-track home studio, it's got plenty of guitar effects and can be used as a simple SD card reader/mass storage device - a whole lot in a box, the size of an early eighties cell phone.
Oh, I digress...

Go with what Dick Cappels posted (post #12) and use any op-amp that settles your need for noise and THD levels - remember, with a guitar, a 1% distortion won't be noticed by even the most golden ear, as it will just be a slight coloring of the sound drowned exceedingly in whatever effect you throw at it - I wouldn't shy off using an LM358 for this, but it's up to you and your budget of course
I'd go with >10k potentiometers at the input - no reason to ride the limits.

If you need help with component values, just shout.

 

I don't quite understand your wish to go from a ZOOM to a crude mixer and into whatever though (the word sacrilege enters my brain )

Well Soren, when ever we(me and other guitarists) get together to jam, we are limited with only one amplifier, so each has to take turns . Sometimes, the playing tends to be so well that we get greedy and not give others a chance . To avoid this i am building this circuit so that all of us can connect and play to a single amp (taking turns of course).

 

If you need help with component values, just shout.

Could you suggest me some good low noise opamps, bjts and fets for audio applications?

 

Well Soren, when ever we(me and other guitarists) get together to jam, we are limited with only one amplifier, so each has to take turns . Sometimes, the playing tends to be so well that we get greedy and not give others a chance . To avoid this i am building this circuit so that all of us can connect and play to a single amp (taking turns of course).

Taking turns? Where's the jam in that?

Could you suggest me some good low noise opamps, bjts and fets for audio applications?

The noise part is the only possible reason to avoid the LM358 (40 nV/√Hz) IMO, but I'd still try it out. With a good quality (turned pin/tulip) socket, you can upgrade to whatever later, if you don't find the LM358 adequate and it's the cheapest way to go. If you put a noise gate between mixer and amp anyway, you'll never hear the noise, as it will be completely drowned when there's a signal.

Guitar electronics is quite another beast than general audio and I'll never understand the craving for the extreme, just to hit it with waahs, flangers, phasers, fuzz and what not - if you can't hear the noise, then trying to remove it, is a colossal waste of time, pure and simple.
BJTs and FETs are sort of out of place in a thread about an op-amp mixer, so I'll skip that part, but for the project you outlined, any dual op-amp (with a few exceptions) will have the same pin-out, so you can try out most, just by swapping.
Classic offers would be: TL082 (25 nV/√Hz), TL072 (18 nV/√Hz), NE5532 (5 nV/√Hz) , OP27A or -E (3 nV/√Hz) and you can get below (1 nV/√Hz), but you won't get a better sound that way and as the noise go down, the price goes up.


I Attached a file with a schematic of a working mixer. Depending on input amplitudes, you can get THD under 0.001%, way better than needed. Should you find it noisy, just hit it with an OP27A or similar.

View attachment Guitar_Mixer.pdf

 

Taking turns? Where's the jam in that?

View attachment 82739

Well i ment to say taking turns to play solos...

 

The noise part is the only possible reason to avoid the LM358 (40 nV/√Hz) IMO, but I'd still try it out. With a good quality (turned pin/tulip) socket, you can upgrade to whatever later, if you don't find the LM358 adequate and it's the cheapest way to go. If you put a noise gate between mixer and amp anyway, you'll never hear the noise, as it will be completely drowned when there's a signal.

Guitar electronics is quite another beast than general audio and I'll never understand the craving for the extreme, just to hit it with waahs, flangers, phasers, fuzz and what not - if you can't hear the noise, then trying to remove it, is a colossal waste of time, pure and simple.
BJTs and FETs are sort of out of place in a thread about an op-amp mixer, so I'll skip that part, but for the project you outlined, any dual op-amp (with a few exceptions) will have the same pin-out, so you can try out most, just by swapping.
Classic offers would be: TL082 (25 nV/√Hz), TL072 (18 nV/√Hz), NE5532 (5 nV/√Hz) , OP27A or -E (3 nV/√Hz) and you can get below (1 nV/√Hz), but you won't get a better sound that way and as the noise go down, the price goes up.


I Attached a file with a schematic of a working mixer. Depending on input amplitudes, you can get THD under 0.001%, way better than needed. Should you find it noisy, just hit it with an OP27A or similar.

View attachment 82739

Whoa...!! there's a lot of info here... Thanks a lot Soren

 

Guys i built the practical circuit little different than what Soren has given... i used 10k and 10uf cap instead of 100k and 1uf, when i used lm358 it sounded crappy, there was no linearity i replaced it with tl072, sounds kickass... M very pleased with the result, Thank you all once again

 

Guys i built the practical circuit little different than what Soren has given... i used 10k and 10uf cap instead of 100k and 1uf, when i used lm358 it sounded crappy, there was no linearity i replaced it with tl072, sounds kickass... M very pleased with the result, Thank you all once again

Great

What exactly do you mean by "linearity"?
Are you referring to distortion?
(Too high an input amplitude would increase distortion to some degree).

The reason for 1µF/100k was simply that a non-polarized 1µF cap is relatively easy to come by and (even without selling your soul to the downstairs guy), while 10µF caps are rare and expensive - you didn't use polarized caps (electrolytics) I hope?

 

Great

What exactly do you mean by "linearity"?
Are you referring to distortion?
(Too high an input amplitude would increase distortion to some degree).

The reason for 1µF/100k was simply that a non-polarized 1µF cap is relatively easy to come by and (even without selling your soul to the downstairs guy), while 10µF caps are rare and expensive - you didn't use polarized caps (electrolytics) I hope?

Yes Soren, I refer to distortion. I had connected my guitar directly into the device, and without even cranking up the gain i was getting overdrive like effect, but now itz resolved, thanks to tl072.

I've used the Polarized capacitor following Dick's advice in Page 1. Why should/should'nt use a Polarized cap?

 

Yes Soren, I refer to distortion. I had connected my guitar directly into the device, and without even cranking up the gain i was getting overdrive like effect, but now itz resolved, thanks to tl072.

OK, good to know - there's a lot of difference in output voltage levels from different pickups, so that might be the reason.

I've used the Polarized capacitor following Dick's advice in Page 1. Why should/should'nt use a Polarized cap?

I can't find anywhere Dick Cappels endorses the use of polarized caps in the input?

The reasons that you shouldn't are legio. Their large non-linear ESR and their capacitance varying over time, temperature and frequency (and the initial value carries a huge tolerance as well).

I tailored the lower (and upper) frequency to fit a guitar with a bit of headroom each end. With electrolytics in the input, there's no way to tell what the lower frequency is, at any given moment (or the next).

I'm not sure if two hot pickups playing together won't be able to put too much reverse voltage on an electrolytic when they're in anti-phase (as they will be every now and then), but even just a small chance of leakage, is quite enough for me to not use them in such places.

If you want to keep using them, make them at least 5 times larger to cater for the time and temperature dependencies, to make sure it won't put the low frequency notes in jeopardy.

As long as it's just for a bit of garage jam, you can use your ears to decide, but the capacitance change over time may slip under, as it won't happen suddenly - maybe you could simply check every now and then, that the open strings are equal in loudness.

 

You also need some other capacitors in your circuit.
Put a capacitor in series with each audio input resistor with the negative end connected to the pot wiper.
.

@Soren.. Thank you for your reply, as of now i'll just let it be as it is, will plan on changing when sound degrades. And here is Dick Cappels post.

 

@Soren.. Thank you for your reply, as of now i'll just let it be as it is, will plan on changing when sound degrades. And here is Dick Cappels post.

Oh that post, yes, thanks.
Not sure why he said so, but anyway - as long as it works for you, you can stop caring about our engineering indifferences - Happy jamming

 

I've heard/read many people telling that electrolytic cap is unrelaiable in long run.... I begin to wonder if they are so unrelaiable what are their uses then, why are they still being manufactured then??!!

 

I've heard/read many people telling that electrolytic cap is unrelaiable in long run.... I begin to wonder if they are so unrelaiable what are their uses then, why are they still being manufactured then??!!

Compared to their size, they have huge capacitance and while they're no good when frequency depends on them, they have oodles of other uses - eg. anytime you need to store energy or decouple supply lines (where you'll typically gang them up with ceramic caps for high frequency handling). Rest assured, if they had no particular purpose, they'd vanish like eg. the E-cell did.