Best op amp for a transparent boost guitar pedal?

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braincelluniverse

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Has anyone ever tried using this Texas Instruments INA103 for a clean boost?

http://www.ti.com/lit/ds/sbos003/sbos003.pdf

Not sure how I would set this up but it seems like it could be very promising. I am really interested in finding an op amp with a very low noise to signal ratio.

Thanks guys!
 
That chip is designed for best noise performance at low impedance. A guitar is a fairly high impedance source and will work best going into a 1M load (or higher). The datasheet of the INA103 mentions some alternatives for higher impedance sources.

You can get good performance with a standard jfet input opamp.

regards, Jack
 
braincelluniverse said:
I am really interested in finding an op amp with a very low noise to signal ratio.
I guess you mean a very high sihnal to noise ratio... ;D
In fact, for guitar, you don't need a particularly stellar noise performance. The output level of an electric guitar is easily in the hundreds of millivolts, so anything that has less than 10 microvolts EIN will be apt enough (after all, that's what most 12AX7-based input stages do).
Indeed, electric guitars present a rather high source impedance (very variable depending on the volume setting) betweeen zero and 500 kiloohms, so a BJT input device is not the best choice (although I had pretty good results with the LM107/307, which run their input transistors at very low current). But definitely you need a FET input opamp. Indeed the OPA134/2134 is an excellent performer; however it may not be stellar on a single 9v supply. I've found the pedestrian TL061/62 to be an excellent performer in this position.
 
Answered in detail at another forum.

For guitar impedances, it is hard to beat TL072 and similar.

I had some thoughts about a discrete BJT guitar interface. I may write that up. I don't think it would sound "better" than TL072, just keep your hands busy.
 
I use a pair of OPA2134's for a loop buffer, and the performance is excellent running on a 9V supply.  It hasn't left my pedal board since the day I built it.  I run then unity gain, but there is no reason that you couldn't boost the gain a little bit.  Just don't go over 7.5V P to P.
 
TL072 all the way ;)

http://www.valvewizard.co.uk/glassblower.html

I've built several and they sound great. Clean and huge headroom and gain. Plus you get a buffer :)

Cheers
Sono
 
PRR said:
Answered in detail at another forum.

For guitar impedances, it is hard to beat TL072 and similar.

I had some thoughts about a discrete BJT guitar interface. I may write that up. I don't think it would sound "better" than TL072, just keep your hands busy.

Hi PRR,
any chance you might share your thoughts on your ideas for a "discrete BJT guitar interface" ?

thank you
 
sonolink said:
TL072 all the way ;)

http://www.valvewizard.co.uk/glassblower.html

I've built several and they sound great. Clean and huge headroom and gain. Plus you get a buffer :)

Cheers
Sono

that looks very handy. also, the iteration with the lil led meter has some serious visual appeal :)
 
PNP NPN transistor booster
A circuit using a Sziklai pair just to build a guitar boost with a Sziklai pair
Gain is under X10 depends on output loading.
http://www.diystompboxes.com/smfforum/index.php?topic=114035.0
There are other boosts in threads at that web site

However a JFET input opamp based boost is a good thing to try as others have posted.
Input resistance makes a difference with passive guitar boosts. 470K and up often leaves in the upper resonant peak when the volume control has less than about 50K series resistance and tone is set full treble to the effect.
When I sim a circuit I often use a simple guitar sim in the larger sim. It does not sim the "sound" of the guitar because it leaves out the neck, body, metal parts etc. part of the tone, however it gives an idea how the tone can change with the volume setting and tone setting.
 
Based on impedance of lead guitar pickup a bifet op amp seems indicated...

back last century I used tl07x . There are better modern op amps available now but if you are stealing power from phantom power to run it (like I did) be careful about using an op amp that is a current hog.

JR
 
Indeed a well designed BJT stage can exhibit the desired high-impedance, but the noise issue is still there. The proposed circuitry has the input transistor operating at about 30uA collector current, which induces an OSI (optimum source impedance) of about 50kohm. A typical guitar wants to see 500+k, and is seen by the input stage as a complex impedance that varies between 0 and 125k (assuming 500k pots). So the BJT stage will operate with a less than optimum source impedance, but not very far; the noise factor should not be more than 6dB, which is adequate considering the relatively high level of guitar pickups. Active guitars will not present any problerm at all in that respect.
However, this type of stage will be challenged with passive piezo undersaddle pickups, that present  an impedance too high for proper noise performance.
I've never had any issues with a pedestrian TL0 in that position. In my latest DI's, Ive used OPA2134 for added "transparency" (read less distortion).
 
abbey road d enfer said:
In my latest DI's, Ive used OPA2134 for added "transparency" (read less distortion).

I'm building some DI's at the moment, do you have any DI circuits with OPA2134 that you could share?

Thanks
 
Whoops said:
I'm building some DI's at the moment, do you have any DI circuits with OPA2134 that you could share?

Thanks

How about: a 1M input resistor (between the ¼" jack's tip and ground), into a non-inverting gain stage with one of the amplifiers, and perhaps use the second amplifier to create differential drive? Add power supply. Done.
 
Andy Peters said:
How about: a 1M input resistor (between the ¼" jack's tip and ground), into a non-inverting gain stage with one of the amplifiers, and perhaps use the second amplifier to create differential drive? Add power supply. Done.
That's about it, IIRC I used a 3M input termination because some people think that more is better.  ;D

JR
 
FWIW, TI's recommendation for audio 'input' circuits that need to span a large source impedance range is the OPA1642 (for dual).  However it's only available in SOIC, so those that shy away from SMD may want to look elsewhere.

As a bonus, its en noise specs are better than the OPA2134.
 
The sim was for fun and something a little different in the guitar effect world. 

It seems sometime people want discrete guitar circuits instead of an IC opamp. I agree there is nothing wrong with an IC opamp buffer for guitar.

There is also bootstrapping a high Hfe transistor emitter follower and if you adjust the bootstrap cap you adjust a bottom bump into the follower.

I posted a number of other screenshots of sims at diystompboxes. The NPN boost ver. 2 is a fun one.



 

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