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Old 29th May 2006, 02:31 PM   #21
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Cool Don´t forget supply current and the parts around the OP-amp

There might be one additional aspect for stompboxes and for onboard preamps in particular - that is the supply current. All of the above mentioned audio-OP-amps need pretty much current (between 3 ang 6 mA per channel). If you are running on on a 9V battery that is a lot. I am just building a preamp for the Music Man Sting Ray bass - using basicly the original schematic but with much better parts. Musis Man / Ernie Ball used an LM 4250 in the original preamp, mainly for the very small supply current and very low supply voltage. For my upgrade I first selected the OPA132 (low supply voltage, good sound). The OPA 132 however needs about 4mA per channel, which is more than 10 times of the LM4250 in the original circuit. Therefore I finally ended up with an AD820, which is not quite the audio quality compared the real high-end audio OP-amps, but it only requires 0,8 mA of supply current, works with low supply voltage and provides good headroom with rail-to-rail at the output. Slew-rate and bandwidth should be good enough as well.

Another major aspect: A lot of guitar amps and effect pedals suffer from bad capacitors, resistors and diodes.
I highly recommend to replace all polyester caps by polypopylene caps, all ceramic caps by silver mica , polyprop caps or polystyrene caps, all standard electrolytic caps by audio-grade electrolytic caps (such like the Panasonic FC).
This will change the tonal quality at least as much as the replacement of an old 4558 or 741 by a state of the art audio OP-amp such like OPA 627, OPA 134, AD823, Ad825.

Last but not least: Unfortunately learly all standard-resistors have a bad influence on sound quality. I have just used vishay dale resistors in an amp-upgrade for the first time and I could hardly believe the difference. Sorry to say - these resistors are pretty expensive and hard to get. There are only very few suppliers, who sell small amounts to other than industry customers.
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Old 5th June 2006, 08:36 PM   #22
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Default Upgrade on OP-Amp AD820 for Guitar / Bass

Following my previous comment above I would like to enclose some remarks on the AD820. In the meantime I have finished my preamp-upgrade (2-band tone control) for my Music Man StingRay bass it is a real success. Instead of the LM4250 in the original preamp I use an AD820. Input and output electrolytic caps are Panasonic FC as are the decoupling caps, which I have enlarged considerably. All other caps are polypopylene and the resistors are Vishay Dale CMF.

The sound is more punchy, less brittle, very dynamic and it got a better bottom end and and a more balanced sound from string to string and along the strings. The instrument is more responsive and thus easier to play.

I also tried the OPA134, but turned back to the AD820, because the OPA134 sounded too laid back and too hifi-like in this application. The AD820 seems to be well suited for guitars and basses and should be a good choice for stomp-boxes as well.
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Old 12th October 2006, 01:07 PM   #23
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Default Re: Don´t forget supply current and the parts around the OP-amp

Quote:
Originally posted by Doc Blues
I am just building a preamp for the Music Man Sting Ray bass - using basicly the original schematic but with much better parts.
Hi Doc,

Do you have a schematic for the original MM SR preamp you could post or email to me please?
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Old 13th October 2006, 03:20 AM   #24
Optical is offline Optical  New Zealand
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screw opamps and screw tubes!

this is where it's at:
http://www.native-instruments.com/in...=guitarrig2_us

much more tunable to a particular sound than trying your luck swapping opamps
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Old 13th October 2006, 05:06 PM   #25
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Software is the definite wave of the future. There is plenty of free suites that work good also. Here is one
http://www.simulanalog.org/guitarsuite.htm

Now we just need to figure out a small cheap, reliable, powerful enough PC that can be hauled around.
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Old 17th October 2006, 03:53 AM   #26
Daveis is offline Daveis  United States
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For hifi the AD8620 has a clean sound, but I prefer OPA627. It has a more warm, brown sound to it. OPA2604 isnt very good sounding for hi-fi, but i can see where people would like it for guitar. I actually prefer the clean, neutral sound of the NE5532 over the OPA2604 for hifi.

What does that have to do with guitar? Honestly, I dont think you want to ever hear your opamps distort. That's a job best left to tubes. In the ts808 tubescreamer, sure they use a JRC4558D but somehow I've got to think it's because it sounded good _and_ was cheap. I think you could do better.

I also have a feeling that the pedals would sound better if built with discrete opamps.

A long time ago I built some germanium diode fuzz boxes and the results were very good. I don't ever remember the opamp I used.

That GuitarRig sounds nice.... maybe approaching a TC Electronics G-Force??? Hard to lug a PC over to a friends place though.
I heard a computer VST plugin, a reverb convolver from Voxengo and some models of a vintage tube reverb and was kind of blown away. It is possible to some degree to emulate the sound of about any piece of vintage equipment. The exceptions are tube overdrive and diode fuzz where I prefer the real thing.
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Old 21st October 2006, 07:09 PM   #27
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There are lot of superstitious beliefs about sonic quality of opamps. In your application you may use any opamps. Better use them in inverting mode to avoid distortions caused by a differential input pair, but anyway any guitar amp is built to distort musically, so any opamp will fit, except some noisiest vintage devices.
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Old 28th October 2006, 02:45 PM   #28
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Default well-made op-amps everywhere

I agree with Vangelis, that the tlo72 works just fine with instrument preamp circuits. One does get something more with newer technology, but its not always what you want. We used a set of ad797 (which I believe I bought at a good price from jack in new jersey here on the forum) for a high fi preamp repair, and those had a noticable clean quality to them. Not sure I'd use them for original instrument signals, a little too much sparkle for my ears.
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Old 1st November 2006, 11:48 AM   #29
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Only a little note :

- The famous 4558 is now replaced with 4560 in almost all electronics
devices. (the 4558 descending from uA741)
- The NE5532 have two internal clipping diode, and it work well
only in a linear application. (not use in overdrive circuit)

For 4558 & 4560 look this:
http://www.njr.co.jp/index_e.htm

bye
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Old 6th January 2007, 03:36 PM   #30
Marito is offline Marito  Argentina
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If anybody have the schematic of the Musicman Sting ray preamp (with 3 tone control) please attach it.
Thank you very much
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