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Author
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Topic: buffer amp for volume pedal
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Bill Myers
Member From: Camp Hill, Pennsylvania, USA
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posted 31 October 2005 07:24 AM
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Has anyone ever built a small buffer amp to build into their volume pedal to convert it from a normal pot pedal to a something more like and L10K? I have seen some plans for these kinds of buffers on the internet, but I am not terrible skilled in electronics and I was hoping someone else may have tried this and could give me some advice.Thanks Bill ------------------
2003 Carter D10, 9x5 Black and 1998 Carter D10 9x5, Evans Amp
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Jack Stoner
Sysop From: Inverness, Florida
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posted 31 October 2005 08:46 AM
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It can be done, but I don't know if it's worth it. You can do the same thing with an external "buffer" amp such as a Goodrich MatchBox, Hilton Digital Sustain, MXR Microamp, etc. |
John Daugherty
Member From: Rolla, Missouri, USA
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posted 31 October 2005 08:53 AM
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Bill, If you try to build your own buffer amp,if and when you get it working properly,you will probably say "should have bought a Hilton".------------------
www.phelpscountychoppers.com/steelguitar
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Bill Myers
Member From: Camp Hill, Pennsylvania, USA
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posted 31 October 2005 11:12 AM
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Where is your sense of adventure! I have looked at the schematics for serveral different versions of the TL071 op amp based buffer amp. The project looks pretty simple and like it might be fun. I am going to try to build one in a little metal box first. If that succeeds, then I might try putting on in an L120 volume pedal. ------------------
2003 Carter D10, 9x5 Black and 1998 Carter D10 9x5, Evans Amp
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Dave Mudgett
Member From: Central Pennsylvania, USA
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posted 31 October 2005 11:58 AM
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Bill - it makes perfect sense to do what you're suggesting. You will need to have decent soldering skills, common sense, and some patience. Be sure to use a high-impedance-in low-impedance-out design, which is pretty much the definition of a buffer. Craig Anderton's "Electronic Projects for Musicians" book has a good schematic for this, and I'm sure there are lots of other sources also.I agree with your plan to first build a small box first. If you put a male plug on the input end and female plugs on the output end (I suggest using at least two or three output jacks, so you can drive two amps and/or send an output to a tuner), then you can just plug the input end into your steel. You may find this works so well you don't need to mod your volume pedal. One of the nice parts about "roll your own" is that once you figure out how to do it, you can modify it to suit your taste. You may also learn more about the things that affect your tone. Knowledge is power. |
Jack Stoner
Sysop From: Inverness, Florida
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posted 31 October 2005 12:23 PM
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The basic op amp circuit is fairly simple but when you get into signal to noise, gain, frequency response, impedences, etc there is more to it than a simple op-amp. Sounds like another post where someone thought they could build an electronic pedal. |
Dave Mudgett
Member From: Central Pennsylvania, USA
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posted 31 October 2005 01:40 PM
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I agree that designing a good buffer that meets specs on signal-to-noise ratio, frequency response, high input impedance, low output impedance, gain, input-level headroom, and so on, is beyond the scope of many hobbyists. But there are good designs out there that can just be put together. The Craig Anderton book I mentioned above is one source for these. That book, and others like it, explain the nuts and bolts, as well as the effect of certain kinds of changes in the circuit. The PAiA company supplied - and apparently continues to supply - kits to build these. I built some of these designs decades ago - they worked nicely, especially the simple 'spluffer' - splitter + buffer - design. I used one of these for years with guitar, and it ran for months on battery power. I believe it used 2-9V batteries to make a bipolar power supply, for increased headroom. I've seen variations with 1-9V battery.Myself, I'd leave everything unity gain. For those of you not electronics savvy, that means ratio of output-level to input-level = 1. If you raise the gain above one, that's overdrive - lower it below one, that's a pad. This design just does what it says - it presents a high-input-impedance to the guitar pickup, and the output of the effect presents a low-output impedance to the rest of the signal chain, and allows the signal to be split without degradation. Some people like them, some don't. The fact is that thousands of guitarists have built their own pedals using this kind of info. Some of these designs are very good, IMO. As long as someone just builds a small box from scratch and doesn't tear apart their volume pedal, I don't see the down side, except, at worst, a little wasted time and money if it doesn't work or they don't like it. I looked at the PAiA website - http://www.paia.com/epfm.htm - the basic spluffer kit without the box is $14.95. They offer more general preamp and other kits as well. I'm sure there are other sources for this kind of stuff, that's just one I know about. |
Michael Barone
Member From: Downingtown, Pennsylvania, USA
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posted 31 October 2005 05:32 PM
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Bill, I thought about trying this with a slight modification to match it up to the input impedance of a Nashville 112:
http://www.till.com/articles/GuitarPreamp/ A Field-effect transistor (FET) pre-amp circuit doesn’t have the drawbacks of an op-amp circuit, depending upon the application.
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Mike Barone
Sho-Bud Pro-1 5&4 with RHL | Nashville 112
Assorted Guitars & Keyboards |
Ken Fox
Member From: Ray City, GA USA
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posted 31 October 2005 05:48 PM
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In the case of the Nasville 112, why not use the pedal loop? How about using the Burr Brown Audio chip as a unity gain opamp? JFET technology and lwo noise. They sound great when I put them in a Profex 2, really cust back the white noise. Great tone as well. Great links above! Thanks!!! |
ajm
Member From: Los Angeles
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posted 31 October 2005 06:06 PM
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To add to what Jack Stoner said, any pedal with active FET switching will probably work as a buffer. Just leave it switched off unless you want to use the effect. You could use a Boss Heavy Metal pedal if you wanted to. It has active switching.
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Artie McEwan
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Michael Barone
Member From: Downingtown, Pennsylvania, USA
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posted 31 October 2005 06:32 PM
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Ken, I use the pedal loop. Agreed, that the input impedance of a NV112 is a little higher there vs. the channel input, but this post, relevant to this topic, got me thinking: http://steelguitarforum.com/Forum11/HTML/007805.html Mike |
Jim Peters
Member From: St. Louis, Missouri, USA
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posted 31 October 2005 06:42 PM
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Just put a tubescreamer in front of the volume pedal, you don't have to have it on distortion mode. It has the buffer built in. JP |
Keith Hilton
Member From: 248 Laurel Road Ozark, Missouri 65721
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posted 31 October 2005 06:42 PM
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Experimenting is fun---go for it. The TLO71 would not be my choice for the best sound quality--just my opinion. Read up on some better sounding op-amps. The TLO is not the bottom of the barrel, like the 741, but it is not at the top of the barrel either. Building the pre-amp is easy, but protection against failure may not of occured to you. When hookup examples are given, application data sheets assume you know a lot about failure mode protection. You can generate 2000 volts walking across a carpet and touching a door knob. A transistor junction on a op-amp will be destroyed if it gets over 24 volts. When powered devices are hooked together, it is common to see huge voltages and currents come down the input, or the output, of a individual circuit in a system. Even with a battery you need reverse polarity protection. If you have a power supply ,other than batteries, you will need filtering and regulation. You will need power supply by-pass protection for the power supply, no matter what type of power supply you use. Otherwise you will get noise. You will need RF protection, especially on the input. Building a pre-amp is easy, protecting it from failure is not easy. Study of failure modes is more than important------ it is everything. Besides total failure, a circuit can experience what is called, "SOFT FAILURE". This means it still works, but does not work up to it's full potential. I take pride in going to extremes when it comes to protection modes. I have done more study about that subject, than any subject in electronics, and for good reason. Some of my competition does not take protection as seriously as I do, and they have a lot of failures. I want to help you--and the advise I offer comes from experience gained the hard way. |
Ken Fox
Member From: Ray City, GA USA
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posted 31 October 2005 06:47 PM
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Yes, I see what you mean. I have a Session 2000 and find it very muddy even in the 3 wire configuration with a pot pedal. I am going back to my old Goodrich with the built in buffer amp, LSW pedal.I find with a Tele that I like going into the pedal return and not even using the input jack and volume control! A tube is a higher input impedance. The JFET was often described as tube without a heater! The Burr Brown uses JFET inputs, I do believe. Making a unity gain preamp with them might be the ticket. The JFET preamp shown above on that link looks good too. I am tempted to try it!!! |
Bill Myers
Member From: Camp Hill, Pennsylvania, USA
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posted 01 November 2005 05:36 PM
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So what is a good op amp. I have a plan for a small buffer that uses a 741 op amp. I have read that the NE553n and the LF351N are good replacements for the 741. Anyone have any further info or advice. Thanks------------------
2003 Carter D10, 9x5 Black and 1998 Carter D10 9x5, Evans Amp
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Ken Fox
Member From: Ray City, GA USA
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posted 01 November 2005 06:22 PM
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The Burr Brown OPA series is about as good as it gets! That was the Lemay mod and Peavey mod chip for Profex 2 and Nashville 400. Very quiet and warm tone. Check this post for more info
http://steelguitarforum.com/Forum11/HTML/006597.html [This message was edited by Ken Fox on 01 November 2005 at 06:26 PM.] |
Jack Stoner
Sysop From: Inverness, Florida
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posted 02 November 2005 03:06 AM
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Bill all 3 op amps that you mention are too noisy for the low level "instrument level" signal. The OPA2604 that Ken Fox mentioned is probably the best on the market right now. Noise is the biggest problem with a lot of the "do it yourself" plans for a lot of the music effects. If you were playing rock and a lot of overdrive (distortion) the noise would not be an issue. But most steeler's want a super quiet, super clean signal. |
jim milewski
Member From: stowe, vermont
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posted 02 November 2005 03:53 AM
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I think the pinouts for many op amps are the same, then you can swap and experiment, I did an upgrade to the Burr Brown chips and really saw little improvement, I know they are superior though, I would use a double op amp package in case at some point (if not in the begining) you want two stages. The book Dave mentioned above is great, get it if you can, I think Craig mentioned there is a cmos digital chip (I think it was a gate or something like that) he experimented with that gave a cool audio sound. I hope you get good results in the buffer amp, go for it. One question, would you use inverting or non inverting which has a higher input impedence, seems I remember inverting had a lower output impedence that may be desirable, then again with a double op amp you could use both |
Bill Myers
Member From: Camp Hill, Pennsylvania, USA
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posted 02 November 2005 02:40 PM
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Just to give everyone and update...I found a small mono preamp kit with is very similar to the buffer amp schematics that I was planning on using. This kit uses a 741 op amp. I built the preamp and put it in the box and as I was told there is a little distortion (it still sounds pretty good with a passive pedal). After doing a little homework I have found a couple of op amps that have the sam pin outs and should be of better quality. They are an NE5534N which is designed for audio applications and a TI OPA134PA which is the old burr brown op amp. I am going to try these out and see what the sound is like. Total cost was $11.00 for the kit another $10 in other supplies and another $10 for the extra op amps (shipping included). Overall this has been a fun project and a good learning experience. Thanks for the advice and I may try building some more!------------------
2003 Carter D10, 9x5 Black and 1998 Carter D10 9x5, Evans Amp
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