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Ernie Ball VP Jr and Tone Suck, what ideas do you have?
Ernie Ball VP Jr and Tone Suck, what ideas do you have?
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Old 28th October 2019, 06:43 PM   #21
IceFyre13th is offline IceFyre13th  United States
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Join Date: May 2013
Location: AZ, you know where the car audio companies are.
Well thanks to USPS not being able to keep there schedule, maybe I will get to play with that mod board today......seriously hate when things are sent via USPS.


But I did download the data sheet on the Quad Op-Amp it uses (attached).


I found a couple of other "buffers" that some others have used in the EB VP Jr too, also attached.


One thing I do see that they all use is the voltage divider DC offset they add into the circuit, totally understand the concept, but hate that way of doing it.
Much cleaner way is to use a Rail Splitter like the TLE2426.


Small add on circuit....


Click the image to open in full size.


Less possible noise that way too.


I do intend to publish my circuit when done and a PCB file so others can build their own too.
Attached Images
File Type: png Little Black Buffer.png (34.2 KB, 80 views)
Attached Files
File Type: pdf FM-Tone-Lossless-buffered-volume-pedal-schematic.pdf (23.8 KB, 9 views)

Last edited by IceFyre13th; 28th October 2019 at 06:45 PM. Reason: missing attachments
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Old 28th October 2019, 06:46 PM   #22
IceFyre13th is offline IceFyre13th  United States
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Join Date: May 2013
Location: AZ, you know where the car audio companies are.
Here, maybe the attachments will stick this time.
Attached Images
File Type: png Little Black Buffer.png (34.2 KB, 73 views)
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Old 28th October 2019, 06:48 PM   #23
IceFyre13th is offline IceFyre13th  United States
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Join Date: May 2013
Location: AZ, you know where the car audio companies are.
looks like the Data sheet for the TL084 is too big......heres a link instead.


http://www.ti.com/product/TL084
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Old 28th October 2019, 07:59 PM   #24
29285 is offline 29285  Europe
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The rail splitter adds its own noise and eats extra battery power. I do not see any advantage around a simple guitar buffer.
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Old 28th October 2019, 11:28 PM   #25
Gnobuddy is offline Gnobuddy  Canada
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The old +9V standard for stomp-boxes made sense when it was introduced, but only because you could go to the store and easily buy 9V flat batteries.

But even in the 1960s, it wasn't enough voltage. There was very little headroom available. Not a problem when the only pedals on the market were fuzz-boxes, but as soon as pedals with "clean" tone arrived (for example, tremolo, chorus, reverb, etc), 9V became rather painfully inadequate.

In recent years fewer and fewer guitarists actually use 9V batteries to power their pedals. Now that switching power supplies are cheap and reliable and supply clean DC, most guitarists have moved over to a pedal power supply. So the only good reason to use 9V has now almost ceased to exist.

Honestly, I'm really surprised that the isn't a +15 V/0 V/-15 V three-rail power supply standard for guitar pedals. Op-amps have been routine in these little boxes for decades now, and it's just silly that we're still running them on a single-supply, +9V rail.

Some months ago I started hunting around for a suitable 3-prong power connector to use along with a three-rail power supply, and to my utter surprise, found that there isn't any kind of an industry standard connector for this purpose. How is this possible, more than five decades after audio op-amps started to be widely used?


-Gnobuddy
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Old 28th October 2019, 11:50 PM   #26
cobretti is offline cobretti  United States
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I use mini XLR connectors for symmetrical power sometimes. I used one for my low noise oscillator. Any other options? Maybe a 3.5mm stereo jack. What else?

Last edited by cobretti; 28th October 2019 at 11:53 PM.
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Old 29th October 2019, 12:48 AM   #27
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by cobretti View Post
Any other options? Maybe a 3.5mm stereo jack. What else?
Many months ago, I ran into the same problem (very few options, all of them obscure and expensive). Things like XLR, mini XLR, aircraft connectors, old DIN connectors, etc.

So I started a thread on the topic, thinking some of our members with lots of manufacturing experience would soon chime in and point me at the "right" connector choice.

To my surprise, that didn't happen - the experienced people did chime in, but they didn't know of any obvious connector choices, either, and suggested the same oddball types mentioned above. Apparently there really aren't any good 3-pin, non-shorting, affordable, compact, power connectors, and there certainly isn't an industry standard. That really surprised me!

By the way: using a stereo or mono 3.5 mm plug / jack for power is a very bad idea. The reason is that as you insert these plugs into the jack, the contacts are briefly shorted to each other. Sparks, arcing, burning, and pitting occur quickly, and the connectors are ruined prematurely.

We have some ancient (and expensive) small equipment at work that uses a 3.5 mm mono jack for power. All the jacks and all the plugs show pitting and blackening. One of these days I'll have to sit down and replace the whole lot with 5.5mm "barrel" power connectors.


-Gnobuddy
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Old 29th October 2019, 07:33 PM   #28
IceFyre13th is offline IceFyre13th  United States
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Location: AZ, you know where the car audio companies are.
I do have the isolated output power supply my pedal board uses, it has two 18 Vdc outputs along with the other eight 9 Vdc outputs.......never even crossed my mind to use a 9 volt battery, no room anyway. (well there is room, but why....cant play my electric guitar without an amp, that's plugged into mains....).

On the rail splitter, this does come down to room on the PCB. Board size is 71mm X 37mm (2.798 X 1.459 for the metric defiant). We have three 1/4 inch phono jacks and a power jack taking up a lot of real-estate, not much room to build a power supply and all the other circuitry needed.

So the 3 pin rail splitter and its supporting cap makes sense, I have used this on other designs. It's way better than injecting DC voltage into the signal path, along with all of the noise it has.

If I use 18 Vdc power that's +9 Vdc and -9 Vdc rails, way more than unity gain will ever need.....but think about the "boost" potential. Heck some pedal power bricks have 24 Vdc out. This makes the power input range 9-24 Vdc....

The Griffin Effect board made it to me last night too, not at all impressed....and they are using a TL074 now, not the TL084 in the picture on their site. Yep, voltage divider into the signal path, no DC blocking cap to the guitar input (wonder if the pickups care about the 4.5 volts on them...).

The whole purpose of the mod is to buffer the tuner and output to prevent loading of the pickups, so why did they put solder pads you have to short for either buffered or direct connection to the input jack to the tuner out? And the goofy LED light..again solder pads to choose color...why oh why?

Not a total loss / waste of money, at least I can use it to check my PCB layout against....and my biggest complaint, where are the instructions......

I now have a semi-plan:

Quad op-amp.

Rail Splitter to keep from injecting DC into the signal path.
Higher quality caps if needed in the signal path.

True buffered in with buffered out on both the tuner and line outputs (unity gain).
Volume control on its own op-amp with possibility of boosting the output.

Any other suggestions?

Last edited by IceFyre13th; 29th October 2019 at 07:37 PM. Reason: Speeling, no god at eet
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Old 29th October 2019, 10:29 PM   #29
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by IceFyre13th View Post
...9 volt battery...why...cant play my electric guitar without an amp, that's plugged into mains...
You have to think back to the time when making a clean 9 volts DC from household AC wasn't such an easy task. Before reliable silicon rectifier diodes existed, never mind Zener diodes, silicon power transistors, or three-terminal linear voltage regulator chips. Back then, you want a clean 9V DC, you use a flat battery!

Times certainly have changed. Now a 9V battery costs a small fortune, while small, reliable, affordable SMPS are everywhere. Nowadays using a small SMPS is such an obvious choice that even Luddite guitarists are adopting them.
Quote:
Originally Posted by IceFyre13th View Post
not much room to build a power supply and all the other circuitry needed.
Have you seen this wonderful doodad? Fifteen bucks (even cheaper in the USA), tiny, +/-15V, completely self-contained: https://www.digikey.ca/products/en?k...c10-15dk%2F277
Quote:
Originally Posted by IceFyre13th View Post
3 pin rail splitter...way better than injecting DC voltage into the signal path...
Electrically speaking, I don't see any difference. Either way, you generate a +4.5V DC rail, halfway between 0V and +9V. There's exactly the same amount of DC voltage involved in either case, no?
Quote:
Originally Posted by IceFyre13th View Post
...along with all of the noise it has.
Put a decently sized electrolytic cap across the lower of the two equal-value series resistors, and you can easily get negligible noise on the +4.5V node. The +9V should be pretty clean to start with, making this even easier.
Quote:
Originally Posted by IceFyre13th View Post
If I use 18 Vdc power that's +9 Vdc and -9 Vdc rails, way more than unity gain will ever need...
Some years ago there was a discussion on diyAudio about how much voltage, exactly, you can expect from a guitar pickup. One member demonstrated, with oscilloscope captures, his ability to get ten-volt peaks straight out of the humbuckers in his guitar.

I think that was 10 volts peak-to-peak. Still, +/- 9V doesn't seem like all that much headroom now, does it?

I've heard more than a few "clean" guitar pedals that produce brief bursts of harsh clipping distortion when the guitar pick hits the strings. I really hate that sound!
Quote:
Originally Posted by IceFyre13th View Post
using a TL074 now, not the TL084 in the picture on their site.
A bit lower noise, I think. Probably not enough to matter.

I only remember seeing two buffers in your schematic - why a quad op-amp, and not a dual?
Quote:
Originally Posted by IceFyre13th View Post
...no DC blocking cap to the guitar input (wonder if the pickups care about the 4.5 volts on them...)
No cap? Really? That is an outright design mistake.

With the guitar volume at full, that puts the DC resistance of the guitar pickup in parallel with the lower of the two resistors in the voltage divider. You won't get 4.5V bias any longer - you may get very much less, depending on the resistor values in the voltage divider, and the guitar pickup DC resistance.


-Gnobuddy
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Old 30th October 2019, 12:33 AM   #30
IceFyre13th is offline IceFyre13th  United States
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Going to leave this here for future discussion.....CUI PDQE20-Q24-D15-D


https://www.mouser.com/datasheet/2/6...-d-1595964.pdf
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