Ernie Ball VP Jr and Tone Suck, what ideas do you have?

A few weekend ago I was in a local second hand music store and came across an Ernie Ball Volume Pedal Jr, this is a passive VP that uses a 250k pot to foot control volume from the guitar.....for 25 bucks it was a deal.


I connected it up with just the guitar to the pedal to the amp and it did everything nicely until......I used the tuner out jack it has, hooked up my TU3 and all of a sudden the highs were gone.


Of course I spent some time looking for the wrong solution, but Google knew....


Seems the tuner out and input are parallel, this make the input impedance real low and that knocks the highs out of the signal path (simplified explanation).


The solution is to modify the passive pedal to be active with a dual buffer, one on each output...lots of people have kits, or send in your pedal to be modded.....but me being DIY, that got me to thinking.....TUBE BUFFERS!!!!!!


I have a multi isolated output power supply that can power a pedal up to 18 VDC (8 @ 9 VDC 150 mA and 2 @ 18 VDC 400 mA).


All we need to do is design the buffer circuit, yes I said we because I think this would be a fun crowd source design exercise.


Is it practical, nope...do tubes belong "under foot", nope.....are there easier ways to do this, yep.......so why ..its just fun to do.


Starting with the power supply:


We have 18 VDC at 400 mA available, we could use a step up power supply to make a more usable voltage. Honestly any of the Fleabay Chineasium DC to DC converters will do.



Or are there any tube choices that would not need this, say 6GM8, 6DJ8, 12B4, or 12B4A


What ideas do any of you have......???
 
The tone suck only happens if I use the tuner output.....I try to keep things out of circuit that are not contributing to the sound.


The EB VPJr version I have is the 250K pot one (normally used at the guitar end), they also have a 25K pot version that would work better in-between pedals or with active pickups.


Easy solution is this, VPJR Volume Buffer Retrofit Kit - Griffin Effects


I thought it would be fun to go silly and play with some type of tube buffer idea.....maybe not so silly as we could come up with something real cool.
 

Gnobuddy

Member
2016-03-01 4:10 pm
...the recent "Nutube" invented by Korg...
The Nutube is expensive, and has an extremely high output impedance (far higher than even a 12AX7). Because of this, it's completely useless as a buffer.

I still like tube guitar amps, and IMO they are the easiest way to make a good-sounding DIY guitar amp. However: tubes have much higher output impedances than common low-voltage solid-state devices (BJTs, JFETs, op-amps). This makes tubes - any tubes - extremely poor choices when you want a buffer with a nice low output impedance. Which is what we want here. :(

The obvious fix for the Ernie Ball VB Jr problem is simply to stick a single JFET in source-follower mode in front of it. This is small, simple, reliable, inexpensive, low noise, and will do a fantastic job of buffering the guitar from the VB Jr's "tone sucking".

I know, I know. The OP wants to tinker with tubes, whether or not they are a good choice in this particular situation. :)

That being the case, all I can say is, you have my best wishes!


-Gnobuddy
 
Let's focus on what needs to be done here:
The OP wants two things:
1) clean tone
2) Tonality not compromised by the user plugging in the tuner.

Seems that the consensus is that the tone is compromised by the input impedance of the tuner loading down the pickup. So why not provide the tuner with an impedance transform, AKA the simplest buffer possible that has a high input impedance and lowish (but not so critical) output impedance. Then you can leave the guitar input as-is and still have a minimum of loading of the guitar pickup. A brand new TC buffer is around 50 bucks new at the big music stores.

If you want to DIY, the classic single-FET buffer works a treat. Search the web, Seymour Duncan even has a full tutorial. This should give you full transparency.
 

Gnobuddy

Member
2016-03-01 4:10 pm
So why not provide the tuner with an impedance transform, AKA the simplest buffer possible that has a high input impedance and lowish (but not so critical) output impedance. Then you can leave the guitar input as-is and still have a minimum of loading of the guitar pickup.
I like your thinking, and this is certainly an option. It will address the primary issue the OP brought up.

However, the Ernie Ball volume pedal in question uses a 250k volume pot. This is low enough to already cause "tone suck" with some guitar pickups, particularly humbuckers, which really don't want to see a load of less than 500k or thereabouts.

Even when the Ernie Ball pedal is used with a guitar with single-coil pickups, there is usually already a 250k volume pot inside the guitar. The external Ernie Ball pedal will parallel that, dropping the load seen by the pickups down to 125k. This is low enough to cause "tone suck" even with single-coil pickups.

This is why I think the better solution is a clean buffer between guitar and Ernie Ball pedal.

I agree with you that there are many easy choices straight from the music store. The old Danelectro Fish and Chips graphic EQ pedal is one example - it was around $30 last I checked, and it does triple duty as a buffer, clean boost, and graphic EQ. The Fish and Chips is no longer in production, but there are other inexpensive graphic EQ pedals available in the same general price range.

If DIY is preferred, a single JFET will do the trick. By the time you buy all the parts, including case, knobs, and paint, you will have spent at least as much as you would on a Donner or similar graphic EQ. Probably more.


-Gnobuddy
 
I like your thinking, and this is certainly an option. It will address the primary issue the OP brought up.

However, the Ernie Ball volume pedal in question uses a 250k volume pot. This is low enough to already cause "tone suck" with some guitar pickups, particularly humbuckers, which really don't want to see a load of less than 500k or thereabouts.

Even when the Ernie Ball pedal is used with a guitar with single-coil pickups, there is usually already a 250k volume pot inside the guitar. The external Ernie Ball pedal will parallel that, dropping the load seen by the pickups down to 125k. This is low enough to cause "tone suck" even with single-coil pickups.

I get it. My 58 Tele is REALLY sensitive to that problem. At one point, I built the single FET buffer into the control pocket on the Tele and crammed a 9V battery in there, it was pretty transparent, but I like the way the tone and volume controls interact on these old geetars so I took it out and am much happier. The magic of a Fender guitar interacting with a Fender input circuit is pretty amazing.

This is why I think the better solution is a clean buffer between guitar and Ernie Ball pedal.

I agree with you that there are many easy choices straight from the music store. The old Danelectro Fish and Chips graphic EQ pedal is one example - it was around $30 last I checked, and it does triple duty as a buffer, clean boost, and graphic EQ. The Fish and Chips is no longer in production, but there are other inexpensive graphic EQ pedals available in the same general price range.

Excellent suggestion! I got a Fish and Chips use off Ebay for around $25 and it really is transparent.

If DIY is preferred, a single JFET will do the trick. By the time you buy all the parts, including case, knobs, and paint, you will have spent at least as much as you would on a Donner or similar graphic EQ. Probably more.

I'm a cheapskate, my buffer is now in a Newman Mints tin!

cheers


-Gnobuddy
 
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Gnobuddy

Member
2016-03-01 4:10 pm

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I like what I see above, all great suggestions.

Yes the tube idea was a little hair brained, its a "What If " idea.

I did a little de-construction last night on the EB VP Jr, the original designer must not of been thinking. I am surprised it even works for some as it really loads down the pickups (that little resistor that can be added via switch to change the swell, oh god what were they thinking).

So I actually ordered that little buffer board I linked to earlier to play with, because from what I can see so far the pot needs to be isolated from the pickups being loaded as well.

Passive circuits have their time and place, used like this....not so good.

Tubes in the circuit, could be done, practical nope (maybe with a JFET follower)....I'm not really tied to them, like I said....What if

What I think we need is a buffer on the front end with an Input Impedance of 500KΩ - 1MΩ

This will keep the pot from being a variable load on the pickups, it will be real easy to change the pot in the pedal to anything usable for a volume cut (unity gain wanted,,,,,maybe a little boost.

Then to an output stage with an Output Impedance of 1KΩ - 10KΩ....

What really would be nice is a input circuit that has impedance matching (adjustable input impedance to match the pickups of the guitar). Bootstrap circuit???

Then cram all that on a PCB that can replace the original one....now I have my work cut out for me....and try to stay away from surface mount stuff so anyone can build it themselves.......and runs on 9 volts (standard pedal power).
 

Gnobuddy

Member
2016-03-01 4:10 pm
...What really would be nice is a input circuit that has impedance matching (adjustable input impedance to match the pickups of the guitar). Bootstrap circuit???...
For a guitar pickup, we don't actually want impedance matching. Instead, what we want is an extremely mis-matched load, a load so high that it's virtually infinite.

In Merlin Blencowe's tube preamp book, he has a section on electric guitar pickups. In a nutshell, the inductance of the guitar pickup interacts with the capacitance of the guitar cable, and any parallel resistance (volume pot, input impedance of amplifier, etc.)

What happens is that the inductance and capacitance together create a peak in the (treble) frequency response, which we hear as a nice attractive treble sound. However, the parallel resistance - the load on the pickup - reduces this treble peak, and makes the pickup sound duller.

If the pickup is unloaded (or loaded by a very high resistance, 1 meg or higher), not much damage is done to the treble peak. But as that resistance drops, the treble peak is suppressed more and more. If you lower that resistance all the way to around 100k, even single-coil pickups become dull-sounding, as the treble peak is almost completely lost. Humbuckers suffer the same fate at even higher input resistance.

All of which means, the ideal load impedance for your guitar is, basically, no load at all, infinite input resistance from the amp! But "infinite" is silly for many reasons, not least because there's already a 250k or 500k pot inside the guitar, and we can't reduce the load below that no matter we do outside the guitar.

So a more practical way to look at it, is that our guitar amp input (or buffer) should have an input impedance that's much greater than 500k.

1 M really isn't "much greater than 500k", so there's maybe a little room for improvement. I think 1 meg was about the practical limit with valve amps, because there is a little bit of grid current flow through that input grid bias resistor. So that value (1 M) is where the industry settled, back in the 1950s or 1960s.

Today we can do better, if we use a JFET as the input stage. There is no harm (and may be a slight benefit) in going up to, say, 2 or 3 M input resistance. I often use 2.2M.

All this time, we've talked about the load resistance. But, let's not forget, the load capacitance plays a huge part in the pickup sound as well!

And that, I think, is where there is room for experimentation. Switching different small-value caps in parallel with the pickup can be an effective treble control, and it doesn't take away the resonant treble peak that makes pickups shimmer and sound good. There was a small company that sold a 12-way rotary switch with a bunch of small SMD caps on it, designed to replace the stock guitar tone control.

I've also seen a clever circuit using a bootstrapped capacitor tied to the input. By varying the amount of bootstrapping, you vary the input capacitance. The idea was this would interact with the guitar pickup in the same way as the rotary switch with caps.

There is a catch, though: the rotary switch thing works because it's inside the guitar, wired straight to the pickups. But there's a volume control between the pickup(s) and the bootstrapped-input-cap circuit - and if that volume control is turned down from max, everything goes bad; the clever bootstrapped input capacitance just rolls off all the guitar treble, causing major "tone sucking".

In short, I don't think there really is a clever way to load a guitar pickup using an external buffer or preamp! We don't want an optimum load, and we can't add an optimum capacitance. All we can do is follow the doctor's Hippocratic oath: "First do no harm." All we need is just a buffer with at least 1 M input impedance, maybe a bit more if possible.


-Gnobuddy
 
Short answer: forget tube buffers.
Lots of disadvantages and ZERO advantages.
WTF you want a tube for?
You won´t even HEAR the d*mn thing because it feeds a Tuner!!!

Not that a tube buffer adds anything useful to low level sound anyway.

Not sure about your tuner either , IF designed for guitar use it should have 1M input.
 
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Gnobuddy

Member
2016-03-01 4:10 pm
Thanks for the kind words!

I over-think the heck out of things, too. Sometimes so much that it completely stops me from even getting started, because why even start if it's not going to be the bestest possible? :rolleyes:

"Paralysis through analysis", as a ballroom dance teacher I knew once called it. In his line of work, if you stop to think, it's all over!


-Gnobuddy
 
I will leave this here as I don't want to be evil.


YouTube


Someone didn't see where I said, just for fun....or get that it might be a fun exercise.


But back to the fun,


The pre-built board will be here tomorrow, I will see what they did and report back. Maybe it will be fine, maybe be something that needs a few better parts to "clean up".


This is it, VPJR Volume Buffer Retrofit Kit - Griffin Effects
 

Gnobuddy

Member
2016-03-01 4:10 pm
I will leave this here...
It's been a long time since I saw the movie. But I remember being quite impressed by Madonna's work, both as an actress, and most especially as a singer.

The thin, whiny, nasal voice I remember from her 1980s hits was gone, and in its place was the beautiful vocal tone colour of a singer who has been taking singing lessons, learning classical singing technique, and working hard at becoming a better singer.

I have no respect at all for Madonna's public persona or the road she took to fame. But I do respect an artist who continues to work to improve her craft.
That looks nicely engineered. I would never have imagined such a niche product existed! It's a bit like finding that somebody makes an upgraded rear window for 1982 Fiat Spider 2000s, to replace the factory one that always turned into an opaque yellow mess within a few years...


-Gnobuddy
 

PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
www.diyaudio.com
Fender liked 1Meg, but when humbuckers overloaded early input he compromised on a 136k divider.

A range of Ampegs used 2.7Meg even 3.9Meg. Different? Probably not a lot, but perhaps audible in the factory break-room.

You adjust guitar load capacitance with cable. A 3-foot cable is bright but limiting. A 30 foot cable dulls the sound. If you only play cowboy rhythm you could make a 100 foot lead, but many amps have a way to dial the treble right out without having to pack a reel of wire.
 

Gnobuddy

Member
2016-03-01 4:10 pm
Fender liked 1Meg, but when humbuckers overloaded early input he compromised on a 136k divider.
I've always wondered about the choice of such a low input impedance, in an era when all pickups were passive. All the humbuckers that have crossed my path become noticeably duller-sounding with a 150k load, compared with 1000k.

I've read that Gibson (the only humbucker-equipped guitars at first) initially aimed their electric guitar offerings at jazz, with its typically duller and more muted sound compared to later genres of popular music.

This applies even to Gibson's first solid-body, the Les Paul; not only did the carved top and traditional body shape mimic their hollow-body archtop jazz guitars, they even signed up a fellow who was primarily a jazz guitarist, albeit one who dabbled very successfully in pop in his later years, to endorse it and put his name on it. The Les Paul is still used for electric jazz: The Les Paul Guitar Can Play Jazz (Here’s Why!) - Tone Topics

So I wonder, did Leonidas or his electronics tech go with that very low input impedance for humbuckers because, at the time, guitars with humbuckers were supposed to sound like jazz guitars?
You adjust guitar load capacitance with cable.
Most of my guitars use humbuckers. I used 10-foot (3 m) cables for a while, but they are so short that they almost mandate sitting down next to your amp while you play. Eventually I compromised on 15-foot (5 m) cables.

At least one of my guitars (a 335-style semi-hollow) gets very dull-sounding as soon as the volume knobs are turned down from "10". The stock pickups are over-wound and too muted on their own, and the lack of treble bleed caps on the internal volume pots makes that worse.

A pickup change and the addition of treble bleed caps are in the works. But this is the hardest type of guitar to do that sort of work on, as you have to install and remove the harness through the narrow f-holes.
If you only play cowboy rhythm you could make a 100 foot lead
I remember reading about some rock guitarist who liked to use a long, coily guitar cable. The cable surely rolled off lots of treble, but the heavily overdriven fuzz-box / distortion pedal / guitar amp put it back.


-Gnobuddy